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Study On The Green Synthesis Of Glycolic Acid And Its Refining Technology

Posted on:2014-01-16Degree:MasterType:Thesis
Country:ChinaCandidate:L L ZhaoFull Text:PDF
GTID:2251330401980000Subject:Applied Chemistry
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Glycolic acid, known as hydroxyacetic acid, containing both hydroxyl and carboxylgroups in its molecular structure leading to its highly reactive activities, is extensivelyused in chemical cleaning, cosmetic industry, pharmaceutical industry and construction.So glycolic acid is largely demanded recently. However, only a few factories produceglycolic acid indoors, and those old synthetic routes are against the demand for marketand environmental protection. Several common synthetic routes are as follows:Chloroacetic acid hydrolysis method, cyanidation and formaldehyde carbonylationmethod.These processes usually suffer from a series of drawbacks, such as seriousenvironmental pollution and inefficiencies. Therefore, it is of great necessity to explore anew route.Glyoxal is an important intermediate product of the80,0000tons of ethyleneengineering industry chain in Wuhan, so it’s imperative to research the follow-up productusing glyoxal as raw material. After referring to extensive literatures on the synthesis ofglycolic acid, a new method of disproportationation reaction of glyoxal to produce glycolicacid is found. The optimal synthetic conditions of the catalytic disproportionation reactionwas determined by investigating on the the type and concentration of catalyst, reactiontemperature, reaction time and other factors affecting the glyoxal conversion rate. At thesame time, different refining methods of hierarchical ion precipitation, multi-stagecirculation crystallization and electrodialysis, ion exchange method were used to purify theprimary glycolic acid. The separation and purification conditions of glycolic acid fromdifferent catalytic systems were obtained.NaOH catalytic system. First, NaOH was used to catalyse glyoxal to producesodium glycollate, and the influence of concentration of NaOH, reaction time, reactiontemperature, and concentration and dosage of acid on the yield were studied. Thenelectrodialysis and ion exchange resin were used to remove Na+respectively. Inelectrodialysis process, we studied the influence of initial concentration of sodiumglycollate, material flow rate and durability of membranes on the electrodialysis efficiency. The results showed that the best operating condition was: the concentration ofsodium glycollate was1mol/L, the flow rate was20L/h. In addition, the membranesshould be cleaned regularly in order to ensure the efficiency. In the ion exchange resinmethod, the influence of exchange time and temperature on the adsorption effect wasstudied. The result was as follows: when the adsorption time was90min and theadsorption temperature was20C, the yield was high.Ca(OH)2catalytic system. First, Ca(OH)2was used to catalyse glyoxal to producecalcium glycollate, the concentration of Ca(OH)2, reaction time, reaction temperature, andconcentration and dosage of acid were studied. The optimized result was as following:mass concentration of Ca(OH)2was about20%, the reaction temperature was between10-30C, reaction time was1h, H2SO4was chosen as acidulant and the amount of H2SO4was same to the amount of Ca(OH)2, BaAc2as anionic remover. At last, the crude productwas purified by a multi-stage crystallization using60-70%glycolic acid solution and highpurity of99%glycolic acid crystal was obtained. Finally, the product was analysed by highperformance liquid chromatography (HPLC) and infrared spectroscopy (IR).
Keywords/Search Tags:Glycolic acid, glyoxal, catalytic disproportationation reaction, separation and purification
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