Production of lactones from glucose
Microbial fermentation method Add nutrients such as magnesium sulfate, potassium dihydrogen phosphate and diammonium hydrogen phosphate to 15% to 35% glucose solution, inoculate Aspergillus niger strain NRRL3, and culture under aeration at 30°C and Ph6.5 for 40h . Filtrate the secluded liquid, and then post-process to obtain lactone crystals.
Glucose oxidase method: Under the conditions of 35-37°C and Ph6, in ethanol aqueous solution (such as 50%), glucose oxidase oxidizes glucose into a balanced solution of lactone and gluconic acid, and catalase is also added during the reaction , to decompose the hydrogen peroxide produced. The obtained gluconic acid solution can obtain lactone crystals through the above-mentioned post-treatment method, and the yield of this method can reach 98%. Catalytic oxidation method will 64mgPdCl. Dissolve in 1mL of concentrated hydrochloric acid, add appropriate amount of water and 3.8g of refined activated carbon (200 mesh), adjust Ph=5 with 10% NaOH solution, then stir the mixture at room temperature and add 67mg of NaOH. (dissolved in 2mL water) solution, the ionic palladium is reduced to metallic palladium, and adsorbed on activated carbon, filtered, washed with water, and dried to obtain 3.838g1% Pd-C catalyst. Add the above-mentioned catalyst to 300g of 8% glucose aqueous solution, feed air at 50°C, and add NaOH solution dropwise at the same time to keep Ph=9.0~9.5. The resin was processed to obtain 310 g of gluconic acid solution. Concentrate under reduced pressure at 70°C to a concentration of 80% to 85%, cool to below 40°C, add seed crystals, filter and dry to obtain 22.6g of lactone after crystallization, and then concentrate and crystallize the filtrate to obtain 5.3g of the product. The total yield is 93.3%.
Production of Lactone Using Calcium Gluconate as Raw Material
In this method, calcium gluconate is decomposed with inorganic acid or decalcified by ion exchange resin to obtain gluconic acid solution. For example, add 100 parts of concentrated sulfuric acid to 500 parts of water, then add calcium gluconate, keep warm at 60-85°C for 1.5h; let stand for 12h and then filter, add oxalic acid to the filtrate, and keep warm at 50°C for 1h; stand and filter to get Gluconic acid solution can be processed to obtain lactone. There are several post-processing methods.
The non-solvent crystallization method concentrates the gluconic acid solution under reduced pressure to a slurry state, adds low-level ketone non-solvents, slowly stirs and cools to precipitate crystals, and then separates, washes, and dries to obtain the finished product. This method is easy to operate and the yield is high.
Fractional crystallization
Concentrate the gluconic acid solution at 52-54°C to 78%-85%, cool to 47-48°C, add gluconolactone seed crystals, and continue to concentrate, and separate the first batch of lactone after the seed crystals grow up crystallization. The mother liquor continues to evaporate and concentrate in the same way. The crystallization is washed and dried to obtain the finished product, with a total yield of 75% to 78%. The advantage of this method is that no organic solvent is used, but the concentrated solution has a high viscosity and the operation of crystallization and separation is difficult.
The azeotropic dehydration crystallization method adds C3-C4 alkanols to the gluconic acid solution, and azeotropically dehydrates at 50°C and 16kPa. Then throw crystal seeds into the concentrated solution, cool down and crystallize, and then separate, wash and dry to obtain the finished product. The advantage of this method is that the viscosity of the system is low, the separation operation is easy, and the single-pass yield can reach more than 91%.
