The Simulation Study On Algal Biomass Under Super/Near-critical Water

With the development of economy and growth of worldwide population,the demand for fossil energy is increasing,while the fossil energy on the earth is non-renewable with limit storge.It is a challenge for our future sustainable development,and it is essential to develop and transform new energy resource.The biomass resource has received extensive attention at home and abroad in recent 30 years,due to the advantages of abundant resources,operation safety,wide distribution,diversity of energy form and so on.Algae,as the third generation biofuels,has a lot advantages of a faster growth rates,a high oil content and nonarable land,which is a promising biomass for biocrude production.Compared to the traditional method for the treatment of algal biocrude(enzyme degradation and pyrolysis),hydrothermal liquefaction of algae is a convenient and efficient way,due to non-pretreatment and close to the higher heat value of gasoline.It has a lot of research on the topic of improving the biocrude yield and quality.However,there is lack of knowledge on the fundmental reaction mechanism for the process hydrothermal liquefaction of algae,which is needed to be deepened and expanded.In order to explore the mechanism of algae hydrothermal liquefaction in the molecular level,the important components(carbohydrates,proteins,lipids)in algae are focus on the mechanism of main products formation during the hydrothermal liquefaction process with experimental and theoretical study,which provide the academic and expediential support for the development of hydrothermal liquefaction of algae.The main work and result are summarized as follows:1.The study of the liquefaction for algal model compound under near-critical water.Using corn starch and cellulose as polysaccharide,soy protein and whey protein as protein,sunflower oil and castor oil as the lipid were designed as the research object in the first part.In order to get a more comprehensive understanding on simulation effects of model compounds,six compounds were firstly divided into the first group(corn starch,soy protein,sunflower oil)and second group(cellulose,whey protein,castor oil).The reaction of a single reactant under hydrothermal conditions was studied to discuss the effects of reaction temperature(300,350 ℃)and time(0-90 min).Then,the work was gradually extended to the binary and ternary reactant mixture.The results show that the effect of model compounds on biocrude yields are ranked as follows:lipids>proteins>carbohydrates.The main products in biocrude from protein are amide compounds,unsaturated hydrocarbons and carboxylic acid in lipid biocrude,and polysaccharide aromatic hydrocarbons and cyclic ketone compounds in carbohydrates.It also get the conclusion that the theoretical formula to forecast the biocrude yield for algae.2.The study of the liquefaction for protein model compound under near-critical water.Soy protein,represented as the algae important component of protein,was studied under hydrothermal condition to discuss the effects of solvents,reaction temperature(200-350 ℃)and time(0-60 min).The Matlab software was also used to fit the kinetic parameters of hydrothermal liquefaction of protein(mainly for rate constant and activation energy).The products in the reaction were characterized and analyzed to propose a reaction pathway for hydrothermal liquefaction of protein.The results illustrated that dichloromethane was a good solvent for extractingbiocrude.Reaction temperature and time have effect on the yield of biocrude and gas,while the yield of liquid was affected by reaction time.It also used the Arrhenius correlation to obtain activation energy of reaction.3.The study of catalytic hydrothermal liquefaction for algal model compound under super-and near-critical water.Using soy protein as model compound to discuss the nitrogen removal under hydrothermal hydrogenation with catalysts,examines the influence of reaction temperature(250-400 ℃),time(1-6 h),catalyst and H2.It is mainly focus on the distribution of hydrogenation products fromcatalytic hydrothermal liquefaction of soy protein.The results illustrated that the Ru/C catalyst is the best catalyst for the effect of denitrogenation of soy protein.With no catalyst,the biocrude mainly has the products as fatty acid,amide and nitrogenous heterocyclic compounds.Under the catalyst of Ru/C,main products were aromatic hydrocarbons and phenols.The HHV value of biocrude from Ru/C was 16%higher than that from no catalyst and the nitrogen level decreased to 45%of that in the noncatalytic product.4.The study of catalytic hydrothermal hydrodenitrogenation of indole under super-and near-critical water.Indole,as a nitrogen-containing compound in biocrude from hydrothermal liquefaction of protein,was studied to discuss the denitrogenation process under hydrothermal condition,which examines the influence of reaction temperature(350-450 ℃),time(0-180 min),catalyst,and H2 on hydrothermal denitrogenation(HDN)of indole.Based on HDN of indole reaction results,it was also used the Matlab software to fit the optimal kinetics equation and kinetic parameters(mainly for the reaction rate constant and activation energy).The intermediates in the reaction process were characterized and analyzed.The results showed that with Pd/y-Al2O3 catalyst,indole takes 90 min to transfer completely at 450 ℃ with main products as ethylbenzene and cyclohexyl ethane.’According to the main prodcuts,it proposed a potential reaction mechanism of indole under hydrogenation denitrogenation.It also discussed the possible factor of deactivation for catalysts under hydrothermal condition.The results indicated that the reason for deactivation of catalysts were the transformation of γ-Al2O3 to the γ-AlOOH andα-Al2O3,fired and reunited phenomenon,and losing of metals.