Patent GB-579781-A (GB)
Title: Alkylation of aromatic hydrocarbons
IPC: C07C15/085
Filed: 1943-11-25
Abstract: Alkylated aromatic hydrocarbons are prepared from aromatic hydrocarbons containing sulphur compounds by pretreatment with concentrated sulphuric acid to reduce the sulphur content followed by reaction of a molar excess of the treated hydrocarbon with an alkylating agent in the presence of an alkylation catalyst.  Acid of at least 95, but preferably below 100 per cent, may be used for the pretreatment of benzene in a ratio of acid to benzene above 1 : 10 by volume, preferably 0.16-0.25 : 1, with intimate contact for at least 3, preferably 4-6 mins. or more, at 10-40, preferably 15-25 DEG  C. Batch treatment in stages with re-use of separated acid in a preceding stage, or continuous treatment may be used.  A subsequent water and alkali wash is preferably effected before alkylating. Excess unreacted aromatic hydrocarbon from the alkylation may be treated with the acid preferably together with the aromatic feed, and returned at least in part to the alkylation.  Aromatic hydrocarbons specified include benzene, toluene, ethylbenzene, xylenes, mesitylene, propyl and butyl benzenes, cymenes, naphthalene and substituted naphthalenes, and petroleum fractions of high aromatic content. The alkylation catalyst may be sulphuric acid, phosphoric acid, hydrogen fluoride, admixtures thereof with adsorbents or coatings on non-porous materials.  80-90, preferably 85-88 per cent sulphuric acid may be used at 40-50 DEG  C., with contact times of at least 10, for example 20-30 mins.  With solid catalysts, pressures of 200-400 p.s.i. are preferably used.  For alkylating benzene with olefins using a solid phosphoric acid catalyst, 200-400 DEG  C. and a hydrocarbon feed rate of 0.1-0.8 gals. per hr. per lb. of catalyst are suitable.  A molar ratio of aromatic hydrocarbon to olefin or like alkylating agent of 3-10 : 1 is preferably used.  With alkylating agents having two alkyl groups such as di-isopropyl ether or sulphate, this molar ratio is doubled.  Other alkylating agents specified include olefinic petroleum cracking products, olefin polymers, ethers, alcohols and esters such as halides, sulphates, phosphates, borates, formates and acetates.  The reactants may be fed to a circulating emulsion of hydrocarbon and sulphuric acid when a molar ratio of aromatic hydrocarbon to alkylating agent of 50-100 or more can be obtained, or a multistage process may be used with split feed of the alkylating agent.  At least 1/10th of the excess aromatic hydrocarbon is treated with the concentrated sulphuric acid before return to the alkylation stage.  A prior alkali treatment is desirable with a dilute aqueous alkali such as alkali metal, calcium or ammonium hydroxide or quaternary ammonium base at above 100 DEG C. and preferably superatmospheric pressure, for example with 10-50 per cent by volume based on the hydrocarbons of 2-10 per cent caustic soda at 100-180, preferably 140-160 DEG  C., for at least 5, preferably 10-30 mins.  This treatment may be applied to the entire hydrocarbon layer from the alkylator, and a fractionation effected to remove low boiling hydrocarbons or to separate alkylate from unreacted aromatic hydrocarbon.  In examples: (1) coal tar benzene is alkylated with propene using a solid phosphoric acid catalyst at 200-250 DEG  C. and 250 p.s.i. Comparative figures for untreated benzene benzene pretreated with 98 per cent acid at 20 DEG  C. are given; (2) the pretreated benzene is alkylated with isobutene or b -butene; (3) benzene containing thiphene is continuously treated by 98 per cent acid, and alkylated with a C3 fraction using sulphuric acid of 88 per cent initial concentration as catalyst.