| The edible oil industry is an important part of the cereal and oil food industry of China and plays an indispensable role in national economic development.During the alkali refining of edible oil,many byproducts are generated.Recycling these byproducts produces soapstock,a biomass-derived waste oil.If handled inappropriately,soapstock can cause serious pollution to the urban environment and water resources.However,soapstock,a valuable raw material,can be converted and developed into a high-quality hydrocarbon-rich bio-oil to meet China's national energy development strategy and is important to the construction of a "Beautiful China".Among the technologies for the high-value utilization of soapstock,catalytic pyrolysis is a promising technology for the production of hydrocarbon-rich bio-oil.However,this technology has some issues,such as low yields of target products and rapid deactivation of catalysts because of coking and high pressure drop of catalyst,which limit its large-scale conversion and utilization.Hence,in this research,the related characteristics of the fast catalytic pyrolysis of soapstock to produce hydrocarbon-rich bio-oil were systematically studied to address these problems.A system comprising a SiC heat carrier with disordered network pores and an ex-situ catalytic reforming of the pyrolytic gas was constructed.A microwave-driven foam ceramic catalyst with microwave-absorbing characteristics was developed on the basis of the interaction between the catalyst and the microwave,and the microwave-driven catalytic pyrolysis of soapstock to produce hydrocarbon-rich bio-oil was studied.The details are as follows.The pyrolysis characteristics of soapstock and different fatty acids sodium salts were analyzed using pyrolysis-gas chromatography-mass spectrometry to study the fast catalytic pyrolysis of soapstock to produce hydrocarbon-rich bio-oil.When the HZSM-5 was used as a catalyst,the relative content of the oxygenated compounds in the condensable organic compounds from the pyrolysis of soapstock decreased significantly.Moreover,the aromatic hydrocarbons increased,and toluene and xylene had the highest relative selectivity.The high catalytic pyrolysis temperature was favorable to the relative selectivity of benzene and toluene but inhibited the relative selectivity of xylene and ethylbenzene.With increasing degree of unsaturation,a gradual decrease in the relative content of aromatic hydrocarbons;decreased relative selectivity of toluene,xylene,and ethylbenzene;and increased relative selectivity of alkylbenzene and polycyclic aromatic hydrocarbons were observed.In addition,the mechanism of the fast pyrolysis of soapstock and its different fatty acid sodium salts was explored and inferred preliminarily on the basis of the chemical characteristics of the pyrolysis products.The effects of the pretreatment conditions on the distribution of co-pyrolysis products were discussed to study the mechanism of the fast microwave co-pyrolysis of soapstock and lignocellulosic biomass.The microwave-assisted acid pretreatment promoted the decoupling of the interaction among cellulose,hemicellulose,lignin,and ash in biomass;improved the yield of bio-oil from co-pyrolysis;and reduced the difficulty of subsequent quality improvement.The reaction mechanism of the co-pyrolysis of soapstock and pretreated biomass were explored preliminarily and revealed that the microwave-assisted acid pretreatment promoted the depolymerization of cellulose and the intramolecular rearrangement of the primary pyrolysis products to form levoglucosan,an important precursor of aromatic hydrocarbons.The dehydration reaction then occurred to form the short-chain active oxygenated compounds,which subsequently reacted with small molecular alkenes from the pyrolysis of soapstock via the Diels-Alder and dehydration reactions to generate aromatic hydrocarbons.Simultaneously,a series of alkanes produced from the pyrolysis of soapstock released hydrogen radicals via the dehydrogenation reaction,which effectively promoted the conversion of lignin to phenols via pyrolysis.A microwave deep pyrolysis system of SiC heat carrier with disordered network pores was constructed to study the production of hydrocarbon-rich bio-oil by combining the microwave deep pyrolysis of soapstock with the assistance of heat carrier and the ex-situ catalysis.Moreover,the mechanism of the conversion of soapstock into hydrocarbon-rich bio-oil coupled with HZSM-5 ex-situ catalysis was studied.At pyrolysis temperature,catalytic reforming temperature,soapstock feeding speed,and HZSM-5 to soapstock mass ratio of 550?,400?,6 g/min,and 1:1,respectively,the relative content of total hydrocarbons in bio-oil was 96.69%,in which the content of aromatic hydrocarbons was 89.24%,and the relative content of oxygenated compounds was 2.45%.Compared with the relative contents of aromatic hydrocarbons(29.46%)and oxygenated compounds(12.06%)in bio-oil obtained via the in-situ catalytic microwave-assisted pyrolysis,the selectivity of aromatic hydrocarbons increased considerably in this system,realizing the hydrocarbon enrichment of bio-oil and effectively enhancing its application value.Furthermore,the correlation among pyrolysis conditions,chemical composition,and characteristics of the products was determined,and the mechanism of the key parameters regulating the changes in aromatic hydrocarbons and oxygenated compounds in the bio-oil was revealed.The basic reaction kinetics of the conversion of aromatic hydrocarbons by combining the microwave deep pyrolysis of soapstock with the assistance of heat carrier and the ex-situ catalysis was inferred preliminarily.The microwave-driven HZSM-5@SiC foam ceramic catalyst was developed through hydrothermal synthesis to study the catalytic pyrolysis of soapstock for hydrocarbon-rich bio-oil production.The XRD pattern of HZSM-5@SiC contained all the characteristic peaks of the SiC foam ceramic and HZSM-5.Furthermore,the typical hexagonal prism crystal structure of HZSM-5 was observed using SEM.The crystals with uniform size formed a continuous and homogeneous thin layer that completely covered the surface of the SiC foam ceramic,thereby proving the successful coating of HZSM-5 on the SiC foam ceramic.In addition,the microwave-driven ex-situ catalytic reforming system was constructed on the basis of the microwave pyrolysis of the SiC heat carrier with disordered network pores and compared with the conventional electric heating catalytic pyrolysis.Compared with the HZSM-5 catalyst,the HZSM-5@SiC foam ceramic catalyst resulted in higher yield of bio-oil and had higher aromatization activity.The characteristic structure of the HZSM-5 thin layer homogeneously growing on the surface of SiC foam ceramic ensured that the catalyst bed had low pressure drop and that the pyrolysis gas could easily enter get to the active sites.Under the microwave heating conditions,the relative content of aromatic hydrocarbons increased from 25.18%to 100%when the mass ratio of the HZSM-5@SiC foam ceramic catalyst to soapstock increased from 0:1 to 1:1.Compared with electric heating catalysis,microwave heating the HZSM-5@SiC foam ceramic catalyst resulted in lower coke yield.After five consecutive uses,the HZSM-5@SiC foam ceramic catalyst still maintained more than 90%catalytic activity and high stability,which provided a scientific basis for the pilot-scale experiments of soapstock catalytic pyrolysis.A pilot-scale system for the production of bio-oil by continuous catalytic microwave pyrolysis of soapstock with an annual treatment capacity of 50 tons was constructed,and the test operation process and application prospect of pilot-scale equipment were evaluated comprehensively.The rotary propulsion stirring technology was innovated.As such,the up and down circular movement of SiC effectively avoided the problem of mixing locking caused by the high density of SiC and strengthened the efficiency of microwave heating to ensure continuous pyrolysis and temperature uniformity.Simultaneously,the use of the bottom cone hole effectively separated SiC and biochar.The effects of feed rate on the product distribution and the bio-oil composition were analyzed.Results revealed that when the pyrolysis temperature and the feed rate were 500? and 6 kg/h,respectively,the relative content of aromatic hydrocarbons in bio-oil was 88.69%,and the monocyclic aromatic hydrocarbons,as high value-added organic chemical raw materials,reached the highest content(63.52%).In addition,the density,calorific value,kinematic viscosity,and condensation point of bio-oil were measured,and results showed that most properties of bio-oil produced by this system met the standard of 0#diesel oil.This research provided technical and integrated support for the scale-up and commercialization of the fast microwave catalytic pyrolysis of soapstock to produce hydrocarbon-rich bio-oil. |
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