Aromatic hydrocarbons from paraffins

However, there are one or two instances where enough is known about catalysts of these types to justify some attention at this point. Some of the most thoroughly investigated cases constitute the group of catalysts used in the ring-closing reactions which lead to the production of aromatic hydrocarbons from paraffins or olefins. These consist of oxides of vanadium, chromium, and molybdenum, or of complex and supported catalysts containing one of these oxides. 

Extraction Solvent. Dimethyl sulfoxide is immiscible with alkanes but is a good solvent for most unsaturated and polar compounds. Thus, it can be used to separate olefins from paraffins (93). It is used in the Institute Fransais du Pntrole (IFF) process for extracting aromatic hydrocarbons from refinery streams (94). It is also used in the analytical procedure for determining polynuclear hydrocarbons in food additives (qv) of petroleum origin (95). 

OCTENAR [Octane enhancement by removing aromatics] A process for removing aromatic hydrocarbons from petroleum reformate by extractive distillation with N-formyl mor-phylane. The product can be blended with gasoline to increase its octane number — hence the name. A paraffin mixture is obtained as a side-product. Developed by Krupp Koppers from its MORPHYLANE and MORPHYLEX processes. 

Several methods, involving solvent extraction or destructive hydrogenation, can accomplish the removal of aromatic hydrocarbons from naphtha. By destructive hydrodegation methods, aromatic hydrocarbon rings are first ruptured and then saturated with hydrogen, which converts aromatic hydrocarbons into the odorless, straight-chain paraffinic hydrocarbons required in aliphatic solvents. 

Separation of paraffinic and aromatic hydrocarbons. Liquid paraffinic hydrocarbons (such as pentane, hexane, and heptane) and liquid aromatic hydrocarbons (such as benzene, toluene, and xylene) have different chemical characteristics for example, the paraffinic compounds are almost completely immiscible with liquid ethylene glycol, while aromatic compounds and ethylene glycol readily form homogeneous liquid mixtures. Parafflnics and aromatics may therefore be separated from each other by blending a mixture of the two... 

Lyophilization stoppers can be a source of volatiles that may contaminate the product during lyophilization or during its shelf life. Pikal and Lans [5] found that paraffin wax-like materials and sulfur from stoppers were a source of haziness in reconstituted antibiotics and that lower pressures during lyophilization exacerbated the problem. Further research determined that unsaturated and aromatic hydrocarbons from halobutyl stoppers were mainly responsible for the formation of the haze [6]. The amount of haziness caused by volatiles varies greatly with the type of stopper used [7]. The investigators [6] showed that Teflon-coated stoppers produced the least amount of haze. However, the data on most of the stoppers tested were not quantitative. Coated stoppers are considerably more expensive and may not seal with the vial well if the coating surface is on the upper flange of the vial [8]. 

Selective adsorption of an aromatic hydrocarbon from a binary mixture of aromatic and paraffin (264). 

A number of physical tests have been proposed for the estimation of catalytic activity, but except for purposes of control in catalyst manufacture none of these is an acceptable substitute for direct cracking tests. In general, such tests as the measurement of the selective adsorption of an aromatic hydrocarbon from a standard binary mixture of aromatic and paraffinic components (Scheumann and Rescorla, 19), or the measurement of the heat of wetting with methanol (Mills, 20) merely reflect the extent of available surface. With a given catalyst composition, these methods may have some utility in following the decline of activity due to the effects of temperature or steam (but not of sulfur) or as a rapid and approximate control method in the manufacture of a catalyst. 

Separation of different organic components from each other is still a matter of laboratory investigation. In the past 15 years considerable efforts have been devoted to develop polymeric membranes to separate, for example, aromatic hydrocarbons from aliphatic ones which resulted in several patents [25, 26], or olefins from paraffins or to separate isomers, e.g. para- and ortho-xylenes, from each other. In the last years additional membranes [27] have become available and the first industrial applications have been reported, e.g. the separation of sulfur-containing aromatics from gasoline [28] and of benzene from a stream of saturated hydrocarbons [29], Further development of membranes, especially of the mixed-matrix type, may lead to improved selectivity and a broadening of these applications. 

Nitromethane can be used in an extractive process to separate aromatic hydrocarbons from aliphatic hydrocarbons due to the lower solubility of the aliphatic fractions in nitromethane [3]. Nitroparaffins are used to separate lactic acid from fermentation beers [4], nitrocellulose from the nitrating solution [5], and plutonium (IV) from aqueous solutions [6]. Nitropropane is used to extract rosin from pine lumber at elevated temperatures [7]. Toluene can be separated from similar boiling-point aliphatic paraffins by azeotropic distillation with nitromethane [8]. Ethylbenzene forms an azeotrope with nitromethane which allows its separation from styrene through a distillation process. 

Coal tar is the condensation product obtained by cooling to approximately ambient temperature, the gas evolved in the destmctive distillation of coal. It is a black viscous Hquid denser than water and composed primarily of a complex mixture of condensed ring aromatic hydrocarbons. It may contain phenoHc compounds, aromatic nitrogen bases and their alkyl derivatives, and paraffinic and olefinic hydrocarbons. Coal-tar pitch is the residue from the distillation of coal tar. It is a black soHd having a softening point of 30—180°C (86—359°F). 

Coke-oven tar is an extremely complex mixture, the main components of which are aromatic hydrocarbons ranging from the monocyclics benzene and alkylbenzenes to polycycHc compounds containing as many as twenty or more rings. HeterocycHc compounds containing oxygen, nitrogen, and sulfur, but usually only one heteroatom per ring system are present. Small amounts of paraffinic, olefinic, and partly saturated aromatic compounds also occur. 

Displacement-purge forms the basis for most simulated continuous countercurrent systems (see hereafter) such as the UOP Sorbex processes. UOP has licensed close to one hundred Sorbex units for its family of processes Parex to separate p-xylene from C3 aromatics, Molex tor /i-paraffin from branched and cyclic hydrocarbons, Olex for olefins from paraffin, Sarex for fruc tose from dextrose plus polysaccharides, Cymex forp- or m-cymene from cymene isomers, and Cresex for p- or m-cresol from cresol isomers. Toray Industries Aromax process is another for the production of p-xylene [Otani, Chem. Eng., 80(9), 106-107, (1973)]. Illinois Water Treatment [Making Wave.s in Liquid Processing, Illinois Water Treatment Company, IWT Adsep System, Rockford, IL, 6(1), (1984)] and Mitsubishi [Ishikawa, Tanabe, and Usui, U.S. Patent 4,182,633 (1980)] have also commercialized displacement-purge processes for the separation of fructose from dextrose. 

Impurities can sometimes be removed by conversion to derivatives under conditions where the major component does not react or reacts much more slowly. For example, normal (straight-chain) paraffins can be freed from unsaturated and branched-chain components by taking advantage of the greater reactivity of the latter with chlorosulfonic acid or bromine. Similarly, the preferential nitration of aromatic hydrocarbons can be used to remove e.g. benzene or toluene from cyclohexane by shaking for several hours with a mixture of concentrated nitric acid (25%), sulfuric acid (58%), and water (17%). 

Evaporative emissions from vehicle fuel systems have been found to be a complex mixture of aliphatic, olefinic, and aromatic hydrocarbons [20,24,33]. However, the fuel vapor has been shown to consist primarily of five light paraffins with normal boiling points below 50 °C propane, isobutane, n-butane, isopentane, and n-pentane [33]. These five hydrocarbons represent the more volatile components of gasoline, and they constitute from 70 to 80 per cent mass of the total fuel vapor [24,33]. 

Natural gas and crude oils are the main sources for hydrocarbon intermediates or secondary raw materials for the production of petrochemicals. From natural gas, ethane and LPG are recovered for use as intermediates in the production of olefins and diolefms. Important chemicals such as methanol and ammonia are also based on methane via synthesis gas. On the other hand, refinery gases from different crude oil processing schemes are important sources for olefins and LPG. Crude oil distillates and residues are precursors for olefins and aromatics via cracking and reforming processes. This chapter reviews the properties of the different hydrocarbon intermediates—paraffins, olefins, diolefms, and aromatics. Petroleum fractions and residues as mixtures of different hydrocarbon classes and hydrocarbon derivatives are discussed separately at the end of the chapter. 

Liquid solvents are used to extract either desirable or undesirable compounds from a liquid mixture. Solvent extraction processes use a liquid solvent that has a high solvolytic power for certain compounds in the feed mixture. For example, ethylene glycol has a greater affinity for aromatic hydrocarbons and extracts them preferentially from a reformate mixture (a liquid paraffinic and aromatic product from catalytic reforming). The raffinate, which is mainly paraffins, is freed from traces of ethylene glycol by distillation. Other solvents that could be used for this purpose are liquid sulfur dioxide and sulfolane (tetramethylene sulfone). 

This chapter reviews the adsorptive separations of various classes of non-aromatic hydrocarbons. It covers three different normal paraffin molecular weight separations from feedstocks that range from naphtha to kerosene, the separation of mono-methyl paraffins from kerosene and the separation of mono-olefins both from a mixed C4 stream and from a kerosene stream. In addition, we also review the separation of olefins from a C10-16 stream and review simple carbohydrate separations and various acid separations. 

---