Performance And Mechanism Study Of Transesterification Catalyzed By Calcium Based Heterogeneous Alkaline For Biodiesel Production

Energy consumption and reserve pattern of "deficient oil, lean gas, rich coal" in China can be improved by developing biomass positively. Now the transesterification catalysts for biodiesel production technology in business is mainly homogeneous alkaline which causes high energy consumption and environmental pollution. The problem can be avoided in transesterification catalyzed by heterogeneous alkaline. But its catalytic activity is low. Therefore, environmental, cheap and efficient calcium based heterogeneous alkaline catalysts for transesterification are prepared based on strontium modification and CS.Calcium based heterogeneous alkaline catalysts based on strontium modification and CS are taken as the research objects, which catalytic transesterification characterizations and mechanics are studied in the thesis from aspects of thermodynamic calculation for transesterification, catalyst characterization, influence rule of reaction conditions and physicochemical indexes of biodiesel.The transesterification thermodynamics calculation of linoleic acid and oleic acid, which are respectively major components of raw oil, are conducted by using group contribution method and empirical formula. Transesterification is composed of three consecutive reversible reactions. R1 is defined as the transformation of triglyceride into diglyceride, R2 is defined as the transformation of diglyceride into monogryceride, and R3 is defined as the transformation of monoglyceride into glycerol. In the scope of 298-498 K, ΔHr(?),ΔSr(?) and ΔGr(?) of R3 increase with an increment of the temperature. So heat release is decreased then heat absorption is increased with decrement of the supplied energy from transesterification system to environment and increment of reverse degree of the reaction. Δk(?) of R1 and R2 increases with increment of T, so reverse degree of the reaction increased. The reaction is forward in the low temperature scope of 298-428 K. Optimal transesterification temperature of peanut oil and palm oil is in the low temperature section near the boiling point of methanol.Orthogonal method is used to design transesterification experiments where the catalysts are NaOH and KOH and raw oil are peanut oil and palm oil. And the range method is adopted to analyze the influence of reaction factors on glycerol yield. The single factor method is used to study transesterification effect characterizations where the heterogeneous alkaline catalysts are CaO and SrO/CaO and raw oil is palm oil. The preparation condition of SrO/CaO is optimized combined with catalysts characterization. The optimal calcinations temperature of 600℃ and molar ratio of Sr/Ca of 0.2:1 for SrO/CaO precursor, which is prepared by excessive impregnation method, gain maximum glycerol yield among corresponding preparation factors in catalyzing transesterification. The optimal glycerol yield of 95.74% for transesterification catalyzed by SrO/CaO is higher than the value of CaO, because Ca0.1Sr0.9O can strengthen its catalytic performance.Response surface method and single factor method are adopted to research transesterification characterizations and mechanism where the heterogeneous alkaline catalyst is CS and raw oil is peanut oil. CS can be transformed into CaO at calcination temperature of 850℃ (GS-850). Quadratic polynomial is used to fit the relationship of reaction factors like molar ratio of methanol to oil, catalyst added amount and transesterification temperature and glycerol yield from transesterification catalyzed by CS-850 and the model is highly significant. In addition, molar ratio of methanol to oil is the most significant among linear variable. The reason why the catalytic performance of GS-850 is superior to CaO is big pore, small particles, big specific surface area and specific pore volume in the mesoporous range. Compared with CS calcined at 700℃ (CS-700) and 800℃ (CS-800), CS calcined at 650℃(CS-650) possesses the bigger specific surface area, smaller particle size and better specific pore volume distributed in the mesoporous range and optimal glycerol yield value is 92.98%. Activation energy of 68.45 kJ·mol-1 for transesterification catalyzed by CS-650 is less than CaO and is more beneficial to accelerate the transesterification.The single factor method is used to analyze influence role on transesterification and action mechanism where the heterogeneous alkaline catalysts are CS loaded with potassium fluoride (KF/CS) and acetic acid modified CS (CSA) and raw oil is peanut oil. KF/GS is prepared by the excessive impregnation method. The reason why the specific surface area and specific pore volume of KF/CS decrease is pore plugging in the formation process of the catalyst:But new crystalline phase such as KCaF3 and CaF2 appear and the glycerol yield value from transesterification catalyzed by KF/CS is 91.89%. Specific surface area and specific pore volume of CSA at calcination temperature of 800℃ (CSA-800) are 19.07 m2·g-1 and 0.0814 cm3·g-1 which is one of the important reasons to ensure its high catalytic performance. The glycerol value of 92.90% can be reached when CSA-800 is reused for five times. The main component of CS after reused is Ca[O(OH)2C3H5]2.Pyrolysis and combustion mechanism of palm oil methyl ester (PAME) and peanut oil methyl ester (PEME) are studied. The maximum content of C-H bond indicates they are easy to burn. Maximum weight loss rate,maximum weight loss temperature and end temperature of weight loss gradually increase with the increment of β. The pyrolysis process of PAME is single, and the process of PEME is complex for a different process. n values of PAME and PEME are respectively in the range of 1.7093-1.8039 and 1.4280-1.4680, indicating the pyrolysis of PAME is intense. Biodiesel pyrolysis reactions are endothermic and the reactions are not spontaneous. The heat absorption of PEME is less than the value of PAME and more energy is discharged from pyrolysis of the former to the environment. The initial weight loss temperature of the biodiesel is higher than diesel under simulated of air atmosphere, so they are easier for storage and transportation. PAME with minimum weightlessness half peak width and maximum weight loss rate is easier for combustion in diesel engines. Combustion reaction order of diesel and biodiesel are between 2 and 3. Besides, the kinetic compensation effect exists in biodiesel combustion process.