A Comparative study of equilibrium and non-equilibrium models for ethyl acetate production in reactive distillation

A finishing reactive distillation (RD) column (50 stage), used for enhanced ethanol conversion, in an ethyl acetate production plant was simulated. This RD column followed a pre-reactor, wherein, homogeneously catalyzed esterification reaction for the production of ethyl acetate using acetic acid and ethanol was carried out. The simulation results of the RD column using equilibrium and rate-based models are compared with the plant data. The column design data for tray holdup, required for the rate-based model, was used. Effects of some design and operation parameters of the simulation results are also discussed.

<p>In the present study, two distinctly different approaches are followed for modeling of reactive distillation column, the equilibrium stage model and the nonequilibrium stage model. These models are simulated with a computer code developed in the present<br> study using MATLAB programming. In the equilibrium stage models, the vapor and liquid phases are assumed to be in equilibrium and allowance is made for finite reaction rates, where as in the nonequilibrium stage models simultaneous mass transfer and reaction rates are considered. These simulated model results are validated from the experimental data reported in the literature. The simulated results of equilibrium and nonequilibrium models are compared for concentration, temperature and reaction rate profiles in a reactive distillation column for Methyl Tert Butyle Ether (MTBE) production. Both the models show similar trend for the concentration, temperature and reaction rate profiles but the nonequilibrium model predictions are higher and closer to the experimental values reported in the literature.</p>

Design and two step process optimization of a reactive distillation column for improving production amount of ethyl acetate and water

Effect of side reactions in hybrid distillation system: Parallel production of ethyl acetate and glycols

In this paper, design of a complete reactive distillation (RD) system has been developed. The reactive distillation system in the study is the production of ethyl acetate (EtAc) via esterification of acetic acid (HAc) with ethanol (EtOH) using sulphuric acid as homogeneous catalyst. A suitable NRTL model parameter set for calculating of liquid activity coefficients has been established with excellent prediction of the compositions and temperatures for the four azeotropes in this system. In the VLE calculations, vapor association of acetic acid due to dimerization has also been considered. A reactive distillation column with an overhead decanter can be designed to achieve over 93 wt% of ethyl acetate composition at organic phase top product stream while the bottom product stream is designed to be rich in acetic acid so that it can be recycled and mixed with fresh acid make-up stream to serve as acid feed to the reactive distillation column. Since the purity of the optimum top organic product is still not good enough for the ethyl acetate product specification in industry, an additional column is designed to purify the ethyl acetate product of the reactive distillation column to over 99.5 wt%. The top draw of the second column will be recycled back to the decanter. In summary, the overall optimum design of this ethyl acetate reactive distillation system includes two columns (including the reactive distillation column and the second column), one decanter, and two recycle streams. The optimum operating condition of the overall system will also be studied to minimize the total operating cost of the overall system while meeting product specifications.

Simulating reactive distillation of HIx (HI–H2O–I2) system in Sulphur-Iodine cycle for hydrogen production

Esterification of acetic acid and methanol to produce methyl acetate and water has been studied in a continuous packed bed catalytic reactive distillation column. Indion 180, an ion-exchange resin solid catalyst has loaded in an equivalent Katapak-S into the reactive section of the column. The experiments were conducted under different operating conditions of reboiler temperature, total feed flow rate of the reactants, methanol to acetic acid mole ratio, feed location of acetic acid and methanol with respect to reactive section, reflux ratio and catalyst amount to investigate the composition of distillate and reboiler respectively. The maximum methyl acetate composition and acetic acid conversion is obtained at reboiler temperature of 80 °C, reflux ratio of 2, total feed flow rate of 16.3 g/min, catalyst loading of 60 g and mole ratio of methanol to acetic acid is 1. From the experimental investigations, it is found that the composition of the methyl acetate in the distillate is 95% by mole at an optimized experimental condition. The experimental data has been compared with equilibrium and non-equilibrium model predictions and found that non-equilibrium model is able to predict the experimental data reasonably good. The calculated error from equilibrium model relative to experimental data is 4.71% and rate based model relative to experimental data is 0.61%. It is observed that the error is less in rate based model compared to equilibrium model.

Dynamic behaviour of reactive distillation columns described by a nonequilibrium stage model

Reactive vapor-recompression distillation for green hexamethylene-1,6-dicarbamate synthesis

A comparison of the equilibrium and nonequilibrium models for a multicomponent reactive distillation column

In this study, we aimed to determine the optimum operating conditions for the production of ethyl acetate (EtAc) through the esterification of ethanol (EtOH) with acetic acid (HAc) in a reactive distillation (RD) column. For this, the designed column was simulated for the production of EtAc. HAc flow rate, EtOH flow rate, HAc feed stage, EtOH feed stage, reflux ratio, and reactive feed temperatures were changed and the effects of these parameters on EtAc production were observed. Central Composite Design was employed to define the optimum operating conditions for the RD column. The determination coefficient R2 was equal to 0.9197 suggesting a good relationship between the predicted and simulated responses. Adjusted R2 and predicted R2 values obtained from the program were 0.8823 and 0.7956, respectively. The optimal conditions for the EtAc production response were HAc flow rate of 120.00 kmol/h, EtOH flow rate of 150.00 kmol/h, HAc feed stage 6, EtOH feed stage 14, reflux ratio 2.2, and feed temperature 70.28 °C, which were designated by the maximum desirability function.

Exergy analysis and optimization of reactive distillation column in acetic acid production process

The models for the production of methyl acetate from the esterification reaction of methanol and acetic acid in a reactive distillation column (RDC) were developed. Six trays were selected as the reactive zone; methyl acetate and water were produced with unreacted acid and methanol in the RDC. Azeotropic mixture of methyl acetatemethanol was formed at the top of the reactive distillation column. The constant boiling mixture of Methyl acetate-methanol was eliminated using pressure swing distillation (PSD) principle simulated in aspen plus. In aspen plus, the reactive distillation was configured as high pressure column (HDC) operated at 14bar and 70oC and a second column as low pressure column (LPC) operated at 0.56 bar 44 oC. The results obtained from two simulation software (ASPEN PLUS and MATLAB) were compared as 0.3967 mole methanol and 0.5983 mole methyl acetate using Aspen Plus and 0.4408 mole methanol and 0.5592 mole methyl acetate using Mat lab before PSD and 0.2710 mole methanol and 0.7290 mole methyl acetate after PSD. The results obtained were validated using literature data, 0.2154 mole methanol and 0.7846 mole methyl acetate were compared with 0.2710 and 0.7290 obtained from aspen plus with percentage deviation of 20.50 for methanol and -7.63 for methyl acetate.

Isopropyl acetates are important organic solvents that are widely used in the production of varnishes, ink, synthetic resins, and adhesive agents. Previous studies developed a process for the production of isopropyl acetate incorporating a reactive distillation (RD) column, a decanter, and a stripper. According to the previous study, the rectifying section of the RD column has a prominent remixing phenomenon. Furthermore, the overhead compositions of RD column and the stripper are all within the liquid–liquid equilibrium envelope. Based on the above observations, a thermally coupled design of this process is established. The key points in the thermally coupled design are: to move the location of the decanter to the stripper side, to totally reflux the organic phase outlet stream, and to sidedraw a liquid stream from the stripper to the RD column. Simulation result shows that 23.14% energy savings can be realized using the proposed thermally coupled design. The control strategy of the proposed design flowsheet is also investigated using tray temperature control loops to indirectly control the product composition. The proposed control strategy is capable of maintaining high-purity product, despite changes in feed composition and throughput.

By combining chemical reaction and multi-stage distillation in one column, a reactive distillation (RD) column can significantly save capital investment and make chemical conversion reach a much higher level. In a previous study, an optimal steady state design for the production of ethyl acetate (EtAc), consisting of two columns (one for RD and one for stripping column) and an overhead decanter, was reported. As a continuous study to that previous work, four alternative plant-wide control strategies for this designed process are studied in this paper. Feed compositions of both Acetic acid (HAc) and ethanol (EtOH) streams are treated as disturbances. These disturbances are used to test the closed-loop performance of each control scheme. It is found that control of the product qualities by modulating two tray temperatures in the RD column and one tray temperature in the stripper is most appropriate. By this control scheme, both of HAc and EtOH impurities in the product stream can be kept effectively within the acceptable product specifications.