591-605 Cap. 10.6 Ing

Introduction An aromatics complex is a combination of process units that can be used to convert petroleum naphtha and pyrolysis gasoline (pygas) into the basic petrochemical intermediates: Benzene Toluene and Xylenes (BTX). Benzene is a versatile petrochemical building block used in the production of more than 250 different products. Ethylbenzene, cumene, and cyclohexane are the most important benzene derivatives. The xylenes product, also known as mixed xylenes, contains four different aromatic isomers: para-xylene, ortho-xylene, meta-xylene, and ethylbenzene. Small amounts of mixed xylenes are used for solvent applications, but most xylenes are processed further within the complex to produce one or more of the individual isomers. The most important C8 aromatic isomer is para-xylene, which is used almost exclusively for the production of polyester fibres, resins, and films. In recent years, polyester fibres have shown growth rates of 5 to 6 percent per year and resin has shown growth rates of 10 to 15 percent per year, corresponding to the emergence of PET (polyethylene terephthalate) containers. A small amount of toluene is recovered for use in solvent applications and derivatives, but most toluene is used to produce benzene and xylenes. Toluene is becoming increasingly important for the production of xylenes through toluene disproportionation and transalkylation with C9 aromatics. Aromatics complexes can have many different configurations. The simplest complex produces only benzene, toluene, and mixed xylenes and consists of the following major process units: naphtha hydrotreating for the removal of sulphur and nitrogen contaminants; catalytic reforming for the production of aromatics from naphtha; aromatics extraction for the extraction of BTX. However, most modern aromatics complexes are designed to maximize the yield of benzene and para-xylene and sometimes ortho-xylene. About one-half of the existing UOP (Universal Oil Products) aromatics complexes are configured for the production of both para-xylene and ortho-xylene. These newer aromatics complexes have not only the major process units mentioned above, but include the following additional major process units: para-xylene extraction for the separation of para-xylene for the other xylene isomers; xylene isomerization for production of an equilibrium mixture of xylene isomers; toluene and C9 aromatic transalkylation for production of xylenes and benzene. An aromatics complex may be configured in many different ways, depending on the available feedstocks, the desired products, and the amount of investment capital available. Because of this wide flexibility, the product slate can be varied to match downstream processing requirements.