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