Method for preparing ethanol and co-producing cyclohexanol by using reactive distillation method
阅读说明：本技术 一种利用反应精馏法制备乙醇并联产环己醇的方法 (Method for preparing ethanol and co-producing cyclohexanol by using reactive distillation method ) 是由 王华军 徐杏 龚建 于 2019-09-20 设计创作，主要内容包括：本发明属于燃料乙醇制备并联产环乙醇工艺领域,更具体地,涉及一种利用反应精馏法制备乙醇并联产环己醇的方法。在反应精馏塔的反应段下部进料乙醇-水混合物,中部进料环己烯；设定回流比及塔顶馏出液流率,使反应精馏塔的塔顶产物经冷凝器冷凝后一部分回流入塔,一部分作为循环物流与新鲜的环己烯进料合并；按设定的侧线采出位置及采出流率,在精馏段直接侧线出料得到燃料乙醇,塔底产物一部分经再沸器汽化入塔,一部分作为塔底产品环己醇被收集。通过利用反应精馏塔中环己烯与水的反应除去乙醇-水混合物中的水,制备得到燃料乙醇并联产环己醇,由此解决现有技术反应精馏制备燃料乙醇方法中存在的副反应多导致乙醇提纯难度加大的技术问题。(The invention belongs to the technical field of preparation of fuel ethanol and coproduction of cycloethanol, and particularly relates to a method for preparing ethanol and coproducing cyclohexanol by using a reactive distillation method. Feeding an ethanol-water mixture into the lower part of a reaction section of the reaction rectifying tower, and feeding cyclohexene into the middle part of the reaction rectifying tower; setting a reflux ratio and a flow rate of the overhead distillate, condensing the overhead product of the reactive distillation column by a condenser, refluxing a part of the overhead product into the reactive distillation column, and combining the part of the overhead product serving as a circulating material flow and a fresh cyclohexene feed; according to the set side draw position and the draw flow rate, the fuel ethanol is obtained by direct side draw in the rectifying section, part of the tower bottom product is vaporized into the tower through a reboiler, and part of the tower bottom product is collected as the tower bottom product cyclohexanol. The reaction of cyclohexene and water in the reaction rectifying tower is utilized to remove water in the ethanol-water mixture, so that the fuel ethanol is prepared and the cyclohexanol is co-produced, and the technical problem that the difficulty in ethanol purification is increased due to more side reactions in the method for preparing the fuel ethanol by reactive distillation in the prior art is solved.)
1. A method for preparing ethanol and co-producing cyclohexanol by using a reactive distillation method is characterized by comprising the following steps:
(1) feeding an ethanol-water mixture into the lower part of a reaction section of the reaction rectifying tower, and feeding cyclohexene into the middle part of the reaction rectifying tower;
(2) setting a reflux ratio and a flow rate of the overhead distillate, condensing the overhead product of the reactive distillation column by a condenser, refluxing a part of the overhead product into the reactive distillation column, and combining the part of the overhead product serving as a circulating material flow and a fresh cyclohexene feed;
(3) according to the set side draw position and the draw flow rate, the fuel ethanol is obtained by direct side draw in the rectifying section, part of the tower bottom product is vaporized into the tower through a reboiler, and part of the tower bottom product is collected as the tower bottom product cyclohexanol.
2. The method of claim 1, wherein the reaction section of the reactive distillation column is filled with an HZSM-5 zeolite molecular sieve catalyst having a silica-alumina ratio of 20 to 50.
3. The method of claim 1, wherein the upper limit of the catalyst loading is located at stages 11 to 20 of the theoretical plates of the reactive distillation column.
4. The method according to claim 1, wherein the operating pressure in the reactive distillation column is 0.1 to 0.5 MPa.
5. The method of claim 1, wherein the ethanol-water mixture is a near azeotropic ethanol-water mixture comprising 85 to 95 wt% ethanol.
6. The process of claim 1, wherein the cyclohexene and water are fed in a molar ratio of 1: 1.
7. The method of claim 1, wherein the reactive distillation column has a theoretical plate number of 22 to 31; cyclohexene is fed from any of stages 15 to 24.
8. The method of claim 1, wherein the reflux ratio in step (2) is 50 to 95; the overhead distillate flow rate is 55-100 kmol/hr.
9. The method of claim 1, wherein the side draw is from stage 6 to 15 of the theoretical plates of the reactive distillation column; the side draw flow rate was 2296-.
10. The method of claim 1, wherein the side draw is from stage 11 to 14 of the theoretical plates of the reactive distillation column; the side draw flow rate was 2299-.
Technical Field
The invention belongs to the technical field of preparation of fuel ethanol and coproduction of cycloethanol, and particularly relates to a method for preparing ethanol and coproducing cyclohexanol by using a reactive distillation method.
Background
Fuel ethanol generally refers to absolute ethanol having a volume concentration of 99.5% or more, and is ethanol that can be used as a fuel and is obtained by a process such as biological fermentation using biomass as a raw material. The fuel ethanol is denatured and then mixed with gasoline according to a certain proportion to prepare the ethanol gasoline for the automobile, and the fuel ethanol has the characteristics of cleanness, high octane number, renewability and the like, and can reduce the emission of carbon monoxide and hydrocarbon in the tail gas of the automobile. In recent years, the demand for fuel ethanol has increased dramatically due to the increasing depletion of fossil fuels.
The fuel ethanol is mainly obtained by liquefying, saccharifying, fermenting, distilling and dehydrating sugar crops and starchiness crops. The mass content of ethanol in mash obtained by biomass fermentation is only about 10%, and most of ethanol is water. The key to the production of ethanol as a vehicle fuel from the fermentation mash is the removal of water therefrom. Because of the azeotropic point of the ethanol-water system under normal pressure, the ethanol with azeotropic concentration can be obtained only by adopting common rectification, wherein the mass content of the ethanol is about 95 percent, and in order to further obtain the fuel ethanol with the ethanol content of more than 99.5 percent, a special purification method is required to remove the water.
At present, the special purification methods for removing water by azeotropic ethanol mainly comprise an azeotropic distillation method, an extractive distillation method, a membrane separation method, an adsorption method, a reactive distillation method and the like. Although the above methods can achieve the purpose of removing water from azeotropic ethanol, each method has some disadvantages. The azeotropic distillation method usually adopts benzene as an entrainer, and uses benzene, ethanol and water to form a ternary azeotrope to remove water, and the method has the main problems of high energy consumption, long flow and complex process; the extractive distillation method adopts ethylene glycol, ionic liquid and the like as the extracting agents, can effectively break the azeotropy of ethanol and water, but the using amount of the extracting agents in the process is large, and the regeneration circulation of the extracting agents increases the energy consumption and equipment cost in the process; the membrane separation method adopts a hydrophilic polymer membrane material to separate ethanol from water by utilizing the difference of component diffusion rates, but the process needs vacuum operation, and the membrane component is expensive and easy to pollute, has higher product cost and is not suitable for large-scale production; the adsorption method adopts molecular sieve or starch substances as an adsorbent, the adsorption capacity of the adsorbent is limited, and the regeneration of the adsorbent causes higher energy consumption in the process. The reactive distillation method is to add a third substance which can be subjected to a hydration reaction with water into a system, and convert the water into another component which has a higher added value and is easy to separate through distillation through a chemical reaction, so as to achieve the aim of removing the water. Compared with the traditional physical separation method, the reactive distillation method has the advantages of high atom economy, simple flow, energy conservation and the like.
Dirk-Faitakis et al, Alberta university, Canada, proposed an isobutylene hydration distillation process for the removal of near-azeotropic ethanol-water mixtures (Dirk-Faitakis C B and Chuang K T.Simulans students of synthetic distillation for removal of water from methanol using a-based kinetic model [ J ]. Ind.Eng.Chem.Res.,2004,43:762 768.), which employs isobutylene as a reactant and a solid acid as a catalyst, first purifies ethanol to near-azeotropic concentrations by conventional distillation, and then performs chemical reactions and product separations in a reactive distillation column. The process adopts a reactive distillation technology, so that the energy consumption is effectively saved, but the hydration reaction alkene-water ratio is up to 5:1, and isobutene reacts with water and can also undergo etherification reaction with ethanol, so that part of ethanol is consumed, the system is complicated, and the difficulty of ethanol purification is increased. The product obtained from the bottom of the reactive distillation column is a mixture of ethanol, tert-butyl alcohol and ethyl tert-butyl ether, and high-purity ethanol cannot be directly obtained.
A method for removing water in a near-azeotropic ethanol-water mixture by virtue of ethylene oxide hydration reaction rectification is provided in Anwei of China oceanic university (An W, Lin Z, Chen J, et al.Simulantion and analysis of a reactive distillation column for removal of water from ethanol-water mixtures [ J ]. Ind.Eng.chem.Res.,2014,53(14): 6056) 6064). The process adopts a reactive rectification technology, utilizes ethylene oxide hydration reaction to remove water in industrial ethanol, and simultaneously produces ethylene glycol and other components as byproducts. But ethylene oxide has active property, the generated ethylene glycol can continuously react with the ethylene oxide to obtain series of diethylene glycol, triethylene glycol and the like, and the ethylene oxide can also generate ethoxylation reaction with ethanol, so that the whole system has numerous side reactions, the product purification and separation difficulty is high, the flow is long, the ethylene oxide is flammable and explosive, and the process operation and control are difficult.
In conclusion, the production cost of the fuel ethanol is an important index related to the difficulty degree of popularization of the whole ethanol gasoline for the vehicle. The dehydration technology is one of the key technologies in the preparation process of the fuel ethanol, the reactive distillation method has the potential advantages of energy consumption saving and cost reduction compared with the traditional physical separation method, and the hydration reaction is the core of the reactive distillation method for producing the fuel ethanol. The hydration reaction with high conversion rate and high selectivity can effectively reduce the difficulty of product purification and furthest exert the potential of the reactive distillation technology.
Disclosure of Invention
Aiming at the defects or improvement requirements of the prior art, the invention provides a method for preparing ethanol and co-producing cyclohexanol by using a reactive distillation method, which removes water in an ethanol-water mixture by using the reaction of cyclohexene and water in a reactive distillation tower to prepare fuel ethanol and co-produce cyclohexanol, thereby solving the technical problem that the difficulty in purifying ethanol is increased due to more side reactions in the method for preparing fuel ethanol by reactive distillation in the prior art.
To achieve the above object, according to one aspect of the present invention, there is provided a method for preparing ethanol and co-producing cyclohexanol by reactive distillation, comprising the steps of:
(1) feeding an ethanol-water mixture into the lower part of a reaction section of the reaction rectifying tower, and feeding cyclohexene into the middle part of the reaction rectifying tower;
(2) setting a reflux ratio and a flow rate of the overhead distillate, condensing the overhead product of the reactive distillation column by a condenser, refluxing a part of the overhead product into the reactive distillation column, and combining the part of the overhead product serving as a circulating material flow and a fresh cyclohexene feed;
(3) according to the set side draw position and the draw flow rate, the fuel ethanol is obtained by direct side draw in the rectifying section, part of the tower bottom product is vaporized into the tower through a reboiler, and part of the tower bottom product is collected as the tower bottom product cyclohexanol.
Preferably, the reaction section of the reactive distillation column is packed with an HZSM-5 zeolite molecular sieve catalyst having a silicon to aluminum ratio (SiO)2And Al2O3The mass ratio of) is 20 to 50.
Preferably, the upper limit position of the catalyst loading is 11 th to 20 th stages in the theoretical plate of the reactive distillation column.
Preferably, the upper limit position of the catalyst loading is stages 13 to 17.
Preferably, the operation pressure in the reactive distillation tower is 0.1-0.5 MPa.
Preferably, the ethanol-water mixture is a near azeotropic ethanol-water mixture, wherein the ethanol content is 85-95 wt%.
Preferably, the feed molar ratio of cyclohexene to water is 1: 1.
Preferably, the theoretical plate number of the reaction rectifying tower is 22-31; cyclohexene is fed from any of stages 15 to 24.
Preferably, the theoretical plate number of the reaction rectifying tower is 25-29; cyclohexene is fed from any of stages 20-23.
Preferably, the reflux ratio in the step (2) is 50-95; the overhead distillate flow rate is 55-100 kmol/hr.
Preferably, the reflux ratio of step (2) is 70-90; the overhead distillate flow rate is 75-95 kmol/hr.
Preferably, the side draw position is the 6 th to 15 th stages in the theoretical plate of the reactive distillation column; the side draw flow rate was 2296-.
Preferably, the side draw is at stages 11 to 14 of the theoretical plates of the reactive distillation column; the side draw flow rate was 2299-.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
(1) the cyclohexene hydration process is combined with the ethanol dehydration process, the cyclohexene hydration reaction selectivity is high, the cyclohexene and the ethanol do not react, and almost no by-product is generated in the system. Meanwhile, ethanol can be used as a mutual solvent, so that the solubility of cyclohexene in water can be enhanced, and the conversion rate of cyclohexene hydration reaction is improved.
(2) Compared with the traditional ethanol dehydration process, the invention adopts a reactive distillation coupling process, and the cyclohexanol is obtained by reacting the water to be removed from the ethanol, thereby realizing the atom economic reaction. The hydration reaction and the rectification separation are simultaneously carried out in one device, the reaction heat is fully utilized, the energy consumption is effectively reduced, and the energy of the whole system is utilized to the maximum extent.
(3) The invention adopts the reactive distillation ethanol dehydration process with side discharge and circulating material flow, fully utilizes the characteristic of intensified reactive distillation process, obtains fuel ethanol by direct side discharge at the distillation section, simplifies the process flow and effectively reduces the operation cost and equipment cost; in the process, the material flow at the top of the tower is circularly fed, and the unreacted cyclohexene in the system is effectively utilized, so that the original cyclohexene feed serving as a reactant can be fed in a molar ratio of 1:1 to water, high-purity cyclohexanol can be obtained at the bottom of the tower, fuel ethanol is extracted from a side line, the component utilization rate is one hundred percent, and the whole process flow is simple, economic and green.
(4) The invention prepares fuel ethanol by reacting cyclohexene with water in an ethanol-water mixture, and can coproduce cyclohexanol. Cyclohexanol is an important chemical intermediate raw material, and is mainly used for producing phthalic amine products such as adipic acid, nylon-66, caprolactam and the like in industry, and meanwhile, the cyclohexanol can be used as a solvent of paint, shellac and varnish, a matting agent of textiles and synthetic fiber fabrics and the like. Cyclohexanol is produced in mainly 3 types: cyclohexane oxidation, phenol hydrogenation, and cyclohexene direct hydration. The cyclohexene hydration method for producing cyclohexanol has the advantages of low hydrogen consumption, good product selectivity, high production safety and the like, and is the most promising cyclohexanol production method at present.
(5) The invention adopts cyclohexene to remove water in a near azeotropic ethanol-water mixture and produces cyclohexanol in parallel, almost no side reaction occurs, the purity of the prepared fuel ethanol can reach more than 99.5 percent, the purity of the cyclohexanol is more than 99 percent, the heat load of a reboiler is 2.42-3.54MJ/kg (a side-line absolute ethanol product), and the energy consumption is lower than that of an ethylene oxide hydration reaction rectification route method (about 5.32 MJ/kg), an azeotropic rectification method (10.05-15.49MJ/kg) and an extractive rectification method (9.21-18.84 MJ/kg).
Drawings
FIG. 1 is a process flow diagram for the process of the present invention; in FIG. 1 EtOH is ethanol, H2O is water, CHE is cyclohexene, and CHOL is cyclohexanol.
The same reference numbers will be used throughout the drawings to refer to the same or like elements or structures, wherein:
a is a condenser, B is a rectifying section, C is a reaction section, D is a stripping section, and E is a reboiler.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The invention provides a method for preparing ethanol and co-producing cyclohexanol by using a reactive distillation method, which is a technological method for preparing fuel ethanol and co-producing cyclohexanol by removing water from reactive distillation near-azeotropic ethanol with side line discharging, and comprises the following steps:
(1) feeding an ethanol-water mixture into the lower part of a reaction section of the reaction rectifying tower, and feeding cyclohexene into the middle part of the reaction rectifying tower;
(2) setting a reflux ratio and a flow rate of the overhead distillate, condensing the overhead product of the reactive distillation column by a condenser, refluxing a part of the overhead product into the reactive distillation column, and combining the part of the overhead product serving as a circulating material flow and a fresh cyclohexene feed;
(3) according to the set side draw position and the draw flow rate, the fuel ethanol is obtained by direct side draw in the rectifying section, part of the tower bottom product is vaporized into the tower through a reboiler, and part of the tower bottom product is collected as the tower bottom product cyclohexanol.
The method utilizes a reaction separation coupling technology, uses cyclohexene as a reactant, simultaneously carries out chemical reaction and rectification separation processes in one tower, leads water which is difficult to remove by a conventional separation method in a near azeotropic ethanol-water mixture to generate cyclohexanol with high added value through cyclohexene hydration reaction, has high conversion rate and selectivity in the hydration reaction process, does not generate byproducts, can directly carry out side-stream discharging in the tower to obtain fuel ethanol, and simultaneously coproduces cyclohexanol in a tower kettle.
In some embodiments, the reaction section of the reactive distillation column is packed with an HZSM-5 zeolite molecular sieve catalyst having a silica to alumina ratio (SiO)2And Al2O3In a mass ratio) of 20 to 50, and a loading amount of 700 to 1000 kg.
In some embodiments, the ethanol-water mixture is a near azeotropic ethanol-water mixture comprising 85 to 95 wt% ethanol. The near-azeotropic ethanol-water mixture with the concentration of 85-95 wt% is adopted, and the purpose is mainly to reduce the energy consumption in the conventional rectification process. In the process of purifying ethanol by conventional rectification, when the concentration of the ethanol is about 85 percent, the energy consumption of the rectification is rapidly increased along with the further increase of the concentration of the ethanol.
In some embodiments, the upper limit of the catalyst loading is from stage 11 to 20 in the theoretical plate of the reactive distillation column, and preferably from stage 13 to 17. At the preferred upper loading limit, the conversion rate of the hydration reaction is high, the product purity is high, and the reboiler load is low.
The feeding molar ratio of the cyclohexene to the water is 1: 1. The stoichiometric ratio of the cyclohexene to water hydration reaction is 1:1, and when the ratio is adopted for feeding, the high conversion rate is obtained, meanwhile, the circulation of unreacted materials can be reduced, and the operation cost and the energy consumption are reduced.
In some embodiments, the theoretical plate number of the reactive distillation column is 22-31, preferably 25-29, the plate number is one of the most important parameters of the reactive distillation column, the separation requirement is difficult to achieve due to too small plate number, and the separation effect can be improved by increasing the plate number, but the equipment investment is increased at the same time. Under the optimized theoretical plate number, the conversion rate of water can reach more than 98%, and the concentration of the ethanol discharged from the side line is more than 99.5%.
Cyclohexene is fed from any stage of stages 15 to 24, preferably from any stage of stages 20 to 23, in the system, the cyclohexene enters a tower to form a binary or ternary azeotrope with ethanol, water and the like, the boiling point of the formed azeotrope is relatively low, the cyclohexene moves towards the upper part of a feeding position along with the azeotrope, and in order to ensure that the cyclohexene and the water can be fully contacted in a reaction section, the cyclohexene is fed at a proper position in the middle of the reaction section. Under the optimal feeding position, the concentration of the side-stream discharged ethanol can reach over 99.5 percent, and the concentration of cyclohexanol can reach about 99.9 percent.
In some embodiments, the reflux ratio in step (2) is 50-95, preferably 70-90, and is also one of the most important parameters of the reactive distillation column, and increasing the reflux ratio can increase the mass transfer driving force in the column, improve the separation effect, reduce the number of theoretical plates, and save the equipment cost, but the increase of the reflux ratio causes the increase of the flow rate of liquid phase and vapor phase material flows in the column, so that the heat load of a condenser and a reboiler becomes large, and the operation cost increases. At the preferred reflux ratio, satisfactory ethanol and cyclohexanol concentrations can be achieved, and reboiler heat duty is not too high.
The overhead distillate flow rate is from 55 to 100kmol/hr, preferably from 75 to 95 kmol/hr. The increase in overhead distillate, at a constant reflux ratio, increases the liquid and vapor flow rates within the column, thereby increasing condenser and reboiler duty, as well as increasing cycle operating costs. At the preferred overhead effluent flow rate, the reboiler duty is lower while acceptable ethanol product is obtained.
The feeding flow rates of the ethanol-water mixture and the cyclohexene are 2400-2600 kmol/hr and 280-810 kmol/hr respectively, and the flow rate of the fuel ethanol extracted from the side line of the rectifying section is 1650-2310 kmol/hr, preferably 2296-2305kmol/hr, and more preferably 2299-2303 kmol/hr. The side-draw amount affects the yield of ethanol, and also affects the flow of vapor and liquid streams in the tower, thereby affecting the separation effect of the tower and the load of a reboiler. At the preferred side draw flow rate, the reboiler duty is low and product purity is satisfactory.
In some embodiments, the side draw is from stage 6 to 15, preferably from stage 11 to 14, of the theoretical plates of the reactive distillation column. At the preferred side draw position, the reboiler has a low heat duty, and the ethanol and cyclohexanol have high purity and high water conversion.
In the embodiment of the invention, the temperature in the reaction section of the reactive distillation column is 115-130 ℃, the temperature at the top of the column is 110-120 ℃, and the temperature at the bottom of the column is 210-220 ℃. The temperature difference between the tower top and the tower bottom is large, and the separation effect is obvious; the pressure used is 0.1-0.5 MPa, and the pressure range can enable the reaction to occur in a liquid phase.
The mechanism of the technical scheme is that HZSM-5 zeolite molecular sieve is used as a catalyst, water in a near-azeotropic ethanol-water mixture with the concentration of 85-95 wt% and cyclohexene react to generate cyclohexanol through a reactive distillation process, the distillate at the top of the tower is used as a circulating material flow and returns to a reaction section, high-purity cyclohexanol is obtained at the bottom of the tower, and the fuel ethanol is obtained through direct side-stream discharging at a distillation section.
The method for preparing ethanol and coproducing cyclohexanol by reactive distillation can adopt a device and a system which are commonly used in the prior art and are used for reactive distillation of fuel ethanol and provided with side line discharging.
The following are examples:
as shown in figure 1, the reaction rectifying tower adopted by the invention consists of a condenser A, a rectifying section B, a reaction section C, a stripping section D and a reboiler E, wherein the reaction section C is filled with a silicon-aluminum ratio (SiO) in HZSM-5 zeolite molecular sieve catalyst2/Al2O3) The catalyst loading was 800kg and the operating pressure in the reactive distillation column was 0.4MPa, at 50. The concentration of the adopted raw material near-azeotropic ethanol-water mixture is 85-95 wt% of ethanol, and preferably 95 wt%; the cyclohexene/water molar feed ratio employed was 1: 1.
The advantageous effects of the present invention are further illustrated by the following specific examples.