Published October 2018
para-Xylene and benzene are the most important and high-value building block chemicals for the petrochemicals industry, because of their various end uses as well as their use as intermediates in chemicals production. Other valuable streams from aromatics complexes, depending on the unit configuration and desired products, include ortho-xylene, toluene, BTX raffinate, and C11+ aromatics. Because of the low value of C7A and C9A/C10A streams, these streams are converted to high-value xylene and/or benzene products by transalkylation, disproportionation, selective toluene disproportionation, and methylation processes.
Because of the higher value of and faster-growing demand for p-xylene product compared with benzene, most aromatics complex configurations are selected to increase the mixed-xylene and subsequently p-xylene yield. Of the above stated C7A and C9A/C10A conversion processes, the transalkylation process is the most widely used and contributes to around 50% of the xylene production from an integrated aromatics complex. The transalkylation process produces an equilibrium mixture of xylene plus ethylbenzene. The xylenes are recovered and isomerized to p-xylene and/or other xylene isomers, while ethylbenzene is either isomerized to xylenes or dealkylated to form benzene.
Recently, UOP has developed a two-stage transalkylation process that shows higher xylene yield compared with conventional single-stage transalkylation process [US patents 6958425 and 6855854]. In this review, we present a technoeconomic comparison of the two transalkylation processes (single-stage and two-stage) for a plant feed capacity of 2,524.89 KTA of C7A/C9+ aromatics mix feed producing commercial-grade mixed-xylene product with >98.7 wt% C8 aromatic content and high-purity benzene product with >99.9 wt% purity at the US Gulf Coast.
The evaluation of the economics presented in this review are PEP’s independent interpretation based on the companies’ patent literature and other open source information, and may not reflect in whole or in part the actual plant configuration. However, we do believe that they sufficiently represent the above-mentioned processes in estimating the plant economics within the range of accuracy for economic evaluations of the conceptual process designs.
The process design was simulated primarily using Aspen Technology’s Aspen Plus® process simulator. We worked out plant and process economics (CAPEX and OPEX) using IHS Markit proprietary PEPCOST® software, using in places our own design judgments based on operational experience.