Dichloromethane manufacture

At ambient temperature the solubility of water in chlorinated solvents ranges from 80 ppm (carbon tetrachloride) to 560 ppm (chloroform) to 2500 ppm (dichloromethane). Manufacturers typically produce these solvents with water levels <100 ppm. In these solvents, commonly used in normal-phase HPLC, the support materials (e.g., silica or alumina) are deactivated by water. As the surface-adsorbed water level on silica increases (typically as a result of increases in the water content of the mobile phase), a dramatic loss of resolution occurs, specifrcally because water in the solvent prevents the active surface sites from playing a role in the retention process. 

Taking the manufacture of polycarbonates as an example, two manufacturing routes are shown in Scheme 3.1. In the first route phosgene is reacted with bisphenol A in dichloromethane. The main environmental concern with this process is the large-scale use of phosgene. In the second... 

Current methodologies for the manufacture of energetic materials such as NHTPB, Poly(NiMMO) and Poly(GlyN) etc. use environmentally undesirable solvents such as dichloromethane. However, the adoption of the Montreal Protocol by most of the countries has limited the use of these halogenated hydrocarbons. To address current and futuristic legislations, DERA Scientists have developed various strategies to enable the manufacture of energetic materials in an environmentally friendly manner. Such an approach is to use Uquid or supercritical carbon dioxide as a solvent Carbon dioxide exhibits supercritical fluid behavior at a temperature >31.1 °C and a pressure >73.8 bar. 

Dichloromethane has been used as an extraction solvent for spices and beer hops and for decaffeination of coffee. It has also found use as a carrier solvent in the textile industry, in the manufacture of photographic film and as a blowing agent for polymer... 

Table 3 summarizes personal occupational exposures measured in various industries using dichloromethane. The levels vary widely by operation and within operations. Concentrations exceeding 1000 mg/m have been measined, e g., in paint stripping, in the printing industry and in the manufacture of plastics and synthetic fibres. Full-shift exposures to levels above 100 mg/m of dichloromethane are possible, e g., in furniture-stripping shops and in certain jobs in aeronautical, pharmaceutical, plastic and footwear industries. 

Dichloromethane is used principally as a solvent, in paint removers, degreasers and aerosol products, and in the manufacture of foam polymers. Widespread exposure occurs during the production and industrial use of dichloromethane and during the use of a variety of consumer products containing dichloromethane. Substantial losses to the environment lead to ubiquitous low-level exposures from ambient air and water. 

A population-based case-control study on brain cancer was carried out in some areas in the United States with petroleum refining and chemical manufacturing industries (i.e., activities suspected of being associated with brain cancer) and is described in detail in the monograph on dichloromethane (see this volume). Probability, intensity, duration and calendar time of life-long individual exposures to each of six chlorinated aliphatic hydrocarbons, including 1,1,1-trichloroethane, were assessed through an ad-hoc job-exposure matrix. Whereas risk excesses of some consistency were associated with exposure to other chlorinated aliphatic hydrocarbons, exposure to 1,1,1-trichloroethane showed little indication of an association with brain cancer (Heineman et al., 1994). 

These solvents include tetrahydrofuran (THF), 1,4-dioxane, chloroform, dichloromethane, and chlorobenzene. The relatively broad solubility characteristics of PSF have been key in the development of solution-based hollow-fiber spinning processes in the manufacture of polysulfone asymmetric membranes (see Hollow-fibermembranes). The solvent list for PES and PPSF is short because of the propensity of these polymers to undergo solvent-induced crystallization in many solvents. When the PES structure contains a small proportion of a second bisphenol comonomer, as in the case of RADEL A (Amoco Corp.) polyethersulfone, solution stability is much improved over that of PES homopolymer. 

Methyl chloride is an important industrial product, having a global annual capacity of ca. 900 000 tons. Its primary use is for the manufacture of more highly chlorinated materials such as dichloromethane and chloroform and for the production of silicone fluids and elastomers. It is usually manufactured by the reaction of methanol with hydrogen chloride with a suitable acid catalyst, such as alumina. To develop a site-specific reaction mechanism and a kinetics model for the overall process, one first needs to identify all the reagents present at the catalyst surface and the nature of their interactions with the surface. The first step in the reaction is dissociative adsorption of methanol to give adsorbed methoxy species. Diffuse reflectance IR spectroscopy (29d) showed the expected methoxy C-H stretch and deformations, but an additional feature, with some substructure, at 2600 cm was... 

Some examples of industrially important uses are the following reactions With alkyl halides or alcohols amines or imines can be manufactured. For example, inethanol forms mono- through trimethylamine dichloromethane yields ethylene imine in the presence of calcium oxide. Amines can also be produced by reacting ammonia with alkyl halides in multistage processes [1425]. 

The sulfur derivative (87) is 1000 times as sweet as sugar and without the bitter after-taste of saccharin however, it was discovered that N-alkylation of (87) removed the sweetness. On the other hand, in the saccharins (88a)-(88e) containing substituents in the 4-position and 6-position, sweetness was retained after N-alkylation. Many sulfamic acid derivatives are sweet, and there have been numerous studies of structure-taste relationships which have highlighted the importance of molecular shape and stereochemistry (see Chapter 9, p. 162). Two sulfamates which are commercial, non-nutritive sweeteners are cyclamate (85) and acesulfame potassium (86) (Figure 11). Cyclamate (85) is manufactured by refluixing cyclohexylamine either with triethylamine-sulfur trioxide in dichloromethane or with sulfamic acid (see Chapter 9, p. 162). 

Conventional processes for the manufacture of dichloromethane are based upon the chlorination of methane or of chloromethane. These reactions have the disadvantage of generating hydrogen chloride as a by-product, and of producing a mixture of all chloromethanes, in addition to dichloromethane. The simple reaction between methanal and phosgene thus... 

Until recently, most of these semi-synthetic penicillin antibiotics were manufactured from penicillin G by chemical methods (Scheme 8.8) [57], which involve many green chemsitry issues, including the use of stoichiometric amounts of the silylating agents, phosphorus chloride, and N,N-dimethylaniline, and a large volume of dichloromethane. Moreover, the chlorination has to be carried out at —40 °C. 

Chlorinated hydrocarbons, containing one or two carbon atoms, constitute a significant fraction of the hazardous substances from industrial, domestic, and agricultural sources. In part, this is due to their high levels of production. Over five million tonnes of 1,2-dichloroethylene (1,2-DCE) are produced annually for use as a solvent and chemical intermediate [1]. Vinyl diloride (VC) is also produced in large amoimts (over three million tonnes annually) for the manufacture of polyvinyl chloride [1]. The solvents tetrachloroethylene (PCE), trichloroethylene (TCE), 1,1,1-trichloroethane (TCA), 1,1-dichloroethylene (1,1-DCE), 1,2-dichloroethane (1,2-DCA), and carbon tetrachloride (CT) have a combined annual production of over 6 million tonnes [1]. Since 1970, annual U.S. production of dichloromethane (DCM) has ranged from 212 to 286 million kg, with the principal application being paint removal [2]. 

---