Design and control of novel reaction–separation–recycle processes for the production of 4-hydroxybutyl acrylate

Two chemistry routes are known for 4-hydroxybutyl acrylate production: the direct esterification of acrylic acid with 1,4-butanediol, and the transesterification of methyl acrylate with 1,4-butanediol. However, very scarce information in the literature is available about industrial production, or design and operation of production processes. In this study, we propose three novel reaction–separation–recycle processes for 4-hydroxybutyl acrylate production by direct esterification based on solid catalyst. Use of solid catalysts may avoid well-known issues of the liquid catalysts like recovery and re-use of the catalyst, difficult product recovery, and corrosion. Due to the nature of the chemical system and reactions conditions, the chemistry is not 100% selective towards the acrylate, important amounts of diacrylate by-product being formed. All processes use fixed-bed tubular reactors to perform the reactions and distillation-based equipment to achieve the required separations. While all processes have a similar separation sequence, each has its key particularities: the RSR-A process accepts the loss of reactants due to formation and elimination from the process of the diacrylate, RSR-B converts the diacrylate into its reactants in the esterification reactor, while RSR-C converts the diacrylate in a dedicated hydrolysis reactor. A key element in the separation sequence is the use of pressure-swing distillation to make the difficult split of the alcohol/acrylate/diacrylate ternary mixture. All processes are capital and energy intensive. The economic analysis shows that the RSR-A process has the most favorable economics: a total annualized cost of 2 million $/y and a specific annualized cost of 100 $/t of product. A control structure for the RSR-C process is presented, the dynamic simulations showing its efficiency in rejecting various disturbances.