Patent GB-771992-A (GB)
Title: Recovery of aliphatic acids from the oxidation products of hydrocarbons
Inventor: ELCE ALEC
IPC: C07C51/44
Filed: 1953-06-25
Abstract: Formic and acetic acids are recovered from the product of the liquid phase oxidation of paraffinic hydrocarbons with a gas comprising molecular oxygen, said product containing (a) "light ends" which are defined as volatile non-acidic oxidation products of boiling point up to 99 DEG  C. in the presence of water, (b) water, (c) aliphatic monocarboxylic acids of 1 to 4 carbon atoms, and (d) higher boiling residues, by distilling the product, desirably from which all or part of the light ends have been removed, to separate from the higher boiling residues a distillate mixture comprising water and the aliphatic monocarboxylic acids of 1 to 4 carbon atoms and then fractionally distilling this mixture, after removal of any remaining light <PICT:0771992/IV(b)/1> ends, to recover the formic and acetic acids.  During the distillation of the oxidation product, small amounts of volatile, coloured, non-acidic materials boiling up to 99 DEG  C. in the presence of water, e.g. ketones and esters, which are referred to as "subsidiary light ends" are formed and these co-distil with the mixture of water and C1-C4 acids and in a preferred embodiment of the invention the distillate mixture comprising water and the C1-C4 acids is subjected to fractional distillation to remove as distillate the subsidiary light ends prior to separating the formic acid-acetic acid fraction by fractional distillation of the residue.  The separation of the mixture of water and C1-C4 acids may be carried out by flash distillation without fractionating, but a degree of fractionation by means of a fractionating column and reflux is preferred.  The separation may be carried out under reduced pressure or at atmospheric pressure and the concentration of water in the base product should not be reduced to below about 8 per cent by weight.  In examples: (1) a product obtained by liquid phase oxidation at 160 DEG  C. and at 300 pounds per square inch gauge of a paraffinic fraction of boiling range 15-95 DEG  C. prepared by the straight distillation of a Middle-East petroleum is fractionally distilled to remove completely the light ends boiling up to 99 DEG C. in the presence of water.  The base product is then freed from the higher boiling compounds by distillation through a fractionating column to yield a crude mixture of water and C1-C4 acids which is then submitted to a further fractional distillation through a packed column up to a head temperature of 99 DEG  C. at atmospheric pressure to remove subsidiary light ends.  The residue is then fractionally distilled first in the presence of isopropyl ether to remove water and then to separate a formic acid-acetic acid fraction boiling at 100 DEG  to 119 DEG  C. at 760 mm. pressure; (2) as in (1) except that the initial oxidation product is prepared by oxidising the same feedstock at 170 DEG  C. and 600 pounds per square inch gauge; (3) as in (2) except that only the more volatile light ends are removed in the first fractional distillation, the head temperature of the column being 60-65 DEG  C., whilst the head temperature in the subsequent distillation to remove subsidiary light ends is about 95 DEG  C.; (4) the same oxidation product as used in (2) is introduced by line (1) (see Figure) into a continuous still (2) operated at a head temperature of about 60-65 DEG  C.  The volatile light ends are removed by line (3) and the base product is passed to a continuous still (5) operated at a head temperature of about 100-110 DEG  C. where it is fractionally distilled to separate the crude mixture of acids from the higher boiling material which is taken off at (6). The aqueous C1-C4 acids distillate is passed to a continuous distillation column (8), the reflux ratio being about 9 : 1 and the head temperature 90 DEG  to 95 DEG  C., to remove subsidiary light ends which are withdrawn through line (9) to a phase separator (10) where the distillate separates into two phases, all or part of the lower liquid phase and/or part of the upper liquid phase being returned to the still as reflux, the remainders being removed.  The base product is passed by line (11) to a continuous dehydrating still 12 using isopropyl ether as entrainer and the still base product is passed to a still (15) in which toluene is used as entrainer.  The overheads pass to phase separator (16), the lower layer comprising formic acid being taken off and the upper layer comprising toluene being returned to the column.  The base product is passed to a continuous fractionation still (18) to separate acetic acid which is then finally distilled to remove traces of toluene and formic acid. The base product removed by line (20) comprises the C3 and C4 acids. Specifications 743,989, 743,990, 743,991, 767,290 and 771,991 are referred to.ALSO:Formic and acetic acids are recovered from the product of the liquid phase oxiation of paraffinic hydrocarbons with a gas comprising molecular oxygen, said product containing (a) "light ends" which are defined as volatile non-acidic oxidation products of boiling point up to 99 DEG C. in the presence of water, (b) water, (c) aliphatic monocarboxylic acids of 1 to 4 carbon atoms, and (d) higher boiling residues, by distilling the product, desirably from which all or part of the light ends have been removed, to separate from the higher boiling <PICT:0771992/III/1> residues a distillate mixture comprising water and the aliphatic monocarboxylic acids of 1 to 4 carbon atoms and then fractionally distilling this mixture after removal of any remaining light ends to recover the formic and acetic acids.  During the distillation of the oxidation product small amounts of volatile, coloured, nonacidic materials boiling up to 99 DEG C. in the presence of water, e.g. ketones and esters, which are referred to as "subsidiary light ends" are formed and these co-distil with the mixture of water and C1 - C4 acids and in a preferred embodiment of the invention the distillate mixture comprising water and the C1 - C4 acids is subjected to fractional distillation to remove as distillate the subsidiary light ends prior to separating the formic acid-acetic acid fraction by fractional distillation of the residue.  The separation of the mixture of water and C1 - C4 acids may be carried out by flash distillation without fractionating, but a degree of fractionation by means of a fractionating column and reflux is preferred.  The separation may be carried out under reduced pressure or at atmospheric pressure and the concentration of water in the base product should not be reduced to below about 8 per cent by weight. In examples: (1) a product obtained by liquid phase oxidation at 160 DEG C. and at 300 pounds per square inch gauge of a paraffinic fraction of boiling range 15 DEG -95 DEG C. prepared by the straight distillation of a Middle-East petroleum is fractionally distilled to remove completely the light ends boiling up to 99 DEG C. in the presence of water.  The base product is then freed from the higher boiling compounds by distillation through a fractionating column to yield a crude mixture of water and C1-C4 acids which is then submitted to a further fractional distillation through a packed column up to a head temperature of 99 DEG C. at atmospheric pressure to remove subsidiary light ends.  The residue is then fractionally distilled first in the presence of isopropyl ether to remove water and then to separate a formic acid-acetic acid fraction boiling at 100 to 119 DEG C. at 760 mm pressure, (2) as in (1) except that the initial oxidation product is prepared by oxidizing the same feedstock at 170 DEG C. and 600 pounds per square inch gauge; (3) as in (2) except that only the more volatile light ends are removed in the first fractional distillation, the head temperature of the column being 60-65 DEG C., whilst the head temperature in the subsequent distillation to remove subsidiary light ends is about 95 DEG C.; (4) the same oxidation product as used in (2) is introduced by line (1) (see Figure) into a continuous still (2) operated at a head temperature of about 60-65 DEG C.  The volatile light ends are removed by line (3) and the base product is passed to a continuous still (5) operated at a head temperature of about 100-110 DEG C. where it is fractionally distilled to separate the crude mixture of acids from the higher boiling material which is taken off at (6). The aqueous C1 - C4 acids distillate is passed to a continuous distillation column (8), the reflux ratio being about 9:1 and the head temperature 90 to 95 DEG C., to remove subsidiary light ends which are withdrawn through line (9) to a phase separator (10) where the distillate separates into two phases, all or part of the lower liquid phase and/or part of the upper liquid phase being returned to the still as reflux, the remainders being removed.  The base product is passed by line (11) to a continuous dehydrating still 12 using isopropyl ether as entrainer and the still base product is passed to a still (15) in which toluene is used as entrainer.  The overheads pass to phase separator (16), the lower layer comprising formic acid being taken off and the upper layer comprising toluene being returned to the column.  The base product is passed to a continuous fractionation still (18) to separate acetic acid which is then finally distilled to remove traces of toluene and formic acid.  The base product removed by line (20) comprises the C3 and C4 acids. Specificatio 743,989, 743,990, 743,991, 767,290 and 771,991 [all in Group IV(b)] are referred to.