Hydrocarbon methane with heavier

Condensable hydrocarbons are removed from natural gas by cooling the gas to a low temperature and then by washing it with a cold hydrocarbon hquid to absorb the condensables. The uncondensed gas (mainly methane with a small amount of ethane) is classified as natural gas. The condensable hydrocarbons (ethane and heavier hydrocarbons) are stripped from the solvent and are separated into two streams. The heavier stream, which largely contains propane with some ethane and butane, can be Hquefied and is marketed as Hquefied petroleum gas (LPG) (qv). The heavier fractions, which consist of and heavier hydrocarbons, are added to gasoline to control volatihty (see Gasoline and other motor fuels). 

Hydrocarbons heavier than methane that are present in natural gases are valuable raw materials and important fuels. They can be recovered by lean oil extraction. The first step in this scheme is to cool the treated gas by exchange with liquid propane. The cooled gas is then washed with a cold hydrocarbon liquid, which dissolves most of the condensable hydrocarbons. The uncondensed gas is dry natural gas and is composed mainly of methane with small amounts of ethane and heavier hydrocarbons. The condensed hydrocarbons or natural gas liquids (NGL) are stripped from the rich solvent, which is recycled. Table 1-2 compares the analysis of natural gas before and after treatment. Dry natural gas may then be used either as a fuel or as a chemical feedstock. 

Liquefied natural gas (LNG) is a very clean fuel in that the few impurities present in natural gas (water vapor, hydrogen sulfide, carbon dioxide, particulates and foreign matter, etc.) are removed almost completely when the natural gas is liquefied. Liquefaction also removes most of the hydrocarbons heavier than propane so that the resulting fuel is 95-99% methane with the remainder being primarily ethane with a smaller amount of propane. The liquefaction process is so efficient at removing contaminants that it removes the odorant placed in natural gas for transmission over pipelines (natural gas odorants are primarily mer-captans which contain sulfur and are relatively large molecules). 

Metal and metal oxide catalysts with this capability were reported in the 1980s. Several of these metals occur in widely distributed petroleum samples and are among the above listed as constituents of primordial Earth planetary orbit dust. In the metallic and compounded state some have the ability to catalyze hydrogenation of carbon to kerogen like high viscosity hydrocarbons. Kerogen, a heavier petroleumlike hydrocarbon mixture occurs in tar sands and porous shales (oil shale). Thus the question of conceivable prehistoric or more recent petroleum from methane generation must be considered. 

Methane accounts for approximately 85 percent of the composition of natural gas with heavier hydrocarbons, nitrogen, and, in some regions, helium accounting for the other 15 percent [1]. Purification of methane is carried out at ambient or low temperature absorption (5—10 thousand ppm and 1—2 thousand ppm, respectively) and low-temperature fractionation (100 ppm) [2]. Impurities in the methane, such as heavier hydrocarbons, promote undesirable side reaction. Methane is also produced in an increasing number of organic waste-disposal plants [3]. Methane is used as feedstock to produce many chemicals, including hydrogen cyanide, carbon disulfide, and chlorinated methanes. 

Table III. Binary Interaction Parameters for Methane (First Component) with Heavier Hydrocarbons...

Now that you know what a radical is I am ready to show you what happens when methane, CH4, is ignited. Much the same happens when you ignite bottled gas, propane, CH3CH2CH3, and even the heavier hydrocarbons of gasoline and diesel, but I shall keep it simple by focusing on methane with its single C atom. 

Steam Reforming Processes. In the steam reforming process, light hydrocarbon feedstocks (qv), such as natural gas, Hquefied petroleum gas, and naphtha, or in some cases heavier distillate oils are purified of sulfur compounds (see Sulfurremoval and recovery). These then react with steam in the presence of a nickel-containing catalyst to produce a mixture of hydrogen, methane, and carbon oxides. Essentially total decomposition of compounds containing more than one carbon atom per molecule is obtained (see Ammonia Hydrogen Petroleum). 

Secondary raw materials, or intermediates, are obtained from natural gas and crude oils through different processing schemes. The intermediates may be light hydrocarbon compounds such as methane and ethane, or heavier hydrocarbon mixtures such as naphtha or gas oil. Both naphtha and gas oil are crude oil fractions with different boiling ranges. The properties of these intermediates are discussed in Chapter 2. 

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