Preparation of chromium anhydride

Abstract

A process for preparing chromic acid anhydride includes such steps as proportionally mixing concentrated sulfuric acid with solution of sodium bichromate, reacting white stirring for 2-3 hr, vacuum evaporating at 105-125 deg.C to educe out crystal of chromic acid anhydride, centrifugal dewatering at 80-95 deg.C, washing with the solution of chromic acid anhydride at 85-95 deg.C, and baking at 100-105 deg.C for 2-3 hr.

Description

technical field [0001] The invention relates to inorganic chemical raw materials, and more specifically relates to a preparation method of chromic anhydride. Background technique [0002] Chromic anhydride is one of the main products of chromium salt series in inorganic salts. It is an important inorganic chemical raw material and is widely used in electroplating, metal passivation, catalysts for manufacturing fertilizers, medicine, chrome yellow pigments, chromium oxide green, and mordants and other industries. , plays an important role in the national economy. [0003] At present, the production of industrial chromic anhydride in various countries all over the world uses sodium red alum as raw material, and the production processes include crystallization, electrolysis and melting. The crystallization method is a clean process and is recognized as the most advanced production method in the world, but this technology is only owned by a British company, and its technical pl...

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Problems solved by technology

Electrolysis is also a cleaning process, currently only used by two foreign chromium salt factories, but due to the large power consumption and high cost, it is difficult to be accepted by other manufacturers

The current methods of producing chromic anhydride in the world, including my country, are the melting method. The disadvantages of the melting method are: a. The temperature of the reaction process is high, not only chromium-containing water vapor and hydrogen chloride escape, but also due to impurities in the red alum sodium Sodium chloride participates in the reaction to generate highly toxic reddish-brown gas chromium chloride, which corrodes production equipment, damages workers' health and pollutes the environment

b. Due to the late stage of the reaction process (including clarification, stratification, and separation), the material temperature (200°C) is higher than the decomposition temperature (190°C) of chromic acid, resulting in the decomposition of chromic anhydride into C r 3+ , and aggravated with the rise of temperature, which not only reduces the yield (usually 92%), but also affects the quality, resulting in inhomogeneous product quality

c. The by-product sodium bisulfate contains quite high water-soluble C r 3+ It is difficult to comprehensively utilize water-insoluble matter. Even if it is reused for neutralization or acidification of sodium chromate, new waste residue containing chromium will be produced, which can only be stored. In addition, the discharge of sodium bisulfate is large, which aggravates the environment. Pollution