Study On Clean Production Technology Of N-propyl Gallate

As a kind of food antioxidant,propyl gallate is widely used at home and abroad.In industrial production,propyl gallate was synthesized in the presence of concentrated sulfuric acid as catalysis by cyclohexane azeotropic dehydration.However,there are certain disadvantages such as high demands on production equipment,nonreusable catalyst,high cost of post-treatment,non-environmental friendship.In contrast,the development of clean production process was studied in this paper,not only the high catalytic efficiency,low production costs,and significantly simplified post-processing.(1)Transesterification:The n-propyl gallate is synthesized,which using an alkaline catalyst via transesterification reaction of methyl gallate and n-propanol.This method avoids a series of shortcomings of concentrated sulfuric acid,but the experimental results show that the yield was too low and there is no industrial application value.(2)The process optimization and improvement were conducted based on the current production process.n-Propyl gallate was synthesised by reactive distillation under solvent-free conditions using concentrated sulfuric acid or p-toluenesulfonic acid as catalyst.In this paper,the influence of multiple process parameters was investigated by orthogonal test.The optimum yield of n-propyl gallate was 88.0%(sulfuric acid as catalyst)and 90.1%(p-toluenesulfonic acid as catalyst).The production time was reduced by this method about 50%compared with the contemporary production process,decreases the amount of catalyst used by about 20%,and does not need water carrying agent,reduces the production cost and improves the production efficiency.But the shortcomings of the catalyst are still existing.(3)A novel process for the synthesis of propyl gallate was investigated by the method of stepwise esterification.The optimum esterification yield was 96.5%(sulfuric acid as catalyst)and 97.0%(p-toluenesulfonic acid as catalyst)by process optimization.When polystyrene sulfonic acid resin was used as the catalyst,the yield of n-propyl gallate was 97.1%under the optimized reaction conditions,and the average esterification yield was 91.2%.This method not only achieved a high yield,but also the catalyst can be reused,and esterification of crude products after a straightforward process was in line with the safety and environmental protection of green technology requirements.