The Investigation Of Bio-oil Preparation From Catalytic Hydrothermal Liquefaction Of Algae

With the continuous development of human society,the traditional fossil energy represented by coal,oil and natural gas has been gradually exhausted,and the energy crisis has become one of the most difficult problems in worldwide.Based on this,the research of various new energy sources is in the ascendant.Among them,biomass energy had attracted much attention because of its wide distribution,huge reserves and renewable advantages.So far,biomass energy had developed to the third generation.Compared to the first and second generations of biomass energy,as the third generation of biomass energy,algae had many advantages such as fast growth rate,high photosynthetic efficiency,no occupation of cultivated land,no impact on grain yield,and the obtained bio-oil was similar to fossil energy structure,et,al.Research on algae biomass energy had been carried out both in China and abroad,and some achievements had been achieved.Among the algae transformation methods,hydrothermal liquefaction method has become the main transformation method because it can avoid the high energy consumption process such as drying.At the same time,the bio-oil produced by algae transformation had some problems,such as low yield,poor quality and low selectivity.Based on the above analysis,firstly,according to the high content and complex composition of biomacromolecules in algae,the microporous-mesoporous core-shell zeolite with hydrogenation function were designed and synthesized.The conversion ability of biomacromolecules was enhanced by enlarging the pore size of zeolite.In view of the insufficient stability of the catalyst under hydrothermal conditions,Ti-Si zeolite with better stability were designed and synthesized as catalysts for the core.Its application in catalytic hydrothermal liquefaction of algae were investigated.Due to the limited conversion of algae by one-step method and the low yield of bio-oil,the two-step method of solvent extraction assisted hydrothermal liquefaction was selected in algae transformation.The results showed that this method can improve the conversion efficiency of algae and obtain high yield and high quality bio-oil.Finally,in order to solve the problems of excessive reaction temperature,insufficient hydrogen supply capacity and limited solubility of products in hydrothermal process,isopropanol was used as reaction solvent under the existence of catalyst and formic acid and high yield and high quality bio-oil was obtained.We hoping to provide reference for further research.The main contents of this paper are as follows:1.Application of core-shell catalyst Pd/HZSM-5@MS in hydrothermal liquefaction of algae transformation.Pd/HZSM-5@MS catalyst was synthesized and applied to catalytic hydrothermal liquefaction of algae to bio-oil.Formic acid was added as hydrogen donor.Firstly,the optimal reaction conditions?0.5 g algae+0.01 g catalyst+2 ml water,380 ^oC,reaction time:2 h?were determined.Under these conditions,the bio-oil yield was 37.30%and the coke yield was only 8.56%.The quality of bio-oil was being satisfied,and the HHV was 32.65 MJ?kg^-1.Secondly,the role of each part of the catalyst in the reaction was studied.Results by elemental analysis and GC-MS proved that Pd/HZSM-5@MS had better hydrodeoxygenation ability,while Pd/HZSM-5 had better hydrodenitrogenation ability.On this basis,we proposed a possible reaction process on the surface of the catalyst,the biomacromolecules contained in algae first cracked on the surface of the molecular sieve to form smaller molecules,then they entered into the mesoporous core of the catalyst,cracked into small molecules,then entered into the pores of HZSM-5 zeolite and continued to react to form products.Then,the recycling performance of the catalyst was investigated.The results showed that the catalyst was unstable in hydrothermal conditions,the mesoporous shell structure was destroyed and the palladium nanoparticles were lost.Finally,the possible reaction path of main product Z-9-octadecenamide was speculated,and it was proved that the content of Z-9-octadecenamide was closely related to the hydrodenitrogenation ability of the catalyst.2,Application of core-shell catalyst Pd/TS-1@MS in hydrothermal liquefaction of algae transformation.Pd/TS-1@MS catalyst was synthesized and applied in the hydrothermal catalytic liquefaction of algae to produce bio-oil.First,the effect of synthesis conditions on the catalytic performance of the catalyst was investigated.The results showed that the catalyst has the best catalytic performance when the mass ratio of TEOS to TS-1 was 3:1 and the hydrothermal synthesis temperature was 100°C.The yield of bio-oil was 42.20%and the coke yield was13.12%.Secondly,the roles of individual components in the reaction were investigated.It was also confirmed that Pd/TS-1@MS has better hydrodeoxygenation performance and Pd/TS-1 has better hydrodenitrogenation performance by elemental analysis and GC-MS.Finally,the recycling performance of catalysts calcined in different atmospheres was studied.The results showed that hydrogen atmosphere was advantageous to the stability of catalyst.Pd/TS-1@MS?H₂?had satisfied stability in recycling.In the fourth cycle,the performance of the catalyst decreased slightly,but the extent was small,which may be due to the destruction of the mesoporous shell.Compared with Pd/HZSM-5@MS?H₂?,Pd/TS-1@MS?H₂?had better recycling effect and hydrothermal stability.3.Solvent extraction assisted catalytic hydrothermal liquefaction of algae to bio-oil.Aiming at the problems of low yield and poor selectivity of components in bio-oil obtained by one-step algae transformation,a two-step solvent extraction assisted algae catalytic hydrothermal liquefaction method was adopted.First,nine solvents?dichloromethane,ethanol,ether,acetonitrile,tetrahydrofuran,ethyl acetate,petroleum ether,toluene and acetone?and two extraction methods?Soxhlet extraction and reflux extraction?were selected to extract the original algae powder.The experiment found that when the extraction solvent was ethanol and the extraction method was reflux method,the yield of extracted oil was the highest and the content of acid compounds was the highest.Second,the extraction conditions were optimized:5 g algae+100 ml ethanol+8 h.Under the optimum conditions,the yield of oil was 10.36%.Then,adding anhydrous MgSO₄ as water absorbent in the extraction process,caused the content of n-hexadecanoic acid disappeared and the content of hexadecanoic acid ethyl ester reached to 48.40%,which had excellent quality.Finally,catalytic hydrothermal liquefaction experiments were carried out on the original algae powder and the PRE algae powder after extraction.The results showed that the total yield of Rh/C bio-oil obtained by two-step method reached 50.98%,which was higher than that obtained by one-step method.The bio-oil had the highest energy value,reaching 81.09 KJ,and the energy conversion rate of bio-oil reached 85.61%.The results of GC-MS showed that the PRE algae powder extracted by Rh/C catalyst contained 55.68%hydrocarbons,which proved that the two-step method could make full use of algae,and the HHV and energy of the obtained bio-oil were also higher.4,Catalytic conversion of algae to bio-oil in super/near-critical alcohol-water mixtures.Isopropanol was introduced into the catalytic liquefaction of algae.First,the effect of reaction conditions on the yield of bio-oil in isopropanol system was investigated,and the optimal reaction conditions were obtained.Second,under the condition of the total solvent volume was 10 ml,different H₂ yields and product compositions were obtained by varying isopropanol to water ratios.The results showed that with the increase of water content,the yield of bio-oil decreases gradually,and the yield of H₂ also decreases.However,the composition and HHV of bio-oil did not change significantly,which indicated that the hydrogen supply effect of the system was limited.Then,with fixed solvent volume unchanged,formic acid was introduced into the reaction system to investigate the bio-oil yield and product composition under different isopropanol-water ratios,and the H₂ yield in gas products was also determined.The results showed that with the increasing of water content,bio-oil yield and H₂ yield decreased,but they remained at a high level.When isopropanol was used as solvent,adding catalyst and formic acid,70.8%bio-oil yield and 68.76 mmol H₂ yield were obtained and the obtained bio-oil contained 63.21%hydrocarbons.The addition of formic acid enlarged the range of yield adjustment,and the range of bio-oil composition variation was also enlarged.On this basis,the corresponding relationship between H₂yield and hydrocarbons,acids and amides in reaction products was found,and high yield and high quality bio-oil was obtained.Finally,the blank experiment without algae proved that the hydrogen supply capacity of isopropanol was limited,and the addition of formic acid and catalyst increased H₂ production.Therefore,in order to obtain higher yield and high quality bio-oil,isopropanol,formic acid and catalyst were all necessary.