The Study Of Biodiesel Preparation From Non-Edible Vegetable Oils

Biodiesel, comprised of mono-alkyl esters of long chain fatty acids, is a renewable, biodegradable, environmentally benign and nontoxic alternative fuel which is derived from vegetable oils, animal fats or waste restaurant oils. However, the existing technology to produce biodiesel suffers from the high production cost. Moreover, our country has different feedstock-supplying situation from the Occident. In order to reduce the total manufacturing cost of biodiesel, low cost feedstock must be used. Thus, the study focused on the biodiesel preparation from two low-cost non-edible oils, i.e. hemp seed oil and rubber seed oil. It included the study of the pretreatment of the crude oils, biodiesel preparation by the transesterification with homogeneous catalysts, the preparation and catalytic performance of solid base catalysts, and the study of the biodiesel properties.The properties and the pretreatment of hemp seed oil and rubber seed oil was studied. It showed that hemp seed oil consisted of little free fatty acids (FFA), while rubber seed oil contained large amounts of FFA. And the both of the oils consisted of some water. Hemp seed oil could be refined by simple deacidification and dehydration while rubber seed oil must be deacidifed by methyl esterification firstly.Biodiesel was made by transesterification of hempseed oil with methanol, using NaOH as catalysts. The experimental results showed that both enhancing reaction temperature and increasing catalyst amount were advantageous to the transesterification. The conversion of methanol increased to the max and then decreased with extending reaction time. With increasing the molar ratio of methanol to oil the yield of methyl esters increased, but the conversion of methanol decreased. Gel permeation chromatography analysis showed that twice transesterification could convert hempseed oil to methyl esters completely.Using the polyacrylate salts as catalyst supports, NaOH/poly(sodium acrylate) (NaOH/NaPAA) solid bases were prepared by in situ polymerization of sodium acrylate in presence of NaOH. And they were characterized by means of Hammett indicator method, IR, XRD and ²³Na NMR spectroscopy. (1) Results showed that adding NaOH could lead to a more complete polymerization of sodium acrylate. And the NaOH/NaPAA solid bases could have high swelling capability. (2) The basic strength of the hydroxide/NaPAA solid bases could be up to 15.0<18.4, and the basicity of alkaline hydroxide/NaPAA was higher than that of alkaline earth hydroxide/ NaPAA. The basic sites with H in the range of 15.0<18.4, 9.3<15.0 and 7.2<93 were attributed to NaOH, Na₂CO₃ and the NaPAA supporter. (3) XRD and ²³Na NMR analysis showed that good dispersion of NaOH in NaOH/NaPAA could be obtained when the loading amount of NaOH was lower than 12.5 mmol/g. And a phase separation of NaOH may have been formed when the loading amount of NaOH was up to 15.0 mmol/g. There may be aggregated and isolated Na⁺ ions in NaOH/NaPAA solid bases. The aggregates of Na⁺ ions can contain approximately two Na⁺ units for every carboxyl group. And the excess Na⁺ ions exist in isolated state. (4) TG/DTA curves indicated that the NaOH/NaPAA sample had good thermo-stabilization. Its heat-resistant temperature was up to 390℃. DSC curves suggested that the NaOH/NaPAA sample had good combination capability with water and the bonding water was 1.0～2.0 g/g dry gel. (5) The NaOH/NaPAA solid bases can only swell limitedly in glycerol, methanol, hemp seed oil and the methyl esters of hemp seed oil. (6) The water absorbance and the alkali loss of the NaOH/NaPAA solid bases were studied. Results showed that the NaOH/NaPAA had strong water absorbability in methanol, ethanol, n-propanol and n-butanol. The sample with lower crosslinking degree could absorb water more rapidly, and with water content had higher water absorbability. Higher crosslinking degree could letdown the alkali loss, while higher NaOH loading amount, higher water content of alcohol and longer chain alcohol accelerate the alkali loss.The NaOH/NaPAA solid bases were applied to catalyze the transesterification of hemp seed oil. Results showed that the samples had high transesterification catalytic activity and catalytic selectivity. The transesterification was less seriously affected than the NaOH-catalyzed one, likely due to that the saponification was restrained by the high water absorbency. The catalysis mechanism of NaOH/NaPAA solid bases were brought forward. In despite of high catalytic performance, the stability of NaOH/NaPAA should be improved since the alkali loss took place.Multiple strontium and aluminum oxides (SrO-Al₂O₃) were prepared by calcinations of mixed nitrate salts. Results showed that the addition of aluminum nitrate could improved the yield of SrO-Al₂O₃ by restraining the sublimation of SrO. The SrO-Al₂O₃ solid bases had basic strength of 15.0<18.4 and high catalytic activity with Sr content higher than 60%. The SrO-Al₂O₃ catalysts can be prepared easily and are noncorrosive, environmentally benign and present fewer disposal problems. More importantly, they had little alkali loss and high catalytic life in the transesterification. The physicochemical characteristics of biodiesel prepared from hemp seed oil and rubber seed oil were determined. It showed that the two oils had higher iodine value, and the fatty acid composition of them consisted of large amounts of unsaturated acids. Most of the biodiesel properties could meet the standards established by our country, America and Germany. The biodiesel form hemp seed oil had good performance at low temperature, while the biodiesel form rubber seed oil had higher cetane number and flash point. The biodiesel/diesel blends of B5 and B20 had lower sulphur content, higher cetane number, solidifying point and cold filter plugging point than the petroleum diesel fuels. And other properties were close to the petroleum diesel fuels. B5 and B20 could be used as alternative fuels of the corresponding petroleum diesel fuels.