Patent ID: 6376736
Filing Date: 2002-04-23
Classification: C07C

Abstract:
A process for integrated processing of a hydrocarbon feed stream consisting essentially of C-8+ aromatic hydrocarbons to recover a high-purity meta-xylene product in combination with efficient separation and recovery of other C-8 aromatic hydrocarbon components including para-xylene and optionally ortho-xylene, said process comprising the sequential steps of:(a) processing the C-8+ aromatic hydrocarbon feed by means of a first splitter column, which comprises a single column or a linked series of at least two separate columns wherein a bottoms feed from an upper column feeds the top of an adjacent lower column and distillate from said lower column feeds the bottom of the adjacent upper column while operating said first splitter column so as to produce an ortho-xylene-rich stream and a first splitter distillate stream containing predominant portions of any ethylbenzene, para-xylene and meta-xylene in all of the feeds to the first splitter column, the proportion of ortho-xylene in said distillate stream being maintained at a level low enough to avoid crystallization of ortho-xylene in a downstream meta-xylene crystallization step; (b) processing the first splitter distillate stream by means of an adsorption treatment carried out so as to separate substantially all of the para-xylene and removing desorbent to leave a meta-xylene-rich residual stream containing substantially all of the meta-xylene; and, (c) passing said meta-xylene-rich residual stream directly without intermediate fractionation to a multi-stage meta-xylene crystallization process comprising at least two crystal reformation stages including: (i) at least one meta-xylene crystallization stage operated at a temperature of about âˆ’53Â° C. to âˆ’95Â° C.; (ii) said first crystallization stage operating in conjunction with at least a second crystal reformation stage, which may comprise a second crystallization stage operated at a temperature below that of said first crystallization stage or a slurry drum operated at a temperature above that of said first crystallization stage, for processing at least a portion of the product from said first crystallization stage so as to produce an end-step slurry of meta-xylene crystals; and (iii) passing said end-step slurry of meta-xylene crystals to a final product separator to produce purified meta-xylene crystals and separator liquid; wherein each of steps (i), (ii) and (iii) is carried out with essentially no heat input to the meta-xylene crystallization process thereby to realize a minimum of net melting of crystals.