Methane inhibitor method

Chlorination of Methane. Methane can be chlorinated thermally, photochemicaHy, or catalyticaHy. Thermal chlorination, the most difficult method, may be carried out in the absence of light or catalysts. It is a free-radical chain reaction limited by the presence of oxygen and other free-radical inhibitors. The first step in the reaction is the thermal dissociation of the chlorine molecules for which the activation energy is about 84 kj/mol (20 kcal/mol), which is 33 kJ (8 kcal) higher than for catalytic chlorination. This dissociation occurs sufficiendy rapidly in the 400 to 500°C temperature range. The chlorine atoms react with methane to form hydrogen chloride and a methyl radical. The methyl radical in turn reacts with a chlorine molecule to form methyl chloride and another chlorine atom that can continue the reaction. The methane raw material may be natural gas, coke oven gas, or gas from petroleum refining. 

Models have been developed to evalnate natnral gas production from hydrates by both depressnrization and heating methods. There are three methods to obtain methane from gas hydrates (1) the depressurization method, (2) the thermal stimulation method, and (3) the chemical inhibition method. The thermal stimulation method and the chemical inhibitor injection method are both costly procedmes, whereas the depressurization method may prove useful when applied to more than one production. 

The method of inhibitors has demonstrated that substitution of chlorine in triphenylchloro-methane by tert-butoxy anion does not follow anion-radical mechanism. This mechanism is widely accepted for the reactions shown in Scheme 4.20 (Bielevich et al. 1968, Ashby et al. 1981). 

Hydrate dissociation is of key importance in gas production from natural hydrate reservoirs and in pipeline plug remediation. Hydrate dissociation is an endothermic process in which heat must be supplied externally to break the hydrogen bonds between water molecules and the van der Waals interaction forces between the guest and water molecules of the hydrate lattice to decompose the hydrate to water and gas (e.g., the methane hydrate heat of dissociation is 500 J/gm-water). The different methods that can be used to dissociate a hydrate plug (in the pipeline) or hydrate core (in oceanic or permafrost deposits) are depressurization, thermal stimulation, thermodynamic inhibitor injection, or a combination of these methods. Thermal stimulation and depressurization have been well quantified using laboratory measurements and state-of-the-art models. Chapter 7 describes the application of hydrate dissociation to gas evolution from a hydrate reservoir, while Chapter 8 describes the industrial application of hydrate dissociation. Therefore in this section, discussion is limited to a brief review of the conceptual picture, correlations, and laboratory-scale phenomena of hydrate dissociation. 

Of the above-mentioned techniques, thermodynamic inhibitors, which include alcohols, salts, and glycols, are by far the most prevalent. For example, adding methanol to a natural gas will shift the equilibrium conditions so that a higher pressure is required to form hydrates, at a given temperature, as illustrated for methane in Fig. 3. Methods for estimating the saturation water content of natural gases and amounts of methanol or glycol required to suppress hydrate formation are discussed by Katz, Sloan,and Campbell. Current practice for the estimations is to use computer software based on phase equilibrium calculations. ... 

Pure Natural gas (methane) has little odor so trace quantities of sulfur such compounds, as ethyl mercaptain, are added. These compounds have a powerful odor and serve to warn of a gas leak. They also tend to reduce hydrogen embrittlement of metals. They have been suggested as a solution to the embrittlement problem. Addition of these materials has the shortcoming that these compounds are toxic and can bum to produce toxic combustion products. Unfortunately, the toxicity and polluting combustion products negate the main purpose for the adoption of hydrogen. The use of chemical inhibitors to provide pipeline safety can be avoided by development of other methods. 

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