Aromatic hydrocarbons from naphtha reforming

The prime purpose of reforming is to make aromatics from each class of non-aromatic hydrocarbons in naphtha. The core reaction of alkane dehy-drocyclisation in reforming is complex and its optimisation has driven catalyst science and reforming technology since the 1960s. 

Adiabatic with Intermediate Heat Transfer. Many tubular reactor systems use a series of adiabatic reactors with heating or cooling between the reactor vessels. For example, naphtha reforming has endothermic reactions of removing hydrogen from saturated cyclical naphthene hydrocarbons to form aromatics. The process has multiple adiabatic reactors with fired furnaces between the reactors to heat the material back up to the required reactor inlet temperature. 

Application The Sulfolane process recovers high-purity C6-C9 aromatics from hydrocarbon mixtures, such as reformed petroleum naphtha (reformate), pyrolysis gasoline (pygas), or coke oven light oil (COLO), by extractive distillation with or without liquid-liquid extraction. 

In Figures 5.7 and 5.8, data are presented for the reforming of a 65-150°C boiling range Persian Gulf naphtha at a temperature of 488°C to produce 96 research octane number reformate (33). The pressure was 28.2 atm, except for a period at 35.0 atm in the approximate time interval from hour 1460 to hour 1710 in each run. The naphtha had a density of 0.7243 g/cm3 and contained, on a liquid volume percentage basis, 70.2% alkanes, 21.1% cycloalkanes, and 8.6% aromatic hydrocarbons. 

While olefins can be obtained industrially by synthesis from shorter molecules, or from functional molecules, aromatic hydrocarbons are not yet produced individually by these two methods. They are produced in a mixture by dehydrocydization as part of naphtha catalytic reforming, and are likely to be produced shortly by the aromatization of short-chain alkanes. 

Ethylene glycol for the synthesis of PET is obfained by air oxidation of ethylene to ethylene oxide (Section 11.8A) followed by hydrolysis to the glycol (Section 11.9A). Ethylene is, in turn, derived entirely from cracking eifher petroleum or ethane derived from natural gas (Section 2.9A). Terephthalic acid is obtained by oxidation of p-xylene, an aromatic hydrocarbon obtained along with benzene and toluene from catalytic cracking and reforming of naphtha and other petroleum fractions (Section 2.9B). 

Naphtha is divided into two main types, aliphatic and aromatic. Aliphatic naphtha is composed of paraffinic hydrocarbons and cycloparaffins (naphthenes), and may be obtained directly from crude petroleum by distillation. Aromatic naphtha contains aromatics, usually alkyl-substituted benzene, and is very rarely, if at all, obtained from petroleum as straight-run materials often reforming is necessary (Fig. 2). 

A typical process flow diagram of a catalytic reformer is shown in Figure 3.17. Desulfurized naphtha is heated in feed-effluent exchangers and then passed to a fired heater, where it is heated to 850 to 1,000° F (455 to 540° C) at 500 psia (3,450 kPa) in a series of reactors and fired heaters. In the reactors, the hydrocarbon and hydrogen are passed over a catalyst (often platinum/rhenium based) to produce rearranged molecules, which are primarily aromatics with some isoparaffins. The reactor effluent is cooled by exchange and then passed to a separator vessel. The gas from the separator is recycled to the reactors. The liquid is fed to a fractionator. 

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