Pure glycerin is a colorless liquid with sweet sticky, it is a ternary alcohol, with triple the general chemical properties of alcohols, you can participate in many chemical reactions to produce various derivatives, glycerol Due to a number of important physical and chemical properties, has become an important chemical raw material. Glycerol in China at present mainly used for production of coatings, salt, medicine, toothpaste, cellophane, insulation materials. In the preparation of bio-diesel process, the by-products is a cavity slide notes contains a certain amount unsaponifiable matter, alkali, and a mixture of methanol, if the direct access to the market, not improve the overall economic benefits of bio-diesel, it needs to be refined crude glycerin . Enter the market, can not improve overall economic efficiency of biodiesel, it needs to be refined crude glycerin.
Raw materials and instruments: crude glycerin, self-made; methanol, phosphoric acid were of analytical grade. centrifugal sedimentation machine; rotary vane vacuum pump.
Bio-diesel and crude glycerin preparation: in with the vacuum dewatering device, thermometer, and reflux condenser 3 neck flask, add 100 g obtained by the extraction of crude rapeseed oil, heated to 120 ℃, vacuum dehydration 1 ~ 2 h, cooled to 50 ℃, adding 20 ~ 45 g of methanol, 1. 0 ~ 4 g potassium hydroxide, heated to 60 ~ 70 ℃, refluxing for 1 ~ 2 h, recovery of excess methanol, cooled to 50 ℃, put it aside 1 ~ 2 h, the upper for the fatty acid methyl esters or bio-diesel, the lower crude glycerin solution shall be.
No bio-diesel refined oil and crude glycerol: Weigh 100 g crude glycerin transferred to the beaker, add 20 ~ 30 g diluent, fully stirred, and then phosphoric acid and, to make the solution pH value reached 4 ~ 7 date. The solution during and after the centrifugal separation, the solution after the separation into three layers, collecting the middle fluid, be moved into the vacuum distillation with a device, thermometer, and reflux condenser in the three-neck flask. 70 ℃ atmospheric distillation recovery of methanol, vacuum distillation to take 164 ~ 204 ℃ of distillate shall be refined glycerin.
Transesterification process conditions to determine: In order to further study the transesterification process conditions, using orthogonal test method, the crude rapeseed oil transesterification reaction conditions were optimized. Examine four factors, methanol and rapeseed oil molar ratio of catalyst (mass fraction), reaction temperature and reaction time on the yield of fatty acid methyl esters (in the quality of rapeseed oil as the benchmark, the same below) effects. Crude rapeseed oil transesterification reaction conditions for the best oil-alcohol molar ratio of 6: 1, amount of catalyst 1%, reaction temperature 60 ℃, reaction time 90 min. Size we can see from the very poor, the amount of catalysts used in the greatest impact on yield, followed by oil-alcohol molar ratio and reaction time, minimal impact on the reaction temperature. Transesterification reaction under optimum reaction conditions of three repeated experiments, the average yield of 98.1%. Also received lower crude glycerin 16. 0 g.
Solvent on the yield of glycerol: glycerol during separation and purification, in order to improve the separation efficiency, the need to join as a diluent solvent, using different solvents glycerol yield difference. In this study, said that taking two 100 g crude glycerin solution were added to methanol, ethanol, each 25 g as solvent. By adding methanol as solvent the yield of glycerin 28.1%, by adding ethanol as solvent glycerol yield of 27.7% (in the quality of crude glycerin as the base, the same below). Experimental results show that methanol and ethanol as solvent, the glycerol yield less the same, but using ethanol as solvent, due to crude glycerol contains a small amount of methanol, so there would be methanol, ethanol recovery exists, so that recovery ethanol, re-use more difficult. Therefore, this experiment uses methanol as solvent.
pH value on the yield of glycerol: Because under alkaline conditions, glycerol, soap, methanol and methyl mixed into a gelatinous body, separate them and give them 11, with settlement or centrifugation very difficult. Therefore, in glycerin separation process, it is necessary to use acid and lower liquid to a suitable pH value, so that you can use sedimentation or centrifugation to separate them (but with the sedimentation method takes a long time to stratification , so it is best to use during and after the centrifugal separation of crude glycerol, is not only a good separation effect, and the separation time is very short). pH, the size of the glycerol yield a great influence, pH value is too large, not easy to separate glycerol, pH value is too small, glycerol yield is not high. , In the pH value is greater than 7, namely, the mixture is alkaline, the glycerol yield is significantly lower, in the mixture was neutral or acidic, the glycerol yield a small difference. But the pH value is not too small, because the acidity is too strong, in the vacuum distillation, the glycerol prone to aggregation, reducing the yield of glycerol. Therefore, the reaction liquid in the lower pH value of 5 or 6 under the conditions of separation is best.
Vacuum distillation temperature on the yield of glycerol:, as the distillation temperature, the glycerol yield increased, when the temperature reaches 200 ℃, the highest glycerol yield, distillation temperature of 214 ℃, the Gan oil yield worse. Therefore, the crude glycerin vacuum distillation process must be a good temperature control. This is because the atmospheric pressure boiling point of glycerol under 290 ℃, glycerol at 204 ℃ when the aggregation and decomposition occurs, and as the temperature rise increased side effects. In order to glycerol to below 204 ℃ under the conditions of gasification must be vacuum distillation, so that 164 ℃ when the glycerin started gasification, distillation temperature period not exceeding 204 ℃.
Crude glycerine refined experimental results: according to the above separation conditions, saying that taking 100. 0 g crude glycerol, with 25. 0 g methanol dilution, and used 8. 0 g phosphoric acid during and after the centrifugal separation, the upper liquid was bio – dissolve a small amount of diesel and glycerin 30. 0 g, the lower solid soap, salt and a small amount of glycerol 41. 8 g, mid-level liquid glycerol and methanol 61. 2 g. Will be mid-level solution for a methanol steam distillation at atmospheric pressure 30. 0 g, followed by vacuum distillation was refined glycerin 31. 2 g, glycerol yield reached 31.2%. Refined glycerin obtained after centrifugation only to calculate the received middle crude glycerol, does not include esterification of the upper fluid, crude glycerol obtained after centrifugation the upper, lower in the small amount of glycerol. By the above process Preparation of refined glycerin was slightly yellow, there is a slight odor, by adding activated carbon bleaching, to get products after taste.
Conclusion A rapeseed oil biodiesel the best reaction conditions for the oil-alcohol molar ratio of 6: 1, amount of catalyst 1%, reaction temperature 60 ℃, reaction time of 90min. In the optimum reaction conditions, bio-diesel yield reached 98.1%.
Glycerin by-product of two bio-diesel refining the optimum as follows: using methanol as solvent, centrifugation the solution pH values between 5 to 7, in this condition, the yield of refined glycerin can reach 31.2%.
3 According to this experiment provided by the method of refining crude glycerine refined glycerine purity can be achieved.
