【作者】 陈金思；

【导师】 胡献国；

【作者基本信息】 合肥工业大学 ， 环保装备及环境监测工程， 2012， 博士

【摘要】 生物柴油是由动植物油脂与短链醇经酯交换反应制得的脂肪酸单烷基酯,采用棉籽油与生物乙醇制备的棉籽油脂肪酸乙酯生物柴油是真正意义上的可再生能源,其生产原料具有不依赖于石化资源的特点。棉籽油脂肪酸乙酯生物柴油具有完全可再生、毒性低、可生物降解、闪点较高、排放的污染物更少的优点,可以直接与柴油调和,用作发动机燃料,也可以单独作为发动机燃料。棉籽油与乙醇制备生物柴油的研究少有报道,有关棉籽油脂肪酸乙酯的制备方法、性能表征的文献也比较少。本学位论文以棉籽油和生物乙醇为原料,通过酯交换法制备棉籽油脂肪酸乙酯生物柴油,并对酯交换反应参数进行优化，探索绿色、高效的生物柴油制备工艺；对棉籽油脂肪酸乙酯的生物降解性、润滑特性、腐蚀特性、挥发性等多项指标进行深入研究,为棉籽油基生物柴油的生产、运输、储存、使用提供理论指导。通过对棉籽油与乙醇在碱性催化作用下发生酯交换反应的研究,结果表明,当乙醇足够过量,碱用量为棉籽油质量的1.25%情况下,反应温度在40-78℃,30min酯交换反应基本达到平衡。棉籽油与乙醇进行酯交换反应在主反应阶段为准二级反应,反应30mmin后为零级反应。酯交换反应在40℃,60℃和78℃时反应速率常数k分别为0.0996,0.1126和0.1286L.mol-1.min-1,在78℃条件下,活化能Ea=21.6075kJ mol-1。可见酯交换反应的速度缓慢,反应需要的活化能较大。为了加快酯交换反应速度,向棉籽油和乙醇反应体系中投加四氢呋喃(tetrahydrofuran,简写成THF)作为助溶剂,同时采用强碱KOH为催化剂,考察了醇油摩尔比、反应时间、反应温度、催化剂用量及助溶剂对酯交换反应的影响。酯交换反应最佳工艺参数为醇油摩尔比14：1,催化剂用量1.25wt%,反应温度78℃,反应时间1.5h,助溶剂与棉籽油质量比1：1,棉籽油脂肪酸的转化率达到97.90%。THF能有效促进油脂与乙醇互溶,提高酯交换反应传质效率,提高反应速度,缩短反应达到平衡所需的时间,且易于从多组分中分离出来,重复使用。所制得的生物柴油各项指标均满足《柴油机燃料调和用生物柴油(BD100)》(GB/T20828-2007)的限值要求。同时,为了全面考察棉籽油脂肪酸乙酯生物柴油的性能,本文用棉籽油与甲醇和乙醇分别进行酯交换反应,制备出甲酯生物柴油(cottonseed oil methyl ester,简写成CSOME)和乙酯生物柴油(cottonseed oil ethyl ester,简写成CSOEE)。然后将它们分别以不同体积比率与0#柴油混合,制备出不同体积比的生物柴油/柴油混合物。采用改进的Sturm生物降解实验方法,比较了棉籽油脂肪酸甲酯、乙酯及其与0#柴油调和的生物柴油／柴油等油样,在水环境中生物降解过程。在水中和有氧的环境中,棉籽油基生物柴油生物降解速率比0#柴油快。历时28d,棉籽油脂肪酸甲酯、乙酯的生物降解率分别达到99.1%和99.7%,而0#柴油的生物降解率仅为49.9%。生物柴油在调和油中比例越大,越有利于生物降解。棉籽油脂肪酸乙酯与0#柴油混合的体积分数分别为100%、50%、20%、5%和2%时,28d生物降解率分别是99.7%、95.7%、81.9%、65.4%和61.5%。生物柴油对0#柴油的生物降解具有促进增效的作用,生物柴油分子中的氧有利于促进其生物降解能力。另外,在温度为25℃和50℃条件下,研究了棉籽油基生物柴油铜片腐蚀特性,考察了棉籽油甲酯和乙酯在铜片腐蚀过程中,它们的理化性能变化规律,并且与0#柴油进行比较。结果表明：在25℃和50℃条件下,腐蚀实验历时2个月,棉籽油甲酯生物柴油和乙酯生物柴油对铜片具有不同的腐蚀现象,且棉籽油甲酯比乙酯的腐蚀性更大。在25℃的条件下,浸蚀铜片60天后,CSOME和CSOEE酸值分别增加了13.92%和20.30%,在50(℃的条件下,浸蚀铜片60天后,CSOME和CSOEE酸值分别增加了35%和36%。温度对不同调和比的生物柴油/柴油的运动黏度影响明显。25℃时浸蚀铜片60天后,B50(CSOME)和B50(CSOEE)运动黏度分别增加14.06%和15.75%；但在50℃时浸蚀铜片60天后,B50(CSOME)和B50(CSOEE)运动黏度分别提高18.7%和19.7%,通过四球摩擦磨损实验机,还考察了棉籽油甲酯生物柴油和乙酯生物柴油与柴油调合油的润滑特性。结果表明：不同碳醇与棉籽油制备的生物柴油对柴油的润滑性能均具有增效作用,且随着生物柴油添加量的增加,柴油的润滑性能得到提高；分别添加体积分数20%的甲酯生物柴油和乙酯生物柴油到0#柴油时,发现调合油的最大无卡咬负荷(PB值)比纯0#柴油分别提升了94.1%和29.4%；而乙酯生物柴油/柴油的减摩性和抗磨性都好于甲酯生物柴油／柴油。最后,采用玻璃表面皿挥发的方法,分别在20℃、30℃和40℃,静风、恒湿的环境条件下,考察了棉籽油脂肪酸甲酯、乙酯及其与0#柴油调合油的挥发性。棉籽油脂肪酸乙酯及其混合燃料的挥发性大小顺序为D>B5>B10>B20>B50>B100。B20、B10和B5三种混合燃料的挥发行为近似0#柴油。棉籽油脂肪酸乙酯调合于0#柴油中,能起到抑制0#柴油挥发作用,生物柴油及其调和油挥发损失量随温度升高而增加。更多还原

【Abstract】 Biodiesel is produced by transesterification with lipid feedstock and alcohol. The biodiesel derived from cotton seed oil and ethanol is really renewable, because the raw material to prepare biodiesel can not depend on petrochemical resources. Cottonseed oil ethyl ester contributes to renewble, non-toxic, biodegradable, higher flash piont and a reduction in most exhaust emissions. Cottonseed oil ethyl ester or blends mixing it with diesel fuel in any proportions can be used as diesel engines fuel directly. The reseach of cottonseed oil ethyl ester has nearly not been reported, and its preparation and performances has not furtherly disussed. Cottonseed oil ethyl ester produced from cottonseed oil and ethanol was investigated in the present dissertation, an eco-friendly process was developed by the optimziton of transesterification parameters. The biodegradability, lubricity, corrosion performance and volatilization behaviors of cottonseed oil ethyl ester were also thoroughly studied. All the results will be beneficial to preparation, transportation storage, usage of the cottonseed and ethanol-derived biodiesel.The kinetics of transesterification for biodiesel produced by cottonseed oil and ethanol in potassium hydroxide was studied well. The transesterification reaction between cottonseed oil and ethanol was carried out with excessful ethanol, the amount of KOH catalyst1.25wt%and reaction temperature at40-78℃. The reaction equilibrium took place after30minutes. The transesterification reaction between cottonseed oil and ethanol was a pseudo second order reaction during the first30minutes and a zero order reaction after30minutes. Reaction rate constants for the transestentcation of cottonseed oil with ethanol at40,60and78℃were0.0996,0.1126and0.1286L/(mol min) respectively, and the activation energy was21.6075kJ/mol. The rate constants of the transesterification reaction is slow, and the reactions demand more activation energy.In order to increase rate constants, biodiesel production by transesterification cottonseed oil with ethanol used tetrahydrofuran (THF) as cosolvent, KOH as catalyst. The main parameters for transesterification were also investigated. The maximal fatty acid conversion of97.90%was observed after1.5h with ethanol/oil of14:1, reaction temperature of78℃, the amount of KOH of1.25wt%and the ratio of THF/oil of1:1. The result showed that triglyceides and ethanol could easily dissolve each other with THF in the reaction mixture. THF has helpful effect on increasing conversion of triglyceides and lessening the time to reaction balance. THF could be used repeatedly by separating from mixture. All fuel properties of cottonseed oil ethyl or methyl ester were compared well with GB/T20828-2007. The biodegradabilities of biodiesels and its mixtures with diesel prepared from cotton seed oil via methyl, ethyl or diesel were investigated by the modified Sturm method. In aquatic aeration cultures, pure cotton seed oil methyl and ethyl esters biodegradability rates were99.7%and99.1%respectively after28days. Biodegradability rates of cotton seed oil ethyl esters in samples of100%,50%,20%,5%,2%were99.7%,95.7%,81.9%,65.4%,61.5%after28days. The more was cotton seed oil methyl and ethyl esters in mixtures, the easier was the biodegradability. The biodegradability of the fuel mixture was enhanced by adding biodiesel.Based on national standard method of petroleum products copper corrosion test (GBAT5096-1990), the corrosion character on copper in cottonseed oil methyl ester and cottonseed oil ethyl ester were detected at25"C and50"C. At the same time, the physical-chemical performances of the two samples were investigated and compared to diesel before and after corrosion. The results showed that variations of the corrosion phenomenon on copper which immersed in the two samples for two months at the25℃and50℃. The corrosion property of cottonseed oil methyl ester was changed seriously. Under the condition of25℃, the acid value of B100(CSOME) andB100(CSOEE) increased by13.92%and20.30%. Under the condition of50℃, the acid value of CSOME and CSOEE increased by35%and36%after60d. Temperature has obvious effect on the kinetic viscosity of biodiesel and its blends. The kinetic viscosity of B50(CSOME) and B50(CSOEE) increased by14.06%and15.75%at25℃, but the kinetic viscosity of B50(CSOME) and B50(CSOEE) increased by18.7%and19.7%at50℃with60d copper corrosion test.Biodiesels were synthesized by the transesterification reaction of cottonseed oil and methyl and ethyl, respectively. The biodiesel/diesel blends were then obtained by mixing the prepared biodiesels and commercial diesel. The lubrication properties of the obtained mixtures were studied on a four-ball tribometer. The results showed that the synthesized biodiesels could improve the lubrication properties of diesel obviously. The increase of the biodiesel had a positive effect on the lubrication properties of the mixtures. Moreover, the lubrication properties could be affected remarkably by the different alcohols. The extreme pressure (PB value) of the mixture was increased by94.1%and29.4%by adding20vol%methyl ester biodiesel and ethyl ester biodiesel, respectively. The biodiesel from ethyl alcohol could improve the lubrication properties more than that from methyl alcohol. Free fatty acids can also affect the lubricity of biodiesel. Finally, the volatilization behaviors of cottonseed oil methyl or ethyl ester and mixtures with diesel were investigated by glass surface dish volatile. The test was conducted in calm and humidity air at20℃,30℃and40℃, respectively. Volatilization loss order of cottonseed oil ethyl ester and it’s blends is D>B5>B10>B20>B50>B100. Volatilization loss will be decreased by diesel blends with cottonseed oil ethyl ester. Volatilization loss of biodiesel and it’s blends increase with temperature imcreasing.更多还原