(307d) Advances in Process Intensification: Using Reactive Distillation for the Conversion of Crude Glycerol

Obakore Agbroko and Tracy J Benson (Lamar University)

With the rise in biodiesel production over the last couple of decades has come the abundance of glycerol, a byproduct from biodiesel manufacturing. A typical biodiesel process includes the transesterification of triglycerides to produce fatty acid methyl esters, followed by fuel clean up steps: product separation, water washing, and acidulation. In short, the glycerol stream also includes water and methanol and is typically considered “crude glycerol.” In this study, crude glycerol was converted to propanediols using isopropanol as a hydrogen donor molecule in a reactive distillation column.

Combining reaction engineering and distillation into a single unit operation presents some interesting challenges, yet, reduces the operational footprint as well as the operating and capital costs of manufacturing. Operational and design challenges include mismatched temperatures between the separating components and the reacting components, unfavorable volatilities, and slow reaction rates generally due to poor reactant/catalyst/product mass transfer rates. Reactive distillation is a likely pathway towards process intensification to minimize overall energy consumption, particularly since distillation accounts for 20 % of total energy used within the U.S. manufacturing sector. Increased reflux ratios typically yield higher product purities but at the cost of reboiler heat duties. In comparison with conventional approaches of reaction followed by distillation, the proposed scheme holds great potential due to its ability for lowering both operating and capital costs.

In this study, Aspen Plus was used to model the conversion of glycerol to 1,3-propranediol and 1,2-propanediol while being separated from methanol, water, and other inorganic components that are commonly found in waste glycerol from biodiesel production processes. Using the Non-Random Two Liquid activity coefficient model, the number of trays, conversion, and product selectivities were estimated. To verify simulation results, laboratory experiments were conducted using a 1-inch ID, packed distillation column. Column temperature profiles as well as reboiler and condenser heat duties were determined. The complete reactive distillation analysis will be presented as well as the extension of this technology into other areas of the chemical process industry.