Catalytic distillation for the synthesis of tertiary butyl alcohol

Abstract

Catalytic Distillation for the synthesis of tertiary butyl alcohol (TBA) is investigated in this thesis. The solvent, ethylene glycol, is proposed as a means of overcoming challenges, which limit the potential benefits of the application of reactive separation for TBA. The proposed action of the solvent is that of extractive distillation entrainer, thus a new unit operation of Catalytic Extractive Distillation (CED) is suggested. The solubility of isobutylene in water, TBA, and ethylene glycol and their binary and ternary mixtures, at different temperatures, is measured and correlated. The solubility is found to be highly non-linear in solutions containing TBA. The kinetics of isobutylene hydration over Amberlyst 15 is characterised in the presence of ethylene glycol. The solvent is found to promote reaction rate, however it is also found to compete for reaction with isobutylene. Water is found to strongly inhibit the reaction of ethylene glycol and isobutylene. The selectivity ratio of TBA to by products is determined and found to improve with increased temperature and lower solvent concentration. Bale packing is chosen as catalytic distillation hardware for the containment of Amberlyst 15 and its two-phase fluid dynamics characterised for the first time. Raschig rings are used as a benchmark for the study. Bale packing is found to exhibit two ranges of backmixing behaviour in the pre-loading regime. This behaviour is attributed to the three levels of porosity of the hardware and indicative of low rates of catalyst/liquid renewal. The effectiveness of ethylene glycol as extractive distillation entrainer for the separation of the TBA/water azeotrope over Bale packing is investigated and the solvent found to be highly effective. The mass transfer resistances to isobutylene transport are determined for countercurrent fixed bed reactor (CFBR) application of Bale packing. It is found that ethylene glycol improves mass transfer coefficients attainable. Catalytic Extractive Distillation is implemented over Bale packing and the ability of the solvent to improve reaction rates and purity of TBA demonstrated. However, the reaction rates achieved have much scope for improvement through increased isobutylene availability. In response to poor liquid renewal of static packing such as Bale packing and the necessity of improved isobutylene transport a new form of catalytic distillation reactor design is proposed, the Basket Impeller Column (BIC). The BIC combines the mass transfer benefits of a rotating basket reactor with that of a dual flow column. Capacity of the new hardware is determined and correlated. Separation and reactive separation are demonstrated to be feasible. It is found that Damköhler number can be varied directly using the additional process variable of speed of rotation.