US2450381A - Treatment by azeotropic distillation of complex mixtures - Google Patents

Description

mpi'. 2g, i948. s. J. RALPH ETAL 2,450,381

TREATMENT BY AZEOTROPIC DISTILLATION 0F COMPLEX MIXTURES Filed Mamil 28, 1944 -9 macnews Inventors A ilqrneys Patented Sept. 28, 1948 'TREATMENT BY AzEoTnorlc DISTILLA- TloN or COMPLEX mx'rUnEs' Sydney Jamieson Ralph and George Anthony Dummett, Point Pleasant, Wandsworth, London, England, assignors to The Aluminium y Plant & Vessel Company Limited, London, England, 'a British company Application March 28, 1944, Serial No. 528,432 Y In Great Britain March 19, 1943 YYSection 1. Public Law 6190., August 8, 1946 Patent expires March 19, 1963 This invention relates to the treatment by distillation of complex mixtures and has for its chief object the provision of an improved method of and means for separating by distillation the components of azeotropic and like mixtures dimcultly resolvable by simple distillation into their components.

It is known, for example, that acetone and methyl alcohol mixed in certain proportions give a constant boiling point mixture and that such a mixture is not resolvable into its components by simple distillation as an azeotrope dlstils over unchanged.

It is also known that paraillnoid and aromatic hydrocarbons of closely related boiling points give mixtures which are not readily resolvable by simple distlllationso that even under conditions of high reux the distillate consists of a mixture Claims. (Cl, 202-42) `ilnoid hydrocarbons and acetone.

of paraiiinold and aromatic hydrocarbons. This may be due to the tendency oi aromatic hydrocarbons to form azeotropes with hydrocarbons of other series.

It is also known that diiculties are experienced in separating acetone from methyl alcohol in the products obtained by the carbonisation of wood, sawdust and the like and in separating the aromatic hydrocarbons from the parafllnoid stocks derived, for example, fromv petroleum, the carbonisation of coal and the like.

According to the present invention an acetonemethanol mixtureis distilled in the presence of a paramnoid-aromatic hydrocarbon mixture so that two components, one from each of the mixtures, are removed ln the top product whilst the 'remaining two components are removed in the bottom product.

If it ls desired to separate acetone from admixture with methyl alcohol, the mixture may be fed to a distillation column together with a mixture of parailinoid and aromatic hydrocarbons and heat is applied in the usual manner. At comparatively low redux ratios, a distillate is obtained containing substantially all the acetone and parainoid hydrocarbons whilst substantially all the methyl Aalcohol and aromatic hydrocarbons are found in the lower part of the column. The acetone may then be removed from admixture with paraihnoid hydrocarbons by washing, for example, with water and decantation followed by concentration in a rectiilcation column or other known means. The methyl alcohol may `be removed by similar treatment of the eilluent mixture ofmethyl alcohol .with aromatic hydrocarbons leaving the base of the column by washing, for instance, with water and decantation followed by concentration in a rectincation column or other known means.

Conversely, if it is desired to separate parafnnoid hydrocarbons from admixture with aromatic hydrocarbons, the mixture is fed to a distillation column together with a mixture of acetone and methyl alcohol and heat is applied in the usualmanner, At comparatively low reilux ratios such as 1 to 1 to 3 to 1, a distillate ls obtained containing substantially all the paraf- The parafiinoids may be recovered by washing with water or other preferential solute for acetone and decanting oft the hydrocarbon layer and freeln same from 4any acetone and/or water remaining in the hydrocarbon layer by running same through a heated stripping column where the acetone and/or water are removed as top products.

Thus'. means are provided for recovering meth-i yl alcohol in the first case and aromatic hydrocarbons in the second case. As both of these will be found in the lower part of the distillation column whence they canv be removed and recovered as commercial products by known means.

For many reasons, it is convenient to carry out this invention in the presence of water. It is not necessary to use anhydrous entralnlng mixtures and satisfactory results have been obtained under continuous distillation conditions with a mixture of acetone and methyl alcohol with more than its own volume of water.

The invention is carried out in a continuous type of distillation apparatus. It has been found that in a continuous type of distillation apparatus ycontaining one column it is possible to perform both the separation of components before described together wlth the regeneration of the acetone from the aqueous solution resulting.

from water washing the distillate, thus obviating the need for a separate acetone recovery column in cases where the products to be removed from the system are hydrocarbons and the need for supplying additional water to resolve the bottom product into its components as substantially all the water fed to the column passes to the lower part thereof together with the methyl alcohol and aromatic hydrocarbons.

It has been found in practice that it is sometimes possible when using an aqueous solution of acetone and methyl alcohol as the entraining agent to form a zone in the distillation column in which 'substantially all the methyl alcohol is held, i. e. it does not appear in either the distillate or eilluent in substantial amounts.

Therefore, under such conditions, the quantity of methyl alcohol in the circulating entrainer solution will be decreased. When the column is working in this manner, the quantity of methyl alcohol passing to the bottom decanter is very small, e, g. 0.1 to 0.5 per cent calculated on the water leaving the base of the column.

Similarly, it is advantageous when separatlng a wood spirit consisting essentially of acetone and methyl alcohol to feed this to the column in the form of an aqueous solution. In this case it may be found preferable to return both -the parainnold and aromatic hydrocarbons .back to the column immediately after decantation of the respective hydrocarbon layers thus using the process as a means of continuously producing acetone and methyl alcohol and using a continuous recirculation of a limited quantity of mixed hydrocarbons to effect the separation.

Conversely, it is possible continuously to separate a mixture oi' aromatic and non-aromatic hydrocarbons by using a limited quantity of a mixture of acetone and methyl alcohol which is recirculated preferably in the form of an aqueous solution.

As an example, a mixed hydrocarbon fraction derived from the carbonization of coal of S. G. 0.844 and of approximate composition:

\ f Percent by volume Non-aromatlcs 25 Aromatics 75 and distilling %@l09.8 deg. C. and 95%@114.4 deg. C. may be used, there being mixed with one volume of this 5.2 volumes of an aqueous solution 'containing 47.5% of acetone and 2.5% of methyl alcohol by volume.

This mixture is fed to a continuous type of col- As a further example', it may be mentioned that a mixed hydrocarbon fraction derived from low .gravity crude benzole of S. G. 0.837 and of approximate composition.: paraffinoid hydrocarbons-30% by volume and aromatic hydrocarbons-70% -by volume, and distilling an Engler distillation 5% to 95% within 5 C. with not less than 90% at 112 C., may be used, there being mixed with one volume of this hydrocarbon mixture 6.49 volumes of an aqueous solution containing 54.9% of acetone and 2.0% of methyl alcohol. The mixture is fed to a. continuous type of column having 45 plates and is distilled under a reflux ratio of the order of 2.5 to 1, the temperature at the top of the column being about 57 C., the temperature at a zone 7 plates from the base of the column being 72/75 C. and the f temperature at the base of the column being umn having 48 plates and is distilled .under a .redux ratio of 1.5 to 1, with a temperature of about 57c C. at the top of the column, a temperature of l0/75 C. at a position about seven plates from the bottom of the column and a temperature of 90/95 C. at the base of the column when it will be found that 2.7 volumes of distil- 'late are obtained and this will contain about 1% of water, the remainder being hydrocarbons and acetone but no methyl alcohol.

This distillate on washing with an equal quantity of water in a counter current scrubber yields 7.7% of its volume (0.21 volume ofthe hydrocarbon feed) as a decanted hydrocarbon layer of S. G. 0.746 containing 93.5% of non-aro- -matic and 6.4% of aromatic hydrocarbons together with a trace of acetone.

The product from the bottom of the column is found to amount to 3.7 volumes containing all the methyl alcohol in the feed with the remainder of the hydrocarbons and water with only a trace `of acetone.

'I'his product separates into two layers when decanted. The top layer which consists of hydrocarbons amounting to 0.79 volume of the hydrocarbon feed has a S. G. of 0.8702 and contains 0.1% of methyl alcohol water mixture in solution. The aqueous layer contains. about 5% by ,tially all the acetone and methyl alcohol in the ysystem diluted to about 50% by volume with water and is recirculated continuously with fresh hydrocarbons as feed to the column.

87/92" C'. In thisI way, it has been found that 3.9 volumes of distillate are obtained which has the following analysis:

Dissolved hydrocarbons (S. G.

' 0.758) 7.3% by volume Methyl alcohol Less than .01% Water 1.4% by volume Acetone Remainder Such distillate on washing, for example, in a countercurrent scrubber with the aqueous solution decanted from the 'eiliuent at the base of the column (3.1 volumes containing 4% of methyl alcohol) has been found to yield 7.3% of its volume (0.28 volume of the hydrocarbon feed) as a decanted hydrocarbon layer of S. G. 0.758 containing about 92% of paraillnoid and 8% of aromatic hydrocarbons with only a. trace of acetone. The eiliuent from the bottom of the column amounts to some 3.8 volumes containing all the methyl alcohol in the feed with the remainder of the hydrocarbons and water with only a trace of acetone. This eiliuent separates into two layers when decanted, the lower aqueous layer amounting to some 3.1 volumes having the following analysis:

Per cent by volume Methyl alcohol 4 Acetone 0.19

Water, remainder.

Such lower layer is removed and recirculated, for example, to the counter-current scrubber wherein vthe distillate is Washed. The top layer decanted from the eiliuent consists of hydrocarbons amounting to 0.72 volume of the hydrocarbon feed, has a density of 0.8680 and contains about 94% aromatics with a small quantity (less than 0.1%) of methyl alcohol in solution and is removed continuously. When refined in known manner, for example, by washing with strong suiphuric acid and redistilling, this fraction yields substantially pure toluene of S. G. 0.8698 with a boiling range (5/9'7%) of 0.19 C. in4 a yield equivalent to about 95% of the toluene present in the original feed.

It is to be understood that unsaturated bodies and/or organic sulphur compounds such as those usually present ln commercial fractions prepared from coal carbonisation or petroleum products may also be present in the original feed. The majority of the unsaturated bodies will be found in the distillate Whereas the sulphur compounds will normally be found in the bottom product.

sorption of 18.8 grams per ml. and organic sulphur compounds equivalent to 0.13% of the total sulphur by weight, the hydrocarbons separated from the distillate may have a bromine absorption of 56.5 grams per 100 ml. and a total sulphur content of 0.02% while the emuent hydrocarbon product amounting to 70.7% by volume of the feed may have a bromine absorption of 3.9 grams per 100 ml. and a total sulphur content of 0.17% by weight. Thus, the distillate contains 85% of the total unsaturated hydrocarbons while the emuent product contains 96% of the sulphur compounds present -in the feed.

Alternatively, there may be used as a feed a fraction containing paramnoid and aromatic hydrocarbons derived `from petroleum. Such fractions are often prepared by thermal and/or catalytic reforming processes or by straight run distillation of aromatic containing crudes. For example, a concentrated cut from reformed naphtha stocks prepared by the Polyform and Houdry processes may -have a S. G. of 0.7695 and contain 17.5% of aromatics by volume together lwith a considerable proportion of methyl cyclohexane and distil at 102.1 deg. C. and 95% at 111.8

' deg. C. Such a fraction whilst not being readily resolvable by simple distillation even at high reflux ratio is separable into its main components by distillation if this takes place in the presence of a mixture of acetone with methyl alcohol in the manner indicated above.

As a further example, a thermally reformed naphtha from a Mid-Continent petroleum crude may be distilled to yield a concentrate fraction of S. G. 0.7794 with true boiling point curve exclusively between 90 and 118 C. and distilling on Engler test 5% at 104.6 C., 50% at 105.8 C. 'and 95% at 110.2 C., and of approximate composition;

paraiiinoid hydrocarbons 78% by volume and aromatic' hydrocarbons 22% by volume with unsaturated hydrocarbons giving a bromine absorption of 43.4 grams per 100 ml. One volume of this hydrocarbon mixture may be mixed with 7.15 volumes of an aqueous solution containing 46.4% of acetone and 3.1% of methyl alcohol and fed to a continuous type of column 29 mm. in diameter and packed with A inch Raschig rings for a total packed height of 8 ft. 6 inches. The mixture is then distilled under a reflux ratio of about 1 to 1 with suflicient input of heat to maintain the temperatures at the top of the column at 57 C., at a point in the column immediately above 1 ft. 8 inches of packing measured from the base oi' the packed column at 74 C. and in the heating section at the base of the column at 94 C. In this way, it has been found that 4.17 volumes of distillae are obtained which has the following analys Percent by volume Dissolved hydrocarbons 18.5 Water 1.8 Acetone, remainder.

6 ing to some 4.01 volumes having the following analysis:

v Percent by volume Methyl alcohol 4.9 Acetone 0.12 Water, remainder.

The top layer decanted from the eiiluent amounting to 0.23 volume of the mrdrocarbon feed, has a s. G. of 0.869 and contains 90.1% by volume of aromatics with a small quantity (less than 0.1%) of methyl alcohol in solution. When refined in known manner, for example, fby washing with strong sulphuric acid and redistilling, this fraction yields substantially .pure toluene of lS. G. 0.871 in a yield equivalent to about'91.5% of the toluene present in the original feed.

In carrying the invention into practice, any suitable form of continuous distillation unit may be used and distillation may be carried out at pressures below or above atmospheric. The accompanying drawing shows diagrammatically and by way of example one convenient form of apparatus 'which is suitable for the purpose in view and which includes a fractionation column 3 provided at a suitable point intermediate between the top and the bottom with a feed pipe i having a control valve 2. The column is equipped with the usual ancillary apparatus including means such as a steam heated calandrla l for producing vapour by heat at the base and means such Such distillate on washing twice with an equal volume of water has been found to yield 18.5% of its volume (0.77 volume of the hydrocarbon feed) as a decanted hydrocarbon layer of S. G. 0.7530 containing about 98.4% of parai'iinoid and 1.6% of aromatic hydrocarbons with only a trace of acetone and having a bromine absorption of 52.5 grms. per 100 m1.

The eilluent from the bottom of the column amounts to some 4.24 volumes containing all the methyl alcohol in the feed with the remainder of the hydrocarbons and water with only a trace of acetone. This eilluent separates into two layers when decanted, the lower aqueous layer amountas a water cooled condenser 5 for condensing the vapours leaving the top of the column.

In operation, a mixture of paramnoid and aromatic hydrocarbons obtained, for example, from the carbonisation of Scottish coal in vertical retorts and having an Engler boiling range (5 to of 5 C. with 90% distilling at about 112 C., is fed to the column through the pipe line l and, at the same time, a solution of acetone and methyl .alcohol in' water which may contain a trace of dissolved hydrocarbons is fed from a balance tankk 6 through a pipe line 1 and control valve 8 to a suitable point in the column. Vapours consist- :ing essentially of non-aromatic hydrocarbons and acetone leave the top of the column 3 through the pipe line 9, are condensed in the condenser 5 and split into two streams by a reflux divider Il or a similar known means for maintaining a constant reflux ratio, one stream being returned to the top of the column as reflux through a pipe line il. The other stream is permitted to flow as product through a pipe line I2 to the base of the scrubbing section of a countercurrent scrubberdecanter Il where it meets in countercurrent ow a stream of a dilute solution of methyl alcohol in water which is fed from a balance tank Il through a pipe line I5 and a control valve I6 to the top of the scrubbing section of the scrubberdecanter.

Here. the mixture separates into two layers, the lighter layer consisting essentially of parafiinoid hydrocarbons rising to the top of the scrubberdecanter and overflowing through the pipe line I1 to storage tank Il. The heavier layer consisting of a solution of acetone and methyl alcohol in water, together Iwith possibly a small trace of dissolved hydrocarbons, is removed continuously from the bottom of the scrubber-decanter by suitable means and is returned through the pipe line I! to the balance tank 6 and thence recirculated back as part of the feed to the column 3.

At the same time, a mixture of aromatic hydrocarbons, methyl alcohol and water substantially free from acetone overflows or is continuously removed by suitable means from the base of the column 3 and is fed through the pipe line 2l to a decanter 2i. The upper layer consisting essentially of aromatic hydrocarbons decants and overlflows through a pipe line 22 to a storage tank 23 and the lower layer consisting of a dilute solution `oi' methyl alcohol in water is removed continuously by known means from the base of the decanter 2| and is fed through a pipe line 24 to the balance tank I4 and is then used as scrubbing agent in the scrubber-decanter i3, as before described.

1. A distillation treatment of complex mixturesof mutually soluble liquids inseparable or separable only with difllculty by simple distillation, comprising continuously distilling a mixed hydrocarbon fraction containing approximately 25% by volume of non-aromatics and 75% by volume of aromatics and continuously distilling between 109.8 and 114.4 C. in a distillation column with an equeous solution containing approximately 47.5% of acetone and r2.5% of methyl alcohol by volume, under a reflux ratio of the order of 1.5 to '1 vwith a temperature of about 57 C. at the top of the column, an intermediate temperature of l70 to 75 C. and 90 to 95 C. at the bottom of the column, so that the acetone from the mixture is continuously removed in the top product with the paraillnoid components while the remaining components are removed' in the effluent from the base of the column.

2,. A distillation treatment of complex mixtures ,of mutually soluble liquids inseparable or separablc only with diliculty by simple distillation, comprising continuously distllling a mixed hydrocarbon yfraction containing approximately by v 'volume of parafiinoid hydrocarbons and 70% by volume of aromatic hydrocarbons and continuously disiiling with not less than 90% at about 112 C., in a distillation column with an aqueous solution containing approximately of acetone and 2% of methyl alcohol by volume under a reflux Iratio of the order of 2.5 to 1 with a temperature of about 57" C. at the top of the column, an intermediate temperature of about 73 C. about one iifth up the column from the base and a bottom temperlature of about 90 C. so that the acetone from the uct with the paralnoid components while the remaining components are removed in the eilluent from the base of the column.

3. A distillation treatment of complex mixtures of mutually soluble liquids inseparable or separable only with dilculty by simple distillation, comprising continuously distilling a mixed hydrocarbon fraction containing about 15% to 25% of aromatic hydrocarbons and to 75% of parafnoids with a true boiling point of to 118 C. in a distillation column with an aqueous solution containing 40 to 50% of acetone and 1% to 8% of methyl alcohol under a reflux ratio of 0.8 to 2.0 to 1 with a. temperature slightly above the boiling point of acetone at the top of the column and a temperature of 93/95 C. in the heating section of the column so that the acetone from the mixture is continuously removed in the top product with the parainoid components while the remaining components are removed in the eilluent from the base of the column.

4. A distillation treatment as claimed in claim 3 in which the vapours leaving the top of the column are condensed and divided into two streams by means adapted to maintain a constant reiiux ratio, one stream being returned to the top of the co;umn as reflux and the other being subjected 'to scrubbing in counter-current flow a stream REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,079,004 Golodetz Nov, 18, 1913 2,198,651 Bludworth Apr. 30, 1940 2,212,810 Field Aug, 27, 1940 2,302,608 Field Nov. 17, 1942 2,341,433 Fisher Feb. 8, 1944 2,356,240 Hamlin Aug. 22, 1944 2,356,348 Patterson Aug. 22, 1944 2,361,493 Patterson Oct. 31, 1944 2,386,755 Spiers Oct. 16, 1945 2,417,355 Dummett et al Mar. 11, 1947

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