导　　师： 曾新安

学科专业： 082202

授予学位： 硕士

作　　者： ;

机构地区： 华南理工大学

摘　　要： 本文以乳酸-乙醇-水体系作为黄酒模拟体系,研究了脉冲电场/(PEF/)对乳酸乙醇酯化反应、乳酸乙酯水解反应的影响,并结合宏观分析采用气质联用、红外光谱的手段从微观角度探究了PEF处理对反应物之一的乳酸水溶液的影响。 1.研究了脉冲电场的电场强度、单次处理时间、反应温度对乳酸乙醇酯化反应的影响,同时通过数据的归纳计算得出脉冲电场对反应活化能的影响。反应温度、反应时间、流速一定时,PEF对乳酸乙醇酯化反应的促进作用随着场强的增强而增强。反应温度30℃,流速50mL//min,反应时间为10h时,场强分别为15、20、25kV//cm的PEF处理所生成乳酸乙酯的量是未施加电场时的1.7、1.9、2.1倍。随着流速不断减少,单次处理时间不断增大,同一循环反应时间内乳酸乙酯生成量不断增加。同一温度下,施加电场相对未施加电场对反应均具有明显的促进作用。PEF处理改变了反应的活化能,20kV//cmPEF处理使反应的活化能从43.43kJ//mol降至25.05kJ//mol。 2.研究PEF作用下不同反应物体系中醇酸比和电导率对反应的影响,并在高电导率体系中进行了PEF处理热对比实验。结果显示,调整电导率后,PEF处理下醇酸比分别为0.5：1、1：1、1.5：1、2：1的四个反应体系仅受醇酸比的影响。体系随着醇酸比的增大,即体系中乙醇浓度的增大,乳酸乙酯的生成量不断增加。未调整电导率,PEF处理下的四个反应体系受醇酸比和电导率两个效果相反的因素的综合影响。场强、流速、反应温度和时间一定时,乳酸乙酯生成量醇酸比1：1体系>0.5：1体系>1.5：1体系>2：1体系>1：1不施加电场体系。热对比实验结果显示：即使在高电导率体系中,仍然存在PEF的非热效应促使酯化反应的进行,且所占比例达到30/%以上 3.考察了PEF处理对乳酸乙酯水解反应的影响。结果显示PEF处理对体系的pH值影响较小,促进乳酸乙酯水解的作用极其微弱。随着PEF场强的增加,体系的电导率值不断升高。 4.简化反应体系,以反应物之一的乳酸水溶液体系为研究对象,从宏观和微观的角度探索了PEF处理对体系的影响。PEF处理对体系的电导率值、粘度影响不明显,而却使体系中的pH值有极微弱的减小。气质联用分析则显示,PEF处理不能使乳酸水溶液产生新的物质,不会造成体系生成新的杂质而与乙醇反应。红外光谱检测结果显示,随着PEF处理场强的逐渐增大,醇O-H伸缩振动频率分别为3431、3430、3418、3407、3401cm-1,吸收峰逐渐向低波数区移动。这说明随着场强的增加,醇O-H周围的氢键缔合逐渐增强。C=O、酸O-H、酸C-O吸收峰位置总体变化不大。随着处理时间的延长，C=O、酸O-H、酸C-O吸收峰位置总体变化不大。醇O-H的特征吸收峰位置则小范围有所波动，最终有向低波数区移动的趋势。PEF处理过的乳酸水溶液经过55天放置后，体系内氢键缔合结构有所破坏。 Latic acid-ethanol-water system was a simulation system of rice wine.Pulsed electric field was used to research its effect on esterification of lactic acid and ethanol、reverse reaction and lactic acid-water solution in this paper. Gas chromatography mass spectrometry /(GC-MS/) and Fourier transform infrared spectrum/(FTIR/) was applied to study the change of the lactic acid-water solution microscopic structure. 1. The influences of electric field intensity, single treatment time with the temperature on the esterification were studied. Then, the variation of activation energy during the esterification was explored. The results indicated that when the reaction temperature was30℃, flow rate was50mL//min, by applying15,20,25kV//cm PEF for10h, the productions of ethyl lactate were1.7,1.9,2.1times of PEF untreated sample, so the reaction was enhanced with increasing intensity; the productions of ethyl lactate were increased with increasing single treat time when the other condition were same; the reaction was enhanced obviously compared to untreated sample at the same temperature; the activation energy was changed by applying PEF,it is significantly decreased from the original43.43kJ//mol to25.05kJ//mol by applying20kV//cm PEF treatment. 2. The influences of ethanol//lactic acid molar ratio and electric conductivity on the etherification were analyzed and non-thermal effect of PEF was explored at high electric conductivity system. The results indicated that as the molar ratio between ethanol and lactic acid was increased from0.5:1to2:1, the production of ethyl lactate was increased gradually as the four systems adjusted the same electric conductivity; when the four systems were not adjusted the electric conductivity, the production of ethyl lactate decreased gradually exhibited an order as1:1,0.5:1,1.5:1,2:1systems; non-thermal effect of PEF was more than30/%of the total enhancement at the high electric conductivity system. 3. Effect of PEF on esterification reverse reaction was studied. It was demonstrated that the pH of the ethyl lactate-water solution have a little change by applying PEF treatment, the enhancement of ethyl lactate hydrolysis was very weak; the electric conductivity of the ethyl lactate-water solution increased with increasing PEF intensity. 4. The macroscopic and microscopic structure change of lactic acid-water solution by applying PEF treatment was explored. The results indicated that electric conductivity and viscosity of the lactic acid-water solution almost have no change after PEF treatment while the pH has a little decrease; GC-MS detection result indicated that no new substance emerged by PEF treatment, so there was no new impurity disturbed the esterification of lactic acid and ethanol; FTIR results indicated that O-H stretching band move to low wave number area with increasing intensity from0kV//cm to33.3kV//cm while C=O and acid O-H,acid C-O stretching band have little change; treatment times were0,0.5,1,1.5,2,2.5,3,3.5,4h, respectively.O-H stretching band fluctuated in a small range then tend to low wave number area while C=O and acid O-H、acid C-O stretching band have not a notable change.The strength of hydrogen bonding at Latic acid and water systems which have been treated by PEF was weaker compared to the former after55days storage.

关 键 词： 脉冲电场 乳酸 乙醇 乳酸乙酯

分 类 号： [O621.25]

领　　域： [理学] [理学]