At present, the preparation methods of biodiesel are mainly direct mixing method, microemulsion method, pyrolysis method and transesterification method. China's source of waste oil widely dispersed, with solid impurities, high moisture content, high acid value characteristics. The preparation of waste oil biodiesel generally first through the water, mechanical cleaning, acid, bleaching and other pretreatment, and then use transesterification or hydrocracking biodiesel prepared.
Preparation of biodiesel by transesterification
Zhang Yong abandoned waste oil as raw material, after pretreatment using two-step esterification process to convert it into biodiesel, the first step is the acid-catalyzed pre-esterification reaction, mainly in the waste oil of free fatty acids into fatty acid A Ester; the second step is the acid-catalyzed transesterification reaction, further converting the triglycerides in the waste oil into methyl esters and glycerol. The optimum conditions of pre-esterification obtained through orthogonal experiment were as follows: the molar ratio of alcohol to oil was 10: 1, the amount of catalyst was 1%, the reaction temperature was 70 ℃ and the reaction time was 4 hours. The optimum conditions of transesterification were alcohol oil Molar ratio of 20: 1, catalyst dosage 6%, reaction temperature 70 ℃, reaction time 4 hours. Under the best reaction conditions, the esterification rate of triglycerides can reach 86.89%. The biodiesel prepared by the method is better than No. 0 diesel oil in the aspects of flash point and cold filter point, and is safer in storage and transportation; meanwhile, the biodiesel can be used in a wider temperature range. The study also found that the biodiesel prepared by this method and No. 0 diesel oil can be blended according to B20 to not only greatly reduce the viscosity of the biodiesel but also improve the volatility while increasing the flash point of the No. 0 diesel fuel at the same time, Lower points make the process of storage and transportation safer, low temperature performance is improved, is conducive to use in a wider temperature range, to meet the requirements.
The preparation of the biodiesel catalyzed by the oleic acid in the furrow is carried out by transesterification of the waste oil with a lower alcohol such as methanol or ethanol under acidic conditions to produce the corresponding fatty acid methyl ester or ethyl ester. Yao Yaguang and other acid as a catalyst, first of the waste oil impurity removal, degumming, decolorization, dehydration pretreatment, acid waste oil under the catalysis biodiesel preparation, through the waste oil and methanol, ethanol esterification orthogonal Experiments show that the optimum reaction conditions for the acid-catalyzed waste oil to produce biodiesel are as follows: the temperature of methanol is 70 ℃, the mole ratio of oleyl alcohol is 1:40, the concentration of catalyst is 7%, the reaction time is 6 hours, : Oleyl alcohol molar ratio, reaction time, catalyst concentration and temperature; the temperature of ethanol was 80 ℃, the mole ratio of oleyl alcohol was 1:30, the concentration of catalyst was 5% and the reaction time was 6 hours. , Temperature, catalyst concentration, reaction time. By this method, biodiesel with excellent properties is prepared. The main advantages are: good flammability (cetane number), evaporation (distillation range and distillation temperature), safety (flash point), viscosity and condensation point temperature, corrosion of the engine (acidity and acid value) , Calorific value. The experimental preparation of biodiesel in many ways with ordinary diesel incomparable superior features.
Fu Yan, etc. to waste oil as raw material to study the waste oil and methanol in the three-stage reactor immobilized lipase synthesis of biodiesel. The waste oil acid value, saponification value and water content were tested. The effects of feed flow rate, solvent and water content on the reaction were investigated. At 40 ℃, n-hexane was used as the solvent, water was added to make up 20% of the quality of the waste oil, and the biodiesel yield was 94% when the molar ratio of methanol to waste oil added in each reactor was 1: 1.
Chen Yingming and other waste oil through the filter, degumming, bleaching, dehydration and other pretreatment, and methanol, n-hexane, water, etc. by a certain percentage of mixed by a blender, with a peristaltic pump filled sheet immobilized enzyme reactor Top, dropping into the reactor, constant temperature circulating water bath. The three reactors are connected in series to form a three-stage reaction system. The molar ratio of oleyl alcohol to that fed into the reactors of each stage is 1: 1. The product of each reaction stage removes by-product glycerol in time. The reaction product is removed by washing with water, distillation, etc. to remove methanol, water and n-hexane to obtain crude biodiesel. The biodiesel prepared by this method was qualitatively analyzed by GC-2010 gas chromatograph and QP2010 mass spectrometer, and the content of fatty acid methyl ester, free fatty acid and glycerol in biodiesel were determined by GC-MS Class of the location, which determine the various components of the GC chromatogram and its content, and by area method and internal standard method for the determination of biodiesel conversion and yield, and ultimately obtained ditch enzymatic enzymatic biodiesel conversion rate of 93.53 %, Yield 77.45%.
Li Weimin and other waste oil as raw materials for the preparation of biodiesel, pre-esterification of the waste oil to reduce the acid value of 2 ± 1mgKOH / g, and then biodiesel transesterification obtained by orthogonal test of the waste oil pre-esterification reaction The optimal conditions were as follows: the amount of concentrated sulfuric acid was 2%, the amount of methanol was 16%, the reaction temperature was 75 ℃ and the reaction time was 4 hours. The optimal conditions for the transesterification of waste oil were: methanol 20%, KOH 1%, reaction temperature 65 ℃, reaction time 2 hours, and the prepared biodiesel to meet the national biodiesel standards.
Zhang Aihua and other pre-esterification technology using polyols to deal with waste oil, alkaline ionic liquid 1-methyl-3-butyl imidazole hydroxide as a catalyst for the preparation of biodiesel. The effects of the amount of ionic liquid, the molar ratio of alcohol to oil, reaction temperature and reaction time on transesterification were investigated. The results showed that the technological conditions for preparing biodiesel from waste oil were as follows: the molar ratio of alcohol to oil was 8:1, the reaction temperature was 70 ℃, the reaction time was 110 minutes and the amount of catalyst was 3.0% of the quality of feedstock. Under these conditions, the fatty acid methyl ester conversion was 95.7%. The effects of glycerol addition, reaction temperature and reaction time on the pre-esterification reaction were investigated experimentally. At the same time, the effect of catalyst amount, molar ratio of alcohol to oil, reaction temperature and reaction time on the transesterification reaction was investigated. Through orthogonal test, the optimal reaction conditions for preparing biodiesel from waste oil pre-esterification-transesterification reaction were determined. Chen An et al. According to the characteristics of high acid value of furrow oil, solid acid and solid base two-step heterogeneous catalysis was used to develop biodiesel. This method avoids the disadvantages of high cost, long reaction time, low esterification rate, waste water and so on of acid plant with homogeneous acid method. It overcomes the problem that the homogeneous base catalyzed transesterification reaction is easy to saponify high acid value waste oil with low yield A large number of waste water and other ills; the same time, also make up the two-phase homogeneous method produces a lot of waste water, affecting the lack of the environment. The best experimental conditions of this method were confirmed as follows: the reaction time was 2.5h, the molar ratio of alcohol to oil was 10: 1, the solid base catalyst was 2.0% of oil, the co-solvent of tetrahydrofuran was 3% and the reaction temperature was 71 ℃. Esterification rate at this time in more than 96%.
Waste oil production by supercritical biodiesel
Supercritical transesterification reaction is catalyzed transesterification. When methanol is in the supercritical state, the alcohol and oil are homogenized to improve the mass transfer effect, the reaction rate is greatly increased, the reaction time is short, and the conversion rate of methyl ester is high. No catalyst is required, but the reaction needs to be carried out under high temperature and pressure. High equipment requirements, energy consumption. Demirbas in the catalyst-free conditions, the volume of 10 ml cylinder pressure vessel using supercritical methanol to prepare biodiesel, and through the single factor test, the impact of the test parameters were optimized in the experimental conditions, Methyl ester conversion rate up to 99.6%. The author compared the test results with base-catalyzed preparation of biodiesel, and found that the supercritical methanol process can save raw materials and save operating costs. Chen Shengjie to acidified oil, ethanol as raw material, in the preparation of biodiesel under supercritical conditions. The reaction conditions were optimized by using the response surface design and analysis method, and the optimum process conditions were obtained. Under this optimal condition, the yield of biodiesel reached 89.7%. In order to improve the method of preparing biodiesel by supercritical transesterification and to overcome its shortcomings, supercritical transesterification with catalyst or cosolvent has become a new field of exploration.
Preparation of biodiesel from waste oil hydrocracking
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