Experimental Study And Mechanism Analysis Of Microwave-Assisted Pyrolysis Of Two Solid Wastes In Vegetable Oil Refining Process

Soapstock（SS）and spent bleaching clay（SBC）come from the process of deacidification and bleaching in vegetable oil refining,respectively.How to avoid their environmental pollution and effectively resourceful disposal has been a concern for vegetable oil processing plants.In this experiment,a microwave-assisted pyrolysis tube furnace was used to investigate the pyrolysis characteristics of SS and SBC at different temperatures.The pyrolysis process and the pyrolysis products of SS and SBC were also compared to investigate the mechanism of the effect of inorganic substances on fatty acid pyrolysis.（1）At 800°C,the SS pyrolysis yielded 37.76 wt.%of non-condensable gas,of which 25.96 wt.%was available for the combustible gas（CO,CH₄,H₂）.The aliphatic hydrocarbons in the pyrolysis oil reached 56.65%at 500°C.The oxygenated compounds continued to decrease with increasing temperature.Ca CO₃,the main inorganic substance in SS,formed stable apatite at high temperature,and S was fixed in the pyrolysis char with increasing temperature.（2）Temperature promoted SBC pyrolysis to produce non-condensable gas and conversion of organic matter to CO,CO₂,CH₄,and H₂.The pyrolysis temperature of 400°C produced the largest yield（11.75 wt.%）of condensate from SBC pyrolysis.Combining the yield and hydrocarbon percentage,SBC at 600°C is the most suitable for the production of alkanes and olefins compounds.Both N and S elements in SBC were gradually fixed in the pyrolysis carbon with increasing temperature,and the adsorption value of methylene blue in the chars reached 239.21 mg/g at 800℃.（3）At 400°C,the pyrolysis oil yields of both wastes was maximum,and the pyrolysis char yields continued to decrease with increasing temperature.SS continued to lose weight after 600°C due to inorganic decomposition,and the starting activation energy of SS pyrolysis reaction（287.51 k J/mol）was higher than that of SBC（173.3 k J/mol）.Saturated fatty acids mainly underwent decarboxylation reactions,and unsaturated fatty acids were prone toβ-cracking reactions to form olefins,followed by Diels-Alder reactions or internal cyclization and dehydrogenation to form Ca²⁺promotes decarboxylation to formα-olefins,and Al₂O₃promotes the formation of long-chain alkanes.