US1848051A - High vacuum steam distillation - Google Patents

Description

March l, 1932.v p, SUBKOW r HIGH VACUUM STEAM DISTILLATION 'Filedy Mach 7, 192e 34 lgVENOR.

A Patented Mar. 1, 19'32 UNITED STATES PATENT OFFICE 3 PHILIP SUBKOW, OF LOS ANGELES, CALIFORNIA, ASSIGNOR TO UNION OIL COMPANY OF CALIFORNIA, OF LOS ANGELES, CALIFORNIA, A CORPORATION OF CALIFORNIA HIGH. VACUUM STEAM DISTILLATION Application led March 7, 1928. Serial No. 259,690.

, This invention relates to a process and apparatus for vacuum distillation, particularly to a process and apparatus for steam distillation under very high vacuum, that is, under 5 very ylow absolute pressure.

It is well known that in ordinary vacuum distillation, the absolute pressure maintainable in the still is in part determinedby the vapor pressure which exists at theterminal receiver immediately preceding the vacuum pump. Thus the minimum pressure maintainable in this receiver will determine the vacuum in the system. This pressure is evidently the vapor pressure of the condensate l5 at the temperature in the terminal receiver. In steam-distillation of materials to produce relatively high boiling point distillates, as in the distillation of lubricating oils, the inal condensate which must be produced is water. When this distillation occurs at very low pressures in the neighborhood of a few millimeters of mercury, it is essential to provide means in the terminal receiver of condensing the steam at this pressure and yto maintain the pressure of the water in the receiver by suiiciently cooling the condensate so as to producey a vapor pressure below the desired pressure, However, in order to maintain the vapor pressure of the steam con- 'densate such as to maintain this very low vacuum, the water must be cooled to very low temperature. Thus, at verylowpressures in the neighborhood of 5 mm. a temperature at the freezing point of water would be required. However, if the steam is` condensed by use of Ordinar coolingy water, the

f average temperature oft e condensate wouldl be 100 F. and perhaps-higher. This is determined by the available cooling water temperature and the proportion of steam con-d densed. Where water is obtained from cooling towers as is usual,`temperatures of less than 100 F. are very costly to maintain. At a 100 F. temperature the vapor pressure of Water is mm.

It iis the object of this invention to obviate the difficulties enumerated above. The object is to make possible high vacuumv distillation with steam withoutexcessive cooling of the condensate, and, in fact, to use only such cooling waternas is available at the plant.

In further discussion, the term available cooling Water temperature 'will be defined as y,

being that temperature which is obtainable by using a cooling water available atv the plantwhere the process'is operated When such coolin' water is used in conventional methods eit er by vdirect. contact with the understood by reference to the accompanying drawing which illustrates the specific eml bodiment, illustrative, but not limiting the invention.

The figure shows a schematic embodiment of one form of the apparatus for carrying out the process in this application.

In the drawing, l is a charging line for liquid to be distilled, in this case lubricating oil stock. The oil is fed to 1, under the desired pressure, steam may be mixed with this oilif desired by injection through line la. The oil is passed to coil 2,i1i furnace 3, where it is raised'to the desired distilling temperature. The heated oil is passed through line 1, this passage being-regulated by valve 5. Valve 5 may be operated to create any desired back-pressure on line 4. Steam may be admitted by line 4a, regulated by valve 5a. The pre-heated feed is then distilled in Vaporizing tower 8. Part of the oil is immediately vaporized on expansion through spray 6, the un-vaporiz'ed oil trickles over obstructions,

` such as tile, and meets an upward stream of steam introduced through 10. The introduction of steam is regulated at la, 5a, and 10. The unvaporized material is withdrawn through 12, by means of a pump, or if the vapoizer is set at a barometric level above ground, it may be discharged through a bar! ometric leg. The resulting vapors pass through mist separator 9, which acts to separate the mechanically entrained unvaporized material. The resulting vapors pass int-o the top section 7, and through line 11, to a series Yof fractional condensers 13, cooled by oil, steam or water, as the case may be, introduced through 14 and exiting through 15. The partial condensates are withdrawn through 16, into collecting tanks 17, and withdrawn through 18, by means of pumps, or if these condensers are set at barometric level, the discharge 4may be through barometric legs.

The unvaporized portion, in this case substantially steam, passes through barometric condenser 20, where it meets the stream of scrubbing liquid adapted to dissolve the steam introduced through line 21. The uncondensed material, usually fixed gases or light volatile oils, is withdrawn through line 22, by high vacuum pump 23. The scrubbed liquid containing the condensed steam passes down to barometric leg 24, into sump 25, from which it is withdrawn through 26, by a pump, passes through heat exchanger 27, and through line 28, and spray 29, into the vaporizing or exhausting tower 30. The material trickles over obstruction 31, adapted to film the material, and meets an upward current ot steam or hot combustion gases introducedthrough 32. The evaporated water exits through 33. Tower 30 may be under vacuum if desired. The hot, concentrated material is Withdra wn through 34, by a pump and passed through 27, in heat exchange with the liquid passed through 26. The liquid then passes to cooler 36, where it is cooled by available cooling water, introduced through 37 and exiting through 38, to a temperature as to produce the desired condensation effect when introduced through 21. The steam jet or blower 39 positioned in line 19, is used when it is desired to raise the pressure in the barometric condenser. Part of the material is by-passed through 40, the amount being controlled by valves 41 and 42, through cooler 36 to the condenser 20. The recirculation of this material helps to control the condensation in 2O by maintaining the correct. amount of solvent iuid and also helps to saturate the solvent. Obviously, however, by closing 42, the material may be sent in a single pass, if this is found desirable`r and economical. rlhe apparatus is so constructed to minimize friction losses and leaks as will be understood by those skilled in this art.

As a specific example illustrating this process in its preferred embodiment,'the following may be given:

Lubricating oil stock is introduced into coil 2, together with steam and heated to about neeaoai 600o F. and introduced into 8. Steam may be introduced via 5a to aid in iashing the oil. Steam also maybe introduced via 10 to aid in the distillation. The pressure is maintained in the tower 8, preferably at not over 25 mm.`

Tn the specilic example, the pressure is maintained at 2O mm. The proportions of the steam and oil are such as to give the steam a partial pressure of 15 mmfand the oil 5 mm.

lln other words, the steam is V4 of the volume of generated vapors in the space 7.

Oil is condensed in 13 ractionally, and steam passes through 19 to condenser 20. Scrubbing liquid such as glycerine is circulated through 21. The temperature and volume are controlled so as to maintain the concentration and temperature of the mixture `thus formed to give the desired vapor pressure. This will be determined by the presf y sure drop through the apparatus, and by the pressure desired to be maintained in the barometric condenser. Thus, if the temperature maintainable in the barometric condenser be 100 F. then the approximate concentration required to give 16 mm. pressure in the condenser will be 64% glycerine-36% water by volume. At concentration of 72% glycerine and 28% water by weight, the vapor pressure will be 8 mm. at 100o F. A concentration of 56% glycerine and 44% water by volume will give a vapor pressure of 23 mm. at 100 F. T a salt is used in concentration for example of 100 grams calcium chloride in 100 grams water the mixture will give a vapor pressure of'll mm. Instead of using calcium one may use KOH or other-electrolyte, which depresses the vapor pressure of water. By regulating the temperature and concentration of the mixture formedin the condenser the desired vapor pressure may be obtained. Knowing the volume of steam and its temperature, and the required resultant pressure in this con# denser, the concentration, volume and temperature of the scrubbing liquids can be readily adjusted.

As an auxiliary method, a partial compression of the vapors may be obtained by introducing the steam et in line 19. This will raise the pressure in 20, asis well known, and will increase the allowable concentration of Water in the condensate mixture. Thus, if the booster be operated to overcome the backpressure of the resistance so as to maintain a uniform pressure throughout'the whole apparatus, i. e. to maintain, for instance25 mm.

tus described is best adapted to the use of glycerine, although any well known apparatus for concentrating glycerine may be employed. The glycerine-water mixture is lpassed through heat exchanger 27, and introduced into tower 30, where'it is distilled vby a stream of combustion gas to de-water the glycerine. Steam may berused in its place, orthe glycerine may be heated in'a tube still before introduction into the tower 30. Provision may be had for reiiuxing the glycerine which may be evaporated. Likewise the evaporator may be operated under vacuum. skilled in the art will be able to concentrate the scrubbing agent. f

The de-watered scrubbing agent is passed through heat exchanger 27, and to cooler 36.

In cooler 36 care must be taken that the temperature is not lowered so low that the glycerine freezes or that salt crystallizes out, if a salt solution is employed. Thus the cooling ous salts are available.

y thevapor pressure of water .by a solute isl and concentration is controlled to give the optimum concentration to effect the necessary concentration in the barometric condenser without crystallizing in the cooler. In the specific example given above, the cooling water may vary from 50-8()o F. in which case, there is no danger of glycerine `freezing especially 'if it carries a little water.

lVhile the specific example describes the use of absolute pressure at 20 min., it'will be understood that the absolute pressure may be lowered as far as 'possible (as far as l or 2 mm. or less), and above 25 mm. as the exigencies of the operation demand. The proc- -es's as described is very flexible. While glycerine and calcium chloride solution have been speciically mentioned, any liquid of relatively high boiling point and sulic-ient water solubility will be applicable. Any V'one skilled in the art will be able to choose the requisite material to suit particular conditions. It is believed that 'glycerine is best suited. Vari'- The principle here is the reduction of vapor pressure by the salt as will be understood by those skilled in the art. The fundamental principle of lowering well understood by those skilledy in this art.

The above explanation is not to be takenas limiting my invention, but descriptive of the best modes of employing my invention, which I claim to be;

l. A methodof high vacuum steam distillation comprising distilling'oil with steamv at high vacuum, condensing the steam and lowering the vapor pressure of the steam condensate formed 1nl said condensation by a solute below the vapor pressure of water at.

the temperature at which the steam is condensed. F l

2. .A method ofhigh vacuum steam distillation comprising distilling oil ywith steam at highvacuum, condensing the resulting oil vapors without condensing the steam, and sub- From the description anyonev operation'.

4. Method of steam distilling oil under` high vacuum which comprises vaporizing oil with steam at high vacuum, condensing the -oil' vapors thus generated without condensing the steam, lscrubbing said steam vapors with a solvent, maintaining the pressure of the mixture below the vapor pressure of water at the temperature obtainable by use of available cooling water.

5. Method of distilling oil at an absolute pressure not greater than 25 mm. mercury with steam, which comprises vaporizing oil with steam at an'absolute pressure not greater than 25 mm. mercury, condensing the oil vapors without condensingthe steam 'and condensing thel steam in the presence of a solute capable. of lowering the vapor pressure of water at an absolute pressure not greater than 25 mm. and at a temperature obtainable by available cooling water.

lation which comprises distilling oil with steam under high vacuum, condensingthe oil vapors but not the steam, increasing the pressure'of the'steam and scrubbing the steam with solvent capable of reducing the partial pressure of the water'in the condenser so as to maintain the `vapor pressure of the mixture, atv available cooling water temperature,

not 'greater than the last mentioned steam pressure.- Y 7. Method of high vacuum steam distillation comprising distilling oil with steam at I' high vacuum, condensing the resulting oil vapors without condensing the steam, `Scrubbing the steam with a solvent at a temperature not less than the available cooling water temperature and at' an absolute pressure-less lthan the vapor-pressure of water at said cooling water temperature, removing the solvent 'water mixture, evaporating water from said solvent, coolinglsaid solvent by heat exchange further steam with; said solvent in cyclic e. .Method of distilling on at a pressure not greater than 25 mm. with steam, which com- Awith available cooling water, and scrubbing i prises vaporizing oil with steam at an absolute pressure not greater than 2.5 mm. mercury,condensing the oil vapors without condensing the steam, scrubbing the' steam with 6. Method of high vacuum steam i.distila solvent at a temperature not less than 7 9 F. and an absolute pressure not greater than 25 mm., evaporating water from the solvent, cooling the solventand re-introducing said solvent into said steam.

9. A method or high vacuum distillation of oil which comprises steam distilling oilat a low absolute pressure, cooling the steam to a temperature insuicient to condense the same at the low absolute pressure maintained thereon, and condensing the steam at said last mentioned temperature and pressure by 10W- ering the vapor pressure 'of the condensate thereof by introducing into said condensate a material which will lower the vapor pressurel of said condensate.

10. A method of high vacuum distillation of oil which comprises steam distilling oil at a low absolute pressure, fractionally separating the oil by not condensing the steam,

coolingV the steam to a. temperature insumcient to condense the same at the low absolute pressure maintained thereon, and condensing the steam at said last mentioned temperature and pressure by lowering the vapor pressure of the condensate thereof by introducimg into said condensate a material which will lower the vapor pressure of said condensate.

1l. A method of Vhigh vacuum distillation of oil which comprises steam distilling of oil at a low absolute pressure, ractionally separating the oil but not condensing the steam, cooling 'the steam to a temperature oit itself insufficient-to condense the steam at the pressure maintained thereon by contacting saidy steam with a solvent and thus condensing the steam at the said pressure'and temperature.

12. A method of high vacuum distillation of oil which comprises steam distilling oil at a pressure not exceeding approximately 25 mm. absolute pressure, fractionally separatasesora Ving the oil but not condensingcthe steam, contacting the steam with a. solvent ata pressure not exceeding 25 mm. mercury and cooling the steam to a'temperature not less than 79 F. andthus condensing the steam at the resultant temperature and pressure, removing the solvent water mixture, evaporating the water :trom the solvent, cooling the solvent and re-introducing the solvent into the steam to be condensed, in cyclic operation.

15. An apparatus for high vacuum distillation comprising av still, a condenser, means for maintaining high vacuum in the still and in the condenser, means for introducing a scrubbing liquid into the condenser, means for withdrawing the scrubbing liquidfrom the condenser, an evaporator, means for introducing the scrubbing liquid into the evaporator, means for withdrawing the scrubbing liquid from the evaporator, a cooler, means for passing the scrubbing liquid from the evaporator through the cooler and to the condenser.

1G. A method of high vacuum steam distillation which comprises distilling oil at a low absolute pressure with steam, condensing the steam at a low' absolute pressure by scrubbing the same with a liquid, evaporating the water from the mixture thus formed, and reintroducing the regenerated liquid to condense further steam in cyclic operation.

Signed at Los Angeles, in the county of Los Angeles and State of California, this 24th day of February, A. D. 1928.

. PHILIP SUBKQVW ing the oil but not condensing thesteam, conl tacting the steam with a solvent at a pressure not exceeding 25 mm. mercury and'cooling the steam to atemperature not less than 79 sultant temperature and pressure.

13. A'1' nethod of high vacuum distillation of oil which comprises steam distilling of oil at a low absolute pressure,`fractionally sepa- 11o F. and thus condensing the steam at the relrating the oil but not condensing the steam,

cooling the steam to a temperature of itselfl insuicient to condense the steam at the pressuremaintained thereon by contacting said steam with a solvent and thus condensing the steam at the said pressure/and temperature, removing the solvent-Water mixture, evaporating the Water from the solvent, cooling the solvent and re-introducing the solvent into the steam to be condensed, in cyclic operation. l

14. A method of high vacuum distillation of oil which comprises steam distilling oil at a pressure not exceeding approximately 25 mm. absolute pressure, fractionally separat-

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