Methyl lactate synthesis using batch reactive distillation: Operational challenges and strategy for enhanced performance

Abstract

Link to original published version: http: //dx.doi.org/10.1016/j.seppur.2015.12.023 Citation: Aqar DY, Rahmanian N and Mujtaba IM (2016) Methyl lactate synthesis using batch reactive distillation: Operational challenges and strategy for enhanced performance. Separation and Purification . AbstractBatch reactive distillation is well known for improved conversion and separation of desired reaction products. However, for a number of reactions, the distillation can separate the reactants depending on their boiling points of them and thus not only reduces the benefit of the reactive distillation but also offers operational challenges for keeping the reactants together. Methyl lactate (ML) synthesis via the esterification of lactic acid (LA) with methanol in a reactive distillation falls into this category and perhaps that is why this process has not been explored in the past. The boiling points of the reactants (LA, methanol) are about 490 K and 337 K while those of the products (ML, water) are 417 K and 373 K respectively. Clearly in a conventional reactive distillation (batch or continuous) methanol will be separated from the LA and will reduce the conversion of LA to ML significantly.Here, first the limitations of the use of conventional batch distillation column (CBD) for the synthesis of ML is investigated in detail and a semi-batch reactive distillation (SBD) configuration is studied in detail where LA is the limiting reactant and methanol is continuously fed in excess in the reboiler allowing the reactants to be together for a longer period. However, this poses an operational challenge that the column has to be carefully controlled to avoid overflow of the reboiler at any time of the operation. In this work, the performance of SBD for the synthesis of ML is evaluated using model based optimization in which operational constraints are embedded. The results clearly demonstrate the viability of the system for the synthesis of ML.

Integrated batch reactive distillation column configurations for optimal synthesis of methyl lactate

“…The column trays are numbered from the top to the bottom. See Aqar et al (2016) for the list of assumptions considered in developing the process model. The i-CBD process model is exactly similar to the CBD column presented in Aqar et al (2016) except that the additional terms added to the system of equations to cater for recycled methanol-rich stream as presented below.…”

“…with methanol recovery and recycle Figure 2 shows a SBD column without methanol recovery and recycle option as considered in Aqar et al (2016). In the i-SBD configuration, the distillate accumulator from the SBD (Figure 2) is further processed in a CBD to recover methanol at a desired purity and mixed up with make-up methanol of the same quality before being fed to the next batch of SBD.…”

“…Note, t S is the combined set up time for SBD and CBD. For the SBD column, the model equations are same as those presented in Aqar et al (2016). In contrast, the second column is a conventional batch distillation without any chemical reaction which is used to separate methanol at a desired purity.…”

“…Most recently, Aqar et al (2016) studied the esterification reaction of lactic acid with methanol producing methyl lactate. For a given separation task (desired amount of ML and its purity), they compared the performances of CBD and SBD columns in terms of total energy consumption or minimum operating time.…”

“…In the methanol distillation column, methanol is separated at higher purity than that is the case in i-CBD and is then fed together with fresh methanol into the i-SBD. While i-CBD does not create operational problem of reboiler overflow, i-SBD creates operational problem in terms of reboiler overflow which is managed by applying the strategy used in Aqar et al (2016).…”