Reforming catalytic

Catalytic reforming is a key refinery process. It improves the octane rating of virgin naphthas and light distillates so they can be used in gasoline formulations. The process has also become an important source of aromatics for use in petrochemical production. 

When gasoline is the main product required, it is usual to remove the Cs-Ce straight-mn naphtha cut before reforming the 100-160°C fraction. This is because separate isomerization of the Cs-Ce paraffins (Section 6.10) gives an overall improvement in octane number. If aromatics are required, a lower-boiling fraction, in the range 80-120°C, is reformed. The heavy naphthas are not reformed because coke forms more readily and quickly leads to deactivation of the catalyst. 

The dehydrogenation of naphthenes to aromatics results in the production of large volumes of extremely valuable, co-product hydrogen. This has been vital for the development of refinery hydrodesulfurization. 

The purpose of catalytic reforming is to boost the octane number by converting molecules with a low octane number into molecules with a high octane number (see Table 2.1). 

The capacity of catalytic reforming is very large. In the western world alone it amounts to over 1 million t/d. The major reactions occurring are  

Clearly, favourable reaction conditions are a high temperature and a low pressure. However, a low pressure is not possible because large carbon deposits are formed. Carbon deposition is lowered by increasing the hydrogen partial pressure. Typical practical conditions are 800 K and 30 bar. Under these conditions, catalyst activity is typically retained over a period of 3 to 6 months. Regeneration is performed by removing the carbon deposits by careful burning in diluted air. 

In practice catalytic reforming is usually carried out in fixed bed reactors (see Fig. 2.2). Because the reactions are endothermic, heat has to be introduced. A conventional scheme is based upon a series of three or four adiabatic fixed bed reactors with interstage heating. Part of the hydrogen produced is recycled to maintain high hydrogen partial pressures. The product mixture from the last reactor is cooled and separated into a gas phase and a liquid phase. The latter is purified by distillation. 

The catalyst is called bifunctional both the carrier and the metallic particles dispersed over the carrier exhibit different catalytic functions. The carrier contains chlorine ions and, as a consequence, it has acid properties and exhibits isomerization and cyclization activities. The metal particles consist of alloys of, for example, Pt/Re which exhibit hydrogenation/dehydrogenation activity. 

Middle distillates (jet and diesel) from high-conversion hydrocrackers meet or exceed finished product specifications. The heavy naphtha, however, usually goes to a catalytic reformer for octane improvement. The fractionator bottoms from partial conversion units can be sent to an FCC unit, an olefins plant, or a lube plant. 

Due to the feet that products from a hydrocracker are less dense than the feeds, the total volume of liquid products is greater than the feed volume by 10 to 30 vol%. This phenomenon is called volume swell. 

Purpose Convert heavy hydrocarbons into lighter hydrocarbons  

Other Reactions Sulfur removal (HDS) Olefin saturation Nitrogen removal (HDN) Aromatic saturation 

Catalysts NiMo on y-alumina (HDS, HDN, aromatic saturation) NiMo or NiW on zeolite (hydrocracking) NiMo or NiW on amorphous silica-alumina (hydrocracking) Pd on zeolite (hydrocracking)  

In a continuous reformer, some particulate and dust matter can be generated as the catalyst moves from reactor to reactor and is subject to attrition. However, due to catalyst design little attrition occurs, and the only outlet to the atmosphere is the regeneration vent, which is most often scrubbed with a caustic to prevent emission of hydrochloric acid (this also removes particulate matter). Emissions of carbon monoxide and hydrogen sulfide may occur during regeneration of catalyst. 

At present, to contend with increasingly stringent energy requirements, the manufacturers are again trying to develop more specific processes. 

in refining, they employ reformers operating at hi severity but wth greater operating stability and improved gasoline yields, and in petrochemicals, the optimization of the production of BTX aromatics by the use of high-temperature reactors. 

On the whole, catalytic reforming remains a refining process, which is extensively described in specialized works. We shall only dw eil here on the main aspects and specific applications designed to produce petrochemical feedstocks. 

Ring extension and dehydrogenation of alkylcyclopentanes to benzene derivatives, 

Hydrocracking of alkanes and cycloalkanes, together with hydrogenation of the cracker products to hydrocarbons with low molecular weight. 

Thermodynamic data for Ce hydrocarbon reactions under catalytic reforming conditions are summarized in Table 3.20. 

When converting paraffins and naphthenes by catalytic reforming into aromatics, hydrogen is released in relatively pure form. Reforming is therefore an important source of hydrogen for the refinery and the associated petrochemical plants. 

The formation of aromatics is facilitated by a low hydrogen pressure and high temperature. Nevertheless, care should be taken since the hydrocarbons carbonize rapidly on the catalyst as the temperature rises. 

This same process is used extensively to produce benzene and other aromatic compounds for use in the manufacture of plastics, medicines, and synthetic materials. (For a discussion of aromatic compounds, as well as branched and cyclic structures, see Chapter 14. What a treasure trove it is.) 

This reaction is an example of converting the potential energy contained in the hydrocarbon bonds to the kinetic energy of the hot gas molecules. The increeise in the number of gas molecules boosts the pressure tremendously, shoving the piston down. The linear motion is then converted to a rotary motion, which powers the wheels. And off you go  

The process of catalytic reforming introduces chains, and catalytic cracking introduces double bonds. Not only do these two processes increase the amount of gasoline that s produced, but they also improve the quality of the gasoline s burning characteristics. Also notice that benzene, an aromatic compound, has an octane value of 106. Its burning characteristics are better than isooctane. Other substituted aromatic compounds have octane ratings of almost 120. However, benzene and some related compounds are health hazards, so they re not used. 

In the early 1920s, scientists discovered that adding a little bit of TEL to gasoline (1 milliliter per liter of gasoiine) increased the oct me rating by 10 to 15 points. 

TEL was quite effective as an additive to increase the octane rating and prevent engine knocking. It was used for many years. However, the Clean Air Act of 1970 indirectly did it in. 

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It is produced from petroleum fractions rich in naphthenes by catalytic reforming in the presence of hydrogen (hydroforming) in this process dehydrogenation .nd dealkylation... 

Commercially, xylene is obtained by the catalytic reforming of naphthenes in the presence of hydrogen see toluene) or was formerly obtained from coal tar. The material so-produced is suitable for use as a solvent or gasoline ingredient, these uses accounting for a large part of xylene consumption. If xylene is required as a chemical, separation into the iso-... 

For the refiner, the reduction in benzene concentration to 3% is not a major problem it is achieved by adjusting the initial point of the feed to the catalytic reformers and thereby limiting the amount of benzene precursors such as cyclohexane and Cg paraffins. Further than 3% benzene, the constraints become very severe and can even imply using specific processes alkylation of benzene to substituted aromatics, separation, etc. 

For example, in the case of light Arabian crude (Table 8.16), the sulfur content of the heavy gasoline, a potential feedstock for a catalytic reforming unit, is of 0.036 weight per cent while the maximum permissible sulfur content for maintaining catalyst service life is 1 ppm. It is therefore necessary to plan for a desulfurization pretreatment unit. Likewise, the sulfur content of the gas oil cut is 1.39% while the finished diesel motor fuel specification has been set for a maximum limit of 0.2% and 0.05% in 1996 (French specifications). 

A key process in the production of gasoline, catalytic reforming is used to increase the octane number of light crude fractions having high paraffin and naphthene contents (C7-C8-C9) by converting them to aromatics. 

The main feedstock for catalytic reforming is heavy gasoline (80 to 180°C) available from primary distillation. If necessary, reforming also converts byproduct gasoline from processes such as visbreaking, coking, hydroconversion and heart cuts from catalytic cracking. 

Catalytic cracking is a key refining process along with catalytic reforming and alkylation for the production of gasoline. Operating at low pressure and in the gas phase, it uses the catalyst as a solid heat transfer medium. The reaction temperature is 500-540°C and residence time is on the order of one second. 

Steam reforming is, along with catalytic reforming, a process that can produce the additional hydrogen needed for upgrading and converting the heavy fractions of crude oil. 

The conversion products, other than gas and hydrogen sulfide (H2S), are essentially a gasoline fraction that, after pretreatment, will be converted by catalytic reforming an average quality distillate fraction to be sent to the gas oil pool and an atmospheric residue or vacuum distillate and vacuum residue whose properties and impurity levels (S, N, Conr. 

Furthermore, the major problem of reducing aromatics is focused around gasoline production. Catalytic reforming could decrease in capacity and severity. Catalytic cracking will have to be oriented towards light olefins production. Etherification, alkylation and oligomerization units will undergo capacity increases. 

Simple conventional refining is based essentially on atmospheric distillation. The residue from the distillation constitutes heavy fuel, the quantity and qualities of which are mainly determined by the crude feedstock available without many ways to improve it. Manufacture of products like asphalt and lubricant bases requires supplementary operations, in particular separation operations and is possible only with a relatively narrow selection of crudes (crudes for lube oils, crudes for asphalts). The distillates are not normally directly usable processing must be done to improve them, either mild treatment such as hydrodesulfurization of middle distillates at low pressure, or deep treatment usually with partial conversion such as catalytic reforming. The conventional refinery thereby has rather limited flexibility and makes products the quality of which is closely linked to the nature of the crude oil used. 

Catalytic dewaxing Catalytic hydrogenation Catalytic properties Catalytic pyrolysis Catalytic reduction Catalytic reforming... 

Toluene disproportionation (TDP) is a catalytic process in which 2 moles of toluene are converted to 1 mole of xylene and 1 mole of benzene this process is discussed in greater detail herein. Although the mixed xylenes from TDP are generally more cosdy to produce than those from catalytic reformate or pyrolysis gasoline, thek principal advantage is that they are very pure and contain essentially no EB. 

A breakdown of the mixed xylene supply sources in the United States is summarized in Table 1 (1). As shown in Table 1, the primary source of xylenes in the United States is catalytic reformate. In 1992, over 90% of the isolated xylenes in the United States were derived from this source. Approximately 9% of the recovered xylenes is produced via toluene disproportionation (TDP). In the United States, only negligible amounts of the xylenes are recovered from pyrolysis gasoline and coke oven light oil. In other parts of the world, pyrolysis gasoline is a more important source of xylenes. 

Fig. 3. General scheme for producing benzene, PX, and OX from catalytic reforming.

Xylenes Produetion Via Toluene Transalkylation and Disproportionation. The toluene that is produced from processes such as catalytic reforming can be converted into xylenes via transalkylation and disproportionation. Toluene disproportionation is defined as the reaction of 2 mol of toluene to produce 1 mol of xylene and 1 mol of benzene. Toluene transalkylation is defined as the reaction of toluene with or higher aromatics to produce xylenes ... 

The majority of xylenes, which are mostly produced by catalytic reforming or petroleum fractions, ate used in motor gasoline (see Gasoline and other MOTORFUELs). The majority of the xylenes that are recovered for petrochemicals use are used to produce PX and OX. PX is the most important commercial isomer. Almost all of the PX is converted to terephthaUc acid and dimethylterephthalate, and then to poly(ethylene terephthalate) for ultimate use in fibers, films, and resins. 

Cyclic Hydrocarbons. The cyclic hydrocarbon intermediates are derived principally from petroleum and natural gas, though small amounts are derived from coal. Most cycHc intermediates are used in the manufacture of more advanced synthetic organic chemicals and finished products such as dyes, medicinal chemicals, elastomers, pesticides, and plastics and resins. Table 6 details the production and sales of cycHc intermediates in 1991. Benzene (qv) is the largest volume aromatic compound used in the chemical industry. It is extracted from catalytic reformates in refineries, and is produced by the dealkylation of toluene (qv) (see also BTX Processing). 

Butanes are naturally occurring alkane hydrocarbons that are produced primarily in association with natural gas processing and certain refinery operations such as catalytic cracking and catalytic reforming. The term butanes includes the two stmctural isomers, / -butane [106-97-8] CH2CH2CH2CH2, and isobutane [79-28-9], (CH2)2CHCH2 (2-methylpropane). 

Butanes are recovered from raw natural gas and from petroleum refinery streams that result from catalytic cracking, catalytic reforming, and other refinery operations. The most common separation techniques are based on a vapor—Hquid, two-phase system by which Hquid butane is recovered from the feed gas. 

Mixtures of CO—H2 produced from hydrocarbons, as shown in the first two of these reactions, ate called synthesis gas. Synthesis gas is a commercial intermediate from which a wide variety of chemicals are produced. A principal, and frequendy the only source of hydrogen used in refineries is a by-product of the catalytic reforming process for making octane-contributing components for gasoline (see Gasoline and OTHER MOTOR fuels), eg. 

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