CN111377801A - Method and system for refining low carbon alcohol - Google Patents
Method and system for refining low carbon alcohol Download PDFInfo
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Abstract
The invention relates to the field of alcohol refining, in particular to a method and a system for refining low-carbon alcohol. (1) Rectifying the low-carbon alcohol raw material mixture to obtain organic wastewater and a first fraction; (2) subjecting the first fraction to a first extractive distillation using a first extractant to further remove water and obtain a second fraction; (3) rectifying the second fraction II to obtain a refined methanol product and a third fraction; (4) performing second extractive distillation on the third fraction by using a second extractant to obtain a refined ethanol product and a fourth fraction; (5) carrying out III rectification on the fourth fraction to obtain a second extracting agent and a fifth fraction; (6) performing IV rectification on the fifth fraction to obtain a crude isopropanol material flow and a sixth fraction; (7) and (3) rectifying the sixth fraction V to obtain a refined n-propanol product and a seventh fraction. The method can obtain refined low-carbon alcohol products with higher purity at low cost and high efficiency.
Description
Technical Field
The invention relates to the field of alcohol refining, in particular to a method and a system for refining low-carbon alcohol.
Background
The low-carbon alcohol is a unit alcohol containing less than 6 carbon atoms, is an important chemical basic raw material and chemical products, and is widely applied to the fields of energy, chemical industry, medicines and the like, wherein methanol and ethanol are important raw materials for preparing substances such as ether, aldehyde, esters and the like; propanol, isopropanol are common industrial solvents; isobutyl alcohol and sec-butyl alcohol are useful as plasticizers, dye dispersants, and demulsifiers, among others.
In the low-carbon alcohol synthesized by different routes, the contents of methanol and ethanol are often higher, the sum of the contents of methanol and ethanol accounts for more than 70% of the total amount of the low-carbon alcohol, and the contents of other low-carbon alcohols are relatively lower. Methanol and water do not have azeotropy, the product can be obtained by adopting a common rectification method, ethanol and water form a low-boiling-point azeotrope, the separation is difficult, and the separation of other low-carbon alcohols is similar to that of ethanol.
CN104788284A discloses a continuous production method for preparing low carbon alcohol from synthesis gas, which comprises the following steps: a) the synthesis gas raw material is divided into at least two parts; b) a first strand of synthesis gas raw material enters a reactor and contacts with a catalyst to obtain a gas-phase product stream; c) the gas-phase product enters a condenser after passing through a gas-gas heat exchanger for heat exchange, and uncondensed gas and condensate are obtained after condensation; d) a second stream of synthesis gas raw material enters a hydrocarbon evaporator, and hydrocarbons in the condensate are stripped to obtain stripped condensate and a gas phase material flow containing hydrocarbons; e) the condensate after steam stripping is decompressed by decompression equipment and then enters a rectifying tower, liquid phase material flow containing methanol is obtained at the upper part of the rectifying tower, products C2 and C3 alcohol are obtained at the lateral line, and C4 is obtained at the tower bottom+A liquid phase stream of alcohol; the liquid phase stream containing methanol and a liquid phase stream containing C4+Returning the liquid phase stream of alcohol to the reactor; f) passing said non-condensable gas and said hydrocarbon-containing gas phase stream through a compression meansCompressed, heat exchanged with the vapor product stream, and recycled to the reactor. The method aims to improve the yield of C2 and C3 alcohol, and does not provide a method for refining alcohol.
CN105130749A discloses a process for preparing low-carbon alcohol by combining synthesis gas and coke oven gas, which is characterized by comprising the following steps: (1) introducing coke oven gas and synthesis gas into a gas holder for fully mixing to form crude feed gas meeting the hydrogen-carbon ratio of low-carbon alcohol synthesis; (2) compressing the crude feed gas, washing and purifying the crude feed gas by low-temperature methanol to remove impurities such as hydrogen sulfide, carbon dioxide and the like, preparing pure gas for synthesizing low-carbon alcohol, removing sulfur from the removed hydrogen sulfide, recovering, and discharging the removed carbon dioxide at high altitude; (3) the purified gas is subjected to a reaction of synthesizing low-carbon alcohol, the obtained gas-liquid two-phase product is subjected to gas-liquid separation, and the separated gas mainly comprises CO and H2And CO2One part of the mixture is sent to low-temperature methanol washing circulation, the other part of the mixture is sent to a torch for combustion and discharge as purge gas, the separated liquid-phase product is an alcohol-water mixture, and the alcohol-water mixture is subjected to alcohol-water separation to obtain water and a low-carbon alcohol product; the coke oven gas has the volume percentage composition of H2：50-60％，CH4：20-28％，CO+CO2:10-18％，N2: 3-8%, and the volume percentage of the synthesis gas is CO: 45-60%, H2：20-28％，CO2：8-18，CH4：7-15％，H2S: 0.15-0.35%; the operating temperature of the low-temperature methanol washing is-35 to-55 ℃, the operating pressure is 2.0 to 6.5MPa, and H in the synthesis gas after the low-temperature methanol washing2S<0.1ppm，CO2<20 ppm; the alcohol-water separation adopts one of benzene azeotropic distillation technology, ion exchange resin, membrane separation technology and molecular sieve dehydration technology, and the operation conditions are as follows: the temperature is 80-150 ℃, and the pressure is normal pressure or reduced pressure; the low-carbon alcohol reaction adopts one or more fixed bed reactors connected in series, and the reaction process conditions are as follows: the reaction pressure is 3-10MPa, the reaction temperature is 240-410 ℃, and the molar ratio of hydrogen to carbon is H22.0-5.0% of/CO, 5000-fold air speed and 50000h-1Synthesizing low-carbon alcohol under the condition; the catalyst adopted for synthesizing the low-carbon alcohol is MoS 2-M-K catalyst of the American DOW chemical company and modified Cu-Zn-Al-K system catalyst of the Germany Lurgi companyThe catalyst is one or more of a Cu-Co-Cr-K catalyst of French petroleum institute, a Zn-Cr catalyst of Shanxi coal chemical institute of Chinese academy of sciences or a Japanese Cu-Ni-Zr-Na catalyst; the low-carbon alcohol product comprises 20-30% of methanol, 40-60% of ethanol, 12-20% of propanol and 8-20% of other alcohols by mass percent. However, this patent application does not provide a specific alcohol purification method.
The master thesis "research on the technology of low-carbon alcohol separation process" proposes a process for separating low-carbon alcohol, wherein the low-carbon alcohol is derived from an acetate hydrogenation product, and a low-carbon alcohol mixture contains: 7.97% of methyl acetate, 44.88% of methanol, 3.01% of ethyl acetate, 35.19% of ethanol, 4.82% of water and a small amount of other alcohols. Various types of azeotropes are easily formed in the raw materials: the lower alcohols (except methanol) form binary minimum azeotropes with water, methanol/ethanol and acetate. In addition, ethanol, water and ethyl acetate also form ternary low boiling azeotropic systems. Because the raw material contains a certain amount of methyl acetate and ethyl acetate, the raw material composition of the raw material has great difference with a low carbon alcohol mixture prepared by the reaction of the synthesis gas, and the raw material is not suitable for refining and separating the low carbon alcohol obtained by the reaction of the synthesis gas. And the process adopts a DMSO + NMP composite extractant, the price of the extractant NMP is higher and is close to 20000 yuan/ton, and the extractant in the extraction and rectification process is lost in the operation process, so that the investment and the operation cost of the process are higher.
CN104529704B discloses a joint production device for synthesizing and separating low carbon mixed alcohol, which is characterized by comprising: a low-carbon mixed alcohol synthesis subsystem and a low-carbon mixed alcohol separation subsystem; the low-carbon mixed alcohol synthesis subsystem comprises a raw material gas treatment module, a low-carbon alcohol synthesis module and a product treatment module which are sequentially communicated; the raw material gas treatment module comprises a raw material gas compressor unit (11) for pressurizing raw material gas and a raw material gas heating unit for heating the raw material gas, wherein a gas outlet of the raw material gas compressor unit (11) is communicated to a gas inlet of the raw material gas heating unit; the low-carbon alcohol synthesis module comprises a low-carbon alcohol synthesizer (21), and a gas inlet of the low-carbon alcohol synthesizer (21) is communicated with a gas outlet of the feed gas heating unit; the product processing module comprises a low-carbon alcohol separation part, the low-carbon alcohol separation part comprises a low-carbon alcohol separator (311), the low-carbon alcohol separator (311) comprises a low-carbon alcohol separator inlet, the low-carbon alcohol separator inlet is communicated to an air outlet of the low-carbon alcohol synthesizer (21), and the low-carbon alcohol separation part is provided with a low-carbon mixed alcohol outlet for guiding a low-carbon mixed alcohol product; the low-carbon mixed alcohol separation subsystem comprises: the methanol rectifying tower (100) is provided with a methanol tower feed inlet, a methanol tower top discharge hole and a methanol tower bottom discharge hole which are connected with the low-carbon mixed alcohol outlet; the discharge hole at the top of the methanol tower is connected with a methanol storage tank (110); the ethanol rectifying tower (200) is provided with an ethanol tower feeding hole connected with the methanol tower bottom discharging hole, an ethanol tower top discharging hole and an ethanol tower bottom discharging hole; the extraction rectifying tower (300) is provided with an extraction tower feed inlet connected with the ethanol tower ejection port, an extractant feed inlet, an extraction tower top discharge port and an extraction tower bottom discharge port; wherein the extraction column feed inlet is located below the extractant feed inlet; a discharge hole at the top of the extraction tower is connected with an ethanol storage tank (310); the n-propanol rectifying tower (400) is provided with an n-propanol tower feed inlet connected with the ethanol tower bottom discharge outlet, an n-propanol tower top discharge outlet and an n-propanol tower bottom discharge outlet; the discharge hole at the top of the n-propanol tower is connected with an n-propanol storage tank (410); the n-propanol bottom discharge port is connected with a mixed butanol storage tank (420), the low-carbon alcohol separation part further comprises a primary separator (23), the primary separator (23) comprises a separator air inlet, a separator first outlet and a separator second outlet, the separator air inlet is communicated with an air outlet of the low-carbon alcohol synthesizer (21), the separator first outlet is communicated with an inlet of the low-carbon alcohol separator (311), the separator second outlet is communicated with a wax product device of the combined production device, the product processing module further comprises a light oil product separation part, the light oil product separation part is communicated with the low-carbon alcohol separation part, the low-carbon alcohol separator (311) further comprises a low-carbon alcohol separator first outlet and a low-carbon alcohol separator second outlet, an inlet of the low-carbon alcohol separator (311) is communicated with the separator first outlet of the primary separator (23), the first outlet of the low-carbon alcohol separator is communicated with the inlet of the light oil product separation part, and the second outlet of the low-carbon alcohol separator is used for outputting a low-carbon alcohol product. However, the alcohol product obtained by the system or the method has low purity, and the product with the desired purity can be obtained by other methods such as combination with membrane separation and purification, and the membrane separation method is limited by efficiency and cost in practical production application; in addition, water can form an azeotrope with other low-carbon alcohols (ethanol, propanol, butanol, pentanol and the like) except methanol, and the system or the method cannot fully separate water out of the system before alcohol refining, so that the circulation of the water in the subsequent refining process not only increases the difficulty in refining and separating the low-carbon alcohol, but also increases the energy consumption.
Therefore, a method for purifying lower alcohols at low cost and high efficiency and with high purity of the obtained products is needed.
Disclosure of Invention
The invention aims to provide a method and a system for refining low-carbon alcohol, which aim to overcome the problems of narrow raw material application, insufficient purity of obtained products, high cost and the like in the prior art.
In order to achieve the above object, a first aspect of the present invention provides a method for purifying a lower alcohol, the method comprising:
(1) rectifying the low-carbon alcohol raw material mixture to obtain organic wastewater and a first fraction;
(2) subjecting the first fraction to a first extractive distillation using a first extractant to further remove water and obtain a second fraction;
(3) rectifying the second fraction II to obtain a refined methanol product and a third fraction;
(4) performing second extractive distillation on the third fraction by using a second extractant to obtain a refined ethanol product and a fourth fraction;
(5) carrying out III rectification on the fourth fraction to obtain a second extracting agent and a fifth fraction;
(6) performing IV rectification on the fifth fraction to obtain a crude isopropanol material flow and a sixth fraction;
(7) and (3) rectifying the sixth fraction V to obtain a refined n-propanol product and a seventh fraction.
The second aspect of the present invention provides a system for refining a lower alcohol, the system comprising:
the first rectifying tower is used for removing organic wastewater and is provided with a first rectifying tower feed inlet for receiving a low-carbon alcohol raw material mixture, a first rectifying tower top discharge port and a first rectifying tower bottom discharge port;
the first extractive distillation tower is used for further removing water and is provided with a first extractive distillation tower feed inlet, a first extractant feed inlet, a first extractive distillation tower top discharge port and a first extractive distillation tower bottom discharge port which are communicated with the first distillation tower top discharge port;
the second rectifying tower is used for refining methanol and is provided with a second rectifying tower feed inlet communicated with the first extractive rectifying tower top feed inlet, a methanol discharge outlet and a second rectifying tower bottom discharge outlet;
the second extractive distillation tower is used for refining ethanol and is provided with a second extractive distillation tower feed inlet, a second extractant feed inlet, a second extractive distillation tower top material outlet and a second extractive distillation tower bottom material outlet which are communicated with the second distillation tower bottom material outlet, and the second extractive distillation tower top material outlet outputs ethanol;
the third rectifying tower is used for recovering a second extracting agent and is provided with a third rectifying tower feeding hole communicated with the second extracting rectifying tower bottom discharging hole, a third rectifying tower top discharging hole and a third rectifying tower bottom discharging hole, and the third rectifying tower bottom discharging hole outputs the second extracting agent;
the IV rectifying tower is provided with an IV rectifying tower feeding hole communicated with the III rectifying tower ejection hole, an IV rectifying tower ejection hole and an IV rectifying tower bottom discharging hole, and the IV rectifying tower ejection hole outputs crude isopropanol material flow; and
and the V-th rectifying tower is provided with a V-th rectifying tower feeding hole communicated with the IV rectifying tower bottom discharging hole, a V-th rectifying tower top discharging hole and a V-th rectifying tower bottom discharging hole, and the V-th rectifying tower top discharging hole outputs the n-propanol.
In practical production application, the method is easy to operate, the cost is low, the purity of the obtained product is high, the purity of the obtained methanol product, the purity of the obtained ethanol product and the purity of the obtained n-propanol product reach more than 99.9 weight percent, the method can also obtain the isopropanol product with high purity, and the purity of the obtained isopropanol product can reach more than 99.5 weight percent.
Drawings
FIG. 1 is a schematic diagram of one embodiment of a system provided by the present invention.
FIG. 2 is a schematic diagram of an embodiment of an isopropanol recovery and purification subsystem provided by the present invention.
Description of the reference numerals
1 the first rectifying tower 2 the first extraction rectifying tower
3 first extractant recovery tower 4 second rectifying tower
5 second extractive distillation column 6 III rectifying column
7 th IV rectifying tower and 8 th V rectifying tower
21 third extractive distillation column 22 third extractant recovery column
23 fourth extractive distillation column 24 VI distillation column
101 low carbon alcohol feedstock mixture 103 first fraction
104 organic waste water 109 first extractant
111 second fraction 112 non-condensable gas components
113 refined methanol product 114 third fraction
115 ethanol product 116 fourth fraction
117 fifth fraction of second extractant 118
119 crude isopropanol stream 120 sixth fraction
122 n-propanol product 123 seventh fraction
203 eighth fraction of third extractant 201
202 ninth fraction 208 fourth extractant
205 crude ethanol product 206 tenth fraction
207 Isopropanol product
Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
The present invention provides, in a first aspect, a method for purifying a lower alcohol, the method comprising:
(1) rectifying the low-carbon alcohol raw material mixture to obtain organic wastewater and a first fraction;
(2) subjecting the first fraction to a first extractive distillation using a first extractant to further remove water and obtain a second fraction;
(3) rectifying the second fraction II to obtain a refined methanol product and a third fraction;
(4) performing second extractive distillation on the third fraction by using a second extractant to obtain a refined ethanol product and a fourth fraction;
(5) carrying out III rectification on the fourth fraction to obtain a second extracting agent and a fifth fraction;
(6) performing IV rectification on the fifth fraction to obtain a crude isopropanol material flow and a sixth fraction;
(7) and (3) rectifying the sixth fraction V to obtain a refined n-propanol product and a seventh fraction.
In the invention, the terms "first extractant", "second extractant", "third extractant" and "fourth extractant" are only used for distinguishing the extractants used in the steps, and are not distinguished successively, primarily and secondarily.
In the present invention, the "first fraction", "second fraction" … … "seventh fraction" … … "tenth fraction" is used only for distinguishing the fractions produced in the respective steps, and is not divided into a first fraction, a second fraction, a third fraction and a fourth fraction.
In the present invention, lower alcohols refer to monoalcohols containing less than 6 carbon atoms.
In the present invention, the lower alcohol means a monoalcohol having less than 6 carbon atoms. The lower alcohol mixture may be a product synthesized by various processes, for example, a mixture of products obtained by preparing lower alcohols from synthesis gas or preparing lower alcohols by other processes such as acetate hydrogenation. The low-carbon alcohol raw material mixture contains water, methanol, ethanol, n-propanol, isopropanol, butanol and the like, wherein the content of the water is 30-80 wt%, the content of the low-carbon alcohol is 20-70 wt%, and the sum of the methanol and the ethanol accounts for more than 70% of the total amount of the low-carbon alcohol.
According to the method, in the step (1), a lower alcohol raw material mixture is subjected to I rectification to obtain organic wastewater and a first fraction, wherein the I rectification conditions comprise that: the temperature at the top of the tower is 60-80 ℃, the pressure at the top of the tower is 0-10kPa, and the reflux ratio is 0.5-1; preferably, the temperature at the top of the tower is 65-75 ℃, the pressure at the top of the tower is 4-6kPa, and the reflux ratio is 0.7-0.9; more preferably, the overhead temperature is 70 ℃, the overhead pressure is 5kPa, and the reflux ratio is 0.8. In one embodiment, the organic waste water is withdrawn from the bottom of the column and the first fraction is withdrawn from the top of the column. The organic wastewater contains most of water, acid, heavy alcohol (alcohol having more than 6 carbon atoms), and the like. In a preferred embodiment, the organic wastewater is subjected to heat exchange with the lower alcohol raw material mixed liquid before being discharged so as to recover heat. In the present invention, unless otherwise specified, the pressures are gauge pressures.
According to the method, in the step (2), the first fraction is subjected to first extractive distillation by using a first extracting agent to further remove water, and a second fraction is obtained, wherein the first extracting agent is selected from at least one of glycol, furfural, dimethylformamide and dimethyl sulfoxide, and preferably, the first extracting agent is a composite solvent consisting of glycol and dimethyl sulfoxide. The conditions of the first extractive distillation comprise: the temperature at the top of the tower is 50-70 ℃, the pressure at the top of the tower is 0-10kPa, and the reflux ratio is 0.35-0.65; preferably, the temperature at the top of the tower is 55-65 ℃, the pressure at the top of the tower is 4.5-5.5kPa, and the reflux ratio is 0.4-0.6; more preferably, the overhead temperature is 62 ℃, the overhead pressure is 5kPa, and the reflux ratio is 0.5. In one embodiment, the first extractant is added from the upper part of the tower, the first extractant is a composite solvent of ethylene glycol and dimethyl sulfoxide, and the volume ratio of the two (ethylene glycol/dimethyl sulfoxide) is (0.5-2):1, preferably (1-2):1, and more preferably 1.5: 1; the feed ratio of the first extractant to the first fraction is 2 to 4, preferably 2.5 to 3.5, more preferably 3.0. In one embodiment, the mixture of the first extractant and water is withdrawn from the bottom of the column and the second fraction is withdrawn from the top of the column via a first extractive distillation. In a preferred embodiment, the second fraction comprises 20 to 60 wt.% methanol, 10 to 40 wt.% ethanol, 0.1 to 1 wt.% water, 10 to 30 wt.% n-propanol, 1 to 10 wt.% isopropanol, 0.1 to 5 wt.% butanol. In one embodiment, the second fraction further comprises from 0.1 to 3% by weight of dimethyl ether. Preferably, the second fraction contains 40-50 wt% methanol, 20-30 wt% ethanol, 0.1-0.5 wt% water, 10-20 wt% n-propanol, 1-7 wt% isopropanol, 0.1-3 wt% butanol and 0.1-2.5 wt% dimethyl ether.
In one embodiment of the method of the present invention, the method further comprises a first extractant recovery step, wherein the first extractant recovery step comprises the step of performing rectification separation on a mixture of the first extractant and water obtained at the bottom of the first extractive rectification step, wastewater is obtained and discharged at the top of the tower, and the first extractant is obtained at the bottom of the tower. The conditions of the rectification for recovering the first extractant include: the temperature at the top of the tower is 40-50 ℃, the pressure at the top of the tower is 5-15kPaA (the pressure is absolute pressure), and the reflux ratio is 1-3; preferably, the overhead temperature is 45 ℃ and the overhead pressure is 10kPaA (here, the pressure is absolute pressure), and the reflux ratio is 2. In a preferred embodiment, the first extractant obtained at the bottom of the column is recycled to the first extractive distillation step after heat recovery in the heat exchange device 9.
According to the method, in the step (3), the second fraction is subjected to II rectification to obtain a refined methanol product and a third fraction, wherein the II rectification conditions comprise: the temperature at the top of the tower is 35-50 ℃, the pressure at the top of the tower is 0-10kPa, and the reflux ratio is 3-7; preferably, the temperature at the top of the tower is 38-48 ℃, the pressure at the top of the tower is 4-6kPa, and the reflux ratio is 5-6; more preferably, the overhead temperature is 44 ℃, the overhead pressure is 5kPa, and the reflux ratio is 5.6. The purity of the refined methanol product can reach more than 99.5 weight percent, even 99.9 weight percent. The recovery rate of the methanol reaches more than 95 percent, even more than 98.5 percent. The second rectification step also produces non-condensable gas components, such as dimethyl ether, which are discharged overhead for further processing.
According to the method, in the step (4), the third fraction is subjected to second extractive distillation by using a second extracting agent to obtain a refined ethanol product and a fourth fraction; the conditions of the second extractive distillation comprise: the temperature at the top of the tower is 70-90 ℃, the pressure at the top of the tower is 0-10kPa, and the reflux ratio is 1-3; preferably, the temperature at the top of the tower is 75-85 ℃, the pressure at the top of the tower is 4-6kPa, and the reflux ratio is 1.5-2.5; more preferably, the overhead temperature is 80 ℃, the overhead pressure is 5kPa, and the reflux ratio is 2. In one embodiment, the second extractant is introduced from the upper part of the column, and the feeding ratio of the second extractant to the first fraction is from 2 to 4, preferably 3.3. The second extractant is at least one selected from ethylene glycol, furfural, dimethylformamide and dimethyl sulfoxide, and preferably is a composite solvent consisting of ethylene glycol and dimethyl sulfoxide, and the volume ratio of the ethylene glycol to the dimethyl sulfoxide is (0.5-2):1, preferably (1-2):1, and more preferably 1.5: 1. The purity of the refined ethanol product can reach over 99.5 percent by weight, even 99.9 percent by weight. The recovery rate of the ethanol reaches more than 95 percent, even 97.5 percent. In one embodiment, a fourth fraction comprising the second extractant and lower alcohol is withdrawn from the bottom of the column and the refined ethanol product is withdrawn from the top of the column via a second extractive distillation.
According to the method, in the step (5), III rectification is carried out on the fourth fraction to obtain a second extracting agent and a fifth fraction; the III rectification conditions comprise: the temperature at the top of the tower is 35-55 ℃, the pressure at the top of the tower is 5-15kPaA (the pressure is absolute pressure), and the reflux ratio is 0.5-1.5; preferably, the overhead temperature is 41 ℃ and the overhead pressure is 10kPaA (here, the pressure is absolute pressure), and the reflux ratio is 1. In one embodiment, the second extractant is taken from the bottom of the column and the fifth fraction is taken from the top of the column via III rectification. Preferably, the second extractant discharged from the tower bottom is subjected to heat exchange and then recycled to the second extractive distillation step.
According to the method of the invention, in the step (6), IV rectification is carried out on the fifth fraction to obtain a crude isopropanol material flow and a sixth fraction; the IV rectification conditions comprise: the temperature at the top of the tower is 75-90 ℃, the pressure at the top of the tower is 3-7kPa, and the reflux ratio is 3-7; preferably, the overhead temperature is 82 ℃, the overhead pressure is 5kPa, and the reflux ratio is 5. In one embodiment, the crude isopropanol stream is withdrawn overhead and the sixth fraction is withdrawn bottoms via a iv rectification. The crude isopropanol stream contains mainly isopropanol and also small amounts of ethanol and water, preferably the isopropanol content of the crude isopropanol stream is in the range of 75 wt% to 95 wt%, preferably 85 wt%.
According to the method, in the step (7), the sixth fraction is subjected to Vth rectification to obtain a refined n-propanol product and a seventh fraction; the rectification conditions of the V < th > comprise: the temperature at the top of the tower is 90-105 ℃, the pressure at the top of the tower is 0-10kPa, and the reflux ratio is 1-3; preferably, the temperature at the top of the tower is 95-100 ℃, the pressure at the top of the tower is 4-6kPa, and the reflux ratio is 1.5-2.5; more preferably, the overhead temperature is 98 ℃, the overhead pressure is 5kPa, and the reflux ratio is 2. In one embodiment, the refined n-propanol product is taken overhead and the seventh fraction is taken bottoms via the v-th rectification. In a preferred embodiment, the n-propanol product has a purity of 99.5 wt.% or greater, more preferably 99.9 wt.%, and an n-propanol recovery of 90% or greater, preferably 95.5% or greater. In one embodiment, the resulting n-propanol product may be used to provide heat by heat exchange to an upstream step, such as reboiler 11 for the second rectification step. The seventh fraction is a crude butanol stream. In one embodiment, the butanol content of the crude butanol stream is from 80 to 95 wt.%, preferably 89.3 wt.%.
In one embodiment of the process of the present invention, the process further comprises subjecting the crude isopropanol stream obtained in step (6) to a third extractive distillation using a third extractant to obtain an eighth fraction; carrying out fourth extractive distillation on the eighth fraction by using a fourth extractant to obtain a crude ethanol product and a tenth fraction; and VI rectifying the tenth fraction to obtain a refined isopropanol product.
In a preferred embodiment of the process of the present invention, the conditions of the third extractive distillation comprise: the temperature at the top of the tower is 75-90 ℃, the pressure at the top of the tower is 0-10kPa, and the reflux ratio is 2-4; preferably, the temperature at the top of the tower is 80-85 ℃, the pressure at the top of the tower is 4-6kPa, and the reflux ratio is 3-4; more preferably, the overhead temperature is 83 ℃, the overhead pressure is 5kPa, and the reflux ratio is 3.2. In a preferred embodiment, the feed ratio of the crude isopropanol stream to the third extractant is in the range of from 2 to 6, preferably 4. The third extractant is at least one selected from ethylene glycol, furfural, dimethylformamide and dimethyl sulfoxide, and preferably the third extractant is a composite solvent consisting of ethylene glycol and dimethyl sulfoxide, and the volume ratio of the ethylene glycol to the dimethyl sulfoxide is (0.5-2):1, preferably (1-2):1, and more preferably 1.5: 1. In one embodiment, the eighth fraction is taken overhead and the ninth fraction is taken bottoms via a third extractive distillation, the ninth fraction being a mixture of the third extractant and water.
In a preferred embodiment of the method of the present invention, the fourth extractive distillation conditions comprise: the temperature at the top of the tower is 70-90 ℃, the pressure at the top of the tower is 0-10kPa, and the reflux ratio is 3-7; preferably, the temperature at the top of the tower is 75-85 ℃, the pressure at the top of the tower is 4-6kPa, and the reflux ratio is 4-6; more preferably, the overhead temperature is 80 ℃, the overhead pressure is 5kPa, and the reflux ratio is 5. In a preferred embodiment, the feeding ratio of the eighth fraction to the fourth extractant is from 2 to 10, preferably 6. The fourth extractant is at least one selected from ethylene glycol, furfural, dimethylformamide and dimethyl sulfoxide, and preferably is a composite solvent consisting of ethylene glycol and dimethyl sulfoxide, and the volume ratio of the ethylene glycol to the dimethyl sulfoxide is (0.5-2):1, preferably (1-2):1, and more preferably 1.5: 1. In one embodiment, the crude ethanol product is taken overhead and the tenth fraction is taken bottoms via a fourth extractive distillation. In a preferred embodiment, the purity of the ethanol in the crude ethanol product is 95 wt.% or greater, preferably up to 97.5 wt.%.
In a preferred embodiment of the process of the invention, the vi rectification conditions include: the temperature at the top of the tower is 30-50 ℃, the pressure at the top of the tower is 12-18kPaA (the pressure is absolute pressure), and the reflux ratio is 0.2-1.5; preferably, the overhead temperature is 41 ℃ and the overhead pressure is 15kPaA (here, the pressure is absolute pressure), and the reflux ratio is 1. In one embodiment, the refined isopropanol product is withdrawn overhead and the fourth extractant is withdrawn bottoms via a vi rectification. Preferably, the fourth extractant removed at the bottom of the column is recycled to the fourth extractive rectification step.
In a preferred embodiment of the process according to the invention, the process further comprises a third extractant recovery step comprising subjecting the ninth fraction obtained in the third extractive distillation step to a VII th distillation under conditions comprising: the temperature at the top of the tower is 40-55 ℃, the pressure at the top of the tower is 12-18kPaA (absolute pressure in the case of the pressure), and the reflux ratio is 1-5; preferably, the overhead temperature is 46 ℃, the overhead pressure is 15kPaA (absolute pressure here), and the reflux ratio is 3. In one embodiment, the third extractant is removed from the bottom of the column via a seventh rectification. Preferably, the third extractant removed at the bottom of the column is recycled to the third extractive rectification step.
According to the method, almost all water in the low-carbon alcohol raw material mixture is removed through the I rectification step and the first extractive rectification step, so that the separation difficulty of the subsequent separation step is reduced, and an alcohol product with higher purity can be obtained more easily; through the specific combination of extractive distillation and rectification, and through the fractional extractive distillation and the arrangement of the extracting agents, for example, a composite solvent consisting of ethylene glycol and dimethyl sulfoxide is selected as the first, second, third and fourth extracting agents. Compared with the method using a single solvent (such as ethylene glycol) and using a composite solvent to separate a multi-component low-carbon alcohol system, the method has the advantages of high product recovery rate, high product purity, low solvent ratio, low energy consumption and the like, and realizes low-cost and high-efficiency separation of the low-carbon alcohol system.
The method can simply and conveniently obtain methanol, ethanol and normal propyl alcohol products with higher purity (the purity can reach 99.9 weight percent), and can obtain isopropanol products with higher purity (the purity can reach 99.7 weight percent). The invention reduces the number of the rectifying tower plates through the combination of specific rectifying and extractive rectifying processes, and realizes that a product with higher purity can be obtained under the condition of lower tower plate number.
In a second aspect, the present invention provides a system for refining lower alcohols, as shown in fig. 1, which is a schematic diagram of an embodiment of the system, and the system comprises:
the first rectifying tower 1 is used for removing organic wastewater and is provided with a first rectifying tower feed inlet for receiving a low-carbon alcohol raw material mixture, a first rectifying tower top discharge port and a first rectifying tower bottom discharge port, wherein the first rectifying tower top discharge port outputs a first fraction, and the first rectifying tower bottom discharge port outputs organic wastewater;
the first extractive distillation tower 2 is used for further removing water and is provided with a first extractive distillation tower feeding hole, a first extractant feeding hole, a first extractive distillation tower top material hole and a first extractive distillation tower bottom material hole which are communicated with the first distillation tower top material hole, wherein the first extractive distillation tower feeding hole receives a first fraction from the first distillation tower top material hole, the first extractive distillation tower bottom material hole outputs wastewater, and the first extractive distillation tower top material hole outputs a second fraction;
the II rectifying tower 4 is used for refining methanol and is provided with a II rectifying tower feeding hole communicated with the first extractive rectifying tower ejection opening, a methanol discharging hole and a II rectifying tower bottom discharging hole, wherein the II rectifying tower feeding hole is used for receiving the second fraction from the first extractive rectifying tower ejection opening, the II rectifying tower bottom discharging hole outputs the third fraction, and the methanol discharging hole outputs refined methanol;
the second extractive distillation tower 5 is used for refining ethanol and is provided with a second extractive distillation tower feed inlet, a second extractant feed inlet, a second extractive distillation tower top material outlet and a second extractive distillation tower bottom material outlet which are communicated with the second distillation tower bottom material outlet, wherein the second extractive distillation tower feed inlet is used for receiving a third fraction from the second distillation tower bottom material outlet, the second extractive distillation tower top material outlet outputs refined ethanol, and the second extractive distillation tower bottom material outlet outputs a fourth fraction;
the III rectifying tower 6 is used for recovering a second extracting agent and is provided with a III rectifying tower feeding hole, a III rectifying tower ejection hole and a III rectifying tower bottom discharge hole which are communicated with the second extracting rectifying tower bottom discharge hole, wherein the III rectifying tower feeding hole is used for receiving a fourth fraction from the second extracting rectifying tower bottom discharge hole, the III rectifying tower bottom discharge hole outputs the second extracting agent, and the III rectifying tower ejection hole outputs a fifth fraction;
the IV rectifying tower 7 is provided with an IV rectifying tower feeding hole communicated with the III rectifying tower ejection hole, an IV rectifying tower ejection hole and an IV rectifying tower bottom discharging hole, wherein the IV rectifying tower feeding hole is used for receiving a fifth fraction from the III rectifying tower ejection hole, the IV rectifying tower ejection hole outputs crude isopropanol material flow, and the IV rectifying tower bottom discharging hole outputs a sixth fraction;
and the V-th rectifying tower 8 is provided with a V-th rectifying tower feeding hole, a V-th rectifying tower top discharging hole and a V-th rectifying tower bottom discharging hole which are communicated with the IV rectifying tower bottom discharging hole, wherein the V-th rectifying tower feeding hole is used for receiving the sixth fraction from the IV rectifying tower bottom discharging hole, the V-th rectifying tower top discharging hole outputs refined n-propanol, and the V-th rectifying tower bottom discharging hole outputs the seventh fraction.
In a preferred embodiment of the system of the present invention, the system further comprises an isopropanol recovery and purification subsystem, as shown in fig. 2, which is a schematic diagram of an embodiment of the isopropanol recovery and purification subsystem of the present invention. The isopropanol recovery and refining subsystem comprises:
a third extractive distillation column 21 having a third extractive distillation column feed inlet, a third extractant feed inlet, a third extractive distillation column top feed inlet and a third extractive distillation column bottom discharge outlet, wherein the third extractive distillation column feed inlet is configured to receive a crude isopropanol stream from the fourth distillation column top feed inlet, the third extractive distillation column top feed inlet outputs an eighth fraction, and the third extractive distillation column bottom discharge outlet outputs a ninth fraction;
a fourth extractive distillation column 23, having a fourth extractive distillation column feed inlet communicated with the third extractive distillation column top feed opening, a fourth extractant feed inlet, a fourth extractive distillation column top feed opening, and a fourth extractive distillation column bottom feed opening, wherein the fourth extractive distillation column feed inlet is configured to receive an eighth fraction from the third extractive distillation column top feed opening, the fourth extractive distillation column top feed opening outputs ethanol, and the fourth extractive distillation column bottom feed opening outputs a tenth fraction;
the VI rectifying tower 24 is provided with a VI rectifying tower feeding port communicated with the fourth extractive rectifying tower bottom discharging port, a VI rectifying tower top discharging port and a VI rectifying tower bottom discharging port, wherein the VI rectifying tower feeding port is used for receiving the tenth fraction from the fourth extractive rectifying tower bottom discharging port, the VI rectifying tower top discharging port outputs isopropanol, and the VI rectifying tower bottom discharging port outputs a fourth extractant.
In one embodiment of the system of the present invention, the system further comprises a first extractant recovery column 3 having a first extractant recovery column feed opening in communication with the first extractive distillation column bottoms discharge opening, a first extractant recovery column top discharge opening, and a first extractant recovery column bottoms discharge opening. In one embodiment, the first extractant is discharged from a bottom outlet of the first extractant recovery column, and the wastewater is discharged from a top outlet of the first extractant recovery column. In one embodiment of the system of the present invention, the system further comprises a third extractant recovery column 22 having a third extractant recovery column feed in communication with the third extractive distillation column bottoms discharge, a third extractant recovery column top discharge and a third extractant recovery column bottoms discharge, the third extractant recovery column feed receiving a ninth fraction output from the third extractive distillation column bottoms discharge. In one embodiment, the third extractant is discharged from a bottom outlet of the third extractant recovery column, and the wastewater is discharged from a top outlet of the third extractant recovery column.
In a preferred embodiment of the system according to the invention, the system further comprises heat exchange means 9 for recovering heat. In a preferred embodiment, the organic wastewater discharged from the first rectifying tower is subjected to heat exchange through a heat exchange device to heat the lower alcohol raw material mixture. In a preferred embodiment, the first extractant obtained from the bottom of the first extractant recovery column is recycled to the first extractive distillation step after heat recovery in the heat exchange device 9.
The present invention will be described in detail below by way of examples.
Example 1
The lower alcohol feed mixture used in this example was from a synthesis unit and had the composition shown in table 1 below.
TABLE 1 Low carbon alcohol feed mixture composition
| Components | Content (wt%) |
| Dimethyl ether | 0.7％ |
| Methanol | 22.8％ |
| Ethanol | 13.7％ |
| N-propanol | 7.3％ |
| Isopropanol (I-propanol) | 2.7％ |
| N-butanol | 3.2％ |
| Pentanol (amyl alcohol) | 1.7％ |
| Acetic acid | 0.5％ |
| Water (W) | 47.4％ |
The setup parameters for each column referred to in the examples are shown in table 2.
TABLE 2
In table 2, pressure is expressed as absolute pressure, and the rest is gauge pressure.
Herein, the overhead temperature is defined as the saturated condensing temperature of the overhead condenser, and the kettle temperature is defined as the kettle reboiler temperature;
the overhead pressure is defined as the overhead condenser pressure and the kettle pressure is defined as the kettle reboiler pressure.
The low-carbon alcohol raw material mixture is separated and purified by the following method.
(1) Heating a low-carbon alcohol raw material mixed solution 101 (the composition of which is shown in table 1), inputting the heated low-carbon alcohol raw material mixed solution into an I rectification tower 1, controlling the tower top pressure of the I rectification tower to be 5kPa, the tower top temperature to be 70 ℃, the reflux ratio to be 0.8, discharging (removing) organic wastewater 104 (containing most of water, acid, heavy alcohol and the like) from the tower bottom in a rectification separation process, exchanging heat between the organic wastewater 104 and the low-carbon alcohol raw material mixed solution 101 in a heat exchanger 9 before discharging to recover heat, and heating the low-carbon alcohol raw material mixed solution 101 to 51 ℃; the first fraction 103 is taken off at the top of the column and enters the first extractive distillation column 2.
(2) In the first extractive distillation column 2, a first extracting agent 109 (a composite solvent of ethylene glycol and dimethyl sulfoxide, the volume ratio of the two is 1.5: 1) is added from the upper part of the column, the feeding ratio of the first extracting agent 109 to the first fraction 103 is 2.9, and the control of the first extractive distillation conditions in the first extractive distillation column 2 comprises the following steps: the overhead pressure was 5kPa, the overhead temperature was 62 ℃ and the reflux ratio was 0.5. The first extractive distillation process is used for further removing residual water, a second fraction 111 obtained at the top of the first extractive distillation tower 2 enters a second extractive distillation tower 4, and a mixture 107 of a first extractant and water obtained at the bottom of the tower enters a first extractant recovery tower 3;
(3) in a first extractant recovery tower 3, the pressure at the top of the first extractant recovery tower 3 is controlled to be 10kPaA (absolute pressure in the case), the temperature at the top of the tower is 45 ℃, the reflux ratio is 2, a mixture 107 of the first extractant and water is rectified and separated, wastewater 108 obtained at the top of the tower is discharged from a system to be treated by a downstream device, a first extractant 109 obtained at the bottom of the tower enters a heat exchange device 9 for heat recovery and then circularly enters the upper part of the first extraction rectification tower 2, and the feed (first fraction 103) of the first extraction rectification tower 2 is heated to 134 ℃;
(4) the second fraction 111 enters a second rectification tower 4 to be rectified II, the pressure at the top of the second rectification tower 4 is controlled to be 5kPa, the temperature at the top of the tower is 44 ℃, the reflux ratio is 5.6, a refined methanol product 113 with the purity of 99.9 weight percent is obtained at the top of the tower in the second rectification process, the recovery rate of the methanol is 98.5 percent, noncondensable gas components 112 such as dimethyl ether and the like at the top of the tower are discharged from a system and enter a downstream device to be further processed, and a third fraction 114 obtained at the bottom of the tower enters a second extraction rectification tower 5;
(5) the second extractive distillation tower 5 is an ethanol refining tower, a second extracting agent 117 (a composite solvent of ethylene glycol and dimethyl sulfoxide, the volume ratio of the two is 1.5: 1) is added from the upper part of the tower, the feeding ratio of the second extracting agent 117 to the feeding (a third fraction 114) of the second extractive distillation tower 5 is 3.3, the pressure at the top of the second extractive distillation tower 5 is controlled to be 5kPa, the temperature at the top of the tower is 80 ℃, the reflux ratio is 2, an ethanol product 115 with the purity of 99.9 weight percent is obtained at the top of the tower through the second extractive distillation process, the recovery rate of ethanol is 97.5 percent, a fourth fraction 116 is obtained at the bottom of the tower, the fourth fraction comprises the second extracting agent and lower alcohol, and the fourth fraction 116 enters a III distillation tower 6;
(6) in the III rectifying column 6, the III rectifying conditions in the III rectifying column 6 were controlled such that the overhead pressure was 10kPaA (here, absolute pressure), the overhead temperature was 41 ℃ and the reflux ratio was 1. A fifth fraction 118 obtained from the tower top enters an IV rectifying tower 7 through the III rectifying process; a second extractant 117 obtained at the bottom of the tower circularly enters the upper part of a second extraction rectifying tower 5;
(7) in the IV rectifying tower 7, the IV rectifying conditions in the IV rectifying tower 7 are controlled to be that the pressure at the top of the tower is 5kPaG, the temperature at the top of the tower is 82 ℃ and the reflux ratio is 5, the fifth fraction 118 is rectified by the IV rectifying process to obtain a crude isopropanol material flow 119 (mainly comprising isopropanol and containing a small amount of ethanol and water) at the top of the tower, the crude isopropanol material flow 119 enters a downstream device for further treatment, and the isopropanol content in the crude isopropanol material flow 119 is 85 weight percent; feeding the sixth fraction 120 obtained at the bottom of the tower into a V-th rectifying tower 8;
(8) in the V-th rectifying tower 8, the conditions for controlling the V-th rectification in the V-th rectifying tower 8 comprise that the tower top pressure is 5kPa, the tower top temperature is 98 ℃, and the reflux ratio is 2. After the rectification process of the V-th, an n-propanol product 122 with the purity of 99.9 wt% is obtained at the tower top, the recovery rate of the n-propanol is 95.5%, a seventh fraction 123 obtained at the tower bottom enters a downstream device for further processing, the butanol content in the seventh fraction 123 is 89.3%, the condensation of the gas phase 121 at the tower top of the rectification tower 8 can provide heat for a reboiler 11 in the rectification tower II 4, the partial reflux of the condensate 121 is realized, and the partial reflux is discharged out of the system as the butanol product 122.
(9) The crude isopropanol material flow 119 enters a third extraction rectification tower 21, a third extracting agent 203 (a composite solvent of ethylene glycol and dimethyl sulfoxide with the volume ratio of 1.5: 1) is added from the upper part of the tower, the feeding ratio of the third extracting agent 203 to the raw material (the crude isopropanol material flow 119) of the third extraction rectification tower 21 is 4, the third extraction rectification conditions in the dehydration extraction rectification tower 21 are controlled to be that the tower top pressure is 5kPa, the tower top temperature is 83 ℃, the reflux ratio is 3.2, an eighth fraction is obtained from the tower top of the third extraction rectification tower 21 through the third extraction rectification process, and the eighth fraction 201 enters a fourth extraction rectification tower 23; and obtaining a ninth fraction 202 at the bottom of the tower, wherein the ninth fraction 202 is a mixture of the third extractant and water and enters the third extractant recovery tower 22.
(10) In the third extractant recovery tower 22, the pressure at the top of the third extractant recovery tower 22 is controlled to be 15kPaA (absolute pressure in the situation), the temperature at the top of the tower is 46 ℃, the reflux ratio is 3, the ninth fraction (mixture of the third extractant and water) 202 is subjected to rectification separation, the wastewater 204 obtained at the top of the tower is combined with the wastewater 108 and then discharged out of a system to be treated by a downstream device, and the third extractant 203 obtained at the bottom of the tower circularly enters the upper part of the third extractive distillation tower 21;
(11) in the fourth extractive distillation column 23, a fourth extractant 208 (a composite solvent of ethylene glycol and dimethyl sulfoxide, the volume ratio of the two is 1.5: 1) is added from the upper part of the column, the feeding ratio of the fourth extractant 208 to the feeding (eighth fraction) of the fourth extractive distillation column 23 is 6, and the conditions of the fourth extractive distillation in the fourth extractive distillation column are controlled to ensure that the pressure at the top of the column is 5kPa, the temperature at the top of the column is 80 ℃ and the reflux ratio is 5. Obtaining a crude ethanol product 205 with the purity of 97.5 weight percent at the tower top through a fourth extractive distillation process, obtaining a tenth fraction at the tower bottom, and feeding the tenth fraction (containing a fourth extractant and isopropanol) 206 into a VI rectifying tower 24;
(12) in the VI rectifying tower 24, the VI rectifying conditions in the VI rectifying tower 24 are controlled such that the overhead pressure is 15kPaA (here, absolute pressure), the overhead temperature is 41 ℃, and the reflux ratio is 1. And (3) performing a VI rectification process on the tenth fraction 206 to obtain an isopropanol product 207 with the purity of 99.7 weight percent at the tower top, and obtaining a fourth extractant 208 at the tower bottom to circularly enter the middle upper part of the fourth extractive rectification tower 23.
The composition of the materials involved in example 1 is shown in table 3 below.
TABLE 3
The method can separate the low-carbon alcohol with higher purity, the purity of the obtained methanol product, ethanol product and n-propanol product reaches 99.9 weight percent, and the method can also obtain the isopropanol with higher purity, and the purity of the obtained isopropanol product can reach more than 99.5 weight percent.
Example 2
The lower alcohol raw material mixture described in example 1 was separated and purified by the method described in example 1, except that the extracting agents (the first extracting agent, the second extracting agent, the third extracting agent and the fourth extracting agent) used were a composite solvent of ethylene glycol and dimethyl sulfoxide, and the volume ratio of the two was 0.8: 1. the product obtained is as follows:
the purity of the methanol product is 99.9%; the purity of the ethanol product is 99.8%; the purity of the n-propanol product was 99.5%; the purity of the isopropanol product was 99.2%.
Example 3
The lower alcohol feed mixture described in example 1 was isolated and purified according to the method described in example 1, except that the extractants used (first, second, third and fourth extractants) were ethylene glycol. The product obtained is as follows:
the purity of the methanol product is 99.4%; the purity of the ethanol product is 99.8%; the purity of the n-propanol product was 90%; the purity of the isopropanol product was 85%.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.
Claims (10)
1. A method of refining a lower alcohol, the method comprising:
(1) rectifying the low-carbon alcohol raw material mixture to obtain organic wastewater and a first fraction;
(2) subjecting the first fraction to a first extractive distillation using a first extractant to further remove water and obtain a second fraction;
(3) rectifying the second fraction II to obtain a refined methanol product and a third fraction;
(4) performing second extractive distillation on the third fraction by using a second extractant to obtain a refined ethanol product and a fourth fraction;
(5) carrying out III rectification on the fourth fraction to obtain a second extracting agent and a fifth fraction;
(6) performing IV rectification on the fifth fraction to obtain a crude isopropanol material flow and a sixth fraction;
(7) and (3) rectifying the sixth fraction V to obtain a refined n-propanol product and a seventh fraction.
2. The method of claim 1, wherein in step (1), the conditions of the I rectification comprise: the temperature at the top of the tower is 60-80 ℃, the pressure at the top of the tower is 0-10kPa, and the reflux ratio is 0.5-1; preferably, the overhead temperature is 65 to 75 ℃, the overhead pressure is 4 to 6kPa, and the reflux ratio is 0.7 to 0.9.
3. The process of claim 1 or 2, wherein, in step (2), the first extractant is selected from at least one of ethylene glycol, furfural, dimethylformamide, dimethyl sulfoxide; preferably, the first and second electrodes are formed of a metal,
the conditions of the first extractive distillation comprise: the temperature at the top of the tower is 50-70 ℃, the pressure at the top of the tower is 0-10kPa, and the reflux ratio is 0.35-0.65; preferably, the overhead temperature is 55 to 65 ℃, the overhead pressure is 4.5 to 5.5kPa, and the reflux ratio is 0.4 to 0.6.
4. The method of claim 1 or 2, wherein the second fraction comprises 20-60 wt% methanol, 10-40 wt% ethanol, 0.1-1 wt% water, 10-30 wt% n-propanol, 1-10 wt% isopropanol, 0.1-5 wt% butanol.
5. The method of claim 1 or 2, wherein in step (3), the conditions for the II th rectification comprise: the temperature at the top of the tower is 35-50 ℃, the pressure at the top of the tower is 0-10kPa, and the reflux ratio is 3-7; preferably, the overhead temperature is 38-48 ℃, the overhead pressure is 4-6kPa, and the reflux ratio is 5-6.
6. The method of claim 1 or 2, wherein in step (4), the conditions of the second extractive distillation comprise: the temperature at the top of the tower is 70-90 ℃, the pressure at the top of the tower is 0-10kPa, and the reflux ratio is 1-3; preferably, the overhead temperature is 75 to 85 ℃, the overhead pressure is 4 to 6kPa, and the reflux ratio is 1.5 to 2.5.
7. The method according to claim 1 or 2, wherein in step (7), the rectification conditions of V comprise: the temperature at the top of the tower is 90-105 ℃, the pressure at the top of the tower is 0-10kPa, and the reflux ratio is 1-3; preferably, the overhead temperature is 95 to 100 ℃, the overhead pressure is 4 to 6kPa, and the reflux ratio is 1.5 to 2.5.
8. The method of claim 1 or 2, further comprising: performing third extractive distillation on the crude isopropanol stream obtained in the step (6) by using a third extractant to obtain an eighth fraction; carrying out fourth extractive distillation on the eighth fraction by using a fourth extractant to obtain a crude ethanol product and a tenth fraction; and VI rectifying the tenth fraction to obtain a refined isopropanol product.
9. A system for refining lower alcohols, the system comprising:
the first rectifying tower is used for removing organic wastewater and is provided with a first rectifying tower feed inlet for receiving a low-carbon alcohol raw material mixture, a first rectifying tower top discharge port and a first rectifying tower bottom discharge port;
the first extractive distillation tower is used for further removing water and is provided with a first extractive distillation tower feed inlet, a first extractant feed inlet, a first extractive distillation tower top discharge port and a first extractive distillation tower bottom discharge port which are communicated with the first distillation tower top discharge port;
the second rectifying tower is used for refining methanol and is provided with a second rectifying tower feed inlet communicated with the first extractive rectifying tower top feed inlet, a methanol discharge outlet and a second rectifying tower bottom discharge outlet;
the second extractive distillation tower is used for refining ethanol and is provided with a second extractive distillation tower feed inlet, a second extractant feed inlet, a second extractive distillation tower top material outlet and a second extractive distillation tower bottom material outlet which are communicated with the second distillation tower bottom material outlet, and the second extractive distillation tower top material outlet outputs ethanol;
the third rectifying tower is used for recovering a second extracting agent and is provided with a third rectifying tower feeding hole communicated with the second extracting rectifying tower bottom discharging hole, a third rectifying tower top discharging hole and a third rectifying tower bottom discharging hole, and the third rectifying tower bottom discharging hole outputs the second extracting agent;
the IV rectifying tower is provided with an IV rectifying tower feeding hole communicated with the III rectifying tower ejection hole, an IV rectifying tower ejection hole and an IV rectifying tower bottom discharging hole, and the IV rectifying tower ejection hole outputs crude isopropanol material flow; and
and the V-th rectifying tower is provided with a V-th rectifying tower feeding hole communicated with the IV rectifying tower bottom discharging hole, a V-th rectifying tower top discharging hole and a V-th rectifying tower bottom discharging hole, and the V-th rectifying tower top discharging hole outputs the n-propanol.
10. The system of claim 9, further comprising an isopropanol recovery refining subsystem comprising:
the third extractive distillation tower is provided with a third extractive distillation tower feed inlet, a third extractant feed inlet, a third extractive distillation tower top feed inlet and a third extractive distillation tower bottom discharge outlet which are communicated with the fourth extraction distillation tower top feed inlet;
the fourth extractive distillation column is provided with a fourth extractive distillation column feed inlet, a fourth extractant feed inlet, a fourth extractive distillation column top discharge port and a fourth extractive distillation column bottom discharge port which are communicated with the third extractive distillation column top discharge port; and
and the VI rectifying tower is provided with a VI rectifying tower feeding hole communicated with the fourth extraction rectifying tower bottom discharging hole, a VI rectifying tower top discharging hole and a VI rectifying tower bottom discharging hole, and the VI rectifying tower top discharging hole outputs isopropanol.
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| CN112110793A (en) * | 2020-09-03 | 2020-12-22 | 南京沿江资源生态科学研究院有限公司 | Process for extracting mixed alcohol from light component at top of high-concentration wastewater pretreatment rectifying tower |
| CN116041150A (en) * | 2022-12-22 | 2023-05-02 | 厦门大学 | Accurate separation method of double-tower low-carbon mixed alcohol |
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