GB743990A - Production of lower aliphatic acids, particularly acetic acid - Google Patents

Abstract

Lower aliphatic acids, particularly acetic acid, are obtained by oxidizing at an elevated temperature in the liquid phase a paraffin hydrocarbon of 4 to 8 carbon atoms with a gas consisting of or comprising molecular oxygen to produce lower aliphatic acids of 1 to 4 carbon atoms, distilling the primary oxidation product to separate as light ends the materials boiling below 99 DEG C. in the presence of water and then oxidizing at elevated temperature in the liquid phase said light ends with a gas consisting of or comprising molecular oxygen to produce lower aliphatic acids. The light ends may be oxidized separately or may be mixed with a paraffin hydrocarbon of 4 to 8 carbon atoms and the mixture oxidized in the liquid phase. The oxidation of the C4-C8 paraffin hydrocarbons may be carried out by the procedure disclosed in Specifications 743,991 and 743,959. The C4-C8 paraffin is preferably one which is normally liquid at room temperature of about 30 DEG C. and atmospheric pressure. On cooling the primary oxidation mixture two liquid layers separate and the process may be operated by removing continuously or intermittently a part of the primary oxidation reaction mixture as a homogeneous liquid, cooling to below 80 DEG C., separating the liquid layers formed, returning all the unchanged hydrocarbon to the reactor and removing at least part of the lower layer as product. The primary oxidation product may be distilled to separate as light ends the fraction which under batch distillation conditions will boil over the range of about 20 DEG C. to about 99 DEG C. in the presence of water. Any water which separates as a lower layer in the distillate may be removed if so desired. The light ends may also be separated by employing a continuous still operated with a head temperature of about 65-70 DEG C. and a base temperature of about 105 DEG C. The products of oxidation of the light ends may be worked up by distillation to yield further light ends boiling below 99 DEG C. in the presence of water and these secondary light ends may also be oxidized with a gas consisting of or comprising molecular oxygen or may be combined with a fresh batch of primary light ends and the mixture oxidised, or they may be combined with the feed of primary light ends and fresh hydrocarbon of 4 to 8 carbon atoms in a continuous oxidation process for oxidation of light ends. On mixing the light ends with fresh hydrocarbon, the aqueous phase which forms may be separated and discarded and the mixture then oxidized. The oxidizing gas may be air or a mixture poorer or richer in oxygen than is air and part of the molecular oxygen may be in the form of ozone. The use of superatmospheric pressure is generally necessary to maintain the reactants in the liquid phase and suitable oxidation temperatures are within the range of 130 DEG to 200 DEG C. An oxidation catalyst may be present. Such catalysts include compounds of metals capable of existing in more than one valency state, e.g. manganese, cobalt, nickel, vanadium, or copper, which may be added in the form of their oil-soluble salts with organic acids. Alternatively, the catalyst metal may be added in the form of an anion whether as the free acid or salt thereof, e.g. as a vanadate. In examples: (1) n-heptane is oxidized with air at 160 DEG C. in the presence of manganese naphthenate and the product, after cooling, is separated into two layers. The lower layer, which is replaced with fresh n-heptane sufficient to keep the total volume in the system constant, is distilled batchwise to recover light ends boiling from 21 DEG to 95 DEG C. in the presence of water followed by a mixture of acids of one to four carbon atoms and water which is dehydrated and distilled to yield the individual acids, viz. formic, acetic, propionic and butyric acids. The light ends are then oxidized at 168 DEG C. using a reactor pressure of 200 pounds per square inch and manganese naphthenate as catalyst, the liquid reaction products being distilled to separate a secondary light ends boiling up to 99 DEG C. in the presence of water followed by a mixture of C1-C4 aliphatic acids and water from which formic, acetic, propionic, and butyric acids are recovered; (2) a straight run gasoline fraction, b.p. 15-95 DEG C., from Middle East petroleum, is oxidized by a procedure such as is followed in (1) and the product distilled to yield a light ends fraction and a base product consisting of water, C1-C4 aliphatic acids, water, and high boiling residues, from which the acids are recovered by distillation. The light ends are oxidized batchwise at 150-170 DEG C. and 300 lbs. per sq. inch pressure and the products obtained are distilled to remove secondary light ends boiling up to 99 DEG C. in the presence of water and the still base subsequently distilled to separate the C1-C4 acids; (3) the secondary light ends recovered in (2) are oxidised batchwise with air and the product distilled to yield tertiary light ends and C1-C4 fatty acids; (4) a straight run gasoline fraction, b.p. 20-95 DEG C., from Middle East petroleum, is oxidized with air by a continuous process wherein the product is cooled and allowed to separate into two layers, the upper hydrocarbon layer, together with some of the lower layer, being returned to the reactor while the remainder of the lower layer is distilled to yield a light ends fraction, which is recycled to the oxidation zone after admixture with fresh hydrocarbon feed, and a base product which is distilled to recover C1-C4 acids. The apparatus used is illustrated diagrammatically by a Figure (not shown). In each example the main product is acetic acid. According to the Provisional Specification the light ends fraction submitted to the oxidation may be the fraction boiling in the range of about 20 DEG to 99 DEG C. or any fraction of narrower boiling range within the said temperatures, e.g. a fraction boiling over the range 30-75 DEG C. or a fraction from which a distillation cut of specified boiling range, e.g. a solvent cut of boiling range 50-60 DEG C. has been removed.