摘要
本论文在综述了国内外生物柴油制备的基础上,对高酸价油脂如餐饮废油、酸化油和地沟油制备生物柴油的路线、动力学影响因素、不同油脂成份结构与生物柴油低温性能关系进行了系统的研究,探索了生物柴油降凝的方法,并对制备生物柴油过程产生的副产物甘油的精制技术进行了深入细致的探索。研究的主要内容及结果归纳如下:
通过选用硫酸、磷酸、对甲苯磺酸、三氯化铁、SO42-/ZrO2等酸性催化剂作为预酯化反应催化剂进行比较,研究表明对甲苯磺酸催化活性好,预酯化反应时间短,几乎不溶解于油脂而溶解于甲醇,预酯化反应后油脂无需水洗直接进入碱催化酯交换反应,催化剂随甲醇一起分出,脱水之后可以直接加入下一次预酯化反应,能够回收部分催化剂,工业化应用能够降低生产成本,有利于环境保护。
研究了动力学影响因素醇酸摩尔比、催化剂用量、反应温度、反应时间对预酯化反应的影响,通过正交实验,考察各反应因素对预酯化反应影响的大小,找出了预酯化工艺的最佳条件,实验结果表明,各因素对预酯化反应影响大小依次为反应温度、催化剂用量、醇酸摩尔比和反应时间,预酯化最优化的工艺条件为:醇酸摩尔比8:1,催化剂用量2%,反应时间120min,反应温度70℃,此条件下酸价100mg/g的油脂经过预酯化酸价能够降低到碱催化酯交换的要求。
优化了预酯化工艺,预酯化反应采用分段反应工艺,通过反应过程中蒸出甲醇带走反应生成的水,脱水效果明显,使反应之后分出的甲醇含水率较低,可以直接用于下一次预酯化反应。分段预酯化工艺较直接回流预酯化反应缩短反应时间1h。
考察了油脂酸价对碱催化酯交换的影响,发现随着酸价升高生物柴油得率明显下降,水洗乳化现象越来越严重,当油脂酸价高于4mg/g时,酯交换油脂水洗分层困难,不能直接进行碱催化酯交换制备生物柴油,必须经过预酯化降低酸价才能达到要求。
研究了生物柴油低温流动性能与自身组分含量和分子结构的关系,得出生物柴油低温性能随其所含脂肪酸甲酯碳链变长和饱和脂肪酸甲酯含量增大而降低。通过冷冻过滤、与柴油掺混使用和添加环氧化油脂能够达到一定的改善生物柴油低温性能的目的。
对副产物甘油的精制进行了系统的研究,考察了酸处理过程中酸溶液的选择、PH值、溶剂的选择、溶剂的用量、反应温度和反应时间对酸处理甘油回收率的影响,得出酸处理最佳的工艺条件:50%的硫酸用量为粗甘油样质量的11%,水作为溶剂用量为原料质量的20%,反应温度60℃,反应时间20min,在最佳的酸处理条件下重复实验,得到酸处理甘油回收率98.3%。考察了碱中和过程中溶液PH对甘油回收率的影响,实验结果显示,当溶液调到PH=7的时候甘油回收率最高,达到96.3%。通过减压蒸馏,得到蒸馏甘油含量97.43%。经过精馏之后的甘油含量98.93%,精馏甘油气质联用分析,气相色谱只有甘油单一峰,有机杂质比较少,利用活性炭对蒸馏甘油、精馏甘油进行脱色,考察了活性炭用量对脱色的影响,加入1%的活性炭,甘油透光率能够达到99.8%,基本接近蒸馏水,脱色之后的甘油含量达到99.12%。
In this thesis, the preparation of biodiesel from high acid value (AV) oil, such as cooking oil,acidification oil and waste oil,was studied.The preparation process of biodiesel,the kinetic factors and the relationship between low temperature property and the molecular structure of fatty acid methyl ester were systematically discussed.Furthermore,the salutions to improve low temperature property of biodiesel and refining processof the by-product glycerine were investigated. The main content and results are summarized as follow:
Used as catalyst in pre-esterification, sulfuric acid, phosphoric acid, toluene-p-sulfonic acid, iron trichloride and toluene-p-sulfonic acid was compared.The results show that toluene-p-sulfonic acid is the best catalyst. It has good catalytic activity and it hardly dissolves in the oil but can dissolve in the methanol. The pre-esterification oil can transesterize directly without washing. The process is environmental. The methanol with catalyst can be used again in the next pre-esterification after dehydration. Most of catalyst can be recovered. It helps to cut down the cost.In the pre-esterification stage, the effect of mole ratio of alcohol and acid, dosages of catalyst, reaction time and reaction temperature was investigated. The optimum conditions for pre-esterification are got by orthogonality experiment. The result shows that the optimum conditions are as follow: mole ratio of alcohol and acid8:1, dosages of catalyst 2%, reaction time 120min and reaction temperature 70℃.
The process of stage pre-esterification can carry off some water from methanol. The effect of dehydration is obvious. The reaction time is shortened 1h and the percent recovery of catalyst is 90%more by the stage esterification.
The influence of acid value (AV) of oil on transesterification was investigated. The results show that the AV of oil could not be more than 4mg/g.
The study showed that the longer carbonchain of fatty acid methyl ester and the more saturation fatty acid methyl ester,the worse low temperature property of biodiesel.we can improve the low temperature property of biodiesel by freezing and filtering,blending with diesel and adding epoxy fatty acid methylester.
This paper also studied on refining glycerine from the by-product of biodiesel. The effect of kind of acid solution, pH, solvent, dosages of solvent, reaction time and reaction temperature on acid treatment was investigated. The optimum acidification conditions are as follow:50% sulfuric acid 11g, water as solvent 20g, reaction time 20min, reaction temperature 60℃.Under this condition, the percent recovery of glycerine is 98.3%. The effect of pH on percent recovery of glycerine in alkali treatment was investigated. The result shows that pH=7 is the best. The percent recovery of glycerine is 96.3%.Under this condition, the glycerine polymerizes rarely and the remainder of distillation is least. The fatty acid of distilled glycerine is low level. The content of distilled glycerine is 97.43%.The content of rectified glycerine 98.93%.Analyzed by GC-MS, the rectified glycerine has single peak. It shows that the rectified glycerine contains few organo-impurity. The distilled glycerine and rectified glycerine is decolored by acticarbon. The effect of dosage of acticarbon on decoloring was investigated. The result shows that the light transmittance arrives at 99.8%. The content of decolored glycerine is 99.12%.
引文
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