Ethyl acetate (abbreviated as EA) is an important organic compound that is colorless, transparent and has an aromatic odor. With its excellent solvency, relatively low toxicity, and easy volatility, it is an indispensable organic chemical feedstock for industrial production.

Ethyl acetate is increasingly used in the production of industrial fibers such as acetate, ethyl fibers, chlorinated rubber, vinyl resins, acetate resins, synthetic rubber, inks, paints, textiles, dyes, binders, etc. It is also used as a raw material for medicines, extractants for organic acids, and fruit spices.

With the rapid development and progress of the pharmaceutical, chemical, construction, and automobile industries worldwide, the demand for ethyl acetate as an important raw material is growing rapidly and its application areas will be gradually expanded.

The following content will illustrate the advanced process and technology for dehydration and recovery production of high-quality and high content ethyl acetate on an industrial-scale production line.

What Is The Production Process Of Ethyl Acetate?

There are mainly four traditional production processes for the manufacture of ethyl acetate: esterification of acetic acid and ethyl ester, acetaldehyde condensation, catalytic dehydrogenation of ethanol, and adductive esterification of acetic acid and ethylene.

Acetic Acid And Ethyl Esterification Method

The direct esterification reaction between acetic acid and ethanol under the catalytic effect of sulfuric acid and other catalysts under certain temperature conditions to produce ethyl acetate is a more widely used production process of ethyl acetate at present. This process is more flexible in production operation, simple in process, mature in method, and easy for large-scale industrialization.

The chemical reaction equation of the process is as follows:

CH₃COOH+CH₃CH₂OH →CH₃COOC₂H₅+H₂O

However, this process is expensive to produce and has certain raw material requirements, requiring sufficient raw materials of both acetic acid and ethanol at the production site, while the crude product of ethyl acetate obtained by this method usually has the remaining ethanol from the reaction as well as a small amount of water, which needs to be further removed by processes such as dehydration or distillation.

Additionally, the catalyst used in this reaction is an acidic compound, which is corrosive to the equipment, easy to carbonize, has many side reactions and the reaction products are complex, and may cause environmental pollution.

While many researchers have made a lot of improvements to the catalyst and production process of this process in recent years and tried various catalysts to replace sulfuric acid, however, these catalysts still have problems such as a rapid decline in catalytic activity, low catalytic efficiency, high cost, and reduced applicability.

Acetaldehyde Condensation Method

Under certain reaction temperature conditions, two molecules of acetaldehyde are directly oxidized and condensed to form ethyl acetate by utilizing alkyl aluminum catalysts such as aluminum chloride, aluminum ethanol, and zinc chloride.

In this process, acetaldehyde and catalyst are continuously fed into the reactor, and the reaction solution is then evaporated, concentrated and distilled to obtain a high purity ethyl acetate product.

This production process is carried out at low temperatures and atmospheric pressure, with high conversion and recovery rates, low production costs, mild operating conditions and little corrosion to the equipment.

However, the used catalyst is prone to hydrolysis reaction with water, and the wastewater produced by the reaction causes some pollution to the environment, and this method is constrained by the source of acetaldehyde raw material, which is limited to areas where acetaldehyde raw material is lacking, and is currently the main process for producing ethyl acetate in Japan and Europe.

The chemical reaction equation of the process is as follows:

2CH₃CHO→CH₃COOCH₂

Catalytic Dehydrogenation Of Ethanol:

Ethanol is dehydroesterified by direct oxidation in the presence of some copper-based catalysts to produce ethyl acetate, and then the azeotropes in the crude product are removed by distillation.

This production process can synthesize ethyl acetate directly by oxidation of ethanol without the help of acetic acid, with simple operation, low production cost, mild reaction conditions, higher recovery rate, good economy, and less corrosion of equipment, producing fewer pollutants and less environmental pollution, which can radically overcome the shortcomings of the old process.

The disadvantages are low selectivity and conversion, immature separation technology, and high ethanol consumption. If there is a shortage of ethanol resources, this method is not suitable for large-scale application.

Addition Esterification of Acetic Acid and Ethylene:

In the presence of water vapor, ethylene reacts with water under the action of catalysts (such as liquid inorganic acids and organosulfonic acids, molecular sieves and polyacids) to form ethanol, and then esterifies with acetic acid to form ethyl acetate.

This production process is simple in operation, less costly in production, less investment, environmentally friendly, easy to apply industrially, and ethylene can be made into ethanol in the presence of a catalyst, which is suitable for regions with insufficient ethanol resources.

However, the ethyl acetate production unit for this process needs to be constructed adjacent to an ethylene production unit or requires an adequate supply of ethylene resources, resulting in higher investment costs.

At present, this production process has been researched and developed in abroad, and is a widely used production process for ethyl acetate by overseas companies. The chemical reaction equation of the process is as follows:

CH₂=CH₂+CH₃COOH→CH₃COOC₂H₅

Separation of ethyl acetate and water by conventional processes include distillation, azeotropic distillation, liquid-liquid extraction, extractive distillation and membrane separation, etc.

These methods of separation have the following shortcomings:

• Conventional distillation methods have high energy consumption and low separation efficiency when separating ethyl acetate binary and ternary azeotropes.
• Special distillation methods such as extractive distillation and azeotropic distillation require the addition of a third component to the azeotrope to form a new binary or ternary azeotrope with the original separation system, resulting in increased separation costs.
• The liquid-liquid extraction, for its part, requires the use of a large amount of organic solvents, high equipment and safety requirements, and multiple staggered flows, poor reproducibility, low recovery, high cost, and complex processes.
• The common point of these traditional separation techniques is that they require complete vaporization of the system to be separated, which results in high energy consumption, difficult operation and low separation efficiency, which makes the overall operating cost high and difficult to separate binary or ternary azeotropic systems composed of ethanol-water, ethyl acetate-water, ethyl acetate-ethanol-water, etc.

At present, ethyl acetate is mainly produced by the conventional process, which has gradually led to the contradiction between supply and demand of the product due to the low level of production technology and high cost, resulting in the decline of production, low profitability or even stopping production and unprofitable operation of certain producers.

Therefore, the pursuit of a new separation technology with low energy consumption, no pollution, and good separation effect is a major trend in the field of industrial production.

Crude Binary Ternary Product Separation Of Ethyl Acetate Using Pervaporation Technique

Separation of Ethyl Acetate binary ternary crude products by pervaporation technique, with inorganic molecular sieve membranes have outstanding chemical stability and separation performance.

Pervaporation (abbreviated as PV) is a new type of membrane separation technology for the separation of liquid mixtures.

With the continuous progress of PV membrane material and performance, the application field of PV is also widening, and it has a very broad application prospect and market in the petrochemical industry, pharmaceutical industry, biochemical industry, food industry, environmental protection, etc.

Specific applications include dehydration of organic solvents, removal or recovery of trace organic and organic-organic mixtures from water, etc.

As a new type of membrane separation technology, permeate vaporization technology has the following outstanding advantages over traditional separation technologies:

• A Wider Range Of Applications.

The separation process is not limited by the gas-liquid equilibrium theory, but is mainly controlled by the permeation rate of the components in the membrane, and can be used to separate constant boiling point and near boiling point mixtures that are difficult to separate by traditional separation techniques, as well as to separate isomers.

• Large Separation Factor.

Suitable pervaporation membranes can be selected according to the different mixture systems to be separated to improve the single-stage separation selectivity of the membrane.

• Simple Process Operation And Easy To Scale-up Coupling.

It requires few additional treatments, no entrainment agents, is relatively easy to operate, and can be coupled with biological and chemical reactions or integrated with other processes, thus improving reaction efficiency.

• Economical And Efficient With Low Energy Consumption.

The pervaporation equipment is of compact structure, small footprint, and low investment. The energy consumption of the whole process of pervaporation includes heating the raw material liquid, condensing the permeate, and creating vacuum conditions in several aspects. The vaporization of the whole process utilizes the latent heat of the feed liquid, and the energy consumption is lower than that of the traditional separation process.

• The entire pervaporation process can be carried out under mild operating conditions and at room temperature and pressure.

Effects Of Process Conditions Of Pervaporation On The Separation Performance Of Ethyl Acetate-water System

In the specific pervaporation process, a process condition is selected and optimized that will largely determine the separation performance of the PV membrane.

The following permeation vaporization process conditions are usually investigated: feed fluid temperature, operating temperature, feed flow rate, feed fluid pressure, operating pressure, feed fluid concentration, vacuum, etc.

• Feed Flow Temperature:

Normally the temperature is too low, the mass of material on the permeate side is less and the permeate flux is lower, although a high temperature is beneficial to increase the permeate flux, the separation factor is often not proportional to the temperature.

So different feed flow temperatures shall be selected and tested to select and optimize the best feed flow temperature on working.

When the raw material liquid composition was selected as 10 wt% of water and 90 wt% of ethyl acetate system for testing, the separation performance of the molecular sieve membrane on the material system was modified by setting different feed liquid temperatures, and the test results showed that the permeate flux showed a continuously increasing trend with the increase of temperature, and the molecular factor decreased slightly.

The reason for this phenomenon is that the increase in temperature during the PV of the molecular sieve membrane will, on the one hand, intensify the thermal movement of molecules and increase the diffusion rate of water molecules in the pore channel of the molecular sieve membrane, making it easier for water molecules to pass through the molecular sieve membrane, and on the other hand, it also accelerates the diffusion rate of ethyl acetate, and the throughput of ethyl acetate molecules increases, thus increasing the permeation flux and decreasing the separation factor.

The optimum preheating temperature of the feed solution was selected to be 50°C based on the combination of permeate flux and separation factor.

• Effects of feed liquid pressure on the separation performance of ethyl acetate-water system

Differential pressure is an important mass transfer driving force in the pervaporation process. The inlet fluid pressure is also one of the key factors affecting the performance of molecular sieve membrane separation.

The appropriate operating pressure is also different for different molecular sieve membranes and different feed liquid systems.

To select the optimal feed liquid pressure for the molecular sieve membrane in the ethyl acetate (90 wt%)-water (10 wt%) system, the feed liquid pressure was set in the range of 100-600 Pa to investigate the effect of different feed liquid pressures on the separation effect of the molecular sieve membrane.

The test results show an overall increasing trend of permeate flux and a decreasing trend of separation factor. When the feed liquid pressure is 100-300 Pa, the separation factor decreases slightly and the permeate flux also increases slightly, and the PV separation performance does not change much. When the feed fluid pressure is greater than 300 Pa, the separation factor starts to decrease significantly, the permeate flux increases and the PV separation performance decreases significantly.

This is because the increased pressure of the feed liquid makes the driving force of molecules through the molecular sieve membrane increase. On the one hand, it accelerates the adsorption and diffusion rate of water molecules on the membrane surface, and on the other hand, it also leads to an increase in the number of inter-crystalline pores and larger voids, which makes it easier for ethyl acetate molecules to pass through the molecular sieve membrane, thus increasing the permeate flux and decreasing the separation factor, resulting in lower separation performance.

Therefore, considering the combined PV and separation factors, the optimum pressure for the PV membrane separation performance in the ethyl acetate (90 wt%)-water (10 wt%) system is 300 Pa.

During the period, the optimized conditions were also used to test the PV separation of the ethyl acetate-ethanol-water mixture, with the composition of ethyl acetate (72 wt%) – ethanol (20 wt%) – water (8 wt%) as the raw material solution.

The permeation fluxes and separation factors are shown in the following table:

It is clear that for both binary and ternary systems, molecular sieve membranes have different levels of separation performance.

We already know that the kinetic diameters of ethyl acetate, ethanol and water molecules are 0.52Nm, 0.45Nm and 0.29Nm, respectively, and the effective micropore diameter of molecular sieve membrane is about 0.41Nm.

Since the kinetic diameter of water molecules is much smaller than the pore diameter of molecular sieve membrane micropores, water molecules can easily pass through the pore channels of molecular sieve membrane and thus penetrate through the molecular sieve membrane.

The kinetic diameter of ethanol molecules is similar to the molecular sieve membrane pore diameter, so a small fraction of ethanol molecules may pass through the pores of the molecular sieve membrane, reducing the flux of water molecules to some extent and thus minimizing the total permeate.

In contrast, compared with ethanol and water molecules, the kinetic diameter of ethyl acetate molecules is significantly larger than the pore diameter of molecular sieve membrane, and they mainly pass through the intergranular defects of molecular sieve membrane, so ethyl acetate molecules are the most difficult to pass through molecular sieve membrane, and the separation factor of ethyl acetate is the highest.

Conclusion:

The increasing demand for ethyl acetate as an important raw material in various industries demands the need for advanced production processes and effective recovery and dehydration technologies.

The traditional production processes, although widely used, face challenges such as high energy consumption, low separation efficiency, and environmental pollution.

The pervaporation technique has emerged as a promising alternative due to its low energy consumption, no pollution, and good separation effect.

The optimization of the pervaporation process conditions can significantly improve its separation performance, making it a highly efficient and economic option for the recovery and dehydration of high-purity ethyl acetate on an industrial-scale production line.

The key to PV separation technology is the selection of membrane materials. Using zeolite membranes in the pervaporation process has shown outstanding chemical stability and separation performance, making it a promising technology for the separation of ethyl acetate-water systems.

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