Published February 2013
This Review presents a technoeconomic evaluation of an isobutylene from t-butanol (TBA) production process based upon the technical information and data available in patents assigned to LyondellBasell (previously ARCO). The design presented herein differs from an actual commercial LyondellBasell process. However, we firmly believe that the process design and economics presented herein would be a reasonably accurate representation of the actual process when commercialized.
The process primarily consists of liquid-phase dehydration of TBA-rich feed in a shell-and-tube type reactor using a homogenous catalyst, p-toluenesulfonic acid (PTSA). The reaction is endothermic and reaction heat is supplied through the shell side via steam. The conceptual LyondellBasell process is carried out preferably at about 329°F (165°C) and 200–210 psia with a 94.5 wt% purity TBA feedstock assumed to be available from an adjacent propylene oxide (PO) oxirane plant (analyzed in PEP Report 2H). TBA dehydration is a reversible reaction with isobutylene production favored at higher temperatures. The catalyst and reaction conditions selected provide a 73% TBA conversion to isobutylene and water. The reactor product is a vapor mixture of isobutylene, TBA, water and additional impurities. The reactor product is cooled and sent to a three-phase separator to recover isobutylene in vapor form which is further purified via distillation to obtain high-purity isobutylene. The remaining product mixture settles into an organic-phase that is recycled back to the reactor, and a water-phase that is treated to remove isobutanol present as feed impurity. A lower reaction temperature for a liquid-phase reaction as compared to conventional vapor-phase technology is expected to generate fewer by-products and conserve energy. The process design includes careful separation of the TBA/water azeotrope that is recycled back to the reactor and the use of a chemical entrainer to recover isobutanol from the water-rich phase.
Our cost analysis is based on a plant producing 150,000 metric t/yr of high-purity isobutylene at a 0.9 stream factor (equal to an installed capacity of 167,000 metric t/yr). Cost estimates, details thereof and relevant assumptions are provided in this Review.
The Review also compares the economics of six different process configurations to produce high-purity isobutylene. These include three stand-alone isobutylene production routes with varying feed sources (TBA from PO process, TBA from raffinate-1, and MTBE from raffinate-1) and three corresponding integrated processes.