US1979185A - Apparatus for the final refining of benzols washed with acid - Google Patents

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Patented Oct. 30, 1934 UNITED STATES APPARATUS FOR THE FINAL REFINING 0F BENZOLS WASHED WITH ACID Emile Augustin Barbet, Paris, France Application February 4, 1932, Serial No. 590,965 In France February 5, 1931 1 Claim. (Cl. 202-154) This invention relates to the refining of benzol in order to obtain in a really pure condition benzene, toluene and xylene or solvents.

Actually, the greater portion of the benzol produced is intended to be incorporated with liquid carburetting agents (petroleum spirits or alcohols); this is the so-called benzol for motors. For this kind of benzol, if the product has been coarsely refined before washing with acid, a real refining is not necessary. It sufiices to effect a simple distillation, separating benzol from resinous tar. which has been produced by the reaction of sulphuric acid.

The problem of refining in order to obtain the various constituents in a pure condition is quite different. Concerning benzene, it must totally distill within half a degree centigrade, between 80 and 81 C. For toluene, within one degree cenfive degrees, for. the reason that, in fact, several xylenes exist, which are somewhat difierent as far as the boiling point is concerned.

Finally, naphtha-solvent is also separated, and then tarry residues which have been formed by polymerization during purification with sulphuric acid.

The continuous rectification of washed benzol is effected in three successive and interconnected plate columns having for function to respectively supply benzene, then toluene, and finally xylene, all of which must satisfy the conditions of receptionj above mentioned.

But purification may be carried to a further degree, and although this seems to slightly complicate the apparatus, it is quite advantageous g to adopt the process thus improved, as extrapurity is obtained without any supplementary expenses either in fuel or inlabour. The general to say, B, B and F, F for benzenev and K for toluene. As far as the column S for xylene and solvent is concerned, as it does not operate really continuously, the double action would be much less easy to control, and in fact, for these products the fractionation is easier and industry is not so exacting concerning their chemical purity.

, 1.Double rectification of benzene It is effected with double action, in two plate columns'BB and FF, the second column FF operating under a certain vacuum (absolute tension between A; and atmosphere) owing to which the boiling point is lowered from 81 C. to

For xylene, there is an allowance of.

about 50 C. This drop of temperature is utilized as follows:

Benzene vapours from BB have a temperature of about 81 C. and pass in a first tubular apparatus D arranged at a higher level than the column BB, so that the benzene condensed in D can-flow back to the top of the column B. A valve 3 is arranged above the outlet fiask d; the said valve is sufficiently closed so that only a very small proportion of benzene vapours may pass into the cooler D.

The head products finally issue through d. A portion of the liquid is admitted in the test gauge b through the pipe 4 and it is sent to a vessel (not shown) containing the motor benzol"; the complement proceeds to the U-shaped pipe 5 and is thus added to the refiuxof D. On one of the plates at the upper part of B is efiected at E a partial extraction of the reflux. This extraction is a benzene which would be already sufliciently pure for satisfying the conditions of reception of trade. But it will be rectified a second time in the plate column FF which will fractionate the last traces of too light products the. U-shaped pipe 6, feeds the column FF.

Boiling is caused to take place in this column FF through the medium of the tubular apparatus D'which acts as second efiect heater. For that purpose, the residual'liquid from the bottom of F, issuing through the pipe 12, and pumped by I, is delivered, through the pipe 13 and the valve 14, in the base of the tubular apparatus D. On the other hand, the benzene vapours generated at about 50 or even 60 C. in D are conveyed, by the large heat insulated pipe 15, to the base of F.

Everything will take place as if D was directly placed against the base of F, but with this difference that, owing to its location at a high level, the vapours of the primary column B can, after condensation in D, directly flow back into B.

If D had been placed at the bottom of the secondary column F, according to the standard arrangement, it is the condensation efiected in D which it would have been necessary to pump in the point 7, in two portions: the most important fiows to the top of F through the pipe 10, whilst the other portion, driven along by the steam ejector-8, ensures the necessary fractionation. The mixture of water vapour and of vapour of too. light benzene issuing from the ejector is used for heating in A the supply of washed benzol from the reservoir A, entering the primary column BB through the cook 1 and pipe 2. The compound liquid condensed-in A passes to the cooler J and from there enters the decanting apparatus J. The water falls to the bottom of the decanting apparatus and issues through'the test gauge 23, whilst the benzol drawn along issues through the test gauge 22.

It is to be understood that instead of creating vacuum by means of an ejector (which appears to be so much the more simple as it is simply necessary to generate a partial vacuumvery easy to obtain) use might be made of a vacuum pump of any type.

At the bottom of the secondary rectifying column FF the residual reflux has retained traces of heavy impurities; it is therefore necessary to provide an issue for a fraction of this liquid, in order to avoid' accumulation of impurities: For

that purpose, the extraction is effected at a point in the length of the delivery pipe (pipe 13) of the pump I; the volume of this extraction is measured in the test gauge :0, and from there, the extracted liquid is conveyed, by the pipe 35, to the primary column BB.

The extra-pure benzene, whichhas been subjected'to a double rectification and extracted from F, is cooled at H; its volume is controlled by the cock 24, the 'pump I sucks it and delivers it, through 25, in the test gauge L.

"Double rectification of toluene It is also effected with double action, and exactly according to the same principles as above; the description of this double rectification can therefore be briefly given.

The primary column K is supplied with the totality of the liquid freed from benzol issuing from the bottom of BB, that is to say from its boiler C. The issue of this liquid continuously takes place by overflow (cock 9, pipe 11). This liquid is automatically raised to about the middle portion of the column K by a live steam emulsifying apparatus L. o

Boiling in the column K is produced by a boiler M provided with a coil. The toluene vapours rise through the plates, being purified in the refluxes of the two tubular apparatus N and P. The cock 36 arranged above the flask n, allows but a very small proportion of light vapours'to pass into P. These light portions issue through the flask p,

pipe 16 and test gauge 6. The remainder flows down through the pipe 26, mixes with the product condensed in N (pipe 27') and forms the reflux necessary for the refining operation in the primary column K.

At 1 is efiected an extraction of pasteurized toluene which will be used for feeding the secondary rectifying column Q.

point by the toluene vapours at 111 C. of the primary column K, exactly as for benzene.

The vapours at about -90 C. produced in N, flow down through the pipe 29 for automatically heating without expense the bottom of the secondary column Q. This time again it is necessary to efiect, at a point on the length of the pipe 38, a slight extraction through the test gauge 70, which extraction will re-enter the primary column The vapours from the secondary column Q are condensed in the condenser-cooler Y. The non-condensed portion is sucked by the steam ejector 32 (pipe 31) and the mixture of water vapour and toluene, conveyed by the pipe 33 in the tubular apparatus X, is used for effecting a complementary heating at the base of the secondary column Q.

The portion condensed in Y issues through the flask y and flows back through the pipe 30, to the top of the secondary column Q.

As for the tubular apparatus A, at the issue of X (pipe 40), will be arranged a cooler, then a decanting apparatus and two test-gauges, one for water, the other for the head toluene, which will re-enter the primary column K owing to the emulsifying apparatus L, or by any other means.

The extra-pure toluene cooled at R, issues through the test-gauge f.

The liquid of the boiler M, which no longer contains toluene, will finally yield the xylene andnaphtha-solvent it still contains. But as this residue still contains a relatively important proportion of tar, resulting from polymerizations efiected by sulphuric acid, it would not be easy, in a continuously operating column, to completely free the tar from the totality of the white spirit with which it is still combined. Therefore the column S.is discontinuously fed.

The liquid from M passes, through the pipe 3% and cook 18, into the boiler T which is provided with a steam coil, as the other boilers, and also with steam bubbling through pipe U.

As soon as the liquid covers the coil, heating is effected by this coil alone, and the boiler M can continuously empty through its overflow m.

Although TS begin to distill, the level gradually rises in T. The rectification takes place owing to the reflux of the condenser V.

The distillate issuing through 1) is divided. in two portions: reflux through the pipe 19, whilst the pipe 20 allows to eifect a small extraction of too light impurities through the'test-gauge g.

All the 'head extractions from the three columns are sent into the vessel containing the motor-benzol. Through s, cooler s and test gauge h issues commercial xylene, whicn must boil within a range of five degrees centigrade.

At the test gauge is drawn off (after cooling in a cooler not shown) a relatively heavy naphthasolvent, the greater part of which boils between 130 and 180 C. I

At a certain moment the boiler T is full. The cock 18 is closed and then the residues from M rise by themselves to the reservoir W, where they will accumulate whilst the exhaustion of the boiler T will be terminated. v

When it is noticed that there is no outflow from the test gauges ghthe live steam is cut off from the coil and, on the contrary, steam 01!, and, through the cock t and the pipe 21, the tar is discharged into the reservoir Z.

The cock t is again closed and as during all this time the reservoir W has filled up, it is pos sible, by opening 18, to send a new batch in the boiler T, and tobegin again another rectification without appreciable loss of time.

It will be understood that, according to commercial requirements, instead of employing the complete apparatus illustrated in the drawing, the double rectification with double action can be used only for benzene, or on the contrary only for toluene, or finally for neither of them.

The process described allows, without any supplementary expense either in fuel or labour, and in a completely automatic manner, to obtain a benzene and a toluene having a chemical purity largely exceeding the tests actually required. The apparatus which has been shown in the drawing by way of example, can obviously receive modifications and even simplifications it it is desired to obtain extra-purity for only one of the two main hydrocarbons: benzene and toluene.

I claim:

Apparatus for refining washed benzene comprising a continuous steam heated primary benzene rectifier adapted to operate at atmospheric pressure, a continuous secondary benzene rectifier adapted to operate at sub-atmospheric pressure. a heater condenser communicating with the primary benzene rectifier adapted to heat the residues of the secondary benzene rectifier and also provide reflux to the primary benzene rectifier, means for feeding the lower part of the secondary benzene rectifier with the vapours of the said residues evolved from the heater condenser thereby heating the said secondary benzene rectifier, means for conveying part of the liquid reflux of the primary benzene rectifier to the secondary rectifier, means for condensing the purified benzene from the secondary benzene rectifier, a continuous steam heated primary toluene rectifier adapted to operate at atmospheric pressure, and a continuous secondary toluene rectifier adapted to operate at sub-atmospheric pressure, means for conveying residue from the primary benzene rectifler to the primary toluene rectifier, a heater condenser communicating with the primary toluene rectifier, adapted to heat residues of the secondary toluene rectifier and provide reflux to the primary toluene rectifier, means for conveying the residue of the secondary toluene rectifier to the said heater condenser, means for conveying the vaporized residues from the heater condenser to the lower part of the secondary toluene rectifier, means for condensing the purified toluene from the secondary toluene rectifier, a steam heated rectifier for the rectification o! the xylene I

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