Improved Design and Control of Triacetin Reactive Distillation Process for the Utilization of Glycerol

Abstract

Glycerol utilization is an important research topic because of recent surging biodiesel production through transesterification of vegetable oils and animal fats. One of the valuable products from glycerol is gained through esterification with acetic acid to produce triacetin. Hasabnis and Mahajani proposed an entrainer-based reactive column configuration with stoichiometric feed ratio to obtain high selectivity and conversion. This paper corrects the kinetic parameters in Hasabnis and Mahajani to better describe this reaction system. A more effective reactive entrainer for this reactive distillation system is also proposed to better carry water to the top of the column. The other modification is to assume feed compositions of the glycerol and acetic acid feed streams containing some water as impurity as opposed to idealistic pure feed assumptions. The operation and control of this system are also investigated. The proposed tray-temperature control strategy is able to maintain product purity despite disturbances from throughput and feed composition changes.

Glycerol Esterification with Acetic Acid by Reactive Distillation Using Hexane as an Entrainer

“…Thus, the parameters for the equilibrium correlations were estimated by the simulator from the molecular structures of these two species, which were fed to the software. Due to their molecular structures, the most favorable isomers to form during the reactions are 1-monoacetin and 1,3-diacetin [9], and thus these isomers were adopted to represent the monoacetin and diacetin in the simulations; 4) the NRTL-HOC thermodynamic model was adopted, because it can well represent aqueous electrolyte systems, and in addition, the Hayden-O'Connell model provides an adequate representation of the vapor phase behavior, since during the reaction gaseous species are generated, mainly due to acetic acid evaporation; the binary interaction parameters were the same ones adopted by Hung et al [3]; 5) The reaction rates were modeled according to the previously described kinetic model, with the kinetic parameters shown in Table II. As in the study by Galan et al [2], four times molar excess of acetic acid was adopted, so that 1 mol of glycerol to 12 mol of acetic acid was fed to the reactive distillation column.…”

“…As in the study by Galan et al [2], four times molar excess of acetic acid was adopted, so that 1 mol of glycerol to 12 mol of acetic acid was fed to the reactive distillation column. 6) The two reagent streams are assumed to contain 5 % of water as impurity (mol base), as adopted by Hung et al [3]. The specifications of these streams are listed in Table III.…”

“…[2] Temperature 120 °C 160 °C k 1 2,38E-04 2,56E-04 k 2 1,20E-01 7,62E-02 k 3 6,30E-04 5,30E-04 k 4 3,14E-03 8,78E-03 k 5 1,09E-04 1,96E-04 k 6 2,59E-03 4,76E-03…”

“…The effect of the entrainer was evaluated for both processes. The authors concluded that the process using entrainer can reduce the total annual production cost by more than 34 % [3].…”

“…However, in this case hexane was adopted as entrainer to promote water removal at the top of the column. In the separation units the NRTL-HOC equilibrium model with binary interaction parameters proposed by Hung et al [3] was adopted. The process conditions that lead to high glycerol conversion and high purity triacetin were studied by means of simulations for different process configurations, in order to identify the optimal conditions in terms of minimum energy consumption.…”