CN1673076A - Active carbon producing process with mixed stalk material - Google Patents
Active carbon producing process with mixed stalk material Download PDFInfo
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Abstract
The present invention discloses the active carbon producing process with mixed stalk material. The mixed stalk material of crop stalk, waste fruit branch and sawdust is produced into powdered or granular active carbon via phosphoric acid process and combined physical process. Or, the mixed stalk material is produced into powdered or granular active carbon in a chemical physical process with potassium hydroxide as activating agent and perchloric acid for pre-treatment of the material. The present invention has small investment scale, low cost, high utility and simple operation, and the product may be used widely.
Description
Technical Field
The invention relates to a production technology of activated carbon, in particular to a method for producing activated carbon by using straw mixed raw materials.
Background
Activated carbon is a black porous solid which is characterized by developed pores and large specific surface area and adsorption capacity. The following briefly introduces the relevant information of the existing activated carbon at home and abroad:
1. physicochemical properties of activated carbon:
the active carbon is composed of microcrystalline carbon and amorphous carbon, contains ash with different amounts, and is a black porous solid. The most important characteristics of the material are that the material has developed pores and large specific surface area and adsorption capacity. For example, the specific surface area of charcoal is generally only 100m2/g～400m2A specific surface area of the activated carbon is up to 1000m2/g～3000m2(ii) in terms of/g. Therefore, activated carbon has a strong adsorption capacity for gases, organic or inorganic substances in solution, colloidal particles, and the like.
The active carbon as a high-quality adsorbent has unique pore structure and surface active functional groups, has sufficient chemical stability, mechanical strength, acid resistance, alkali resistance, heat resistance and other properties, is insoluble in water and organic solvents, is easy to regenerate after being used and failed, and is widely applied to various departments.
2. General overview of production and application of foreign activated carbon
2.1 the United states is the first major country in the world to produce and use activated carbon, and the production capacity is 17.24 million tons in 1994. Because of the large import of cheap activated carbon in southeast Asia and the increasing of domestic regenerated carbon yield, the yield of the activated carbon is not changed greatly in recent years, full-load production is not achieved, and the yield is maintained at about 70 percent of the production capacity.
The American activated carbon is mainly prepared from wood, lignite, coconut shells, charcoal and bituminous coal. The activating furnace used for production comprises a multi-layer harrow furnace, a rotary furnace, a fluidized bed furnace and the like. The product comprises powdery carbon and granular carbon. The regeneration of the activated carbon is very important in the United states, the regenerated activated carbon is an important component of the production of the activated carbon in the United states, and the yield of the regenerated activated carbon in the United states is about more than 4.8 million tons according to incomplete statistics. Due to the low production cost of the regenerated activated carbon, resource conservation, environmental pollution reduction and activated carbon import reduction, the development of the regenerated carbon is supported by the government ten branches, and the yield of the regenerated carbon in the United states is estimated to be further increased for a period of time in the future.
2.2 in more than 20 years, the production of the Japanese activated carbon has developed rapidly, for example, in 1975, the yield of the Japanese activated carbon is 4 ten thousand tons, and in 1985, the yield is 8.4 ten thousand tons; in 1994, 8.9 ten thousand tons is achieved, and the yield in twenty years is doubled.
The development of the production of the activated carbon also promotes the development of scientific research institutions. The new research results of the activated carbon promote the development of the production to a higher and more recent level. Promotes the development of the active carbon technology, and new products and new processes are continuously generated. In recent years, high-grade new products such as activated carbon fibers, spherical activated carbon, carbon molecular sieves and the like are developed and produced. Grade of traditional productContinuously increased, high benzene content and high Cl content4The active carbon and the low-ash active carbon are coming out continuously, the road of the active carbon industry is wider and wider, the yield is larger and larger, and the quality is better and better.
2.3 kinds of activated carbon
The types and names of the activated carbon are many, and the activated carbon can be classified according to production raw materials, production methods, appearance forms, applications and the like. These categories and names are shown in table 1.
TABLE 1 variety of activated carbon
| Basis of classification | Category and name |
| Raw materials | Wood charcoal: comprises wood chip charcoal, shell charcoal (such as coconut shell charcoal), kernel charcoal, and coal charcoal Other raw material carbon: such as pitch, synthetic resin charcoal, activated carbon fibers |
| Production process | Chemical activation activated carbon (chemical carbon) (acid activated carbon) Physical activation method activated carbon (physical carbon) (basic activated carbon) |
| Appearance form | Powdered carbon Granular carbon: including amorphous carbon, cylindrical carbon, spherical carbon, honeycomb carbon, and the like Activated carbon fiber: comprises activated carbon fiber cloth, felt, paper and the like |
| Absorbability of sorption | Single type (selective) activated carbon Composite (diversity) active carbon |
| Use of | Gas phase adsorption of activated carbon: comprises protective carbon, air purification carbon, desulfurization carbon and the like Liquid phase adsorptionCarbon property: comprises water purifying charcoal, injection charcoal, sugar charcoal, monosodium glutamate, gold charcoal, and medicinal charcoal Catalyst carrier active carbon Carbon molecular sieve |
The activated carbon raw material is divided into wood raw material activated carbon, coal raw material activated carbon, asphalt activated carbon, synthetic resin activated carbon and the like. Wood activated carbon has the oldest history and includes various woods, chips, charcoal, husks, kernels, etc. The chemical components of the raw materials mainly comprise lignin and cellulose, and compared with coal raw materials, the raw materials have less impurities and low ash content, and can be applied to the fields with higher quality requirements such as food, medicine and the like. The wood charcoal is mainly powdery charcoal, and is widely used for sugar liquor decolorization, monosodium glutamate, glucose refining, pharmacy and the like. Coconut shell charcoal is the best quality of wood charcoal, is amorphous particles, and has good adhesion performance and high mechanical strength. The kernel carbon also has the characteristics similar to coconut shell carbon, and has better using effect like peach kernel carbon and apricot kernel carbon. Due to limited wood resources and higher cost, the development of the wood activated carbon is limited, so that the coal activated carbon is developed rapidly. The coal-based activated carbon has the advantages of rich resources, various types and low price. The most serious defects are high ash content and more impurities.
The production process is divided into two categories, namely the production of activated carbon by a chemical activation method and the production of activated carbon by a physical activation method. The chemical activation method uses chemicals as activating agents, such as commonly used zinc chloride, etc., and sulfuric acid and hydrochloric acid are used as activating agents in individual units, which are called chemical carbon for short. Activated carbon made with zinc chloride generally has many macropores and transition pores, and many acidic surface oxides, and is generally called acidic activated carbon. The physical activation method uses an oxidizing gas such as steam or carbon dioxide as an activator, and is also called a gas activation method. The activated carbon is called physical carbon for short. Physical carbon generally has a more microporous structure and generates more alkaline surface oxides during activation, and is therefore called alkaline activated carbon. The two main types of activated carbon have different properties and different purposes due to different manufacturing methods. The chemical method is a multipurpose wood raw material, and the production process and equipment are simpler. But the most serious defects are environmental pollution, waste gas pollution to the atmosphere and large amount of waste water containing chemicals generated during product rinsing. Therefore, the development of chemical carbon has been limited in the history of activated carbon development, while physical carbon has been developed rapidly, and the yield of physical carbon is now higher than that of chemical carbon. This trend will continue.
From the appearance, the activated carbon can be divided into two categories, namely powder activated carbon and granular activated carbon, and the granular activated carbon is divided into amorphous activated carbon and shaped activated carbon. Amorphous carbon is also known as crushed carbon. The raw materials are directly crushed into certain particle size and then processed, and the raw materials are also crushed into blocks. The formed activated carbon includes cylindrical activated carbon, spherical activated carbon and activated carbon of other shapes, which are different from each other in forming method. The powdered activated carbon can be processed into different fineness according to the use requirement. The powdered activated carbon has fine granularity and large external surface area, so that the powdered activated carbon has high adsorption speed and is particularly suitable for liquid phase adsorption. The granular activated carbon, which is currently the most productive cylindrical activated carbon, is formed into strips by a strip extrusion forming method, and then the strips are cut into particles with the length-diameter ratio of less than 5, and sometimes the strips are automatically broken into the required particles in the drying process. The mechanical strength of the activated carbon is high because a certain amount of adhesive, such as coal tar and the like, needs to be added in the strip extrusion molding process and high pressure is applied during strip extrusion. Spherical activated carbon is a recently developed granular activated carbon. Compared with cylindrical and amorphous activated carbon, since it is a spherical object with a smooth surface, it has small fluid resistance, is wear-resistant, and is less likely to generate chips and powder in use. Granular activated carbon is mostly used for operation of adsorption columns or adsorption towers, and the adsorption operation can be continuous operation after multiple towers are connected in series. The granular activated carbon has another characteristic of convenient regeneration, and can be continuously used after regeneration treatment after the activated carbon is invalid. The granular active carbon has coarse granularity, long path for the adsorbate molecules to diffuse in the active carbon and small external surface area, so that the adsorption speed is slow and the adsorption capacity is difficult to fully exert.
The activated carbon can be classified into activated carbon for gas phase, activated carbon for liquid phase, carbon molecular sieve for pressure swing adsorption, etc. according to the application. Different types of activated carbon have different uses depending on the pore structure of the activated carbon. A large number of micropores are required for gas phase adsorption; in addition to requiring a large number of micropores, liquid phase adsorption requires a certain number of macropores and transition pores. Because the specific application has specific quality requirements on the activated carbon, a plurality of varieties of special activated carbon appear, such as gold carbon for gold production, sugar carbon for sugar liquor decolorization, monosodium glutamate carbon for refined monosodium glutamate, medicinal carbon for medicine, carrier activated carbon used in catalysts, desulfurization activated carbon special for coal gas desulfurization and the like.
2.4 raw materials and Binders
The production of high quality activated carbon requires the selection of appropriate raw materials. After the variety and specification of the activated carbon are determined, the raw materials are selected through tests, and then the process flow, equipment and operating conditions are determined.
In general, many carbonaceous feedstocks can be used to produce activated carbon. The raw materials for producing the active carbon at present mainly comprise two types: plants and minerals. The plant material mainly comprises wood, sawdust, fruit shell, fruit stone, etc. The mineral raw materials mainly comprise different types of coal, such as peat, lignite, bituminous coal and anthracite; different petroleum cokes, petroleum asphalts, etc. In addition to the above two main raw materials, sucrose and synthetic resins are used as raw materials for preparing activated carbon with very low ash content, for example, thermosetting resins include phenol resin, furan resin, urea resin, etc., and thermoplastic resins include polyvinyl chloride resin, polyvinylidene chloride resin, polycarbonate, etc. The raw materials for producing the activated carbon fiber comprise polyacrylonitrile fiber, fiber spun by phenolic resin, pitch-based carbon fiber, waste plastic, waste rubber and the like.
When selecting raw materials in industrial production, the method considers the difficulty of ① molding, carbonization and activation, whether the quality of the active carbon produced by ② meets the use requirement, whether the raw material resources of ③ are rich and the price of ④ is high and low.
At present, the raw materials of the granular activated carbon produced industrially still mainly comprise shells, fruit stones, wood and coal; the raw material for producing the powdery active carbon mainly comprises wood dust; the raw materials for producing the fibrous active carbon mainly comprise organic fibers and pitch fibers. So far, the applicant has not seen reports of adopting crop straws as raw materials to produce activated carbon.
2.5 chemical and physical activation methods
The chemical activation method is a method for manufacturing activated carbon by activating a carbon-containing substance by using a chemical as an activating agent. This approach has been in the past one hundred years. The activated carbon in the early stage of China is mainly produced by the method of zinc chloride. According to the investigation of agriculture and forestry departments, the commercial activated carbon produced by the zinc chloride method accounts for about 66 percent of the total production quantity in China. The chemical method is mostly used for producing powdered activated carbon, and the granular activated carbon produced by the method has poor strength and is not resistant to impact and abrasion. The greatest disadvantages of the chemical activation process are severe corrosion of equipment and environmental pollution. This is currently a very significant problem. It volatilizes many harmful and corrosive gases during carbonization and activation, and pollutes the atmospheric environment. During the aftertreatment, a large amount of waste water is produced during the rinsing. Therefore, the method is relatively slow to develop recently, and the proportion of the activated carbon produced by the method in the total yield of the activated carbon in China is reduced to about 1/3.
The chemical activation method and the physical activation method have different activation mechanisms, so that the produced activated carbon has great difference in pore structure and physical and chemical properties. The active carbon produced by physical method has main pore structure with micropores and less macropores and transition pores. The activated carbon produced by the chemical method has more transition holes, and the surface oxide of the activated carbon has more acidic oxides and is acidic, and the surface oxide has electronegativity. The physical activated carbon is mainly alkaline oxide and alkaline, and the surface of the activated carbon is positively charged. The active carbon produced by the chemical method has more transition holes and is suitable for adsorbing larger molecules, so the caramel decoloring capacity of the active carbon is stronger than that of physical active carbon. The chemical activated carbon is more suitable for liquid phase adsorption. The activating agent used in the production process of the chemical method is mainly zinc chloride, and potassium sulfate, potassium sulfide and the like are also used. The activating agent used in enterprises in China mainly adopts a zinc chloride method.
Disclosure of Invention
The invention aims to provide a method for producing activated carbon by adopting straw mixed raw materials, which adopts aphysical and chemical combined activation method to produce powdery activated carbon and granular activated carbon. Meanwhile, the mixed straw raw material is pretreated by adopting a potassium hydroxide activating agent and perchloric acid to develop powdery and granular activated carbon with better product quality.
In order to achieve the purpose, the invention adopts a technical scheme that the method for producing the activated carbon by using straw mixed raw materials is characterized in that the method adopts straw, waste branches of fruit trees and tree sawdust as the mixed raw materials, and adopts a phosphoric acid method and a physical combination method to produce powdery or granular activated carbon, and specifically comprises the following steps:
1) raw material preparation
Pulverizing the above materials with a pulverizer to particle size of 1-2mm, fine grinding with a rolling mill, sieving with 120 mesh sieve, and drying;
2) preparation and compounding of phosphoric acid impregnation liquid
Preparing the concentration and the pH value of the phosphoric acid impregnation liquid according to the type of the activated carbon; the formula requirements of the sugar activated carbon are as follows: at 50-57 DEG Be'/60 ℃, the pH value is 3-3.5; the formula of the industrial activated carbon is as follows: at 45-47 DEG Be'/60 ℃, the pH value is 1.0-1.5, and the ratio of the phosphoric acid and straw mixed wood chips for producing the industrial activated carbon is 0.75: 1; the ratio of the phosphoric acid of the sugar activated carbon to the straw mixed wood dust is more than 1.6: 1;
3) by dipping or wet kneading
The purpose of dipping or wet kneading is to fully and uniformly mix the straw mixed wood chips with the phosphoric acid solution, the phosphoric acid is permeated into the straw mixed wood chip particles, the dipping time is longer than 8 hours, and when wet kneading is adopted, a mechanical stirring device is used for forcing the straw mixed wood chips to be kneaded with the phosphoric acid, and the kneading time is 10-15 minutes;
4) charring and activating
Carbonizing the kneaded phosphorus scraps at the furnace temperature of 500-700 ℃ and the material temperature of 300-400 ℃; the carbonization time of each batch of the phosphorus chip material is 30-60 minutes;
further activating the carbonized raw materials, wherein the furnace temperature during activation is 700-800 ℃, the material temperature is 500-600 ℃, the activation time is 2-2.5 hours, and the material is turned once every 15-20 minutes;
stacking the discharged activated materials for 8-16 hours, continuously polluting by using material humidity, and adjusting the aperture;
5) recovery of phosphoric acid
Extracting the activated material by using a low-concentration phosphoric acid solution, and returning the recovered solution obtained by the first extraction to the production flow for use if the concentration of the impregnation solution is met; extracting for many times by using a phosphoric acid solution with lower concentration, and finally washing by using hot water until the content of phosphoric acid in the activated carbon is lower than 1 percent, wherein the time of the whole recovery process is about 1.5 to 3 hours;
when the recovered phosphoric acid solution containing impurities is recycled, zinc sulfate is required to be added into the recovered solution to remove the impurities;
6) rinsing
The rinsing comprises two steps of acid washing and waterwashing:
the acid washing is to add a proper amount of phosphoric acid into the activated carbon after the phosphoric acid recovery in a rinsing barrel, introduce steam and boil for 2 hours to change water-insoluble impurities into water-soluble compounds, and remove the water-soluble compounds along with the water;
after acid washing, adding alkali to neutralize acid to generate phosphate ions, repeatedly washing with hot water to remove various water-soluble impurities, and washing with water until the content of the phosphate ions in the filtrate is lower than 0.16%;
7) dewatering and drying
Dehydrating by adopting an ion machine to reduce the moisture content of the activated carbon to 60-65%; then drying is carried out, so that the moisture content of the activated carbon after centrifugal dehydration is further reduced to below 10 percent;
8) grinding
And grinding the dried activated carbon by using a continuous ball mill to obtain powdery or granular activated carbon.
The straws are wheat straws, corn straws and cotton stalks with the ratio of 1: 1.
The invention adopts another technical scheme that: a method for producing activated carbon by straw mixed raw materials is characterized in that the method adopts wheat, corn, cotton straw, waste branches of fruit trees and tree sawdust as raw materials, adopts a chemical and physical combination method, takes potassium hydroxide as an activating agent, and uses perchloric acid to pretreat the raw materials to produce powdery or granular activated carbon, and specifically comprises the following steps:
1) the raw materials are wheat straw, corn straw, cotton stalk, waste branches of fruit trees and tree sawdust in a ratio of 1: 1. Crushing the raw materials by a crusher, finely grinding the granular straws by a fine grinding machine, and sieving the finely ground mixed raw materials by a 120-mesh sieve;
2) weighing 145g of mixed raw material powder, adding 10mL of hydrochloric acid with the concentration of 36.5%, 10mL of hydrofluoric acid with the concentration of 73%, 20mL of perchloric acid with the concentration of 37% and 50mL of water, uniformly stirring, and soaking for 24h at room temperature;
3) washing the raw materials by using a suction filtration device, placing the washed raw materials in an electrothermal blowing drying oven for drying water after the pH value is 6, weighing 10g of dried mixed straw sawdust, adding 10mL of 10% potassium hydroxide solution as an activating agent, stirring the mixture into paste, placing the paste into a porcelain boat, placing the porcelain boat in an activating furnace, introducing nitrogen with the flow rate of 1.0L/min, raising the temperature to 800 ℃ at the temperature rise speed of 8-10 ℃/min, preserving the heat for 45min, and cooling to obtain an activated product;
4) soaking the activated product in hydrochloric acid solution for 20min, washing with water to pH 6, dehydrating, and drying to obtain activated carbon with iodine value of 980mg/g and specific surface of 1180m2In g of powdered or granular activated carbon.
The activated carbon series produced by the method has the advantages of small investment scale (about 200 ten thousand yuan), low cost, high income, quick response and convenient operation, and can be organized and produced by 30-50 people. The product is not only used in industry, light industry and the like, but also has obvious ecological effect on the aspects of purifying air, water quality, environment, medical treatment and health and the like. Has no toxicity and public nuisance, and belongs to a product without residual toxicity and pollution. And a good foundation is laid for further comprehensive utilization of biological waste resources. The invention can be widely used in the fields of industry, agriculture, medical treatment, sanitation, epidemic prevention, environmental protection, production, life and the like.
Drawings
FIG. 1 is a schematic view of the process for continuously producing powdered activated carbon using phosphoric acid according to the present invention;
FIG. 2 is a flow (I) of phosphoric acid process for powdered activated carbon;
FIG. 3 is a flow diagram of phosphoric acid process granular activated carbon (II).
The invention is described in further detail below with reference to the figures and the specific examples given by the inventors.
Detailed Description
For a clearer understanding of the present invention, the mechanism of action of the physicochemical binding activation method is first described:
mechanism of physical-chemical combined activation method
Although chemical activation methods have a long history, the activation mechanism is not well understood, and some views are not uniform. Further understanding and studying chemical and physical activation mechanisms are of great practical significance to improve the process, improve product quality and develop new activated carbon with higher adsorption capacity. The following mainly describes the activation mechanism of the combination of the phosphoric acid method and the physical method (water vapor method).
1. Swelling and peptization
The main chemical composition of the straw mixed with the wood chips and other material raw materials is saccharides, namely carbohydrates such as cellulose, hemicellulose, pectin and the like. The cellulose of higher plants accounts for 60-70%. When the phosphorus oxide solution is impregnated and kneaded, cellulose and the like are swollen, and hydrolysis and oxidation simultaneously occur. It is exacerbated with increasing temperature. At 150-200 ℃, cellulose can be dispersed into a colloidal state, a high molecular compound is depolymerized into smaller molecules, and the whole material has plasticity and viscosity. When the phosphoric acid method is used for preparing granular activated carbon, the fully kneaded phosphorus crumbs have good plasticity and are prepared into granules.
2. Changing the thermal decomposition course of organic substances
The straw mixed with the wood chips generates various volatile organic compounds such as acids, alcohols, aldehydes, ketones, tar and the like and gases such as carbon dioxide and the like in the pyrolysis process. Due to the decomposition and escape of a large amount of carbon-containing compounds, the finally remained mixed wood chip carbon only accounts for about 15 percent of the absolutely dry mixed wood chips. When the straw and wood chips are mixed and dipped in phosphoric acid or other chemicals, the thermal decomposition process of the straw and wood chips is changed. First, it is shown that the thermal decomposition temperature is lowered. For example, the temperature at which the gas evolution rate is maximum under normal conditions is 250-350 ℃ and decreases to 150-300 ℃ after phosphoric acid impregnation (1: 1). Secondly, the catalytic action of phosphoric acid promotes the decomposition of hydroxyl and dehydration reaction, thereby inhibiting the formation of carbon-containing volatile substances and retaining more carbon in the solid-phase product. Therefore, the absorption rate of the activated carbon is greatly improved and is generally about 40 percent of the absolute dry weight of the straw mixed wood chips. If calculated by the carbon content, the carbon utilization rate of the activated carbon reaches about 80 percent. And thirdly, the chemical is impregnated to inhibit the generation of tar during the pyrolysis of the straw mixed wood chips, so that the pores generated by the pyrolysis are prevented from being blocked by the tar, the closed pores are reduced, and the number of effective air gaps is increased.
In the phosphoric acid impregnation process, the peptization effect is generated, so that the cell walls of the original plants are swelled, and the whole plant tissues generate glucose, aldopentose, furfural and the like with small molecular weights through hydrolysis and oxidation reactions. They thermally decompose at temperatures above 300 ℃ and then thermally condense at higher temperatures into polycyclic aromatized structures, finally forming turbostratic crystallite structures with developed pores.
3. Skeleton action
The phosphoric acid makes the straw mixed with the sawdust peptized into plastic colloidal substances which are uniformly distributed in the raw materials. When the raw material is carbonized, organic matters are decomposed, and phosphoric acid becomes the surface of pyrolytic carbon deposition. When these phosphoric acids and water dissolve, the surface of the carbon is exposed, forming the internal surface area of the activated carbon. The space occupied by the original phosphoric acid becomes the pore structure of the activated carbon. Therefore, under certain conditions, the porosity and specific surface area of activated carbon are proportional to the amount of phosphoric acid used.
4. Specific effects of differentchemicals
Different chemicals affect the surface molecular structure of the activated carbon and the spatial arrangement of the carbon atoms.
One part of this effect may be due to the change in the carbonization, activation temperature, and the other part may be due to the fact that some non-carbon atoms are gettered on a certain area of the surface of the carbon, so that the positions of those carbon atoms which are preferentially removed by erosion during the oxidation process are affected. Also, this effect includes oxidation at the bond sites with the inorganic component.
Different non-carbon atoms activate carbon differently. For example, potassium can penetrate between planes of the microcrystalline hexagonal carbon network to influence the interlayer spacing of the carbon network in a turbostratic structure and further influence the pore structure. The oxygen may form a surface oxide on the carbon surface. According to the research, the method has been found. The combination of sulfur and carbon is also a chemical combination similar to a surface oxide. Nitrogen and carbon are combined in a similar nitrile group form. Some non-carbon atoms firmly bonded to the activated carbon provide some adsorption bonds to the activated carbon, resulting in an increase in the adsorption capacity of the activated carbon. For example, some activated carbons have a specific adsorptive capacity and catalytic action because non-carbon elements such as oxygen, iron, nitrogen, etc. are present on the surface of the activated carbon.
5. Physical and chemical properties of straw mixed raw material active carbon
The main chemical element of the straw mixed raw material active carbon is carbon. The carbon in the activated carbon basically has two structures, one is a microcrystalline structure of graphite, and the other is an irregular cross-linked structure of carbon. The former structure has hexagonal carbon mesh planes, which are also stacked with parallel layers like graphite, so that the same bands as graphite can be seen on an X-ray diffraction pattern, demonstrating that activated carbon has a graphite-like structure but has a size of only several tens of a °, and thus, is called a graphite crystallite structure. The parallel layers of crystallites are not perfectly aligned along a common vertical axis, and the angular displacement of one layer to another is disordered. It is precisely because the individual layers are stacked irregularly on top of one another that there are no macroscopic crystallographic properties, but only two-dimensional turbostratic crystallites of different sizes. Compared with the complete graphite structure, the structure has the following characteristics:
the 5.1 layer plane is not perfect and has various defects such as holes, dislocations, heteroatoms and other impurities.
5.2 the stacking of the layer planes is not perfectly ordered and all perpendicular to the C-axis, but the normal to the layer planes is at an angle to the C-axis, with poor preferred orientation.
5.3 the layer spacing is large. Typically between 3.36 and 3.44A DEG, and carbon atoms, hydrogen atoms or other groups are present between layers.
5.4 the crystallites are relatively small, typically not exceeding 600A.
The other structure of the straw mixed raw material active carbon is a completely disordered carbon cross-linking structure. Some carbons are hexagonal carbon network planes, and some carbons are distorted or form heterocyclic structures due to the presence of other heteroatoms. The irregular cross-linked structure of carbon does not show any bands characterizing the crystal characteristics in X diffraction, and the structure is true amorphous carbon.
The structure of the activated carbon is related to the raw materials and the preparation process conditions. In general, activated carbon produced by liquid-phase carbonization often has a mosaic type in the final product because of the presence of an intermediate phase in the thermal decomposition process.
TABLE 1 comparison of physicochemical Properties of physically and chemically activated carbon
| Item | Water vapor method activated carbon | Phosphoric acid process activated carbon | |
| Hole(s) Gap Knot Structure of the organization | Body of the aperture Micropores (%) Transition hole (%) Macropore (%) Specific surface area (m)2/g) | Mainly comprising micropores About 80 7 20 1180 | With more transition holes About 50 30 17 1000 |
| Surface oxide | More carbon oxides, alkaline oxides positively charged | The acidic oxide is more and has electronegativity | |
| Adsorption characteristics | The adsorption force to iodine is large, and the adsorption force to caramel is small. Liquid phase adsorption Low speed | The adsorption force to iodine is small, and the adsorption force to caramel is large. The liquid phase adsorption speed is high | |
| Strength of granular carbon | High mechanical strength and not easy pulverization | Poor mechanical strength and easy pulverization | |
6. Matters of attention
6.1 starting materials
According to the mechanism of the phosphoric acid activation method, the raw material needs to have a certain oxygen content and hydrogen content so as to form a fine pore structure by generatingwater during carbonization and activation. Generally, it is desirable that the oxygen content be greater than 25% and the hydrogen content be greater than 5%. In addition to wood, peat and lignite of shorter ages (young lignite) are suitable for the condition, but through experimental research and analysis and production practice, the adoption of crop straws as raw materials has the characteristic of low cost and high benefit.
In addition, in order to sufficiently penetrate the phosphoric acid solution into the interior of the raw material structure during the impregnation process, the raw material is required to have sufficient initial porosity. Hard materials almost lack fully developed pores, and domestic raw materials used for a phosphoric acid method mainly comprise wood chips, wood shavings, oil-tea camellia shell powder, bagasse and the like, but no reports of straw as a raw material exist. In foreign countries, the amount of chemically activated carbon produced by peat and lignite of shorter ages (young lignite) is not small, and there is no precedent for using straw as a raw material.
The kind of raw materials has great influence on the adsorption performance of the activated carbon. For example, when the sugar activated carbon is manufactured, the China fir sawdust is better than the pine sawdust, the hardness of the pine sawdust is better than that of the miscellaneous wood chips, the straw mixed raw material integrates the advantages of various plant straws, and the proportion is scientific and reasonable. Qualified sugar activated carbon is produced by optimizing process conditions. The new process, the new method and the new product adopt the method of mixing the straw mixed raw materials, so that the product quality is continuously improved to reach the design standard.
The water content of the straw mixed wood chips influences the absorption capacity and the permeation speed of the phosphoric acid solution. The straw mixed wood chips have high moisture content, and the quantity of the phosphoric acid which can be absorbed during the impregnation is small. For example, when producing granular activated carbon, a certain amount of phosphoric acid solution with low concentration must be absorbed, so that the moisture content of the straw mixed wood chips is required to be less than 5%, and when producing activated carbon for sugar, a sufficient amount of high-concentration phosphoric acid solution is required to be absorbed, for example, the moisture content of the straw mixed wood chips is high, so that the concentration of phosphoric acid tends to be reduced, and the pore size distribution of the activated carbon is finally influenced.
The moisture content of the straw mixed wood chips influences the permeation speed of the phosphoric acid, so that the impregnation time is influenced, and generally, when the moisture content of the straw mixed wood chips is above the fiber saturation point, the permeation speed of a phosphoric acid solution is slow. Therefore, when the water content of the straw mixed wood chips exceeds 30%, the dipping time is required to be more than 8 hours. When the kneading machine is used for mixing the straw sawdust and the phosphoric acid solution, the water content of the straw sawdust is required to be below 15% due to short kneading time.
When the powdery active carbon is produced, the straw mixed wood dust particles are 6-40 meshes. When producing granular activated carbon, the straw mixed wood dust particle size has an effect on the strength and specific gravity of the granular activated carbon, especially when the phosphorus dust is relatively small. For example, when the ratio of phosphorus chips is 80%, the strength is 93% when the grain size of the straw-mixed wood chips is 0.25mm, the specific gravity is 0.707, and the grain size is 1.6 to 2.0mm, the specific gravity is 86% and 0.658, respectively.
6.2 impregnation conditions
The impregnation conditions and the phosphorus scrap ratio can determine the quality of the prepared activated carbon, various activated carbon varieties can be adjusted and prepared, and the activated carbon with high quality can be prepared by adjusting the impregnation conditions and the phosphorus scrap ratio of different raw materials.
The pH value of the phosphoric acid solution is low when the concentration of the phosphoric acid solution is high, and the pH value of the phosphoric acid solution with the concentration of 50 percent is about 3.2 generally. The pH value of the phosphoric acid solution has a great relationship with the quality and variety of the product. For hard wood and straw cutin, the pH value is preferably low when the paper is soaked in phosphoric acid solution.
The impregnation temperature and the impregnation time are interrelated, the impregnation time is prolonged when the temperature of the phosphoric acid solution is low, otherwise the impregnation material is not completely penetrated, and the quality of the activated carbon is influenced. On the contrary, the temperature of the impregnation liquid is high, and the impregnation time can be shortened. But the temperature cannot be too high, for example, when the straw and the mixed wood chips are soaked in the phosphoric acid solution at 90 ℃, the soaking material is easy to hydrolyze and peptize into a slurry body, and the redundant phosphoric acid solution cannot be precipitated and separated. And (3) according to the content of 20% of the raw materials, soaking the raw materials in a phosphoric acid solution with the concentration of 50% for more than 8 hours at the liquid temperature of 30-50 ℃, and isolating the redundant phosphoric acid solution. The ratio of the raw material to the solution is in the range of 1: 4.5 to 6.0. In order to reduce the dipping time and enable the phosphoric acid solution to better permeate into the straw wood chips, a kneader is used for kneading for 10-15 minutes.
6.3 activation temperature
The activation temperature refers to the highest temperature of the activated material during activation. It is another important factor affecting the quality of activated carbon.
The effect of activation temperature on activated carbon quality is shown in table 2.
TABLE 2 influence of activation temperature on quality of activated carbon
| Ratio of phosphorus to scrap (％) | Temperature of (℃) | Benzene absorption rate (mg/g) | Strength of (％) | Specific gravity of | Specific pore volume (ml/g) | ||||
| Specific pressure | Total pore space | Micro-pores | Filter hole | Macropore | |||||
| 0.12 | 0.90 | ||||||||
| 80 | 400 500 600 700 800 | 451 588 466 421 409 | 538 544 612 454 430 | 88 87 88 92 93 | 0.634 0.615 0.630 0.658 0.709 | 0.996 1.043 1.012 0.970 0.877 | 0.513 0.555 0.529 0.478 0.462 | 0.099 0.063 0.053 0.038 0.024 | 0.384 0.425 0.430 0.454 0.398 |
| 200 | 400 500 600 700 800 | 476 596 592 562 533 | 825 956 910 820 756 | 88 76 80 85 87 | 0.499 0.405 0.427 0.451 0.501 | 1.490 1.886 1.791 1.670 1.441 | 0.542 0.676 0.674 0.638 0.606 | 0.390 0.410 0.361 0.294 0.254 | 0.430 0.789 0.756 0.738 0.586 |
As seen from Table 2, in each test, the activated carbon produced at 500 ℃ had the largest specific pore volume, the smallest specific gravity and strength, and the largest benzene adsorption rate. This is because the volume occupied by phosphoric acid in the formed carbon skeleton is maximized at 500 ℃, and then, as the activation temperature increases, the amount of phosphoric acid vaporized in the carbon increases, and the carbon begins to shrink, so that the specific gravity and strength increase.
6.4 activation time
The activation time is the time of incubation at a certain activation temperature. When the activationtemperature is 600 ℃ or less, the strength of the activated carbon can be improved by extending the activation time in the range of 2 hours.
The following are examples given by the inventors:
example 1: production process of straw mixed raw material active carbon
In the embodiment, crop straws are mixed according to a certain proportion, the mixture of the crop straws, the waste branches of fruit trees and the sawdust of trees is 1: 1, the straws are cotton stalks, wheat straws and corn straws, and powdery activated carbon, such as activated carbon for sugar, activated carbon for injection, activated carbon for pharmacy and monosodium glutamate decoloration, medicinal activated carbon, reagent activated carbon and the like, is produced. The combination of phosphoric acid activation method and physical method can also produce granular active carbon through practical research.
1. Production of powdered activated carbon by phosphoric acid process
1.1 Process flow
The process flow for producing the powdery activated carbon is shown in attached figures 1-3 and generally comprises three parts of pretreatment, carbonization, activation and post-treatment. The pretreatment comprises screening and drying the straw mixed wood chips; the preparation of phosphoric acid impregnation liquid and the quality and/or the impregnation of the straw mixed wood chips and the impregnation are high. Carbonization and activation are the main work of production, and the impregnation material is treated by high-temperature flue gas. The main purpose of the post-treatment is to recover phosphoric acid and rinse the product to meet the requirement of impurity content. The post-treatment also comprises grinding and drying of the product and three-waste treatment. The three-waste treatment comprises a waste gas treatment system and a waste water treatment system which is mainly used for recovering phosphoric acid in waste gas. The flue gas treatment comprises the steps of firstly removing dust through a settling chamber and other multi-stage dust removal, reducing the temperature of the flue gas to 120 ℃ through natural cooling equipment, removing most of carbon dust, and then entering a vapor phase separator to remove fog drops formed by phosphoric acid and water vapor and residual carbon dust. At this time, the temperature of the flue gas is reduced to below 100 ℃. Then the flue gas enters a condenser for condensation, so that the temperature of the flue gas is reduced to be below 50 ℃, and most of phosphoric acid water vapor mist is condensed. The flue gas from the condenser is pollution-free and has no recycling value. Before emptying, the acid mist is sprayed and washed by water through a Venturi tube, and then is further removed through a mist separator and an absorption tower. The phosphoric acid-containing wastewater generated in rinsing and flue gas treatment is treated by a common flocculation method, and is further recycled after meeting the standard.
1.2 production operating procedure
1.2.1 preparation of the starting Material
The straw wood scraps are screened by a vibrating screen or a drum screen to remove wood blocks, powder, plant straw phloem, pulp cavities and other impurities. If tree sawdust, fruit tree branches and straw are used as raw materials, the ratio of the raw materials is 1: 1, the raw materials are crushed to proper granularity (1-2mm) by a crusher, and then the raw materials are sieved by a 120-mesh fine powder sieve through a rolling grinder.
The water content of the common straw mixed wood chips is about 40 percent. When the kneading process is adopted, the water content of the mixed raw material is required to be 10-20%. When the impregnation method is adopted, the moisture content of the straw mixed wood chips can be higher, but is lower than 30%, and the concentration of the phosphoric acid impregnation liquid is increased.
The drying method of the straw mixed wood chips comprises two methods, one is drying by an airflow dryer, and the other is drying by a rotary furnace. The heating media of the airflow dryer are two types: one is that the flue gas generated by combustion is mixed with air and directly contacted with mixed wood chips for heat exchange; the other is an indirect heating mode, air is heated by high-temperature flue gas, and the hot air is used as a heating medium to carry out heat exchange on the straw and wood chips. The former has high thermal efficiency, but straw wood dust is easy to catch fire and spontaneously combust.
When the rotary furnace is used for drying, high-temperature flue gas generated by the heating furnace permeates air, the temperature is reduced to about 400 ℃, the flue gas is in direct contact with the straw mixed wood chips in the rotary furnace downstream, heat exchange is carried out, the drying time is generally 20 minutes, the moisture content of the straw mixed wood chips is reduced to 20-25%, the temperature of the flue gas is reduced to about 120 ℃, and the flue gas is discharged into the atmosphere.
1.2.2 preparation of phosphoric acid impregnation solution
The concentration and pH value of the phosphoric acid impregnation liquid are related to the types of products and crops of straw mixed wood chips, and are also determined by the impregnation mode and the phosphorus chip ratio. Phosphoric acid concentration is often expressed in Baume degrees. The formula requirements of the common sugar activated carbon are as follows: the temperature of 50-57 DEG Be'/60 ℃, the PH value of 3-3.5, and the formula of the medicinal active carbon is as follows: at45-47 DEG Be'/60 ℃, and at a pH value of 1.0-1.5.
1.2.3 compounding, kneading or impregnating
The phosphorus scrap ratio is related to the pore structure of the activated carbon, and the obtained activated carbon has high porosity, large pores and developed transition pores. The phosphorus scrap ratio for producing the industrial activated carbon is 0.75: 1; the phosphorus-containing dust ratio of the sugar activated carbon is more than 1.6: 1.
The quality of the dipping and the kneading aims to ensure that the straw mixed wood chips are fully and uniformly mixed with the phosphoric acid solution, and the phosphoric acid is permeated into the mixed wood chip particles. The time for dipping is longer, generally more than 8 hours, and when wet kneading is carried out, a mechanical stirring device is used for forced kneading, so that the time is only 10 to 15 minutes.
The batch process conditions are shown in Table 3
TABLE 3 kneading Process conditions
| Item | Industrial charcoal | Charcoal for sugar |
| Concentration of phosphoric acid solution pH of phosphoric acid solution Ratio of material to liquid Kneading time | 45～47 1～1.5 1∶3 10～15 | 50～57 3～3.5 1∶4～5 10～15 |
1.2.4 charring and activating.
The carbonization and activation are key processes of a phosphoric acid activation method, and are related to the consumption of phosphoric acid, the yield of activated carbon, the pollution severity and the like.
The principle of determining the carbonization and activation temperatures is to ensure the completion of the carbonization and activation processes, ensure the product quality and control the temperature to be in a lower state. The reason is that in addition to energy conservation, the evaporation escape of phosphoric acid steam is reduced, so that the consumption of phosphoric acid is reduced, and environmental pollution and equipment corrosivity are reduced. The carbonization temperature is generally set to 400 ℃ or lower. The activation temperature is controlled between 500 ℃ and 600 ℃. Since the partial pressure of phosphoric acid vapor is not high, the escape is very small.
The structure of the rotary kiln is similar to that of the rotary kiln used in the physical activation method.
The inner diameter of the furnace body is 1 meter, the length is 13 meters, and the inclination is 2-5 degrees. The production capacity is 1-2 tons of daily-produced activated carbon.
The kneaded phosphorus crumbs are fed into the furnace tail by a hopper and a screw feeder. The material slowly moves to the furnace end by the rotation and the inclination of the cylinder. The furnace end has no combustion chamber, and uses coal gas or crude oil as fuel, and the high-temperature flue gas produced by combustion can be directly fed into the furnace, and can be flowed from furnace end to furnace tail, and can be counter-flowed and directly contacted with material. In order to prevent blockage, a shape-displaying scraper connected in series by a chain is arranged in the furnace, and the shape-displaying scraper continuously impacts the furnace wall along with the rotation of the furnace body to scrape the caking materials adhered to the furnace wall.
The rotary kiln carbon activation process conditions are listed in table 4.
TABLE 4 Rotary kiln carbon activation Process conditions
| Item | Process conditions | Remarks for note |
| Temperature (. degree.C.) of the material in the activation zone Carbon activation time (minutes) Filling factor of furnace material (%) Cylinder rotating speed (rotating/minute) Furnace internal pressure (mmH)2O column) Furnace end temperature (. degree. C.) Temperature of furnace end (. degree. C.) Interval time of discharge (minutes) | 500～600 About 40 degrees 15～20 1～3 Slightly negative pressure 700～800 200～300 20 | Furnace dependent estimation The material occupies the volume of the furnace chamber Discharging from a discharge chamber |
During carbonization, the furnace temperature is required to be 500-700 ℃, and the material temperature is required to be 300-400 ℃. The furnace fire is required to be uniform, the material is turned over at regular time, and the caking is prevented. The carbonization time of each batch is 30 minutes to 60 minutes.
During activation, the furnace temperature is 700-800 ℃, the material temperature is 500-600 ℃, and the activation time is 2-2.5 hours. And turning over once every 15-20 minutes. The discharged activated material is piled for 8-16 hours, and the material is continuously polluted by using the material humidity. The aperture is adjusted to improve the quality of the product.
Therefore, great attention must be paid to the recovery of phosphoric acid in flue gas and the treatment of the flue gas in the carbonization and activation operations.
1.2.5 recovery of phosphoric acid
The recovery of the activated material is a key process for reducing the consumption of phosphoric acid, the production cost and the environmental pollution. Often, a low concentration phosphoric acid solution is used to extract the activated material. The concentration of the recovered liquid obtained by the first extraction is higher, and if the concentration of the recovered liquid meets the concentration requirement of the impregnation liquid, the recovered liquid can be returned to the production flow for use. And then extracting for multiple times by using a phosphoric acid solution with lower concentration. Finally, washing with hot water until the content of phosphoric acid in the activated carbon is lower than 1%. The time of the whole recovery process is about 1.5 to 4 hours. Because some metal oxides in the active carbon neutralization equipment react with phosphoric acid to generate soluble salts, impurities in the phosphoric acid solution are increased, and the quality of the product after the solution is recycled is influenced. At this time, zinc sulfate is added to the recovered solution.
1.2.6 rinsing
The purpose of rinsing is to remove various impurities from raw materials and production processes, so that the content of various impurities of the activated carbon meets the quality index requirements, such as ash content, acid soluble content, iron content, chlorine content, sulfate content, cyanide content, sulfide content, heavy metal content and the like, and pH value. The rinsing step includes two steps of acid washing and water washing. Adding appropriate amount of phosphoric acid into the recovered activated carbon in a rinsing bucket, introducing steam, boiling for 2 hr, and removing water-insoluble impurities to obtain water soluble compound. After acid washing, adding alkali to neutralize acid to generate phosphate ions, and repeatedly washing with hot water. The main purpose of the water washing is to remove various water-soluble impurities. The filtrate is generally washed with water until the phosphate ion content is less than 0.16%. The total water wash time is about 5 hours or so.
1.2.7 dehydration and drying
The purpose of dehydration is to reduce the moisture content of the activated carbon and reduce the drying load and the heat energy consumption. Generally, an ion machine is adopted for dehydration, and the moisture content of the activated carbon is reduced to about 60-65%. The aim of drying is to further reduce the moisture content of the activated carbon after centrifugal dehydration to below 10%. The common drying equipment is an external heating rotary drying furnace, and the specification of a cylinder body is phi 1000 multiplied by 7000. The external heating type has the advantages that the flue gas is prevented from directly contacting with the activated carbon, the possibility of product pollution is reduced, but the iron content of the activated carbon is increased due to mutual friction of the activated carbon and the iron furnace wall. The temperature of the materials in the rotary drying furnace is required to be within 120-130 ℃. In order to prevent the dry char from igniting, the furnace temperature and the charge amount are strictly controlled. The freshly tapped activated carbon, because of its relatively high temperature, is preferably cooled in a closed vessel.
1.2.8 grinding
The dried activated carbon has non-uniform particles. The grinding aims to ensure that the granularity of the product is uniform and meets the requirement of quality index. Grinding to below 120 mesh is generally required.
Grinding is usually carried out using a continuous ball mill, and in order to avoid an increase in iron content during the ball milling, the ball mill is generally lined with a hard wood plate and ceramic balls are used instead of the iron balls. In order to avoid the influence of the too fine particle size of the activated carbon on the filtering speed during use, an intensified drying pulverizer or a Raymond pulverizer can be adopted.
1.2.9 treatment of three wastes
When the flue gas is treated, the temperature of the flue gas is reduced to 120 ℃ by multi-stage dust removal and natural cooling equipment such as a settling chamber, and most of carbon dust is removed. Then enters a vapor-liquid separator to remove partial phosphoric acid and fog drops formed by water vapor and residual carbon dust. At this time, the temperature of the flue gas is reduced to 100 ℃. Then the flue gas enters a condenser for condensation, so that the temperature of the flue gas is further reduced to below 50 ℃, and most of water vapor and phosphoric acid mist are condensed. The flue gas from the condenser only contains a small amount of phosphoric acid mist foam gas and has no recycling value. Before emptying, the acid mist is sprayed and washed by water through a Venturi tube, and then is further removed through a mist separator and an absorption tower. Phosphoric acid wastewater generated in rinsing and flue gas treatment is treated by a common flocculation method, and is further recycled after meeting the discharge standard. Adding potassium carbonate (K) into the water for temporary use2CO3) And further neutralizing the third-level sedimentation tank for later use.
2 phosphoric acid method for producing granular active carbon
When the granular active carbon is produced by using straw and other raw materials and using a phosphoric acid method, a binder is not generally added. In order to improve strength and adsorption properties or to use bituminous coal or the like as a raw material, a binder such as polyvinyl alcohol, coal tar, coal pitch or the like is used.
2.1 technological process. The technological process of producing powdered and granular active carbon by phosphoric acid process is different depending on the raw material. The process flow of using straw mixed wood chips as raw materials is respectively shown in figure 2.
2.2 production operations
2.2.1 raw material screening and drying. In order to ensure the mechanical strength of the granular activated carbon, the powdered activated carbon produced by mixing the raw material straw and wood chips is thin and generally less than 0.8 mm. The excessively coarse straw mixed wood chips are crushed and ground in advance.
The moisture requirement of the straw mixed wood chips is 5%. The drying equipment is a rotary furnace and a pneumatic dryer.
2.2.2 preparation of phosphoric acid solution. The concentration of the phosphoric acid solution used for producing the granular activated carbon is higher, generally more than 50 percent, and the acidity of the solution is higher, so that the straw mixed wood chips are hydrolyzed and saccharified.
2.2.3 batching, kneading and shaping. The strength and other physical and chemical properties of granular activated carbon are affected by the phosphorus chip ratio and the conditions of impregnation and kneading. Under the same condition, the phosphoric acid ratio is large, so that the strength of the particles is lower, the transition holes are developed, the adsorption performance is good, and the volume weight is small. On the other hand, the smaller phosphorus debris ratio has a smaller pore volume, a larger volume, a higher strength, and a lower adsorption. The ratio of phosphorus to scrap used in industry is 0.8 to 1.5, which is adjusted according to the type of the activated carbon.
Different from the preparation of powdered active carbon, the phosphoric acid solution dipping and kneading process has a plasticizing process, i.e. the wood chip dipping material is mixed, heated, hydrolyzed and saccharified to produce pulpy hydrolyzed furfural solution, the dipping material is softened under the heating condition of about 150 ℃, and then repeatedly kneaded and rolled to uniformly mix the dipping material, so that the dipping material has cohesiveness and plasticity. When the straw is mixed with the sawdust and the phosphoric acid method to prepare the granular activated carbon, no other binder is added, so the quality of plasticization is very important. The key to plasticization is the plasticizing temperature and time. The plastic can be plasticized by heating for half an hour at 130-150 ℃, and the water content is about 12-15%.
The forming method is various, and the shaped activated carbon has a cylindrical shape formed by extrusion, a spherical shape formed by rolling discs and a sheet shape formed by impact. Preparing amorphous activated carbon: the plasticized material is pressed into blocks, and then the blocks are broken into irregular small particles after carbonization. The most domestic method is extrusion molding. Since the mechanical strength of the granular activated carbon is largely determined by the molding pressure, a certain molding pressure is required regardless of the molding method. In addition, the moisture content during molding also has a great influence on molding. The water content is required to be 12-18% during extrusion forming.
The particles after molding are dried before carbonization. The process requires a long drying time at low temperature,which ensures the strength of the granules. If the drying is rapid, the water evaporates too quickly and cracks can form on the surface of the particles, which can seriously affect the strength of the activated carbon. Therefore, the drying temperature is generally not more than 180 ℃.
Product quality standard
The technological parameters are as follows:
the water content is 6.8%
2.1 percent of ash content
Volatilize 9.5 percent
Fixed carbon of 81.6 percent
The particle size is 0.3-7.0 mm, and the average particle diameter is 2.35mm
200 mesh powder
Bulk density 506kg/m3
The technological parameters are as follows:
feeding 35kg/h
The temperature of the combustion chamber is 1050 DEG C
The temperature of the activation furnace is 850 DEG C
Air quantity 150m3/h
Saturated steam amount 70kg/h, (gauge pressure 50GPa)
Bed pressure difference of 700 +/-50 Pa
The yield of the activated carbon is 12.5kg/h
Example 2: method for preparing activated carbon by straw environment-friendly physical and chemical combination method
In the embodiment, the activated carbon sample with better performance is developed by taking crop straws (mixed) as raw materials and potassium hydroxide as an activating agent through acid pretreatment and steam activation. Experiments show that the optimal temperature of the activity is 750-800 ℃, the optimal temperature rise speed is 5-10 ℃/min, and the dosage of the activating agent is 1: 1 (the mass ratio of the raw materials to the activating agent). The iodine adsorption value of the activated carbon sample is 980mg/g, the specific surface area is 1180m2(ii) in terms of/g. At the same time, the KOH activation mechanism is discussed. The wide application of the activated carbon has certain significance in the development of the activated carbon. One of the main research directions of straw activated carbon.
The basic structural units of organic matters of the straws of different types of crops are different. Cutin with low lignification degreeThe basic structural unit of the straw contains fewer cores and more side chains and functional groups. The medium straw has few oxygen-containing official energy groups, few alkyl side chains, enlarged aromatic nucleus and reduced bridge bonds among structural units. The aromatic core with high cutin and lignification degree of the straw is obviously increased, and is an ideal raw material for preparing the active carbon. Therefore, the above different kinds of wood are used for active carbon development, the straw with low lignification degree has loose structure and low graphitization degree during carbonization, and the ideal active carbon can be prepared through weaker activation environment (physical activation), but the yield is low, the mixed straw raw material has the structure tending to lattice and is easy to graphitize during carbonization, so that the microcrystals are orderly arranged, the porosity during activation is low, the activation effect is influenced, and the high-chlorine acid is used for pretreatment and then is used for CO2The specific surface prepared by the activation method reaches 1600m2Per g (yield 30%) of activated carbon.
The physical activation time is long, and the activation temperature is high. The crop straws have rich yield,wherein some straws such as cotton stalks, fruit branches and the like have high fixed carbon content and low ash content (as low as 5.18 percent), and are suitable to be used as raw materials for preparing the active carbon. The active carbon is taken as a raw material, and is subjected to acid pretreatment and activated in a chemical and physical combined mode, so that the active carbon with the specific surface area of 1180m is developed under certain activation conditions2The yield is 50 percent.
1 experimental part
1.1 instruments
The method comprises the steps of self-making an activation furnace, a QM-4H grinder, an electric heating blowing drying box and a PE-60X100 jaw crusher.
1.2 methods
Crushing straws coarsely by using a crusher, finely grinding granular straws by using a fine grinding machine, screening mixed straw sawdust powder by using a 120-mesh sieve, weighing 145g of mixed straw sawdust powder, adding 10mL of hydrochloric acid (36.5%), 10mL of hydrofluoric acid (73%), 20mL of 10 perchloric acid (37%) and 50mL of water, uniformly stirring, and soaking for 24 hours at room temperature.
Washing the above raw materials with a suction filtration device until the pH value is 6, and drying in an electrothermal blowing drying oven. Weighing 10g of dried mixed straw sawdust, adding 10mL of potassium hydroxide solution (10%), stirring into paste, putting the paste into a porcelain boat, putting the porcelain boat into an activation furnace, introducing nitrogen (the flow is 1.0L/min), raising the temperature to 800 ℃ at the heating rate of 8 ℃/min, preserving the heat for 45min, cooling, soaking the product in hydrochloric acid solution for 20min, washing the product with water to the pH value of 6, and drying to obtain the activated carbon with the iodine value of 980mg/g and thespecific surface of 1180m2Per gram of activated carbon product.
2 results and discussion
2.1 starting materials
The raw material adopts mixed straw and the industrial analysis result is shown in table 1
TABLE 1 Industrial analysis results of mixed straw
| Item | Analysis of Ash (%) | Ash melting Point (. degree. C.) | ||||
| SiO2 | Al2O3 | Fe2O3 | DT | ST | FT | |
| Index (I) | 61.54 | 27.36 | 2.67 | 1000 | 1060 | 1260 |
As is clear from Table 1, SiO is the main component in the ash2And the ash content of the raw material in the process of preparing the active carbon can prevent the formation of micropores and has adverse effect on the product performance, so a hydrofluoric acid ash removal mode is adopted. The ash content is reduced to 1.2 percent after acid treatment.
By treatment of the straw mixture with perchloric acid, the conclusion is reached: the perchloric acid treatment has an important influence on the subsequent physical activation process: firstly, the activation effect can be improved; secondly, the surface activity of the raw material is increased after the pre-oxidation of the raw material. According to the thermal analysis result of the mixture of KOH and the raw material straw powder, the DTG reaches an extreme value of (-1.7%/min) at 210 ℃, at the moment, perchloric acid and carbon in the mixed straw possibly react to generate carbon dioxide, and gas molecules penetrate through the raw material particles to form a plurality of channels with the diameters of 1-10 nm, so that the chemical activation at high temperature is facilitated, and the activation effect is improved.
2.2 Effect of activation conditions
To find the ideal chemical activator, K is used2CO3、Na3PO4、H5PO4、KOH、ZnCl2And H2SO4The mixed crop straws are activated, and the activation conditions and the activation effects are shown in table 2.
TABLE 2 table of activation effect of different activators
| Activating agent | Activation temperature (. degree.C.) | Activation time (h) | Iodine value (mg/g) |
| K2CO3 | 800 | 1 | 640 |
| Na3PO4 | 800 | 1 | 240 |
| H5PO4 | 800 | 1 | 740 |
| KOH | 800 | 1 | 710 |
| ZnCl2 | 800 | 1 | 650 |
| H2SO4 | 800 | 1 | 380 |
KOH was chosen as the activator according to the data in Table 2. The activation conditions such as activation temperature, activation time, heating rate and the dosage of the activating agent have great influence on the activated product. Under the condition that the ratio of KOH to raw materials is 1: 1, the heating rate is 10 ℃/min, and activation is respectively carried out at 600 ℃, 700 ℃, 750 ℃, 800 ℃ and 850 ℃ (the activation time is 30 min).
At a certain temperature, the activation time also has an effect on the activation effect. Under the condition that the activation temperature is 800 ℃, the ratio of KOH to raw materials is 1: 1, the heating rate is 10 ℃/min, the activation is carried out for different time respectively, and the activation effect is shown in table 2.
In order to discuss the influence of the dosage of the activating agent on the activating effect, the activating temperature is increased by 10 ℃/min at the temperature of 800 ℃ for activation, the activating time is 45min, and the activating is respectively carried out by using KOH and raw materials with different proportions.
Under the conditions that the activation temperature is 800 ℃, the temperature rise speed is 10 ℃/min, the activation time is 45min and the ratio of KOH to raw materials is 1: 1, the activation is carried out at different temperature rise speeds, and the iodine value is reduced when the temperature reaches 850 ℃.
2.3 Properties of the samples
The iodine value is one of the main performance indicators of activated carbon. The iodine adsorption value of the activated carbon product prepared by mixing the straws without acid pretreatment and the activated carbon sample prepared by mixing the straws with acid pretreatment are respectively measured according to the standard, the iodine value of the activated carbon prepared by mixing the sawdust powder without acid treatment is 707mg/g, the iodine value of the activated carbon prepared by mixing the wood powder with acid pretreatment is 980mg/g, and the sample adsorption performance is obviouslyimproved after the straws are pretreated with acid.
An activated carbon sample with an iodine value of 980mg/g is determined to have a specific surface area of 1180m by using a Langmuir adsorption program through the adsorption characteristics of the activated carbon in a methylene blue solution2/g。
By infrared spectrum analysis (infrared spectrum outline), the results show that: activated carbon prepared from mixed sawdust powder without additive at wave number of 1628cm-1And 1442cm-1The strong absorption peak is generated, and the resonance is probably obtained by the resonance of two adjacent carbonyl groups, so the surface group of the compound is of a quinoid structure, and the adsorption characteristic of the compound is required to be further researched.
The potassium hydroxide activation method is a new activation method, which is used for mesophase carbon microbeads, asphalt, polyacrylonitrile-based pre-oxidized fabrics, coal slime, bituminous coal and the like, and has good KOH activation effect from the aspect of the performance of the prepared activated carbon, but because of the corrosivity of KOH, the requirement on equipment is high, and industrial production is not formed in China, so that the research on the adaptability and the activation mechanism of the raw material mixed straw has certain practical significance.
From the thermal analysis result of the KOH and raw material mixture, the weight loss of the raw material reaches 13.5 percent at the temperature of 150-300 ℃, and the weight loss part mainly comprises water and small molecular substances contained in the raw material. During the activation, the temperature was raised to 280 ℃ by taking a liquid sample and analyzing it by gas chromatography (carrier gas: hydrogen; separation column; detector; thermal cell). As can be seen from the chromatogram, the componentwith the retention time of 0.57min is water, and the components with the retention times of 1.42min and 3.38min are small molecular alcohols or esters in the raw materials. When the temperature of thermal analysis is raised to 350-550 ℃, the quality of the sample is basically kept unchanged, at the moment, the activating agent potassium hydroxide (melting point: 360 ℃) is molten, KOH begins to decompose:
while the reaction is taking place, the generated-OK radicals replace some H atoms in tar in the raw material, the raw material begins to dehydrogenate and is released in the form of hydrogen, so that when the temperature is further increased to 600 ℃, alkali metal compounds (such as K) are generated2O、K2CO3) The reaction with carbon is started, so that the carbon is released in the form of oxide, and simultaneously alkali metal potassium is formed, and potassium passes through between the planes of the graphite microcrystals to generate etching on the unexposed surface, thereby enlarging the micropore structure, changing the aromatic plane structure in the microcrystals and the electron distribution condition thereof, and improving the performance of the activated carbon.
And (3) obtaining the relationship between the weight loss and the temperature of the activator, the raw material and the mixture of the activator and the raw material respectively through a thermal analysis experiment. The activation process, when the temperature is raised above 200 ℃, perchloric acid etches away part of the carbon to make it lose weight.
The actual loss on ignition of the activator and raw meal mixture is quite different from the curve calculated theoretically (assuming no effect between KOH and raw meal): after 600 ℃ due to K2O and K2CO3The actual mass loss rate due to chemical reaction with carbon is much greater than calculated due to the alkali metal compound (e.g., K)2O、K2CO3) The carbon begins to react with the carbon to release the carbon in the form of oxide, when the temperature is higher than 800 ℃, on one hand, the loss on ignition is increased, the product yield is low, on the other hand, the loss on ignition of excessive carbon can cause the collapse of a microporous structure, so that the pore diameter distribution of the activated carbon is not generatedIdeally, the activation temperature is between 750 ℃ and 800 ℃.
3 conclusion
3.1 when mixed straw wood chips are used as raw materials and KOH is used as an activating agent, the pretreatment of mixed acid has obvious advantages, ash content can be reduced, and the activation reaction is facilitated.
3.2 when the activated carbon is prepared by using the mixed straw sawdust powder as the raw material and KOH as the activating agent, the proper activation temperature is 800 ℃, the activation time is 60min, the ratio of the activating agent to the raw material is 1: 1, the iodine value of the prepared activated carbon is 980mg/g, and the specific surface area is 1180m2/g。
Claims (4)
1. A method for producing activated carbon by straw mixed raw materials is characterized in that crop straws, waste branches of fruit trees and tree sawdust are used as mixed raw materials, a phosphoric acid method and a physical combination method are adopted to produce powdery or granular activated carbon, and the method specifically comprises the following steps:
1) raw material preparation
Pulverizing the above materialswith a pulverizer to particle size of 1-2mm, fine grinding with a rolling mill, sieving with 120 mesh sieve, and drying;
2) preparation and compounding of phosphoric acid impregnation liquid
Preparing the concentration and the pH value of the phosphoric acid impregnation liquid according to the type of the activated carbon; the formula requirements of the sugar activated carbon are as follows: at 50-57 DEG Be'/60 ℃, the pH value is 3-3.5; the formula of the industrial activated carbon is as follows: at 45-47 DEG Be'/60 ℃, the pH value is 1.0-1.5, and the ratio of the phosphoric acid and straw mixed wood chips for producing the industrial activated carbon is 0.75: 1; the ratio of the phosphoric acid of the sugar activated carbon to the straw mixed wood dust is more than 1.6: 1;
3) by dipping or wet kneading
The purpose of dipping or wet kneading is to fully and uniformly mix straw mixed wood chips with a phosphoric acid solution, the phosphoric acid is permeated into the mixed wood chip particles, the dipping time is longer than 8 hours, and when wet kneading is adopted, a mechanical stirring device is used for forcing the straw mixed wood chips to be kneaded with the phosphoric acid, and the kneading time is 10-15 minutes;
4) charring and activating
Carbonizing the kneaded phosphorus scraps at the furnace temperature of 500-700 ℃ and the material temperature of 300-400 ℃; the carbonization time of each batch of the phosphorus chip material is 30-60 minutes;
further activating the carbonized raw materials, wherein the furnace temperature during activation is 700-800 ℃, the material temperature is 500-600 ℃, the activation time is 2-2.5 hours, and the material is turned once every 15-20 minutes;
stacking the discharged activated materials for 8-16 hours, continuously polluting by using material humidity, and adjusting the aperture;
5) recovery of phosphoric acid
Extracting the activated material by using a low-concentration phosphoric acid solution, simultaneously adding 5% hydrochloric acid of the activated material, and returning the recovered solution obtained by the first extraction to the production flow for use if the concentration of the impregnation solution is met; then, phosphoric acid solution with lower concentration is used for multiple times of extraction, and finally, the extraction is washed by hot water until the content of the phosphoric acid in the activated carbon is lower than 1 percent, and the time of the whole recovery process is 1.5 to 4 hours;
when the recovered phosphoric acid solution containing impurities is recycled, zinc sulfate is required to be added into the recovered solution to remove the impurities;
6) rinsing
The rinsing comprises two steps of acid washing and water washing:
the acid washing is to add a proper amount of phosphoric acid into the activated carbon after the phosphoric acid recovery in a rinsing barrel, introduce steam and boil for 2 hours to change water-insoluble impurities into water-soluble compounds, and remove the water-soluble compounds along with the water;
after acid washing, adding alkali to neutralize acid to generate phosphate ions, repeatedly washing with hot water to remove various water-soluble impurities, and washing with water until the content of the phosphate ions in the filtrate is lower than 0.16%;
7) dewatering and drying
Dehydrating by adopting an ion machine to reduce the moisture content of the activated carbon to 60-65%; then drying is carried out, so that the moisture content of the activated carbon after centrifugal dehydration is further reduced to below 10 percent;
8) grinding
And grinding the dried activated carbon by using a continuous ball mill to obtain powdery or granular activated carbon.
2. The method of claim 1, wherein said crop straw is wheat straw, corn straw, and cotton straw in a ratio of 1: 1.
3. A method for producing activated carbon by using mixed straw raw materials is characterized in that crop straws, cotton stalks and fruit tree branches are used as raw materials, a chemical and physical combination method is adopted, potassium hydroxide is used as an activating agent, the raw materials are pretreated by perchloric acid, and powdery or granular activated carbon is produced, and the method specifically comprises the following steps:
1) the raw materials are crop straws, waste branches of fruit trees and tree sawdust which are fully mixed according to the proportion of 1: 1; crushing the raw materials into coarse straws by a crusher, finely grinding the granular straws by a fine grinding machine, and sieving the finely ground sawdust with a 120-mesh sieve;
2) weighing 145g of sawdust powder, adding 10mL of 36.5% hydrochloric acid, 10mL of 73% hydrofluoric acid, 20mL of 37% perchloric acid and 50mL of water, uniformly stirring, and soaking at room temperature for 24 hours;
3) washing the raw materials by using a suction filtration device, placing the washed raw materials in an electrothermal blowing drying oven for drying water after the pH value is 6, weighing 10g of dried mixed straw sawdust, adding 10mL of 10% potassium hydroxide solution as an activating agent, stirring the mixture into paste, placing the paste into a porcelain boat, placing the porcelain boat in an activating furnace, introducing nitrogen with the flow rate of 1.0L/min, raising the temperature to 800 ℃ at the temperature rise speed of 8-10 ℃/min, preserving the heat for 45min, and cooling to obtain an activated product;
4) soaking the activated product in hydrochloric acid solution for 20min, washing with water to pH 6, dehydrating, and drying to obtain activated carbon with iodine value of 980mg/g and specific surface of 1180m2In g of powdered or granular activated carbon.
4. The method of claim 3, wherein said crop straw is wheat straw, corn straw and cotton straw in a ratio of 1: 1.
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