With heavier hydrocarbons

ER E, the S T organization of the World largest oil company, ExxonMobil, was not very prolific in R D activities related to biocatalytic refining, but was focused on addressing a few key problems identified in BDS. They began in early 1990, with works on gas treatment however, the developments took an oil twist towards the end of the decade when they became involved with heavier hydrocarbon feedstocks. This company possesses inventions, which are protected with six patents ... 

Five binary-hydrocarbon mixtures of ethane or ethylene with heavier hydrocarbons were studied (Table III). The only substrate used in these studies was water. If an RPT did not occur, ice always formed rapidly. When n-butane or n-pentane was the heavier component, RPTs were 100% reproducible over a particular composition range. This was not, however, true if the heavier component were propane. 

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. 

From Figure 9.8, we see that only reactions with ethane and/or methyl radicals are thermodynamically possible at temperatures over 300°C. All reactions with heavier hydrocarbons or radicals are possible only at temperatures below... 

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

The predictions (not correlations) resulting from Equations 5 to 7 are compared with the results obtained using Equation 4 with the substance-specific parameters reported by Reid et al. [2] and with experimental data in Figure 5. While all the models show similar behavior, the best results are obtained with the Orbey-Sandler model, especially at lower temperatures and with heavier hydrocarbons. The Orbey-Sandler model also has the advantage that it has been generalized to make predictions [13], and in a modified form can be used for heavy oils and bitumens, and with dissolved gases [14] as will be discussed later. 

Where the distance to the customer is very large, or where a gas pipeline would have to cross too many countries, gas may be shipped as a liquid. Gas has to be chilled to -160°C in a LNG plant to keep it in liquid form, and is shipped in refrigerated tankers. To condition the gas for liquefaction any COj, HjS, water and heavier hydrocarbons must be removed, by the methods already discussed. The choice of how much propane and butane to leave in the LNG depends upon the heating requirements negotiated with the customer. 

With this type of burner, a wide variety of raw materials, ranging from propane to naphtha, and heavier hydrocarbons containing 10—15 carbon atoms, can be used. In addition, the pecuhar characteristics of the different raw materials that can be used enable the simultaneous production of acetylene and ethylene (and heavier olefins) ia proportioas which can be varied within wide limits without requiring basic modifications of the burner. 

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). 

The resultant viscosity is in centipoise (mPa-sec) if 7 and 7 are given in K and Pa, respectively. This method can also be used for hght nonhydrocarbon gases except for hydrogen where, special N s are required. For hydrocarbons below ten carbon atoms, average errors of about 3 percent can be expected, with errors increasing to 5-10 percent for heavier hydrocarbons. 

As stated earlier, turboexpanders are normally used in cryogenic processes to produce isentropic expansion to cool down the process gas. Two common applications are natural gas processing plants and chemical plants. In natural gas processing plants, turboexpanders are installed to liquify heavier hydrocarbon components and produce lean natural gas with specified dew point limits to meet required standards. 

Figure 3.24 shows the process flowsheet for an ethylene/ethylbenzene plant, Gas oil is cracked with steam in a pyrolysis furnace to form ethylene, low BTU gases, hexane, heptane, and heavier hydrocarbons. The ethylene is then reacted with benzene to form ethylbenzene (Stanley and El-Halwagi, 1995). Two wastewater streams are formed R ... 

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. 

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. 

The first step in the production of synthesis gas is to treat natural gas to remove hydrogen sulfide. The purified gas is then mixed with steam and introduced to the first reactor (primary reformer). The reactor is constructed from vertical stainless steel tubes lined in a refractory furnace. The steam to natural gas ratio varies from 4-5 depending on natural gas composition (natural gas may contain ethane and heavier hydrocarbons) and the pressure used. 

In general, crude oils and natural gases are composed of a mixture of relatively unreactive hydrocarbons with variable amounts of nonhydrocarbon compounds. This mixture is essentially free from olefins. However, the C2 and heavier hydrocarbons from these two sources (natural gas and crude oil) can be converted to light olefins suitable as starting materials for petrochemicals production. 

Drizo A variation of the glycol process for removing water vapor from natural gas, in which the water is removed from the glycol by stripping with a hydrocarbon solvent, typically a mixture of pentanes and heavier aliphatic hydrocarbons. The process also removes aromatic hydrocarbons. Last traces of water are removed from the triethylene glycol by stripping with toluene in a separate, closed loop. Invented in 1966 by J. C. Arnold, R. L. Pearce, and H. G. Scholten at the Dow Chemical Company. Twenty units were operating in 1990. U.S. Patent 3,349,544. 

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