Patent GB-713247-A (GB)
Title: Improvements in or relating to a process for the concentration of individual xylene isomers
Inventor: LIEN ARTHUR PHILLIP
IPC: C07C7/10
Filed: 1950-08-16
Abstract: Individual xylene isomers are concentrated from a solution of at least two in liquid HF and BF3, the solution containing at least 1 mol. BF3 per mol. of xylenes, by withdrawing BF3 from said solution to reduce the concentration to below 1 mol. BF3 per mol. aromatic hydrocarbons originally present and to convert said solution into two immiscible layers, one consisting of xylenes in a ratio different from their ratio in the solution, and the other consisting of a second solution of xylenes in liquid HF and BF3, the ratio of xylenes being different from their ratio in the original solution, and separating said layers.  The original solution may also contain at least one C10 aromatic, viz. diethylbenzenes and/or ethylxylenes, at least 1 mol. BF3 being present per mol. dissolved aromatics, which C10 aromatics appear in the second layer obtained by the process. Suitable sources of the xylene mixtures are hydroformed, cracked or dehydrogenated naphthene fractions, solvent extracts or xylene isomerization products.  A hydroformed aromatic fraction may first be fractionated or the total cut subjected to extraction with HF, which contains at most 10 per cent of water, and BF3.  Diluents comprising low - boiling saturated hydrocarbons may be added.  Generally, 1.25-2 or more mols. BF3 and 5-100 mols. HF per mol. xylenes are used to ensure complete extraction of xylenes.  Where it is desired to extract diethylbenzenes and ethylxylenes, which may be formed by disproportionation of ethylbenzene, additional BF3 is necessary. Temperature may be about 0-150 DEG  F.  The charge flows up against a counterflow of extractant in a packed tower, and the raffinate may be led off at the top to a stripper for HF, BF3 and diluent which are recycled.  The primary extract phase withdrawn at the base may be treated either by stripping all the HF and BF3, followed by selective extraction with HF and BF3 and partial BF3 withdrawal, or by removing part of the BF3 to give two immiscible layers.  In the first method, a stripping tower is operated at 100-160 DEG  F. and 0-20 p.s.i.g. with injection of low-boiling paraffins if desired, the stripped hydrocarbons are optionally fractionated to remove C10, and extracted in a tower as above, but using less than 1, e.g. 0.2-0.8 mol. BF3 per mol. xylenes.  A raffinate depleted in m-xylene is obtained and is stripped and fractionated to give o- and p-xylene concentrates.  The extract phase containing at least 1 mol. BF3 per mol. xylenes is heated to reduce the BF3, preferably to 0.75-0.9 mol. per mol. xylenes, stratified, and the raffinate and extract layers treated as above. If C10 hydrocarbons are not removed, they occur in the extract and are separated from the m-xylene by fractionation.  In the second method, the primary extract phase is treated to reduce p  the BF3 to 0.5-0.9 mol. per mol. aromatics by heating at 100-160 DEG  F. and 0-75 p.s.i.g. when two phases separate and are worked up to give m-, and a mixture of o- and p-xylenes respectively.  Under severe conditions of m-xylene isomerization, disproportionation thereof to yield toluene and trimethylbenzenes may also occur.