| Vanillin is the first fragrance synthesized in human history.In addition to being widely used in various types of tobacco,toothpaste,cosmetics and daily chemicals,it can also be used to produce pharmaceutical intermediates.In recent years,the application of vanillin in medicine has gradually become its potential development area.At present,domestic production of vanillin basically uses rectification method for purification and separation.The high energy consumption of distillation and high temperature will affect the content of vanillin.In view of this phenomenon,this study considers energy conservation and environmental protection,practical benefits A systematic study was conducted on the crystallization and purification of vanillin.First,the thermal stability of vanillin was studied,and the change of vanillin content and the content of impurities in the system after 12 h heating at different temperatures were studied.According to the experimental results,the vanillin damage increased with the increase of the experimental temperature.Vanillin was heated at 150 °C for 12 hours under nitrogen protection.Compared with no nitrogen protection,the vanillin damage was significantly reduced.It can be known that blocking the air can effectively protect vanillin.Second,the "equilibrium method" was used to determine the solubility data of o-vanillin in water,ethanol,n-propanol,three pure solvents,and binary solvents with different proportions.The experiments show that o-vanillin is easily soluble in organic solvents such as ethanol and n-propanol,and its solubility in water is relatively small;at low temperatures,the solubility of o-vanillin changes more gently with temperature,and the solubility changes with temperature after a certain temperature Steep;in binary mixed solvents,the solubility gradually increases with the increase of the proportion of organic solvents in water-ethanol.In water-n-propanol,the solubility is maximum when the water-n-propanol ratio is 4: 6,and the solubility decreases sequentially when the ratio is 2: 8,6: 4,8: 2;when water: n-propanol = At8: 2 and the temperature is higher than 288.15 K,liquid-liquid separation occurs.Apelblat simplified empirical equation and Van?t Hoff equation were used to correlate the experimentally measured solubility data in different solvents.By comparing the R2 and RMSD values,it was found that the fitting effect of Apelblat's simplified empirical equation is more ideal.,And the equation is simple,easy to calculate,and more practical for engineering use.In addition,the binary phase diagram of vanillin-o-vanillin was measured,and the lowesteutectic point was obtained.The binary phase diagram can provide a purification direction for any known percentage vanillin-o-vanillin mixture,and can provide basic data support for the actual crystallization of vanillin-o-vanillin in the actual production.From the previous experimental data,we know that vanillin is a thermosensitive substance.At present,crude vanillin is purified by distillation,and high temperature will affect the yield and purity of vanillin.This experiment comprehensively considers the purification of vanillin by melt crystallization from the aspects of energy consumption,environmental protection and new technologies.Combining the solubility data of o-vanillin and the binary phase diagram of vanillin-o-vanillin,after several experimental comparisons and optimizations,the optimal conditions for melt crystallization were determined: 66 ?-46 ?/20 h during crystallization;sweating Process 46 ?-72 ?/13 h.The purity of vanillin can be purified to 98.26%,and the yield is 48.9%.Purification of the mixture of vanillin and ortho vanillin from the company by the melt crystallization method not only has a certain innovation value,but also provides basic data and theoretical guidance for the company's engineering amplification and industrialization design. |
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