Aromatic hydrocarbons from olefins

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). 

Flowever, information concerning the characteristics of these systems under the conditions of a continuous process is still very limited. From a practical point of view, the concept of ionic liquid multiphasic catalysis can be applicable only if the resultant catalytic lifetimes and the elution losses of catalytic components into the organic or extractant layer containing products are within commercially acceptable ranges. To illustrate these points, two examples of applications mn on continuous pilot operation are described (i) biphasic dimerization of olefins catalyzed by nickel complexes in chloroaluminates, and (ii) biphasic alkylation of aromatic hydrocarbons with olefins and light olefin alkylation with isobutane, catalyzed by acidic chloroaluminates. 

Several metal oxides could be used as acid catalysts, although zeolites and zeo-types are mainly preferred as an alternative to liquid acids (Figure 13.1). This is a consequence of the possibility of tuning the acidity of microporous materials as well as the shape selectivity observed with zeolites that have favored their use in new catalytic processes. However, a solid with similar or higher acid strength than 100% sulfuric acid (the so-called superacid materials) could be preferred in some processes. From these solid catalysts, nation, heteropolyoxometalates, or sulfated metal oxides have been extensively studied in the last ten years (Figure 13.2). Their so-called superacid character has favored their use in a large number of acid reactions alkane isomerization, alkylation of isobutene, or aromatic hydrocarbons with olefins, acylation, nitrations, and so forth. 

Catarole Also spelled Catarol. A process for making aromatic hydrocarbons and olefins by cracking petroleum fractions over copper turnings. Invented by C. Weizmann in England in 1940 and developed by Petrochemicals, which used it from 1947 in its refinery at Carrington, UK, to make ethylene, propylene, and a range of aromatic hydrocarbons. 

The basic sources of petrochemical synthesis are benzene and its homologues. The production of these compounds from petroleum is profitable. In 1996, the world requirements for benzene will grow up to 24-26 million tons per year. Non-oxidizing dehydrogenation of alkanes is a subject of intensive investigation. So, the selection and increase of the assortment of highly effective catalysts for the synthesis of olefins and aromatic hydrocarbons from alkanes are very important for development of this branch of industry. There are three main catalysts for non-oxidized dehydrogenation ... 

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. 

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. 

Radical cations can be derived from aromatic hydrocarbons or olefins by reaction with one-electron oxidants. Antimony pentachloride and cobaltic ion are among the oxidants that have been used. Most radical cations have limited stability, but the sensitivity of EPR spectral parameters to structure have permitted many conclusions about the nature of radical cations despite their limited stability. 

Thus, under ordinary reaction conditions, methanol is almost exclusively consumed by the reaction with olefins. Once certain amounts of olefins are formed in the zeolite cavities, they undergo various reactions such as dimerization and isomerization of olefins, and cracking of higher hydrocarbons through carbenium intermediates. For example, the formation of aromatic hydrocarbons from lower olefins csm be expressed by the following scheme. ... 

The feedstocks used ia the production of petroleum resias are obtaiaed mainly from the low pressure vapor-phase cracking (steam cracking) and subsequent fractionation of petroleum distillates ranging from light naphthas to gas oil fractions, which typically boil ia the 20—450°C range (16). Obtaiaed from this process are feedstreams composed of atiphatic, aromatic, and cycloatiphatic olefins and diolefins, which are subsequently polymerized to yield resias of various compositioas and physical properties. Typically, feedstocks are divided iato atiphatic, cycloatiphatic, and aromatic streams. Table 2 illustrates the predominant olefinic hydrocarbons obtained from steam cracking processes for petroleum resia synthesis (18). 

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. 

Tetracyanoethylene is colorless but forms intensely colored complexes with olefins or aromatic hydrocarbons, eg, benzene solutions are yellow, xylene solutions are orange, and mesitylene solutions are red. The colors arise from complexes of a Lewis acid—base type, with partial transfer of a TT-electron from the aromatic hydrocarbon to TCNE (8). TCNE is conveniendy prepared in the laboratory from malononitrile [109-77-3] (1) by debromination of dibromoma1 ononitrile [1855-23-0] (2) with copper powder (9). The debromination can also be done by pyrolysis at ca 500°C (10). 

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]. 

The petrochemical industry is mainly based on three types of intermediates, which are derived from the primary raw materials. These are the C2-C4 olefins, the Ce-Cg aromatic hydrocarbons, and synthesis gas (an H2/CO2 mixture). 

Alpha A process for making aromatic hydrocarbons and LPG from C3-C7 olefins. The catalyst is a metal-modified ZSM-5 zeolite. Developed by Asahi Chemical Industries and Sanyo Petrochemical and used since 1993 at Sanyo s Mitzushima refinery. 

To assess, at least qualitatively, how much of the observed shift in the triphenylcarbonium ion is due to the change of hybridization from to sp and how much to the effect of the positive charge, a comparison of the chemical shifts of the triphenyl-C -carbonium and trimethyl-C -carbonium ions with their parent sp -hybridized covalent precursors and with some C -compounds having p -hybridization is useful. Data of Table 9, indicate that the C -shifts of ap -hybridized compounds (olefins and aromatic hydrocarbons), at least in the molecules studied (Lauterbur, 1957,1962), are very similar and fairly independent of the nature of the molecules. 

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