Conceptual design of a glycerol biorefinery

Abstract

Glycerol is considered as the major waste from biodiesel production since every 1L of biodiesel produced is accompanied by 0.1 L of glycerol by-product. Utilizing this waste as a biorefinery feedstock will not only promote biodiesel production but also reduce challenges related to waste disposal. There are various ways through which glycerol can be transformed into valuable products. This study used an insight-based approach (CHO ternary diagrams) to determine the performance of glycerol-biorefinery via reforming pathway prior to a detailed design. It was shown that to produce syngas that fulfils the requirement for methanol synthesis( H2 CO ~2), glycerol should be mixed with methane in a ratio of 1/2 (in terms of molar ratio) using steam as a reforming agent. A high-level economic as well as environmental analysis in terms of economic potential, carbon efficiency, atom economy, and E-factor was assessed. It was found that the price of raw glycerol has a significant impact on the economic potential during the synthesis of methanol. The raw glycerol price range that generated a positive economic potential was found to be $0.025/kg - $ 0.90/kg. At this raw glycerol price range, the approximate economic potential of the entire process was found to be $ 7169.12 - 239.12 $ million per year. The carbon efficiency, atom economy, and E-factor were also calculated and found to be 100%, 100 %, and 0 respectively. Based on these CHO ternary diagram targets an entire flowsheet for methanol synthesis was developed using Aspen Plus. It was determined that Aspen Plus could not exceed targets set by CHO ternary diagrams in terms of methanol flow rate, carbon efficiency as well as atom economy. CHO ternary diagrams further revealed that it is possible to synthesize DME from a mixture of glycerol and linear low-density polyethylene (LLDPE) (25% glycerol-75% LLDPE). It can be inferred from various analysis conducted that the production of methanol from glycerol obtained from biodiesel is economical.