Walnut Shell Carbon-based Heterogeneous Acid Synthesis And Activity In Catalyzing Esterification Of Oleic Acid With Ethanol Investigation

Biodiesel is an excellent alternative to fossil diesel fuel,which is green,renewable,low-emission,and biodegradable.It is a hot topic at home and abroad and has attracted worldwide attention.The main method for the production of biodiesel is the exchange of acid and alkali catalyzed by the exchange of flora and fauna with short-chain alcohol.The catalytic activity of alkaline catalyst is strong,and the reaction time is short,but the acid value and moisture content of raw material oil which need are extremely harsh.High quality feedstock oil has greatly increased the production cost of biodiesel,and studies have shown that cost issues are the main bottlenecks currently restricting the commercialization of biodiesel.It over 5 Mt of waste cooking oils(WCOs)are generated every year in China and the biodiesel production cost would be hugely decreased,accompanying with the economical feasibility improvement,if the low quality feedstock with high FFAs levels can be utilized.so It is of great significance to study how to use high acid value raw oil to prepare biodiesel to solve the energy crisis and environmental problems.Jacobson et al.have shown that the two-step method of acid catalyzed pre-esterification of deacidification-base catalyzed transesterification is the most economically valuable and development potential for the production of biodiesel from low grade feedstock oils.In the pre-esterification process,homogeneous acid catalysis will bring about difficult recovery,purification will produce a lot of waste water,corrosion equipment and other issues,if the catalyst into a solid acid catalyst will be able to solve the problem.Among them,carbon-based solid acid is one of the most promising biodiesel catalysts because of its green high efficiency and simple preparation.In this paper,A series of novel carbon-based heterogeneous acid catalysts are synthesized from walnut shell through the dual-step approach of partial carbonization with sulfonation in succession and are subjected to estimate their activity in catalyzing esterification of oleic acid with ethanol.The synthesized conditions are optimized as carbonization temperature of 350 ? and duration of 2h,and sulfonation temperature of 90 ? and duration of 2h.Meanwhile,the synthesized catalysts are characterized by energy dispersive X-ray spectroscopy(EDX),thermogravimetric analysis(TGA),X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FT-IR)and acid sites density with acid strength measurement to reveal the catalytic mechanism.The-SO3Hgroups are introduced into the walnut shell carbon-based heterogeneous acids,which exhibit amorphous carbon structure and high thermal stability with the maximum acid amount of 1.97 mmol·g-1.Then,performances of the heterogeneous acid in catalyzing esterification are investigated under different conditions,where acid value reduction efficiency of 98.8%is achieved at the molar ratio of ethanol to oleic acid of 8,heterogeneous acid added amounts of 7%,esterification temperature of 80? and esterification duration of 2h,and esterification efficiency of 88.69%could be supplied by the reactivated heterogeneous acid after the fifth re-usage.However,the heterogeneous acid showspoorer reusability in esterification of oleic acid with ethanol than with methanol and should be consolidated.in addition,a longer reaction time for solid acid catalyst of the problem,this paper will introduce the process of microwave walnut shell carbon based catalyst preparation and catalytic sulfonation process of ethyl oleate,compared with water bath method,microwave introducing carbon carrier sulfonated walnut shell process can effectively shorten the sulfonation time and reaction time.The best catalyst preparation and catalytic esterification of oleic acid under microwave conditions:microwave power 480W,reaction time is 2 hours,the carbonization temperature is 350?,sulfonation time 10min,sulfonation temperature 90?,reaction time 1h,reaction temperature is 80 ?,adding amount of catalyst 8%,molar ratio of alcohol to oil 1:8.The results show that microwave heating is an effective heating method.Using FTIR infrared characterization,the sulfonic acid group was successfully introduced into the microwave sulfonated walnut shell carbon based solid acid.The results of nitrogen adsorption showed that the microwave sulfonated walnut shell carbon based solid acid had better pore structure.The results of SEM show that it has obvious pore structure and no flaky amorphous carbon deposit.