Phosgene plant operation

The above processes are only selected examples of a vast number of process options. In the case of carbonylation, the formation of by-products, primarily isocyanate oligomers, allophanates, and carbodiimides, is difficult to control and is found to greatly reduce the yield of the desired isocyanate. Thus a number of nonphosgene processes have been extensively evaluated in pilot-plant operations, but none have been scaled up to commercial production of diisocyanates primarily due to process economics with respect to the existing amine—phosgene route. Key factors preventing large-scale commercialization include the overall reaction rates and the problems associated with catalyst recovery and recycle. 

Operating requirements typical of those required for the production of phosgene in a modern plant are given in Table 4.2 [311a]. In addition, the modern phosgene plant will... 

In most cases, the plants producing Schedule 3 chemicals are dedicated and are usually in continuous operation. The majority of them produce large volumes of chemicals. For example, the aimual production for phosgene plants normally ranges from 10,000 to 100,000 toimes ear, and... 

From 1922 onward the phosgene plant at Edgewood lay idle as the War Department forbade the manufacture of toxic agents. In 1937 the CWS rehabilitated and operated the plant for a brief period to produce phosgene and to provide the Technical Division with engineering data for a larger plant. The design was ready in 1939, and the new plant constructed and placed in operation in July 1941. ... 

Meanwhile, the plants making both phosgene and mustard gas went into overdrive. In response to Churchill s constant demands, the output of gas increased markedly. Once manufactured, the gas was stored in underground mines in North Wales. The statistics available show a steady increase and indeed by the middle of 1944 Britain had stockpiled more than five million gas-carrying shells and bombs. In the event, of course, the phosgene and mustard gas were never needed. The RAF stopped the Luftwaffe in the Battle of Britain and in October 1940 Hitler called off Operation Sealion (the invasion of Britain) and turned his attention to Soviet Russia. 

The Dow Chemical Company recommends canned-motor pumps or magnetic-drive pumps for phosgene service. Phosgene is an example of an extremely hazardous material. These pumps should have a secondary containment such that failure of the can does not create a phosgene release. The secondary containment should meet pipe specifications for pressure or relieve to the scrubber system in the plant. These pumps must have automated block valves on the suction and discharge. Operation of these valves should be managed such that the thermal expansion does not damage the pump. 

Phosgene storage and handling operations should be in a remote location from the rest of the plant. 

The process is normally operated on a continuous basis, employing a high degree of automation. Owing to the toxicity of phosgene, extensive safety features are an integral part of the plant design. 

The metering operation is considered to be critical with regard to the economics of the plant. If the metering of the reactants is not controlled within precise limits, then excess of carbon monoxide must be used to prevent dichlorine contamination of the final product. This is wasteful not only of carbon monoxide, but also of phosgene product in the condenser... 

The commercialization of phosgene processes based on hydrogen chloride, rather than dichlorine, would permit, for example, isocyanate plants to be sited at locations not dependant on chloralkali-producing facilities or large chlorine-consuming (e.g. vinyl chloride) plant. However, it is not known for certain whether any of these processes are currently commercially operated. 

Another way of avoiding less economical and toxic phosgene involves the use of dimethyl carbonate for the production of isocyanates and polycarbonates. In Japan, Ube have operated the first pilot plant for the highly selective gas-phase carbonylation of methanol. Further liquid-phase processes for the production of dimethyl carbonate are in operation at Daicel and Mitsui Sekka. 

Although they have only been used in a limited number of cases, they have proved to give excellent results in special applications. For example, they are used in many plants and operations of the chemical industry for personal exposure monitoring of phosgene. Other examples include the determination of personal exposure doses of formaldehyde or ethylene oxide in clinical applications. 

Among the chlorinated C2 hydrocarbons, per-chloroethylene is the one that gives oif most phosgene when heated by flame cutting or contact with a very hot surface. Since it is very difiicult for an operative to detect this gas before receiving a harmful, or even fatal, dose, plant cleaning before hot work is important. 

Prior to January 2010, the DuPont BeUe plant in West Virginia, about 8 miles east of Charleston on the Kanawha River, had the best safety record of any DuPont production facility. It was therefore something of a surprise when this plant had three separate incidents within about 33 hours on January 22-23, 2010. The three incidents involved, respectively, the release of methyl chloride, oleum (or fuming sulfuric acid), and phosgene. The last incident (phosgene) caused the death of an operator [1]. 

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