Patent GB-767100-A (GB)
Title: Improvements in or relating to production of 1,3,5-ethylxylene, meta-xylene, ethylbenzene and benzene
IPC: C07C15/02
Filed: 1953-08-20
Abstract: The C8 aromatic components of a hydrocarbon charging stock consisting chiefly of mixed xylenes and ethylbenzene are converted into benzene, meta-xylene and 1,3,5-ethyl xylene by complexing at least a portion of said aromatic components in the substantial absence of water with 6 to 12 mols. of HF and 0.7 to 1.5 mols. of BF3 per mol. of aromatic hydrocarbon in a complexing zone, effecting homogeneous phase conversion by maintaining the resulting HF solution of complex and any uncomplexed hydrocarbons at 50 DEG  to 70 DEG  C. for 0.4 to 4 hours under a pressure greater than the vapour pressure of hydrogen fluoride at said temperature, then reducing the pressure on the products to liberate HF and BF3 and leave about 6 mols. of HF and about 1 mol. of BF3 per mol. of C8 and heavier aromatics in the product, scrubbing the product with a wash liquid, e.g. a saturated low-boiling hydrocarbon such as pentane, to remove substantially all hydrocarbons which are not complexed with HF and BF3, reducing the pressure on the scrubbed complex, heating said complex at said reduced pressure in an evaporator to liberate further HF and BF3, stripping the liquid from the evaporator at 10 to 200 mm. and 100 DEG to 150 DEG  C. to decompose remaining complex, recycling liberated HF and BF3 to the complexing step, removing residual HF and BF3 from the hydrocarbons released from complex in a stripping zone and fractionating said hydrocarbons to recover meta-xylene and 1,3,5-ethylxylene.  The wash liquid containing the uncomplexed hydrocarbons is distilled, the wash liquid recycled, and the uncomplexed hydrocarbons fractionated to obtain pure benzene.  In a modification of the above process, the complex solution is formed by contacting the charge with 6 to 12 mols. of HF and 1 to 1.2 mols. of BF3 per mol. of xylene in the charge at a temperature of - 25 DEG  C. or below and uncomplexed hydrocarbons are separated from the resulting HF solution of xylene complexes at this low temperature before the homogeneous phase conversion and subsequent steps of the process.  In this way ethylbenzene may be recovered by fractionation of the uncomplexed hydrocarbons.  The complexed hydrocarbons may be subjected to homogeneous phase conversion and then worked up as above to recover metaxylene and minor amounts of 1,3,5-ethylxylene, ethyltoluene and mesitylene.  Two embodiments of the process are described in detail and suitable apparatus is illustrated. Experiments are described which show the effect of temperature, BF3 concentration and contact time on the disproportionation of ethylbenze when a mixture of ethylene benzene, p-xylene and n-heptane is complexed with HF and BF3; similar experiments are made on mixtures of ethylbenzene with o-, m- and p-xylenes; further experiments show the interaction of xylene and ethylbenzene to form ethylxylene when complexed with HF and BF3, using n-heptane as a diluent.  In these experiments, the feed, diluent, HF and BF3 are agitated in a reactor for the desired time, then, after settling, the two phases are drawn into separate receivers. The complexes are decomposed with water, the hydrocarbons so released are washed free of HF and BF3 with aqueous caustic and then fractionated.