CN1319927C

CN1319927C - Method of microwave dehydrogenation for producing sodium oxalate

Info

Publication number: CN1319927C
Application number: CNB2004100403032A
Authority: CN
Inventors: 谢扩军
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2004-07-26
Filing date: 2004-07-26
Publication date: 2007-06-06
Anticipated expiration: 2024-07-26
Also published as: CN1727322A

Abstract

The present invention discloses a method for producing sodium oxalate by using microwave dehydrogenation, which is a method for utilizing advanced microwave heating techniques to replace traditional external heat source conduction to heat materials. The present invention is characterized in that sodium formate solution or sodium formate solids are added into microwave resonant cavity and are rapidly heated to 350 to 450 DEG C (temperature for typical dehydrogenation is from 380 to 420 DEG C) by utilizing microwave energy, which decreases the generation of side reactions in a temperature section from 280 to 300 DEG C. The use of the method for producing sodium oxalate by using microwave dehydrogenation of the present invention has the advantages of easy control of material temperature in the microwave resonant cavity, rapid heating, simultaneously harmonious heating inside and outside of materials, reduction of the generation of side reactions, yield improvement, reduction of energy consumption, high safety, no fire, easy realization of automatization, etc.

Description

Method for producing sodium oxalate through microwave dehydrogenation

Technical Field

The present invention belongs to the field of organic chemical industry and carboxylate preparing technology, and is especially synthetic process of producing oxalic acid.

Background

Oxalic acid is an important chemical raw material, synthesis methods are mostly adopted to produce oxalic acid at present, and a dehydrogenation process is one of the important processes for producing oxalic acid by the synthesis methods.

The basic chemistry of dehydrogenation production is: concentrating 25% sodium formate solution produced in the synthesis process, heating in a dehydrogenation pot, dissolving the sodium formate in the dehydrogenation pot to 400 ℃ after water in the solution is evaporated, and decomposing the sodium formate in the dehydrogenation pot under normal pressure to generate sodium oxalate and hydrogen. The chemical reaction formula of the dehydrogenation process is

The existing dehydrogenation method adopts a pot-type dehydrogenating device for dehydrogenation, concentration, solidification, melting, temperature rise and dehydrogenation of sodium formate are all carried out in a dehydrogenation pot, the whole process is long in time, more materials are used, the heating area is small, the materials are heated unevenly, so that the reaction is incomplete, the side reaction is more, the dehydrogenation conversion rate cannot be improved, and the highest dehydrogenation conversion rate can only reach 80%; in addition, hydrogen is released in the dehydrogenation process, and the hydrogen can explode when meeting open fire or being mixed with air, so that the hydrogen often explodes in the dehydrogenation process, and potential safety hazards exist.

The main problems of the existing sodium formate dehydrogenation production process of the coal chafing dish type dehydrogenator are as follows:

(1) severe energy loss

The coal has low combustion heat efficiency in the hearth, the heat of the pot body is radiated, and the sodium formate exposed in the air is radiated.

(2) Low yield

The reasons for the low yield are:

① dehydrogenation of sodium formate is carried out at 380-420 ℃, because the temperature rise rate before dehydrogenation is slow, the following side reactions occur at 280-300 ℃:

it is clear that the slower the rate of temperature rise, the longer the time to go through this temperature period, the higher the conversion of this side reaction and the lower the yield of the positive reaction will be.

② the temperature of the materials at the bottom and the upper part is not consistent because the sodium formate is exposed in the atmosphere, when the bottom sodium formate reaches the dehydrogenation temperature, the middle and the upper part do not reach the same temperature, i.e. the lower part and the upper part do not react, which affects the yield.

③ when the temperature of sodium oxalate is higher than 700 ℃, the following side reactions occur:

(3) the operation environment is bad, the labor intensity of workers is high

The dehydrogenation section of a common scale is that a plurality of dehydrogenation pots are operated simultaneously, and because the time of dehydrogenation reaction can not be predicted and accurately controlled, the heating, water-adding cooling and charging time of each dehydrogenation pot can not be consistent or ordered, the automation of coal-adding and ash-removing can not be realized, operators need to add coal and remove ash by shovels, the operation environment is severe, and the labor intensity of the operators is high.

(4) Safety problem

The dehydrogenation pot is opened, the open fire is arranged below the pot for heating, the wall of the hearth pot is extremely easy to be burnt and cracked, the stove is not easy to be found and repaired after the burning crack, and the gas generated by the dehydrogenation reaction is particularly easy to ignite due to the leakage of the open fire, so that the detonation is caused, and the personal injury and the equipment damage are caused.

(5) Serious damage to equipment

The temperature of the pot bottom is very high due to open fire heating and twice solidification in the dehydrogenation process, the pot bottom is often burnt to be convex, the pot bottom, the wall, the stove opening and the like are also easily burnt out, the temperature of flue gas is high, and the service life of an induced draft fan is shortened.

The synthesis method is used for producing oxalic acid, and most of the dehydrogenators of the method adopt coal chafing dish type dehydrogenators; a fluidized bed continuous dehydrogenation unit (ZL 97110656.8, CN 87102067A); all the methods and devices are based on the traditional heat conduction heating method (coal heating, resistance wire heating or high-temperature gas and the like), the heat transfer is slow and uneven, and for the sodium formate dehydrogenation process, the more even the heat transfer is, the more beneficial the reaction is; the faster the heat transfer rate, the shorter the time for the entire dehydrogenation process, the shorter the time to undergo side reactions, and the higher the conversion of dehydrogenation. Therefore, changing the heat transfer mode of the dehydrogenation process and increasing the heat transfer rate become the key for realizing the continuous dehydrogenation.

Disclosure of Invention

The invention aims to provide a method for producing sodium oxalate through microwave dehydrogenation, which can reduce the occurrence of side reactions in a dehydrogenation process, improve the yield, reduce the energy consumption and increase the safety.

The invention provides a method for producing sodium oxalate by microwave dehydrogenation, which is characterized by comprising the following steps:

step 1, adding 25-100% of sodium formate solution or sodium formate solid into a microwave resonant cavity (microwave dehydrogenation furnace chamber);

step 2, starting microwave power of a microwave source, inputting microwaves into a microwave resonant cavity (a microwave dehydrogenation furnace) through a microwave transmission system to heat material sodium formate, quickly heating by full-power microwaves, after several minutes to dozens of minutes (when the input amount of the material sodium formate and the water content of a sodium formate solution are large, the time is long), when the temperature of the sodium formate reaches the dehydrogenation temperature of 350 ℃ -450 ℃ (the typical dehydrogenation temperature is 380 ℃ -420 ℃), enabling the sodium formate to be molten, carrying out hydrogen discharge reaction to generate sodium oxalate, properly adjusting microwave power, keeping the temperature of the material sodium formate at 380 ℃ -420 ℃ for proper time (the determination of the proper time is determined by the input amount of the material sodium formate, the microwave power and other parameters), and finishing dehydrogenation;

step 3, after the dehydrogenation is finished, closing the microwave power, expanding the generated sodium oxalate into a loose and porous state, and quickly pumping the sodium oxalate into a microwave resonant cavity (a microwave dehydrogenation furnace) to input sodium carbonate old alkali liquor for cooling and diluting so as to prevent the decomposition and carbonization of materials and facilitate the discharge of the product sodium oxalate;

and 4, discharging the dehydrogenated product sodium oxalate in time.

It should be noted that:

the 25% -100% sodium formate solution or solid in the step 1 is preferably more than 75% solid of sodium formate, and the sodium formate preferably contains 2% NaOH as catalyst;

when the material sodium formate is heated in the microwave resonant cavity (microwave dehydrogenation furnace) in the step 2, the material can be stirred by a stirrer, so that the uniformity of material heating is improved;

and (3) discharging the hydrogen generated in the dehydrogenation process in the step (2) through an exhaust port, and enabling the discharged hydrogen to enter a subsequent treatment and gas storage device.

The essence of the invention is as follows: by utilizing the characteristics of easy control of microwave power and temperature, quick heating, simultaneous heating inside and outside the material and uniform heating, the advanced microwave heating technology is used for replacing the traditional method for heating the material by conduction of an external heat source. Because the microwave heating is that electromagnetic energy permeates into the material sodium formate in the form of waves, the sodium formate absorbs microwaves and instantly generates heat by self dielectric loss, the temperature rises quickly, the microwave power is adjusted to enable the material to reach 350-450 ℃ (the typical dehydrogenation temperature is 380-420 ℃) in a few minutes, and the material simultaneously generates heat inside and outside without conduction, so the residence time of the material sodium formate at 280-300 ℃ is very short, the side reaction at 280-300 ℃ can be reduced, meanwhile, the microwave energy is almost free of inertia when being closed, the microwave power can be timely closed to prevent the temperature of the material from continuously rising, and the side reaction at 700 ℃ high temperature can be prevented. Because the material sodium formate absorbs the microwave and heats by medium loss, the microwave heating has no open fire, and is safe and reliable. Because the materials are heated uniformly inside and outside, the materials are heated uniformly, so the dehydrogenation is synchronous, the dehydrogenation conversion rate is high, and the product quality is excellent. Because microwave heating does not need heat conduction, and the container is not heated (the metal inner wall of the microwave heating chamber only reflects microwaves but does not absorb microwaves), the energy consumption can be reduced.

The invention has the innovation that: the method replaces the traditional method for heating the material by external heat source conduction by using the advanced microwave heating technology by utilizing the characteristics of rapid microwave heating, simultaneous heating inside and outside the material, uniform heating and easy control of microwave power and reaction temperature.

The invention has the advantages that:

① reducing the occurrence of side reactions

By adjusting the microwave power, the reaction temperature is easy to control, the material absorbs microwave to instantly generate heat, the temperature rises rapidly, the material can reach 350-450 ℃ (the typical dehydrogenation temperature is 380-420 ℃) in a few minutes under the action of high-power microwave, the material simultaneously generates heat inside and outside without heat conduction, so the stay time of the material at 280-300 ℃ is very short, the side reaction at 280-300 ℃ can be reduced, meanwhile, the microwave energy is almost closed without inertia, the microwave power is timely closed, the temperature of the material can be prevented from continuously rising, and the side reaction at 700 ℃ high temperature can be prevented.

② improving product quality

Because the materials are heated uniformly inside and outside, the materials are heated uniformly, so the dehydrogenation is synchronous, the dehydrogenation conversion rate is high, and the product quality is excellent.

③ high-efficiency energy-saving

The efficiency of converting microwave energy into heat energy is usually 80% -90% (while the heat efficiency of the coal-fire dehydrogenation stove is only about 12%), the microwave heating time is very short, and the sealing property of microwave power, the permeability to materials and the instantaneity of converting the microwave energy into heat form the basic characteristic of microwave heating energy saving, the microwave heating reduces the time of the heat conduction process of the traditional method, namely the time of uniformly distributing the temperature, thereby greatly reducing the heat loss to the environment, and simultaneously the microwave does not heat a container (the metal inner wall of the microwave heating cavity only reflects the microwave but does not absorb the microwave), thereby reducing the energy consumption, saving the energy by about 50%, and having considerable economic benefit.

④ the microwave heating is safe and reliable without open fire.

⑤ is easy to realize automatic continuous production.

In summary, the present invention adopts the microwave heating process, because the microwave heating is the heating caused by the electromagnetic energy penetrating into the medium in the form of wave to cause the medium loss, and does not need to be conducted, it has instantaneity, it means fast heating, and it is the heating inside and outside simultaneously, and it has the characteristic of even heating for even medium. The microwave heating mode can overcome the defect of slow heating in the traditional method, thereby reducing the occurrence of side reactions, improving the yield and reducing the energy consumption. The microwave rapid heating is heated by the medium loss of the material, no open fire exists, and the safety can be ensured.

Drawings

FIG. 1 is a process flow diagram of the process of the present invention

The specific implementation mode is as follows:

a microwave power source of 915MHz/20kW is adopted for a single unit, a microwave transmission system and a microwave resonant cavity are connected, 150kg of 75% sodium formate solution or sodium formate solid containing 2% NaOH as a catalyst is added into the microwave resonant cavity from a feeding port, the microwave power of the microwave source is started, microwaves are input into the microwave resonant cavity through the microwave transmission system to heat the material sodium formate, full-power microwaves are used for rapid heating, a stirrer in the microwave resonant cavity is started to stir the material while the microwave power of the microwave source is started, the material is heated for about 60 minutes, when the temperature of the material sodium formate reaches the dehydrogenation temperature of 380-420 ℃, the sodium formate is molten, the dehydrogenation reaction is carried out to generate sodium oxalate, the microwave power is properly adjusted to keep the temperature of the material sodium formate at 380-420 ℃ for several minutes, and the microwave power is timely turned off after the dehydrogenation is finished; the generated sodium oxalate swells to be in a loose and porous state, and at the moment, a pump is quickly started to input sodium carbonate old alkali liquor from a water injection port into microwave resonance for cooling and diluting so as to prevent the decomposition and carbonization of the material sodium oxalate. And discharging the dehydrogenated product sodium oxalate in time. And hydrogen generated in the dehydrogenation process is discharged from an exhaust port, the discharged hydrogen enters a subsequent treatment and gas storage device, and the dehydrogenated product sodium oxalate is discharged from a feed opening of the microwave resonant cavity.

Claims

1. A method for producing sodium oxalate by microwave dehydrogenation is characterized by comprising the following steps:

step 1, adding 25-100% of sodium formate solution or sodium formate solid into a microwave resonant cavity;

step 2, starting microwave power of a microwave source, inputting microwaves into a microwave resonant cavity through a microwave transmission system to heat material sodium formate, quickly heating by full-power microwaves, after several minutes to dozens of minutes, when the temperature of the sodium formate reaches the dehydrogenation temperature of 350-450 ℃, the sodium formate becomes molten, carrying out hydrogen discharge reaction to generate sodium oxalate, properly adjusting the microwave power to keep the temperature of the material sodium formate at 380-420 ℃ for proper time, and determining the proper time according to the input amount of the material sodium formate, the microwave power and other parameters to finish dehydrogenation;

step 3, after the dehydrogenation is finished, closing the microwave power, wherein the generated sodium oxalate is swelled into a loose and porous state, and quickly pumping to input sodium carbonate old alkaline liquor into the microwave resonant cavity for cooling and diluting so as to prevent the decomposition and carbonization of materials and facilitate the discharge of the product sodium oxalate;

and 4, discharging the dehydrogenated product sodium oxalate in time.

2. The method for producing sodium oxalate through microwave dehydrogenation according to claim 1, wherein the method comprises the following steps: the 25-100% sodium formate solution or solid in step 1 is sodium formate solid with concentration over 75% and 2% NaOH as catalyst.

3. The method for producing sodium oxalate through microwave dehydrogenation according to claim 1, wherein the method comprises the following steps: when the material sodium formate is heated in the microwave resonant cavity in the step 2, a stirrer can be adopted to stir the material.