Mercuric chloride, catalysts

Hydrochloric acid may conveniently be prepared by combustion of hydrogen with chlorine. In a typical process dry hydrogen chloride is passed into a vapour blender to be mixed with an equimolar proportion of dry acetylene. The presence of chlorine may cause an explosion and thus a device is used to detect any sudden rise in temperature. In such circumstances the hydrogen chloride is automatically diverted to the atmosphere. The mixture of gases is then led to a multi-tubular reactor, each tube of which is packed with a mercuric chloride catalyst on an activated carbon support. The reaction is initiated by heat but once it has started cooling has to be applied to control the highly exothermic reaction at about 90-100°C. In addition to the main reaction the side reactions shown in Figure 12.6 may occur. 

On November 8, 2000, U.S. EPA listed as hazardous two wastes generated by the chlorinated aliphatics industry.18 The two wastes are wastewater treatment sludges from the production of ethylene dichloride or vinyl chloride monomer (EDC/VCM), and wastewater treatment sludges from the production of vinyl chloride monomer using mercuric chloride catalyst in an acetylene-based process. 

Vinyl chloride can be synthesized by reaction of acetylene with hydrochloric acid over a mercuric chloride catalyst at 500 K and 5.0 atm total pressure. An undesirable side reaction is the subsequent reaction of vinyl chloride with HCl. These reactions are illustrated below. 

On the basis of this correlation, Hutchings predicted that gold would be the most active catalyst for ethyne hydrochlorination [255], and his subsequent research confirmed this prediction [252,253,256-259]. Gold catalysts were found to be about three times more active than the commercial mercuric chloride catalysts (see Fig. 6.7). 

Gold catalysts supported on activated carbon were found to be about three times more active than commercial mercuric chloride catalysts for vinyl chloride production and to deactivate much less rapidly than other supported metal catalysts. Deactivation can be minimised if high loadings of gold are used [18,248,249], Also, Au catalysts can be reactivated by treatment offline with HCl or CD, and by co-feeding NO with the reactants from the start of the reaction, deactivation could be virtually eliminated [259]. Gold is thus the catalyst of choice for this reaction [6,7,18,213,248,249,258,259],... 

Vinyl chloride was first discovered in the early 1800s. It was made from the reaction of dichloroethane and alcoholic potash. Later it was discovered that vinyl chloride polymerized spontaneously on prolonged exposure to sunlight, and studies of the white solid product, polyvinyl chloride, were carried out and published in 1872. In 1912, a commercial process for vinyl chloride produced from acetylene and hydrochloric acid with a mercuric chloride catalyst was patented in Germany and assigned to Chem-ische Fabrik Griesheim-Electron. By 1930, vinyl chloride was being produced as a commercial product based on this process 117,18]. 

Production of vinyl chloride by the gas-phase reaction of HCl and acetylene with a mercuric chloride catalyst. Small amounts of water are removed from both feed gases by adsorption to prevent corrosion of the reactor vessel and acetaldehyde formation. 

Vinyl chloride (chloroethene). The production of vinyl chloride naturally attracted the attention of those companies already involved in chlorination processes. The quantities of by-product hydrogen chloride available were often an embarrassment and the relatively facile production of vinyl chloride from acetylene and anhydrous HCl, over a supported mercuric chloride catalyst, provided a valuable outlet. 

A. M. Reeves and Capt N. H. Hale, M-1 Process Development, Mercuric Chloride Catalytic Process, Corrosion Resistance of Miscellaneous Materials to Mercuric Chloride, Catalyst Solution and Crude M-1. TDMR 326, 21 Nov 41. 

Patents for his process were issued to Griesheim-Electron in 1912/1913. They described a mercuric chloride catalyst supported on coke or pumice. The early catalysts described in 1912 could only operate for short periods because mercury compounds sublime at reaction temperature. Although the 1913 patent described reaction in aqueous solution with the mercuric chloride catalyst, this process was never used industrially. A further patent in 1913 claimed that the process only took place in the presence of the mercury catalyst that accelerated the reaction. ... 

With mercuric salt catalysts, hydrogen chloride adds to give 2-chloroallyl alcohol, 2-chloroprop-2-en-l-ol [5976-47-6] (27). 

Until about 1980, mercuric chloride was used extensively as a catalyst for the preparation of vinyl chloride from acetjiene (7). Since the early 1980s, vinyl chloride and vinyl acetate have been prepared from ethylene instead of acetjiene, and the use of mercuric chloride as a catalyst has practically disappeared. 

WeU-cleaned aluminum filings react at room temperature in the presence of mercuric chloride (20,21). In an autoclave, metallic aluminum and ethyl alcohol react without a catalyst at 120°C (22). The reaction can also be promoted by the addition of sodium ethoxide (23). Aluminum should be avoided as a material of constmction for ethanol service. 

Halogenation and dehalogenation are catalyzed by substances that exist in more than one valence state and are able to donate and accept halogens freely. Silver and copper hahdes are used for gas-phase reactions, and ferric chloride commonly for hquid phase. Hydrochlorination (the absoration of HCl) is promoted by BiCb or SbCl3 and hydrofluorination by sodium fluoride or chromia catalysts that form fluorides under reaction conditions. Mercuric chloride promotes addition of HCl to acetylene to make vinyl chloride. Oxychlori-nation in the Stauffer process for vinyl chloride from ethylene is catalyzed by CuCL with some KCl to retard its vaporization. 

When they are used as catalysts, such as sulfuric and hydrofluoric acid and mercuric sulfate and mercuric chloride. 

CH3.CHCH2, col liq having a smell taste resembling chloroform, fr p -97.6°, bp 57.3°, flash p -8.5°, d 1.1601 at 30°, nD 1.41638 at 20°, Qcomb 267.4 kcal/mol at Cv expl limits in air 5.9 15.9% by vol less narcotic but more toxic than chloroform can be produced by reacting HC1 with vinyl chloride in the presence of Al, Ferric or Zn chloride catalyst, or by reacting HC1 with acetylene in the presence of mercuric-ferric chloride catalyst at RT (Refs 1 35 p 148)... 

It is convenient, however, to use the commoner monochloride, with which a similar reaction readily occurs at 75° to 80° C. the sulphur produced can be reconverted continuously into monochloride by means of a current of chlorine, and the formation of the thionyl chloride can be assisted by the addition of suitable catalysts, such as antimony trichloride or mercuric chloride. 

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