Study On Catalytic Conversion Of Biomass-based Materials To Hydrocarbons

The increasing of global energy demanding and the amount of CO2released become the two major problems in the worldwide. The limited stocks of fossil fuels required the governments to develop technology in finding new alternatives for fossil fuels. As we all know, biomass is a kind of widely restored and clean energy resource. It is considered as an effective alternative for fossil fuels, which makes biomass conversion technology a hot domain all over the world. Biomass-based energy contains both lignocelluloses-based and triglyceride-based materials. It has large amount of oxygen in it resulting in a low energy value. Before direct application in modern engines, biomass needs to be upgraded. One technology in upgrading biomass called "deoxygenation process" allows us remove the oxygen in biomass-based materials, resulting in liquid alkanes. These alkanes have around5-20carbon numbers which is similar to that of real diesel. Another technology called "carbon chain elongation process" converts the light carbon containing materials to high carbon chain-based diesel precursors. Through these two technology, biomass-based materials can be selectively converted to diesel-like hydrocarbons.In the present dissertation, we investigated selective hydrodeoxygenation of triglyceride-based and lignocelluloses-based model compounds over a series of palladium-based catalysts. Catalyst screening includes activity tests, characterizations and mechanism study. Some conclusions drawn from the research are provided as follows:(1) Metal oxides (MOx) supported Pd catalyst reveals high activity in conversion of stearic acid to liquid hydrocarbons. The deep hydrogenation of stearic acid was related to the acidity of the catalyst. Catalyst with higher amount of medium and strong acid site favors the hydrogenation of stearic acid, resulting in C18alkane yield. The experimental parameters study over Pd/TiO2reveals that hydrogen was required in efficient conversion of stearci acid to liquid alkanes and reducing the by-products. (2) HZSM-5supported Pd catalyst showed high activity in conversion of sunflower oil. However the yield of liquid long chain alkanes was low. The strong acid sites of HZSM-5was considered as active sites in cracking C-C bonds of the triglycerides, resulting in low yield of long chain alkanes but high yield of smaller liquid and gas products. The liquid products contain amount of aromatics produced from aromatization of triglycerides in the pore of HZSM-5. The comparison study of Pd/HZSM-5and Pd/Hbeta catalysts revealed that suitable amount of medium and strong acid sites and pores are more favorable in conversion of triglycerides to liquid diesel-like hydrocarbons.(3) Hydrodeoxygenation of sunflower oil was performed in an autoclave over5.0wt.%Pd/Al-SBA-15(Si/Al molar ratios from22to300) and Pd/HZSM-5(22). The effects of acidity of the catalysts and the reaction temperatures on the activity of the catalysts were investigated. Pd/Al-SBA-15(Si/Al=300) showed a high activity as74.4%liquid yield and72.9%C15-C18diesel-like hydrocarbons yield at250℃. At300℃, the higher activity over Pd/Al-SBA-15(Si/Al=50,100and300) catalysts compared with that over Pd/Al-SBA-15(22) and Pd/HZSM-5(22) indicated that strong acidity of the catalysts was not favorable for converting sunflower oil into C15-C18diesel-like hydrocarbons at a high temperature.(4) The hydrothermal stability of TiO2-and ZrO2-based materials was studied by exposing the samples to liquid water at523K for60h in a batch reactor. No phase transformation or loss in BET surface area was observed for TiO2-based materials that had initial BET surface area of less than52m2/g. In contrast, the BET surface area decreased and the primary crystallite size increased for all ZrO2-based materials tested. The BET surface area decreased and the primary crystallite size increased for high BET surface area TiO2(156m2/g) and ZrO2(246m2/g). Silica-containing TiO2only lost30%of its high BET surface area (from128to90m2/g). In contrast a material composed of silica-phosphate-ZrO2lost56-72%of its BET surface area. Using the crystalline TiO2as a support, we prepared and tested a Pt-ReOx/TiO2catalyst for hydrodeoxygenation of sorbitol. Pt-ReOx/TiO2was almost2times more active on a total Pt basis than Pt-ReOx/C catalyst. Between0.1and0.9wt%of coke formed on the catalyst surface after reaction depending on the reaction conditions. The coke could be removed and the catalyst activity completely regenerated by an oxidation-reduction treatment. The catalyst showed only minimal change in BET surface area, TiO2phase and TiO2crystallite size after more than163h of time on stream. The CO chemisorption of Pt—ReOx/TiO2increased after reaction which was probably due to migration of ReOx species away from the Pt during the reaction. The results shows that Pt-ReOx/TiO2catalyst can be regenerated though an calcination-reduction process while Pt-ReOx/C catalyst was hard to be regenerated.(5) Investigation on conversion of triglyceride-based and lignocelluloses-based model compounds showed that TiO2was suitable support in both nonaqueous and aqueous conditions. It’s possible to design a process to convert triglyceride-based and lignocelluloses-based materials simultaneously over TiO2supported catalysts.