US2473224A - Process of making alcohol - Google Patents

Description

Patented June 14, 1949 TENT OFFICE PROCESS OF MAKING ALCOHOL Helmuth G. Schneider, Westfi'eld, and Vincent'F.

' Mistretta, Fanwood, N. J., assignors, by mesne assignments, to Standard Oil Development Company, a corporation of Delaware No Drawing. Application December 31,1945,v

Serial No. 638,590

10Claims. 1

This invention relates to improvements in the manufacture of aliphatic alcohols, and more particularly to the manufacture of aliphatic alcohols from olefinic hydrocarbons.

In the production of aliphatic alcohols as, for example, secondary alcohols from hydrocarbon naphthas or gases, the naphtha is contacted with an acid, usually sulfuric acid, to form an acid extract. The strength of the acid employed depends upon the olefin to be extracted. For the absorption of propylene it is customary to use 90-95% H2804, and for normal butenes, acids of 80-90% on a hydrocarbon-fre basis are employed. After the acid extracts are formed, they are diluted with water or other aqueous materials to an acid concentration of 30-60% on a hydrocarbon-free basis, hydrolyzed and stripped to recover the alcohol. During the recovery of alcohols from these acid extracts there is always appreciable decomposition of the extract to olefins which lowers the alcohol recovery yield. The regeneration of olefin is particularly noticeable in the manufature' of butyl alcohol. In order to conserve the regenerated olefin, it has been suggested that the olefin be cooled and recycled to the extract as it leaves the absorber or at some point between the absorber and the hydrolyzer. The difiiculty with this suggestion is that the strong acid extracts contain considerable amounts of entrained or physically dissolved saturated hydrocarbons. The result is that when such extracts are stripped, the regenerated olefin from the stripping stills is contaminated with a large amount of saturated hydrocarbons. Where the gases containing regenerated olefins and saturated hydrocarbons are recycled to extract, which also contains saturated hydrocarbons, as has been suggested, the saturated hydrocarbons quickly build up in the recycle system to the point where the recycle gases are largely saturated hydrocarbon, and the olefin absorption efficiency of the recycle system is thereby lowered. It therefore becomes necessary to vent the saturated hydrocarbon at some point in the recycle system in order to prevent the build-up described. Although requisite in such a system, the venting of saturated hydrocarbons entails a certain loss in olefins.

The present invention has for its principal object keeping at a minimum the amount of saturated hydrocarbons present in the hydrocarbon gases produced in the alcohol stripping step of a process wherein aliphatic olefins are converted to aliphatic alcohols. A further object is to accomplish the substantial elimination of saturated hydrocarbons from the efiluent gases of an alcohol stripping still without incurring any considerable loss of potential alcohol in the form of These and other objects are I diluted aqueous solutions of acid may be used if desired in which case the acid would be the same as that used to absorb the olefin in the first instance. 'In practice the strong acid extract is diluted to an acid concentration of 40-75% on a hydrocarbon-free basis and the degassing is conducted at atmospheric pressure or substantially atmospheric pressure. Dilution of the saturated acid extract and reduction in pressure may be carried out simultaneously, although it is preferred, for reasons of olefin conservation, to dilute the saturated extract to the desired acid concentration and then cool to a temperature of SO-l0 C. The step of liberating the saturated hydrocarbons from diluted acid extract requires from 5-15 minutes, depending upon the acid concentration of the diluted extract and the temperature employed. After removal of the saturated hydrocarbon, the diluted extract may then be hydrolyzed'and stripped to recover alcohol in the usual manner. Some olefin in substantially pure form will be regenerated during hydrolysis and stripping. This olefin can be recycled to the saturated extract fromthe absorber without addin appreciably to the amount of saturated hydrocarbons present in the saturated extract. The efiluent gases liberated from the diluted extract when the pressure is released will consist predominantly of saturated hydrocarbons and a small amount of regenerated olefin. Such gases may be recycled to the absorber to recover the olefins contained therein.

It is preferred to carry out the degassing of acid extracts at low acid strength, i. e. 40-75%, on a hydrocarbon-free basis for the reason:

1) That the absorption of olefin by acid is normally conducted at superatmospheric pressures. This results in increased solubility of saturated hydrocarbons in the extract. When the pressure on such an extract is subsequently relieved considerable foaming occurs which in commercial operation is difiicult to control.

If, however, the saturated extract is diluted with water before or during the pressure releasing step, the foaming is almost entirely eliminated, and

(2) degassingacid extracts either after or during dilution results in a more complete removal of the saturated hydrocarbon contained therein.

It has been found that, when thepressureon a saturated extract, which may also be-desi'gnated as a strong extract in the sensethattheacid:on;

a hydrocarbon-free basis is still; of the. 3&11'1810011'. centration used in absorbing: olefin; isIeduced, only about half the saturated hydrocarbons: are

removed. This is due to the fact that. evenat. atmospheric pressure saturatedhydrocarbonsareappreciably soluble in strong acid extracts. On the other hand, when the extract is dilutedprior to the release of pressure-it is possible to get substantially complete removal of; the saturated hydrocarbons.

It-is important in carryingout the degassing of dilute extracts thatthe operating, conditions be,- carefully controlled, to avoid decomposition of the extract to olefin. Any olefin regenerated during the degassing step represents the loss ofpotential alcohol in the extract. Close control of theacid. strength in the extract and temperature to;.which; saturated hydrocarbons-are liberated needs; close; supervision to maintain olefin regeneratiomat a. minimum. When a strong acidextract is ;diluted:. the reaction is exothermic and there is sufficient heat liberated to raise the temperatureof themix ture to 50-60 C. from an extract temperatureof 30-35 C. At temperatures of.50.-609 C. the; rate ofdecomposition of the extract to olefin isquite rapid, and the contact time in the degassing drum should be much shorter thanwould berequired. at lower temperatures; shorter contact time at high temperatures there is much larger decomposition than at 30-40 Accordingly, the acid extract is cooled during dilu: tion in order to maintain the temperature-between the limits of 30-40 C., or after diluting the extract to the desired acid concentration it isimmediately cooled to 30-40 C. following thedilution. stageand prior to the-degassing operation in order to reduce the decomposition of the extract to; olefin. to a minimum.

The following examples-will serve to illustrate the invention:

Example 1 For the purpose of demonstrating the solubility" of saturated hydrocarbonsin extract, a butyl extract of 1.179 molar saturation (mols C4Hs/mo1" H2804) and 38% acid strength was agitated with- Crnaphtha at 20. C; and 20 lbs. gauge pressure for 60 minutes, and then permitted to settle for 120 minutes. A sampleof this extract'was-then diluted with water, maintainingthe temperature during dilution at less than 40'C..to --acid strength. 10% acid strengthwas chosen because atthis strength or lower, diluteaoid and acid extracts do not dissolve hydrocarbons. The pressure was then released. and the gasgiven 0115 measured. The volume of gas recovered was equivalent to 2.33 cubic feet per gallon of extract.-

Example-2 The following experiment shows;that,by:releasing pressure on a butyl extract. (88%. acid strength) it is possible to remove only abouthalf; the entrained saturated hydrocarbons in.the.ex--

tract. Without water dilutionit would be diificult to remove the remainin }saturatedhydrm carbon. dissolved at atmospheric pressure.

However, evenwith the;

Samples of, the extract made as described in Example 1 were then diluted with water, maintaining the, temperature at 40 C. to give acid strength of 42.6%, 51.5 61.7% and 75.7%. The gas givenoff on degassing these dilute extracts at a temperature of 40 C. and atmospheric pressure was measured and analyzed with the. following; results:-

. Contact Time Acid Strength I saturate.

1n-Degess1ng of Extract Drum Removal.

Per cent Minutes Per cent.

It. will be noted from. the above. that with these.- dilute. extracts. degassing is, practically complete andcontact time between: 10 and 15.. minutes is. sufficient toremovethe saturated, hydrocarbons...

Exampl e 4 It has beenfound thatacid extracts-decomposa to some. extent under, alldegassing conditions.

However, this decomposition canbe held .to amine imum by controllingthe degassing temperaturezat: 40 C;. or. less. The effects of acidstrength and;

temperature. on. olefin regeneration. from acid. ex. tracts during. the liberation of saturated hydrocarbons. is. illustrated .in. the table. shown. below.

Samplesoi extractspreparedas described. in. Example 1. were diluted. to approximately 40.-

60"and 70 C. under atmospheric pressure. The;-

gases liberated during degassing. were collected.

measured and. analyzed for saturated hydrocar bons and olefin with thefollowing results:

Extract" Acid; Degassmg 1 Contact saturates 1 Strength Temp; Time Removed. gg gggg Ber Cent; C. Min. Percent. Per-Cent. 42. 6 40 5 84. 3. 0. 24 15 I 95. 6 0. 56 40: 2. 50 5 100 1.23. 15 1. 48. 40. 7. 50 5 100 The results of these experiments show that as the acid strength and temperature increase, decomposition of extract to olefin also increases. The acid strength used for degassing will be dictated largely by the conditions required for subsequent hydrolysis and stripping to recover alcohol. The result is that the decomposition on degassing will have to be controlled largely by the temperature and contact time. From the above results it can be seen that the temperature should be as low as possible, preferably between 30-40 C. and the contact time sufficiently long, -15 minutes to permit the saturant to escape. Lower temperatures require that the extract be cooled subsequent to dilution. If this is not done the only other alternative, as shown by the foregoing results, is to have a very short contact time and provide plenty of surface such as a packed tower for the removal of saturated hydrocarbons. However, the latter will give somewhat higher olefin regeneration for a given saturated hydrocarbon removal.

What is claimed is:

1. A process for removing saturated hydrocarbons from an acid extract which comprises contacting a hydrocarbon stream containing monoolefins and saturated hydrocarbons with a strong mineral acid absorbent at a temperature of C. to 100 C. and at a pressure of 15 to 500 p. s. i. g. to form an acid extract, maintaining the acid extract at a pressure of 15 to 500 p. s. i. g. while diluting the acid extract with an aqueous diluent to an acid strength of 40 to 75 wt. on a hydrocarbon free basis, cooling the extract to a temperature below 40 C., thereafter reducing the pressure on the cooled extract to atmospheric pressure to release saturated hydrocarbons therefrom and separating the released saturated hydrocarbons from the acid extract.

2. A process for removing saturated hydrocarbons from a sulfuric acid extract which comprises contacting a hydrocarbon stream containing mono-olefins and saturated hydrocarbons with sulfuric acid of 70 to 98 Wt. concentration at a temperature of 15 C. to 100 C. and at a pressure of 15 to 500 p. s. i. g. to form a sulfuric acid extract, maintaining the sulfuric acid extract at a pressure of 15 to 500 p s. i. g. while diluting the acid extract with water to an acid strength of 40 to 70 wt. on ahydrocarbon free basis, cooling the extract to a temperature below 40 C., thereafter reducing the pressure on the cooled acid extract to atmospheric pressure to release saturated hydrocarbons therefrom and separating the released saturated hydrocarbons from the acid extract.

3. A process for producing n aliphatic monohydric alcohol which comprises contacting a hydrocarbon stream containing mono-olefins and saturated hydrocarbons with a strong mineral acid at a temperature of 15 C. to 100 C. and at a pressure of 15 to 500 p. s. i. g. to form an acid extract, maintaining the extract under pressure of 15 to 500 p. s. i. g. while diluting the extract with an aqueous diluent to an acid strength of 40 to 75 wt. on a hydrocarbon free basis, cooling the extract to a temperature below 40 C., thereafter reducing the pressure on the cooled extract to atmospheric pressure to release saturated hydrocarbons therefom, hydolyzing the degassed extract and recovering aliphatic monohydric alcohol from the hydrolyzed extract.

4. A process according to claim 3 in which the strong mineral acid is to 98 wt. sulfuric acid on a hydrocarbon free basis, and in which the aqueous diluent is water.

5. A process for producing secondary butyl alcohol which comprises contacting a hydrocarbon stream containing normal butenes and saturated hydrocarbons with sulfuric acid of to 93 wt. on a hydrocarbon free basis at a temperature of 15 to 75 C. and at a pressure of 15 to p. s. i. g. to form an acid extract, maintaining the acid extract under pressure of 15 to 100 p. s. i. g. while diluting the extract with water to an acid strength of 40 to 75 wt. on a hydrocarbon free basis, cooling the extract to a temperature below 40 C., thereafter reducing the pressure on the cooled extract to atmospheric pressure to release saturated hydrocarbons therefrom, hydrolyzing the degassed extract and recovering secondary butyl alcohol from the hydrolyzed extract.

6. A process according to claim 5 in which the dilution and cooling operations are carried out simultaneously.

7. A process according to claim 5 in which the cooled extract is held at atmospheric pressure for about 10 to 20 minutes.

8. A process for producing isopropyl alcohol which comprises contacting a hydrocarbon stream containing propylene and saturated hydrocarbon with sulfuric acid of 65 to 93 wt. concentration at a temperature of 15 C. to 100 C. and at a pressure of 75 to 500 p. s. i. g. to form an acid extract, maintaining the extract under pressure of 75 to 500 p. s. i. g while diluting the extract with water to an acid strength of 40 to 75 wt. on a hydrocarbon free basis, cooling the extract to a temperature below 40 C., thereafter reducing the pressure on the cooled extract under atmospheric pressure to release saturated hydrocarbons therefrom, hydrolyzing the degassed extract and recovering isopropyl alcohol from the hydrolyzed extract.

9. A process according to claim 8 in which the acid extract is diluted and cooled simultaneously. 10. A process according to claim 8 in which the acid extract is held at atmospheric pressure for about 10 to 20 minutes.

HELMUTH G. SCHNEIDER. VINCENT F. MISTRETTA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,365,048 Ellis June 11, 1921 1,486,646 Ellis Mar. 11, 1924 1,809,788 Merley June 9, 1931 2,096,879 Brooks Oct. 26, 1937 2,365,264 Groombridge et al. Dec. 19, 1944 OTHER REFERENCES Guinot, APC Serial No. 373,691.