Aromatic-Range Hydrocarbons

Mobil MTG and MTO Process. Methanol from any source can be converted to gasoline range hydrocarbons using the Mobil MTG process. This process takes advantage of the shape selective activity of ZSM-5 zeoHte catalyst to limit the size of hydrocarbons in the product. The pore size and cavity dimensions favor the production of C-5—C-10 hydrocarbons. The first step in the conversion is the acid-catalyzed dehydration of methanol to form dimethyl ether. The ether subsequendy is converted to light olefins, then heavier olefins, paraffins, and aromatics. In practice the ether formation and hydrocarbon formation reactions may be performed in separate stages to faciHtate heat removal. 

Hydrocarbons, compounds of carbon and hydrogen, are stmcturally classified as aromatic and aliphatic the latter includes alkanes (paraffins), alkenes (olefins), alkynes (acetylenes), and cycloparaffins. An example of a low molecular weight paraffin is methane [74-82-8], of an olefin, ethylene [74-85-1], of a cycloparaffin, cyclopentane [287-92-3], and of an aromatic, benzene [71-43-2]. Cmde petroleum oils [8002-05-9], which span a range of molecular weights of these compounds, excluding the very reactive olefins, have been classified according to their content as paraffinic, cycloparaffinic (naphthenic), or aromatic. The hydrocarbon class of terpenes is not discussed here. Terpenes, such as turpentine [8006-64-2] are found widely distributed in plants, and consist of repeating isoprene [78-79-5] units (see Isoprene Terpenoids). 

Lube oil extraction plants often use phenol as solvent. Phenol is used because of its solvent power with a wide range of feed stocks and its ease of recovery. Phenol preferentially dissolves aromatic-type hydrocarbons from the feed stock and improves its oxidation stability and to some extent its color. Phenol extraction can be used over the entire viscosity range of lube distillates and deasphalted oils. The phenol solvent extraction separation is primarily by molecular type or composition. In order to accomplish a separation by solvent extraction, it is necessary that two liquid phases be present. In phenol solvent extraction of lubricating oils these two phases are an oil-rich phase and a phenol-rich phase. Tne oil-rich phase or raffinate solution consists of the "treated" oil from which undesirable naphthenic and aromatic components have been removed plus some dissolved phenol. The phenol-rich phase or extract solution consists mainly of the bulk of the phenol plus the undesirable components removed from the oil feed. The oil materials remaining... 

In order to avoid the necessity of operating at the high pressures typical of carbon dioxide flooding (1500-3000 psig, or 10-20 MPa), which would require heavy bracing of the model faces and highrpressure inlet and production systems, substitute fluids were used. In place of carbon dioxide, a non-aromatic kerosene-range hydrocarbon was used, with a viscosity of 1.3 cp (or kPa-s). This is about 20 times the viscosity of carbon dioxide under normal... 

Paraffins, naphthenes, and aromatic hydrocarbons in gasoline and other distillates boiling up to 200°C (392 F) are determined by multidimensional gas chromatography (ASTM D-5443). Olefins that are present are converted to saturates and are included in the paraffin and naphthene distribution. However, the scope of this test does not allow it to be applicable to hydrocarbons containing oxygenates. An extended version of the method can be used to determine the amounts of paraffins, olefins, naphthenes, and aromatics (PONA) in gasoline-range hydrocarbon fractions (ASTM D-6293). 

The conversion of chloromethane over ZSM-5 to gasoline-range hydrocarbons occurred under conditions comparable to those for the conversion of methanol. The reaction was typically conducted at constant temperature, whereas conversions and product distributions were determined as functions of space velocity or catalyst time-on-stream. The mass-selective detector allowed identification of most of the components in the liquid samples. Generally, the products contain ten carbons or less, and a large fraction of the products are aromatic. The ZSM-5 catalyst was stable under extended exposure to chloromethanes. Figure 2 illustrates the catalyst activity after nearly 700 hours of exposure to chloromethane, during which time the catalyst had been oxidatively regenerated to remove coke that had been deposited on the catalyst. 

Reaction of (C2-C5) olefins over H-ZSM-5 zeolite produces aromatic gasoline range hydrocarbons up to approximately Cjq (ref. 3). However, at increased pressure and moderate temperatures distillate range hydrocarbons are formed (ref. 4-7). 

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