| The wet spinning process with sodium thiocyanate as solvent was widely used for acrylic fiber production at home and abroad, in which the consumption of sodium thiocyanate was the key factor affecting the production cost. More than 600 tons of sodium thiocyanate was consumed every year in the Acrylic Fiber Plant of Daqing Petrochemical Company, which was the average level among the national craft brothers. Research was performed aiming at the low recovery rate of the waste recovery system and the high pH, high sulphate and high NVI(non-volatile impurities) in the sodium thiocyanate product. First, More than 10 resins from the major resin plants around China were tested, as a result, a kind of weak-base anion styrene resin with larger pores was chosen. This resin was characterized by larger capacity and concentrated behavior of exchange and regeneration. After the employment of the new resin, the capacity of every working cycle was increased from 400kg to 700kg, hence greatly enhancing the capacity of the unit. Secondly, a kind of full capacity exchange technique was adopted, in which excessive sodium thiocyanate was added to convert most of the functional groups into thiocyanate type. As a result, impurities were separated from the product, and product with low NVI was gained. Thirdly, the leakage liquid was recycled so as to improve the recovery rate of sodium thiocyanate. Fourthly, a kind of set alkali solution technique was adopted to separate the alkaline from the product, hence a neutral product was produced and the consumption of sodium hydroxide was reduced. Since the newly developed process was put into commercial use in 2003, the plant had been running steadily. It was determined that the recovery rate of sodium thiocyanate was increased from 56.4% to 84.7%, pH of the product was reduced from 12.4 to 7.6, NVI of the product was reduced from 0.86% to 0.43%, and the removal rate from 88% to 93%. As a result, an annual profit of 2 million RMB was gained. |
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