Patent GB-743989-A (GB)
Title: Production of aliphatic acids
Inventor: HABESHAW JOHN
IPC: C07C51/215
Filed: 1952-10-15
Abstract: Acetic acid and other aliphatic acids are obtained by oxidizing in the liquid phase at elevated temperature with a gas consisting of or comprising molecular oxygen, a paraffinic hydrocarbon fraction containing a mixture of hydrocarbons within the C4 to C8 range, at least 40 per cent by weight of said fraction consisting of hydrocarbons selected from the C6 to C8 range, wherein at least 40 per cent by weight of the paraffins selected from the C6 to C8 range in said fraction consists of paraffins having one or more methyl branch chains per molecule and wherein said fraction boils at a temperature not exceeding 100 DEG  C.  Preferably the said fraction boils within the range of about 15 DEG  to 95 DEG  C.  Suitable feed stocks are straight run petroleum fractions containing a high proportion of branched molecules, the products from isomerization of predominantly straight-chain paraffins by aluminium chloride or from other known isomerization processes, the products obtained by the alkylation of olefines with isoparaffins, or the product obtained by hydrogenation of the mono-olefines produced by polymerization of lower olefines such as propylene and isobutene.  A suitable feedstock is a straight run gasoline fraction from a Middle East petroleum boiling between about 15 DEG  and 95 DEG  C. which on oxidation with air at elevated temperature and pressure yields a higher yield of C1-C4 acids and a lower yield of high boiling residues than is obtained from a hydrocarbon fraction of the same origin but having a boiling-point up to 150 DEG  C.  The oxidizing gas may be air or a mixture poorer or richer in oxygen than is air, or part of the molecular oxygen may be in the form of ozone.  The use of high pressures may be necessary to maintain the reactants in the liquid phase.  The preferred temperature range for the oxidation is 130-200 DEG  C.  Oxidation catalysts such as compounds of certain metals may be present and solvents for the hydrocarbons and peroxides or other oxidation initiators may be added, if desired.  The oxidation may be carried out batchwise or continuously.  Thus the process may be operated by removing continuously or intermittently a part of the reaction mixture as a homogeneous liquid which is then cooled to below about 80 DEG  C. to form two liquid layers.  The upper layer is returned to the reactor and all or part of the lower layer is removed as product, the product withdrawn being replaced with an equal amount of fresh hydrocarbon so as to maintain a constant volume of liquid in the reactor system.  An example of this type of procedure is given, the hydrocarbon feedstock being a 15-95 DEG  C. paraffinic distillation fraction from crude petroleum having an initial boiling-point (A.S.T.M.) of 31.5 DEG  C. and a final boiling-point (A.S.T.M.) of 96.5 DEG  C.  This feedstock comprises a mixture of C4 to C7 paraffinic hydrocarbons as well as small amounts of cycloparaffins, benzene, and toluene.  The C6 to C8 paraffins constitute 40-55 per cent of the feedstock and of the C6 to C8 paraffins, those having methyl branch chains constitute 22.85 per cent of the feed-stock.  The paraffins having methyl branch chains are mainly 2-methyl pentane, 3-methyl pentane, 2-methyl hexane and 3-methyl hexane.  The oxidation is carried out with air in a stainless steel reactor at 160 DEG  C. and 300 pounds per square inch pressure, no catalyst being used.  The lower layer containing the product is distilled to recover the separate constituents, namely, volatile non-acidic products, lower aliphatic acids, together with water, and high-boiling residues.  The aliphatic acids are dehydrated and the anhydrous acids recovered in successive fractions.  Acetic acid is the main product, some formic, propionic and butyric acids being also obtained.  Appreciable amounts of volatile non-acidic products and of high-boiling residues are also obtained. Comparative results are given to show that when a paraffinic distillation fraction from a Middle East crude petroleum having an initial boiling-point (A.S.T.M.) of 31.5 DEG  C. and a final boiling-point (A.S.T.M.) of 150 DEG  C. is used as the feedstock the proportion of high boiling residues in the product is increased. Specification 743,991 is referred to.