Study On The Process For Preparation Of High-purity Solid Glyoxylic Acid

Glyoxylic acid is an important organic chemical intermediates.It is sold mainly in the form of 30wt%-50wt% aqueous solution,which also contains significant amount of water,oxalic acid and colored impurities.This form of glyoxylic acid could not meet today’s pharmaceutical and food industries’ demand for high quality glyoxylic acid.And the aqueous solution can not be utilized in the non-aqueous phase reaction,limiting the application scope of glyoxylic acid.Therefore there is a strong need for high-purity solid glyoxylic acid(monohydrate glyoxylic acid ≥ 98wt%)in today’s chemical market.Currently there is no domestic production of high-purity solid glyoxylic acid..This thesis researches on the processes for the preparation of high-purity solid glyoxylic acid through a sieses of single variable experiments and orthogonal experimentation.In the end,solid glyoxylic acid with 98% purity was prepared using processes developed in the thesis research.Total yield of its up to 79% after repeated crystallization.The prepared solid glyoxylate were characterized and confirmed by IR,1H NMR,13 C NMR and its melting point was measured as 51.2-52.1oC,consistent with the value reported in literature and its purity is also confirmed by HPLC.The high-purity solid glyoxylic acid could be prepared through six process steps: decolorization,removal of oxalic acid,concentration,crystallization,filtration and vacuum dessication.The decolorization of glyoxylic raw materials was carried out with active carbon,reducing the color degree of the raw material from 450 to 150.The oxalic acid impurity was removed via precipitation with a specid metal ion,lowering the concentration of oxalic acid from 0.92wt% to 0.22wt%;Thereafter,the solubility of glyoxylic acid in water at different temperatures was studied.Then we studied the influence of each single variable on the yield,purity,crystalline form and appearance of the glyoxylic crystal.Those single variables include initial crystallization concentration,initial crystallization temperature,amount of crystals seed,stirring speed,cooling rate,final temperature,the holding time,filtration,drying method and time.It is found that the most significant factor influencing solid crystalline purity and yield is the initial concentration.The stirring speed mainly affects glyoxylate solid crystalline form and size.Other factors can also affect the product purity and yield to some different extent.Based on the results of single variable experiments,orthogonal experiment was conducted to obtain the optimal crystallization conditions: the initial concentration(monohydrate glyoxylic acid)75wt%,the initial crystallization temperature at 5oC,crystal seed at an amount of 0.07wt%,stirring speed at 150r/min,cooling rate at 4oC/h,final crystallization temperature at-5oC,holding time at 2.5h,nitrogen atmosphere protection for filtration,vacuum drying for 15 hours at 20 ℃.Under the optimal conditions,the purity of solid glyoxylic acid can reach more than 98%.Finally,we studied the recycling of the mother liquor of each crystallization to improve the overall yield of crystallization.It is found the mother liquor could be reused twice to achieve 79% yield and 98% purity of the solid glyoxylic acid.The purity decreases if the mother liquor was used three times or more.An cost-effective process for the prepation of highpurity solid glyoxylic acid has been successfully developed.This developed process is stable,effective and could be used in the large scale production of solid glyoxylic acid.The research result of the thesis has a great significance in guiding industrial production of high-purity solid glyoxylic acid.