مقاله انگلیسی رایگان در مورد جداسازی اتیل بنزن و پارا-زایلین با تقطیر عصاره ای – الزویر 2019

Though p-xylene derived from naphtha reformate is in high demand as a raw material in the production of polyesters and polyethylene terephthalates, its separation from the FCC reformate is not easy due to close boiling points among the components in the reformate. When a proper solvent for the p-xylene separation is available, an extractive distillation can be applied in the separation. Currently the separation utilizes an adsorption process requiring a large amount of costly adsorbent and a desorption process followed by distillation. In the proposed extractive distillation here, p-dinitrobenzene has been utilized to improve the separation of p-xylene from its ethylbenzene mixture. The VLE data of the ternary mixture estimated with the UNIFAC were compared to those computed from molecular simulation to show their reliability. An extractive distillation and solvent recovery were applied to obtain 99.6% purity p-xylene with 99.1% recovery. The economics of the proposed process demonstrates its comparability to the existing Parex process.

Introduction

Xylene isomers and ethylbenzene are coexisting components in naphtha reformate, and they are separated by distillation as a group. Before the separation, the C8 compounds are in the aromatic compounds mixture, including benzene and toluene, contained in the extracts of extractive distillation using sulfolane [1]. Further distillation splits the C8 components of close boiling points from others. Among the mixture p-xylene has high demand to produce terephthalic acid, a raw material in the production of polyesters and polyethylene terephthalates (PETs). The separation processes of p-xylene based on solvent extraction [2] or crystallization [3,4] were not efficient with only 60–65% recovery rate. The extractive distillation of ethylbenzene and p-xylene has been studied for many years [2,5,6–9], but no commercial process was developed due to no effective extractant found. Recently searching effective extractants extended to ionic liquid solvents in many extractive distillation processes [10–12]. In 1971, the Universal Oil Products (UOP) commercialized a new separation method of p-xylene, an adsorption process, called the Parex process with a 95% recovery rate [13,14]. Though the adsorption process is largely effective and efficient in the separation of a specific component from a mixture with high recovery and high purity, it requires a large volume of high-cost adsorbents. Moreover the next stage of the adsorption includes a desorption process to recover the adsorbate from the adsorbent using a desorbent [15]. The recovery and recycling of the desorbent accommodate a distillation column separating the targeted p-xylene. A continuous processing has been desired for a large throughput of chemical production, and distillation and extraction are suitable for the processes. On the other hand, because the adsorption was a batch process, a simulated moving bed (SMB) operation [16], a quasi-continuous process, requiring multiple beds of adsorbents was introduced to the Parex process [13,17]. While one of the beds releases the adsorbate, the product, other three beds are preparing for the next production in sequence. Consequently, the SMB operation necessitates a large volume of high-cost adsorbents [18]. In this study, an efficient solvent, p-dinitrobenzene, for the separation of p-xylene from the mixture of ethylbenzene and p-xylene, two main components in the naphtha reformate, is suggested, and the separation process of p-xylene is designed for 99.1% recovery and 99.6% purity of p-xylene using an extractive distillation. The design procedure is explained to present the performance of the proposed separation process. The estimated VLE data of ternary mixture of ethylbenzene, pxylene and p-dinitrobenzene used in the process design are probed by comparing to the computed ones with molecular simulation. The separation performance and economics of the proposed process are measured to the Parex process.