The Research Of Hydrothermal Gasification Of Long-chain Fatty Acids In Supercritical Water

With the rapid population growth and economic development,the consumption of fossil fuels has been increased meteoricly.However,the fossil fuels are not renewable and their reserves are very limited,so it becomes an urgent demand for humans' sustainable development to change the energy structure and to utilizethe new generation energy which is renewable and environmental friendly.Biomass energy is widely regarded as a major alternative to fossil fuels due to its richness and abundance in raw materials,and safe operation processes.As an important component of biomass energy,lipid is a hotspot of new generation biomass energy thanks to its high proportion,wide distribution and high heat value.Compared with the traditional biomass industrial transformation pathways(enzymatic degradation and thermal cracking),it is convenient converting it into gas by hydrothermal gasification.It does not need additional treatments like dehydrationor extractionwhich consume lots of energy and organic solvent.The process is green and can obtain the fuel gas with higher heat value.In this paper,a series of model compounds were selected according to the main hydrolyzation constituent of lipids under the supercritical water conditions,fatty acids.We used a quartz kettle device for biomass supercritical water gasification experiment research in order to provide experimental data reference and theoretical basis for the fatty acid supercritical water gasification reactions.The main contents of this paper are as follows:1.Non-catalytic supercritical water gasification of fatty acids.We used pentadecanoic acid as the main research object,while tetradecanoic acid and oleic acid were used as validation.In the absence of catalyst,the effect sequence of experimental factors on fatty acid SCWG was as follows:reaction temperature>reaction retention time>mass fraction of reactants.The rise of reaction temperature would increase the gas composition,the element recovery ratio and HHV will also rise;in certain reaction temperatures and pressures,with the reaction retention time increased,in most conditions,the gas yield,element recovery and HHV increased,but with the reaction retention time further increased,the gas yield,element recovery and HHV growth rate decreased.With the increase of the mass fraction of the reactants,the gas yield,element recovery ratios and HHV of the fatty acid SCWG reduced.C element recovery was higher at 400-450?,and the highest value was 16.8%in the measured temperature range;the recovery of H element is higher at 500-550 ?,and the highest value was 57.1%;HHV was up to 16.8 kJ· g-1,which is approximately equivalent to 57%of the heat value of standard coal.Liquid products were mainly straight-chain hydrocarbons from derict decarboxylation of fatty acids besides residual fatty acids,aromatic hydrocarbons and high polymers also existed.Access to the relevant literature and combine with gas products distribution data and the characterization of liquid products,the effects of four important intermediate reactions on fatty acids non-catalytic supercritical water gasification were investigated.2.Catalytic supercritical water gasification of atty acids.The effects of Pd/C,Pt/C,Rh/C and Ru/C catalyst on the reaction of fatty acids SCWG were investigated.By studying the distribution of SCWG gas products,we found that the catalytic effect of Ru/C catalyst on fatty acid catalyzed SCWG reaction was best.The C recovery ratiowas up to 95.67%,and the H recovery ratio was up to 135.73%.The HHV was up to 36.38 kJ· g-1,which was about 124%of the heat value of standard coal.The results show that the total gas yield of SCWG and the recovery ratio of C element increased with all four catalysts.The recovery ratio of H element almost unchanged with Pd/C catalyst,and increased with the addition of the other three catalysts.HHV slight declinedwith the addition of Pd/C catalyst,and much improvedunder the other three catalysts.Fatty acids have an almost complete conversion under catalyzed SCWG,with only a very small amount of residual fatty acids.Linear saturated hydrocarbons became the main component of liquid products,while the concentration of aromatic hydrocarbons and other unsaturated hydrocarbon species greatly reduced.The catalytic mechanism of the catalyst and the effect on the content of each product were analyzed by the gas products distribution data and the characterization of liquid products.