【作者】 于海银；

【导师】 崔政伟；

【作者基本信息】 江南大学 ， 机械设计及理论， 2008， 硕士

【摘要】 本课题研究了利用微波真空加热技术对液体物料中的低浓度醇类物质进行分离,主要以乙醇和甲醇为例,研究出了分离动力学数学模型,并对二者的分离效果进行了比较,然后将该技术应用于低醇黄酒的生产,并对生产出的低醇黄酒的品质、特性进行了检测和评定,最后对小型连续性微波真空分离设备进行展望。甲醇和乙醇的整个微波真空分离过程,可分为两段:恒速段和降速段,恒速段的速率可依据能量平衡方程计算,而降速段不能根据能量平衡方程计算,从经验角度出发,找出影响分离常数的主要因素,赋予它们各因素指数的乘积关系,然后利用实验结果回归得到各指数和未知常数。分析不同微波真空条件下的分离曲线得出,分离速率随微波功率和真空压力的增大而增大。另外,溶液中的甲醇和乙醇含量并不能降至零,而是降到其所能达到的最低浓度后基本保持不变,这主要和它们本身的化学性质以及分子间作用力有关。对相同浓度的甲醇和乙醇水溶液进行实验,研究二者的温度分布和温度变化情况。实验表明,整个加热过程主要分为两个阶段,第一阶段为均匀加热段,在该阶段,溶液的温度线性增至接近该真空度下水的饱和温度,此阶段基本没有水分和醇的蒸发,且均匀加热段的时间非常短;第二阶段为温度缓慢上升段,在该阶段,水分和醇大量从溶液内部蒸发迁出,几乎没有阻力;分离后期,当醇的浓度降至最低时,溶液中水分继续吸收微波能,温度继续缓慢上升。甲醇和乙醇均属于低碳醇化合物,但是因为二者的介电特性不同,所以吸收微波的能力不同,导致分离速率的不同,在相同的微波真空操作条件下,单一的乙醇和甲醇水溶液中后者的分离速率要大于前者,而在甲醇和乙醇的混合溶液中,乙醇分离速率比单一的乙醇水溶液中乙醇分离速率略有增大,甲醇的分离速率与单一的甲醇水溶液的分离速率相比增加的比较明显。将微波真空分离技术应用于经过正常发酵生产的黄酒,对其中的低浓度乙醇进行分离,通过正交实验找出乙醇含量降至最低的条件,进而达到制取低醇黄酒的目的,并与蒸馏法制得的低醇黄酒进行比较。微波真空法制得的低醇黄酒不仅效果好、所需时间短,而且颜色基本没有变化,而蒸馏法所需时间长,颜色明显加深,而且所达到效果并不理想。应用固相微萃取,气-质联谱技术对两种方法处理前后黄酒中的挥发性风味成分及其含量的变化进行了检测和比较,结果显示,其挥发性成分含量有一些变化,但不影响黄酒固有的风味。应用微波真空分离技术对稀溶液中的醇类物质进行分离是可行的,但是,间歇式微波真空分离设备效率低下,所以,研制小型连续式微波真空分离设备是非常有必要的,连续性设备不仅分离速度快,可以极大地提高生产能力,而且比间歇式设备能够达到更好的分离效果。更多还原

【Abstract】 The sepatation of low concentration alcohol of liquid material by microwave-vacuum technique and the dynamics mathematical model were studied in this paper, mainly take the ethyl alcohol and the methyl alcohol as the tested materials, and their separation effects were compared, then apply this technology to produce the low-alcohol rice wine. The qualities and functionality of the low-alcohol rice wine are tested by experiments. Finally, the small continuous microwave vacuum separation equipment was proposed.The microwave-vacuum sepatation process of methanol and ethanol experienced two periods. The constant rate period can be described by a theoretical model based on the energy conservation. However the model wasn’t fit for the period when the rate declined. Here with an empirical model is chosen and the effect of process variables was embodied in the expression of the phenomenological parameters. The regression method is used to estimate the best model parameters. The separation curves were tested and found that the separation rate increased with the improving of the microwave power and the vacuum pressure. Moreover, the content of methanol and ethanol in the solution cannot drop to zero, but after falling the lowest density which it can achieve and maintaining invariability, maybe this is related to their chemical property as well as the intermolecular action.Temperature distribution and changes were tested with the same concentration of methanol and ethanol-water solution in the experiment. The experiments showed the heating process mainly experienced two distinct periods: a warming-up period without removal of moisture and alcohol when the solution temperature increased linearly with heating time until it reached the corresponding saturation temperature of water at the vacuum pressure; a slow rise period in which most of the moisture and alcohol evaporated and flowed out of the sample efficiently with little resistance; in later period, when the alcohol concentration decrease to the lowest value, the moisture continues to absorb the microwave energy, the temperature of the solution continues to rise slowly.The methanol and ethanol belong to the low-carbon alcohol compound, but their dielectric characteristic are different, therefore the abilities of absorption microwave are different, resulting in the segregation rate are different. In the same vacuum pressure, in the sole ethanol and methanol-water solution the methanol’s segregation rate is bigger than the former, but in mix ethanol and methanol-water solution, the segregation rate of ethanol increases slightly, but the segregation rate of methanol increases quite obviously.Appling the microwave vacuum separation technology to produce the low-ethanol rice wine e. g., separating the ethanol from it. It was found that the content of ethanol can be dropped to the lowest by microwave vacuum heating. Compared to the distilled one the low-ethanol rice wine not only have good color and flavor, but also retain the most nutrition resulted from shorter heating and low temperature. The volatiles of originol rice wine, rice wine after distillation and microwave vacuum heating were concentrated by solid-phase microextraction (SPME), separated and identified by gas chromatography–mass spectrometry (GC-MS). By comparison the experiment dates, it can be found that low-ethanol rice wine prepared by the current methods was a little changes of the compositions and contents of flavors.It’s feasible for separating alcohol of dilute solution using the microwave vacuum heating technology, but the efficiency of the intermittent microwave vacuum separation equipment is low, the development of small continuous microwave vacuum separation equipment is necessary. It’s will not only sharpen the productivity enormously, but also can achieve the better separation effect compared to the intermittent equipment.更多还原