Modeling and optimization of solvent recovery section in PVA process

Abstract

In this study, the optimal operating condition is proposed in solvent recovery section of poly(vinyl alcohol) process. Poly(vinyl alcohol) is water-soluble and bio-degradable polymer, so it is highly profitable product as material of wide rage goods. But poly(vinyl alcohol) have no monomer-vinyl alcohol, so after polymerization of vinyl acetate and followed by saponification of poly(vinyl acetate), the poly(vinyl acetate) is produced. As polymerization and saponification are exothermic reaction, this process does not need much steam, but the solvent recovery section of the poly(vinyl alcohol) process, which recover the un-reacted raw material and solvent, needs very much amount of steam. If the optimal operating conditions are found in N columns, the total utility cost will be saved in poly(vinyl alcohol) process, so the cost of product can be lowered. Modeling, simulation and optimization of operation were implemented on the solvent recovery section and the by-production section of poly(vinyl alcohol) with Aspen Plus. The performance of the model was good in respect that the temperature, pressure, composition fractions, and flow rates of streams of columns were similar to real data. The objective of the optimization was to maximize the total profit, which means that the sum of revenues of the products minus the sum of the utility costs. Column specifications were selected as decision variables. Methanol vapor flowrate, reboiler duty and direct steam and fraction of products had their constraints. The economic profit was increased by A%, B won/yr as a result of optimization of operating conditions. By considering the capacity of columns of interest, it has been shown that the economic profit can be increased to C won/yr, D% increment.