Heterogeneous catalytic hydrogenation and purification applied to commercial processes
Three distinct chemical processes have been investigated, with the aim of producing high purity 1,5-pentanediol (PDO), 1,4-butanediol (BDO) and tetrahydrofurfuryl alcohol (THFA) and thereby improving the efficiency of their manufacture. The production of 1,5-pentanediol via the low-pressure vapour phase hydrogenation of 1,5-dimethylpentanedioate has been studied using a copper manganese heterogeneous catalyst system and found to be as good as the usually favoured copper chrome, which is now becoming difficult to operate commercially due to toxicity concerns. The optimum conditions were determined for a commercial process. The purification of the PDO produced, to the high standards dictated by polymer manufacture, has also been examined. Simple distillation was not possible because reactive oligomeric species were present. To overcome this, a reactive distillation scheme was developed and demonstrated experimentally. During the manufacture of 1,4-butanedlol, a by-product (4-hydroxybutyl)-2- tetrahydrofuran, known commercially as "Acetal", is formed during hydrogenation and proves very difficult to remove by conventional means. By conversion of this compound to more volatile species, by hydrogenation over a nickel catalyst, it was demonstrated that the purity of BDO obtained was greater than that previously possible.