Colombié S, Tweddell R J, Condoret J S, Marty A
Laboratoire de Biotechnologie-Bioprocédés, INSA, UMR 5504, L.A. INRA, Complexe Scientifique de Rangueil, 31077 Toulouse Cedex 04, France.
Biotechnol Bioeng. 1998 Nov 5;60(3):362-8.
During continuous lipase-catalyzed oleic acid esterification by ethanol in n-hexane, the oleic acid conversion, initially at 95%, decreases to 20% after 2 h. This decrease is caused by the accumulation of the water produced in the course of the reaction in the packed-bed reactor (PBR). In order to improve the PBR efficiency, it is necessary to evacuate the water produced. In this study, different approaches have been tested to control the water content in the PBR during continuous esterification. The first approach consisted in improving the water solubility by increasing the reaction medium polarity. The addition of polar additives to n-hexane, the use of more polar solvents, and the use of solvent-free reaction medium were tested as a means to favor the water evacuation from the PBR. First of all, the use ofn-hexane supplemented with acetone (3 M) or 2-methyl-2-propanol (1 M) enabled the conversion to be maintained at higher values than those obtained in pure n-hexane. The replacement of n-hexane by a more polar solvent, like the 5-methyl-2-hexanone, resulted in the same effect. In all cases, conversions at steady-state were always less than 95%, as obtained in pure n-hexane. This is explained by a decrease in the enzyme activity due to the increase in the medium polarity. Nevertheless, an increase in enzyme quantity allowed 90% conversion to be maintained during 1 week using 3 M acetone amended n-hexane. Good results (a steady-state conversion of about 80%) were obtained when esterification was carried out in a solvent-free reaction medium containing 2 M 2-methyl-2-propanol as a polar additive. The second approach consisted in the evaporation of the accumulated water by use of an intermittent airflow. Although this process did not enable constant esterification rate to be maintained, it did enable the initial conversion (95%) to be restored intermittently.
在正己烷中，脂肪酶连续催化乙醇与油酸进行酯化反应的过程中，油酸转化率最初为95%，2小时后降至20%。这种下降是由于填充床反应器（PBR）中反应过程产生的水不断积累所致。为提高PBR效率，有必要排出产生的水。在本研究中，已测试了不同方法来控制连续酯化过程中PBR内的水分含量。第一种方法是通过增加反应介质极性来提高水的溶解度。向正己烷中添加极性添加剂、使用极性更强的溶剂以及使用无溶剂反应介质，都作为促进水从PBR排出的手段进行了测试。首先，使用添加丙酮（3 M）或2-甲基-2-丙醇（1 M）的正己烷，能使转化率维持在比纯正己烷中更高的值。用极性更强的溶剂如5-甲基-2-己酮替代正己烷，也产生了相同效果。在所有情况下，稳态转化率始终低于纯正己烷中的95%。这是由于介质极性增加导致酶活性降低所致。然而，增加酶量可使使用3 M丙酮改性正己烷时在1周内维持90%的转化率。当在含有2 M 2-甲基-2-丙醇作为极性添加剂的无溶剂反应介质中进行酯化反应时，取得了良好结果（稳态转化率约为80%）。第二种方法是利用间歇气流蒸发积累的水。尽管此过程无法维持恒定的酯化速率，但确实能间歇性地恢复初始转化率（95%）。
