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16SCIENTIFIC PROGRESS VOLUME 4 I ISSUE 5 I 2023 _ISSN: 2181-1601
Scientific Journal Impact Factor (SJIF 2022=5.016) Passport: http://sjifactor.com/passport.php?id=22257
PROCESS FOR PRODUCTION OF ETHYL ACETATE BY AN ENHANCED EXTRACTION PROCESS OF THE INTEGRATION
Niginabonu Qobil qizi Jamilova Mizrobjon Khalim ugli Zaripov
Assistant, Bukhara Institute of Engineering Assistant, Bukhara Institute of Engineering and Technology and Technology
ABSTRACT
The paper presents a study on the performance of a conventional plant-producing ethyl acetate from ethanol and acetic acid. Process models were compiled in the simulator . The impact of key parameters on the performance of individual installation nodes was examined by sensitivity analysis.
Key words: ethyl acetate, toxicity, azeotrope, acid anhydrides, green chemistry, stoichiometric, esterification
Solvents, such as ethyl acetate, are the substances used in many industrial processes, including the chemical industry. Due to their wide range of application, world demand for solvents is constantly growing. Increasingly stringent regulations on emissions of harmful pollutants from production processes make the importance of so called "green chemistry" (non-toxic chemicals to the environment and living organisms) well recognized There is, therefore, an urgent need for commonly used solvents to have a lower health and environmental impact. Ethyl acetate is characterized by low toxicity and, imporotantly, it is biodegradable. These advantageous features caused a significant increase in the market demand for this product of "green chemistry". On the other hand, a sustainable development and good engineering practice are the drivers towards a lowered consumption of energy and utilities, as well as a reduced wastes production— an economy of the closed cycle. A technology improvement presented herein responds to all these environmental and economy requirements. In order to minimize the losses of raw materials and the consumption of auxiliary media, it is necessary to optimize the technology. This will both improve the economy of the process and minimize the environmental impact by reducing pollutant emissions. Our improved variant of the classic ethyl acetate plant includes additional subcooling of azeotrope, which improves extraction efficiency, making the organic phase enriched with ethyl acetate. This increases the efficiency of the other installation units, and reduces the heat duty of the plant and the emission of pollutants. A closed circulation of the extractant was also applied, which contributes to reducing the amount of wastewater.
Ethyl acetate (EA) in the chemical industry is obtained mainly by the classic Fischer esterification reaction, where the substrates are ethanol (ET) and acetic acid
SCIENTIFIC PROGRESS VOLUME 4 I ISSUE 5 I 2023 _ISSN: 2181-1601
Scientific Journal Impact Factor (SJIF 2022=5.016) Passport: http://sjifactor.com/passport.php?id=22257
(AA), and water (W) is a by-product of the reaction . Esters, including ethyl acetate, can also be synthesized in a number of other reactions using compounds such as acid anhydrides, acid chlorides, amides, nitriles, unsaturated hydrocarbons, ethers, aldehydes, ketones, alcohols and other esters (transesterification reaction) However, due to the relatively high price of raw materials and the possibility of undesired by-products forming by these pathways of alternative synthesis, the classic Fischer esterification is found to be the most commonly used reaction for the EA synthesis. The Fischer reaction of esterification of alcohols with carboxylic acids is carried out at elevated temperatures, in the presence of catalysts. Both homogenous and heterogeneous catalysts are employed . The former are usually inorganic acids such as sulfuric and phosphoric acid, and hydrochloric acid, while the latter include acidic ion exchange resins. In the presence of the mentioned catalysts, the ethyl acetate synthesis is carried out under the temperature ranging between 70-90 °C. The temperature of the reaction mixture is controlled at a level assuring efficient removal of the vapors of the lighter key product in the esterification reaction . The reaction of liquid phase esterification is reversible and insignificantly exothermic. The value of the equilibrium constant of the reaction depends primarily on the structure of alcohol and acid. In the reaction of acetic acid with ethyl alcohol, the equilibrium constant may vary in the range of 4-4.5, which corresponds to a conversion of 66-68% at a stoichiometric ratio of substrates. Ionic liquids can also be used as a catalyst for the reaction. In the esterification process, it is possible to carry out the reaction already at room temperature, while obtaining high yields. Another advantage of using this type of catalyst is the fact that the reaction product is eliminated from the reaction medium as a separate phase, thus shifting the reaction equilibrium towards the product. The homogeneous catalyst, which is an ionic liquid, can therefore be reused by returning it to the process after purification Due to their corrosiveness, ionic liquids are rarely used on an industrial scale to produce ethyl acetate. The process can also take place in the steam phase. The catalysts are then oxides of metals such as ZrO2, TiO2, Al2O3, Fe2O3, and the reaction is carried out at a temperature that allows the evaporation of the reactants . In the case of ethyl acetate, the conversion rate of the reactants can be as high as 100%; however, depending on the catalyst used, by-products may be formed. An alternative method is the Tishchenko reaction, in which acetaldehyde disproportionates in the presence of base to the alcohol and the acid that then esterify in situ . The most common catalyst of this reaction are aluminum alkoxides. In this reaction, the obtainable yield of ethyl acetate by adding aluminum ethoxide to acetaldehyde at -20 Co is 61% . However, this method is less popular than the classical Fischer esterification due to the availability and price of the raw material . There are also other methods of synthesis, such as ethanol dehydrogenation and synthesis from ethylene and acetic acid. These methods require
SCIENTIFIC PROGRESS VOLUME 4 I ISSUE 5 I 2023 _ISSN: 2181-1601
Scientific Journal Impact Factor (SJIF 2022=5.016) Passport: http://sjifactor.com/passport.php?id=222ff7
difficult process conditions (T > 200 °C, p > 20 bar), which significantly increases the investment costs of the plant. Selectivity of the ethyl acetate synthesis from ethylene and acetic acid is almost 100% [17], but the efficiency of this process is not so high. Depending on the catalyst used, the maximum achieved conversion degree of this process ranges between 40% and 50% . On the other hand, many by-products are formed in the ethanol dehydrogenation reaction such as other esters, alcohols, aldehydes and ketones. The reaction mixture contains components with boiling points similar to ethyl acetate, including components which can form azeotropes . This is a particular problem when high purity ethyl acetate is desired . Considering the advantages and disadvantages of individual methods, a classic Fischer esterification reaction was selected in the modeled installation.
In this study, the conventional process of ethyl acetate synthesis was considered . Raw materials in this technology are acetic acid and anhydrous ethanol. The main goal of this paper is to optimize the process conditions of synthesis and purification of ethyl acetate. A study was carried out based on a model built with the use of flowsheeting software Chemcad 7. The shame of the modeled installation is shown in Figure 1
Acetic acid and ethanol are mixed , heated up and directed to the reactor. The esterification reaction takes place in the reactor evaporator at a temperature of about 90 ◦C, under atmospheric pressure. The vapors from the reactor are directed to the column , in which unreacted acetic acid is separated from the product by azeotropic distillation the first stage of EA purification. The bottom product is recycled to the reactor evaporator. The distillate is a triple EA-ET- W azeotrope. The azeotrope is washed with water to extract ethanol the second stage of EA purification. In case of the
SCIENTIFIC PROGRESS
VOLUME 4 I ISSUE 5 I 2023 ISSN: 2181-1601
Scientific Journal Impact Factor (SJIF 2022=5.016) Passport: http://sjifactor.com/passport.php?id=222ff7
improved approach, the extractor feed is cooled down to enhance extraction advantageous shift of extraction equilibrium . The organic phase from the extraction process is partly recycled to the azeotropic column as reflux, while the remainder is directed to the product rectification columnfinal product distillation. In this column, pure ethyl acetate is obtained as the bottom product , and the subcooled distillate is recycled to the extraction process he aqueous phase after extraction , containing ethanol and ethyl acetate is directed to the wastewater column , where ethyl acetate and ethanol are recovered. The distillate is recycled to the reactor and the bottom product is recycled as a washing water to the extraction process, partially refreshed with a fresh portion of water . The impact of key parameters on the performance of individual installation nodes was examined by sensitivity analysis. On the basis of the analysis, the optimal conditions for the process were selected. For comparison purposes, three installation approaches are presented:
k2 = 0.0545 exp(-9314/(RT)) [1/min] Optimization of the Reaction System The continuous stirred tank reactor CSTR was used to model the reaction system . The key parameters affecting the degree of conversion are the temperature and the residence time of the reaction mixture in the reactor. The influence of these parameters on the composition of the post-reaction mixture was examined using the sensitivity analysis tool. The analysis assumed a constant composition of the reactor input stream. The results of the analysis are shown in Figure 2.
D.S5
0.5
0.45
0-J
Î 0.35
0.3
0.25
0-2
* *
i-t- ■ * * * *
/ K * , n nJLO-U BOP , ^ T T - _ ^ , ^ ^ n nnn n V ir w
* JD-e^ 0-*
Ten pe raturç:
—*— 70 °C
75 *C SO °C -H5 "C 90 *C
t[h]
The results obtained by simulation prove that the temperature increase in the reactor positively affects the EA content in the output stream, but only up to a certain point. The highest degree of reagent conversion was obtained at 85 Co. Above 85 Co, the EA content drops significantly. This is due to the increased and excessive evaporation of ethanol from the reaction system, which shifts the equilibrium of the reaction towards
SCIENTIFIC PROGRESS VOLUME 4 I ISSUE 5 I 2023 _ISSN: 2181-1601
Scientific Journal Impact Factor (SJIF 2022=5.016) Passport: http://sjifactor.com/passport.php?id=222ff7
the substrates. Apparently, the optimum residence time at elevated temperatures should be kept in the range of 3-4 h.
Optimization of Azeotropic Distillation The azeotropic column is used to strip acetic acid from the reactor vapors and for distillation of the EA-ET-W triple azeotrope. The reactor vapors are fed to the last stage of the column, while the reflux a distillate washed with water is fed onto the first stage. The obtained distillate is an azeotrope with a mass composition of 83.1% ethyl acetate, 8.7% ethanol, 8.2% water which is directed to the water extraction process. The bottom product from the column containing the stripped acetic acid is recycled to the reaction node. Azeotropic distillation is limited by the amount of acetic acid in the distillate. The product of appropriate quality should not contain more than 0.005 wt%. To assure the required contents of AA in the distillate, both reflux ratio (R/V) and the number of stages were adjusted. The results are shown in Figure 3. required contents of AA in the distillate, both reflux ratio (R/V) and the number of stages were adjusted.
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