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NITROSATION OF LIGNOSULFONATES BY ELECTROCHEMICAL TREATMENT
Abstract
Technical lignins are by-products formed in the amount of about 70 million tons annually during the chemical and biochemical processing of plant biomass in the world. Most technical lignins are burned for energy. No more than 2% of technical lignins are supplied to the market mainly in the form of lignosulfonates due to their good solubility and surface activity. Modification of lignosulfonates can improve their properties and expand the field of practical use. In this study, we carried out a modification of sodium lignosulfonates by nitrosation under the conditions of electrochemical treatment in the presence of sodium nitrite. Chemical nitrosation with a mixture of sodium nitrite and hydrochloric or acetic acid was also performed for comparison. Electrochemical processing was performed in a diaphragmless cell using stainless steel electrodes. The process was controlled by spectrophotometry of the resulting solutions with a change in the voltage (3?20 V) and sodium nitrite consumption (0?30%) for 15?40 min. The final solutions of nitrosated lignosulfonates were subjected to ultrafiltration. The molecular weights of the products in concentrates were determined using high performance liquid chromatography. The elemental composition of nitrosated lignosulfonates in the concentrate was determined after drying. The nitrogen content in the product reaches 1.8%. The number-average molecular weight changed from 6.3 kDa (initial lignosulfonates) to 7.3?20.7 kDa depending on the processing conditions. Electrochemical nitrosation eliminates the use of acid and achieves a similar degree of nitrosation in less time.
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