Pyrolytic Biodiesel From Vacuum Pyrolysis of Plant Oil Asphalt Catalyzed By Sodium and Potassium Compounds

Plant oil asphalt (POA) is the residue biomass generated in biodiesel and fatty acids (FAs) industry. POA is named after its characteristics as high-density , high-viscosity black liquid. Recently , production capacity of POAs presents a rapidly increase owing to the booming development of biodiesel (FAMEs , fatty acids methyl esters) and FAs industry. At present , POA is mainly landfilled or used as boiler fuel , which cause adverse effects on economy and environment. A POA sample from a biodiesel plant in China was used as raw material for pyrolysis. Our previous work found that the POA is a mixture of polymeric products of FAMEs and some natural components like waxes origin from plant oils. Non-catalytic vacuum pyrolysis of POA could obtain 71 wt% of pyrolytic oil. It contains 65wt% C6-C19 FAMEs/FAs and 33 wt% C7-C24 hydrocarbons. A pyrolytic biodiesel product was obtained via esterification of the pyrolytic oil. Compared with hydrocarbons fuel , the pyrolytic biodiesel had a few disadvantages stemming from the high content oxygen at 9.10 wt% , namely less than ideal storage stability , unfavorable cold flow properties and relatively low heating value. Therefore , it is objective to obtain pyrolytic biodiesel with more hydrocarbons content via enhancing deoxygenation reaction during pyrolysis. In this work , vacuum pyrolysis of POA for hydrocarbons catalyzed by sodium and potassium compounds was investigated in a semi-batch reactor. The catalysts employed include NaOH , Na2CO3 and KOH , K2CO3. Both sodium and potassium compounds could enhance deoxygenation reactions , contributing to pyrolytic oil with higher oxygen content than non-catalytic. However , the catalysts improve the pyrolytic oil yields in the order of KOH (73 wt%) > K2CO3 (71 wt%) ~ no catalyst (71 wt%) > NaOH (55 wt%) > Na2CO3 (49 wt%). Sodium compounds increase yields of bio-gas and bio-char simultaneously. While for potassium compounds , increase of bio-gas and decrease of char offset each other. When 5 wt% KOH was added , the pyrolytic oil consists of 74 wt% C6-C24 hydrocarbons and 23 wt% C7-C19 FAMEs/FAs. Finally , the oxygen content of the pyrolytic biodiesel was decreased to 2.17 wt% compared with non-catalytic. Besides , a pyrolysis pathway and kinetics for thermal decomposition of POA were explored. We believe that POA can become a new valuable biomass resource and the results from this work lay a foundation for further study on pyrolysis of POA.