Hydrodechlorination process

HyChlor Formerly called DHC. A catalytic hydrodechlorination process which converts organic chlorides to hydrogen chloride and saturated hydrocarbons. The UOP HyChlor process recovers and recycles both the organic and inorganic reaction products in order to minimize waste disposal requirements and maximize yield. Used for treating wastes from the production of chlorinated petrochemicals such as vinyl chloride. Developed by UOP but not commercialized as of 1992. 

Murena, F., and E. Schioppa. 2000. Kinetic analysis of catalytic hydrodechlorination process of polychlorinated biphenyls. Appl. Catal. B Environ. 27(A) 257-67. 

The subject of this paper is the investigation of chlorine-containing nickel silicide phases. These are obtained by the reaction of silicon-rich phases with nickel(ll)chloride in evacuated ampoules during sufficiently long testing periods (Eq. 3). The compounds thus obtained have chlorine contents between 0.02 and 0.6 wt. %. In generally, the chlorine-containing silicides and their route of formation can be used as models to describe the catalytically active phases in the hydrodechlorination process [4],... 

Thus, as is the case for the st pincer derivatives with nickel, Moulton and Shaw also reported the first PCP pincer rhodium and iridium derivatives and studied their reactivity toward carbon monoxide [4]. Hence, the (PCP) rhodium derivative (38) affords complex (40), as a product of the decomposition of the unstable hydrido chloro carbonyl intermediate (39) via a hydrodechlorination process, although this compound is obtained impure. To favor the hydrodechlorination process, an alternative route was attempted employing EtONa as base. This approach afforded exclusively compound (40) (Scheme 2.21). It is noteworthy that analogous reactions with the iridium analogous to complex (38) only afford impure samples of the carbonyl species analogous to complex (40). 

Figure 8.13 Illustration of the h3fpothesized reductive hydrodechlorination process of DCB on the bimetallic Pd/Fe surface and recapturing of Fe ions by chitosan.

Hydrogenation of Carbon Tetrachloride. Carbon tetrachloride can be hydrogenated, ie, hydrodechlorinated, to chloroform over a catalyst (25,26) or thermally (27). Although there are no industrial examples of this process at this time, it will receive more attention as more carbon tetrachloride becomes available as the CFC-11 and -12 markets decline (see, Chlorocarbons and chlorohydrocarbons, carbon tetrachloride). Chloroform can be further hydrodechlorinated to methylene chloride (28,29). 

Scheme 4.30 Hydrodechlorination of chlorobenzene using active flow cells in a continuous-flow microwave process.

The next example originates from our own laboratory Two potential intermediates for the angiotensin-converting enzyme inhibitor benazepril can be synthesized using cinchona modified noble metal catalysts (3). While the hydrogenation of the a-ketoester has been developed and scaled-up into a production process (10-200 kg scale, chemical yield >98%, ee 79-82%), the novel enantioselective hydrodechlorination reaction (see Section in) could be a potential alternative to the established synthesis where the racemic a-bromobenzazepinon is used [75]. At the moment both selectivity and productivity of the catalyst are too low and substitution reactions occur less readily with the chloro analog. 

The development of CFC alternatives has focused on non-chlorinated compounds, such as hydrofluorocarbons (HFCs), which have similar physical properties, but break down in the lower atmosphere.110 111 Consequently, hydrodechlorination is a simple method for the production of HFCs and also for destruction of CFCs108,109,112-114. Palladium is unique among the catalytic metals for its activity and selectivity in this process,102-108,115,116 but using Pd-Au/SiC>2 (Pd Au = 60 40) increased the selectivity for difluoromethane from difluorodichloromethane (CFC-12) shown by Pd/Si02 at 453 K from 40 to 95%.109,112-114... 

In situ catalytic hydrodechlorination of chlorinated hydrocarbons in wastewater can be used for detoxification of process wastewater or groundwater contaminated with low-molecular weight chlorinated hydrocarbons such as trichloroethylene and trichloroethane. The advantage of this approach is that it consists of a single-step process which can be carried out under ambient conditions. 

A number of low-grade transition metal ores (for example, minerals containing nickel oxides) can be used as catalysts. Smuda has demonstrated that microwave or radiofrequency irradiation of a mixture of such ores with a carbon source initiates reduction of the oxide to metal. With this approach, poisoning the active sites of the catalyst will not be critical for the process since there will be a constant supply and generation of active catalyst with the feed material. In addition to well-known catalytic properties of nickel in organic reactions, it was also shown that Ni on carbon and other supports, catalyzes hydrodechlorination and dehydrochlorination of chlorinated organic waste streams [22-24],... 

Vapor phase catalytic hydrodechlorination of 1,1,1-trichloroethane (TCA) has been studied using various supported platinum catalysts in a plug microflow reactor. The reactor was operated at temperatures ranging from 250 to 350°C, a H2 TCA He ratio of 10 1 89, a space velocity of 24 L/g cat-h, and atmospheric pressure. To study the deactivation process, tests were carried out by dividing the catalyst bed into three segments (inlet, middle, outlet) separated by glass wool plugs. 

Figure 1. Process flow diagram for hydrodechlorination of 1,1,1 trichlorethane.

Dichloropropane, referred as to 12DCP, is one of these troublesome chlorinated organic compounds. A process based on the hydrodechlorination of 12DCP to propene has received considerable attention in recent years [2]. Metals like platinum and palladium supported on activated carbon have been used as catalysts for this process [3]. This makes it possible to economically recycle the 12DCP to useful products, such as propene, at a high yield. 

Although Pt and Cu supported on activated carbon catalysts exhibited promising catalytic properties in the hydrodechlorination of I2DCP [3], little work has been done on fundamental research relevant to these catalysts. For instance, adsorption data, which is an essential aspect in catalysis, are hardly available. Catalyst deactivation is a major problem that hampers the application of these catalysts in industry. The effect of coke formation on catalyst deactivation needs to be clarified and the kinetics of coke formation modeled before an industrial process can be designed. 

The catalytic hydrodechlorination of silicon tetrachloride into trichlorosilane [1] is a process of far-reaching importance for the silicon industry (Eq. 1). 

The drop-in replacement selected for the most widely used CFC refrigerant, CCljFj, was 1,1,1,2-tetrafluoroethane, CHjFCFj (Figure 7.2). One of the routes to this compound used the existing technology for the fluorinated chromia-catalyzed route to CCljFCFj followed by a hydrodechlorination step the other used a new zinc-doped chromia catalyst precursor in a two-step process to convert CHQ=CCl2 to CH2FCF3 directly [16]. The doped chromia developed is described later in this chapter. 

The Naugatuck Chemical Company, Connecticut, a subsidiary of U.S. Rubber, was the first company to manufacture styrene. The process, however, was based on the hydrodechlorination of ethylbenzene and the product was not sufficiently pure for use in polymer applications. The company had received assistance from Igor Ostromisslenski, a well-known Russian emigrant, who held several patents in the field." ... 

---