US1742933A - Process of mineral-oil distillation - Google Patents

Description

Jan. 7,4 1930. A. BREW. JR., mi AL PROCESS OF MINERAL OIL DISTILLATION Filed 'laren 17. 192k:

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W/f/VESS Patented Jan. 7, 1930 UNITED STATES PATENT OFFICE ARTHUR E. '.PEW, JB., 0F BBYN MAWR,

AND HENRY THOMAS, OF-BI'DLEY PABX, PENN- A CORPORATION OF NEW JERSEY PROCESS OF MINERAL-OIL DISTIILATION Appimauon mea umh 17, 1924,.v serial mi. 699,615.

The object of the invention is to distill mineral oils or any 'distillate or residuum thereof by a process and apparatus adapted to produce the highest grades of refined products. Furthermore specific, objects o the invention are toprevent or minimize decomposition and cracking, to dispense with the usual refining step of treatment with sulfuric acid and caustic soda and filtration, to effect distillation in a continuous manner, and to substantially reduce the refining cost.

In the process of distilling oil most com? monly practiced, the hot gases formed by the combustion of fuel are brought into contact with a steel tube or pipe containing the oil. The heat is transferred from the hot gases to the oil and then distillation proceeds. In all such processes, there is necessarily a great difference in temperature between the li ot gases and 'the oil, and substantial decomposition and cracking inevitably occur. In these processes, also, it is found impracticable to provide sufficient heating surfaces to absorb 'the heat from the flue gases, and as a result all the processes are either ineflicient or unduly costly.

In accordance with the present invention,-

the oil to be distilled, preferably a reduced crude oil, from which it is desired to extract lubricating oils, is caused to flow down through a vaporizing chamber over heated tubes contained in the chamber; the oil spreading over the surface of the tubes in a thin layer so as to expose, to the greatest possible degree, every particle of the oil to the influence of heat and thereby effect a relatively rapid rise in its temperature; the oil fiowing by gravity from tubes at a higher level to tubes at a lower lever, the lighter fractions of the oil, in the course of its downward progress, being vaporized, the vapors being conducted from the vaporizing chamber and condensed. To heat the tubes, a hot fluid is caused to circulate therethrough, heat being absorbed from the circulating fluid by 'the downwardly flowing oil. The heating fluid is thus reduced in temperature in the course of its iow through the tubes.

In order to `separately remove and con- 50 dense oil vapors of substantially diiferent boiling points, it is preferred to employ a series of vaporizers, one above another (say three). The tubes of one vaporizer may be connected with the tubes of an adjacent vaporizer and the heating fluid may be caused the lowest vaporizer and then successively through hi her vaporizers, so that the heat conditions 1n the several vaporizers will be substantially different; the uppermost vaporizer being maintained at the lowest temperature, the lowermost vaporizer at the highest temperature and the intermediate vaporizer at an intermediate temperature. Therefore, the lightest fractions of oil will distill off in the uppermost vaporizer, and successively heavier fractions in the succeeding lower vaporizers. The number of vaporizers and the temperatures at which they are maintained are controlled by the character oil the oil to be distilled and the products desired to be obtained therefrom. The several nests of tubes' in the several vaporizers may, however, be arranged in multiple, instead of in series; that is, the heating fluid may be caused to iiow from the boiler independently and directly to the several vaporizer chambers, any suitable means being provided to regulate the temperature of the heating fluid entering each vaporizer. It is preferred to regulate the temperature of the heating fluid by maintaining it under different absolute pressures, varying, as desired, from a high degree of vacuum to at or neai` atmospheric pressure or even super-atmospheric pressure. In carrying yout our process, we prefer to maintain the heating fluid under a relatively high vacuum in the uppermost vaporizer and under progressively increasing absolute pressures in the succeeding vaporizers, `thereby affording a convenient means for producing progressively higher temperatures in the successive vaporizers.

A serious problem arising in connection with the practice of the above distillation process, so far as it has been described, is the provision of a suitable heating uid for circulation through the pipes'. An operative heating fluid is an oil of suitable high boiling point, but a fluid of this character deposits to circulate first through the tubes ofcarbon on the inner walls of the tubes, necessitating their frequent cleaning. Any heatthe degree desired, should be one that will 'permit' of the continuous operation ofthe down to a vacuum of twenty-eight inches, is

approximately the same temperature range as is desirable for the distillation of the lubricating oils contained in petroleum. Its first cost is high, but bearing in mind that the cooled and condensed mercury Vapor is reheated and used indefinitely, and that the loss by leakage is so small as to be an almost negligible factor, the cost of the mercury required to fill the system is essentially a part of the plant investment. i

Another feature of the process is that that part of the system through which the oil and oilvapor circulate and in which the oil condenses and accumulates is maintained, preferably, under vacuum, which may be more or less partial but which, to secure the best results, should' be an almost perfect vacuum, say from one to twenty-five millimetersmercury absolute pressure. That part of the system containing mercury may be maintained at different absolute pressures, as above explained, varying from over twentyeight inches of vacuum to atmospheric pressure. ,We prefer that the mercury vapor in the uppermost vaporizer shall be maintained under a vacuum of about twenty-eight inches, the vacuum being progressively lower in progressively lower lvaporizers.- In fact, the mercury in the lowermost vaporizer may be at or near atmospheric pressure. The vaporizers carrying the higher vacuum should be located at a sufficiently higher level than those containing a lower vacuum to enable condensed mercur to flow freely to the control tank.

The construction of the apparatus and the operation of the process will be readily comprehended, with the aid of the above description, by reference to the drawing, which is a diagram of a complete distillation plant. For convenience, there are shown but two vaporizers, although it will be understood, from the foregoing description, that the number-of vaporizers that will be preferably employed depends on the character of the reduced crude or other product to be distilled and on the characterl and variety of the products desired.

Each vaporizer a and I) comprises a nest of tubes c and connecting headers d, d. An

-oil-inlet pipe e communicates with a distributor in the top of the Aupper vaporizing cham er, from which the oil flows down over lng fluid, to be etlicient and economical to` vin each of pipes 'vv the tubes c therein. The residue from the upper vaporizer chamber through an oil seal y into a in -the top of the lower vaporizer chamber, from rwhich oil flows down over the tubes c therein, the residue flowing out through outlet-pipe z'.

From the two vaporizer chambers extend vapor-outlet pipes j and c respectively to condensers m and n respectively, which communicate respectively with oil tanks o and p. By means of a vacuum pump r, any desired degree vof vacuum may be maintained in the oil-containing part of the system. s and t are pumps for removing the distillate, from time to time, from the tanks o and p.

A mercury boiler u communicates with passes down f distributor h pipes o and w opening into headers'of the respective vaporizers.

A throttle valve, or automatic control valve,

w, may be positioned y regulates the level of mercury in the boiler. z is a mercury supply tank. Y

10, 11 are pipes extending from headers of the respective vaporizers and throu h which condensed mercury is conveyed to t e mercury line extending to the boiler. From a header of the upper vaporizer extends a mercury vapor outflow pipe 12 to a tank 13 containing a coil through which cold water and lw. A control tank circulates and which is provided with a catch basin 14 at the bottom to collect the condensed mercury, which flows out through a pipe 15 to pipe 10. A dry vacuum pump 16,is connected with the tank 13, thereby maintaining 'the desired degree of vacuum in the mercury vapor containing part of the vaporizer a.

It herebefore has been stated that that part of the system through which oil and oil vapors circulate should be maintained under a more or less partial vacuum, preferably equivalent to from one to twenty-five millimeters mercury absolute pressure. In ordinary processes for distilling lubricating oil, it is necessary toheat the oil to be distilled to a temperature so high that it is partly decomposed, thereby producing distillates containing decomposition products that require expensive purification treatment to remove; and their complete removal can never be effected. It is, of course, well understood that by distilling oil under a partial vacuum, the distillation temperatures-'of the fractions to be distilled are materially reduced, thereby enabling the distillation to be eli'ected at lower temperatures and hence with less decomposition. It is also well understood that as an absolute vacuum is aproached the boiling points drop at al rate that rapidly and progressively increases, so that, if it were ssib e to reasonably closely approach an a solute vacuum, the boiling points of all exce t the heaviest fractions could be reduced to below the temperature at which any substantial amount of decomposition occurs. In distilling the high :massebomng poimfmaons, are

y lifhest vacuum that it is practicable, with m ern engineering methods, to secure, is desirable. With a a maximum racticable vacuum, it would be 'ble to istil' crude oil practically down to coke at such relatively low-temperatures as to produce abnormally heavy and viscous lubricants that would contain so small a proportion of cracked products that they could be said to be almost free therefrom and would require no subsequent expensive purification treatment.

Known hi h vacuum distillation processes so-called) o not, however, aiford the conitions required to avoid the formation of decomposition products, and in some, if not all, cases, do not even succeed in securing the high vacuum that they are supposed to secure. Thus, in batch distillation, the ab solute ressure above the body of oil might be an a solute vacuum, and yet the oil would actually vaporize at an .absolute pressure substantially in excess of the minimum degree ofvacuum which it is sought to obtain; for the reason that the hydrostatic pressure toward the bottom of the column, where vapor globules begin to form, is such that the vapor as it forms is in fact subject to an absolute pressure substantially above the desired, intended and necessary absolute pressure. Not only does vaporization occur at a much higher temperature than that calculated to be necessary on the basis of the degree of vacuum above the oil body, but the vapor after it forms is subjected to such higher temperature, accompanied by the formation of such decomposition roducts as are produced at that temperature y cracking or otherwise.

It has also been proposed (although applicants are not advised whether the conception antedates the present invention) to run oil through a longltube in a li uid stream whose volume is muc less than that of the tube, to heat the tube in the usual way by hot furnace gases, and to convey, through the tube, the vapors, formed during the passage of the oil through the tube, to a fractional condensing apparatus, whereby distillates of different cuts may be obtained. In this process, the vapors are not only forced to travel through the tube for a considerable distance in contact with the iiowing oil, but such vapors, while they are in the tube, are subject to the heat of the heating medium (which, owing 'to the low heat conductivity of hot gases, must be several hundred degrees higher than is necessary to produce the vapors) thus subjecting the oil vapors, as well as the liquid oil, to local overheating. In fact, the conditions required to avoid local burning of the oil and cracking of oil vapors are not avoided at all, regardless 'ofthe degree of vacuum that may be obtained within thetubes. Moreover, in such process, the vapor is compelled to travel for a long distance through the tube to the outlet thereof. f It is impossible, in auch an elon ated stream of vapor, to avoid a substantia pressure drop from a point distant froml the vapor exit tothe -vapor exit; and

even though a condition of high vacuum may exist at the outlet end ofthe tube, the ab-` solute pressure at points more or less distant from such outlet is substantially above that which it is sought to obtain and which it is necessary .to obtain in order to satisfactorily distil the highest boiling point products.

By means of the present process we provide all the conditions required to successively practice a high vacuum process and have succeeded in converting the entire body of oil, except asmall percentage of residual coke, into lubricants that require no sub uent expensive purification, rand some o` which ossess characteristics heretofore wholly unown.

The principal conditions whereby wesecure the results sought may be enumerated as follows:

(1) The maintenance above the oil, while it is being heated (except -in the distillation of relatively low boiling fractions) of a vacuum. of not lower than substantially twenty-nine inches,'that is, not lower than that corresponding to an absolute pressure of twenty-five millimeters mercury. It is preferred, however, to reduce the absolute pressure to as nearly an absolute vacuum as secure a substantially higher vacuum than that specified.

(2) The avoidance of4 a column of oil of any substantial height, thereby making the factor of hydrostatic pressure negligible.

(3) The maintenance of the smallest practicable temperature difference between the oil and the heating medium. `This is accomplished in our process by the use, as a heating medium, of 'a substance having the characteristics of mercury vapor, which, because of its high heat conductivity, need be at a temperature not very greatly above the temperature of the oil to be vaporized.

(4) The application of heat, principally if not wholly, to only the liquid oil, and the avoidance of conditions whereby the vapors when formed continue to be subject to the temperature conditions required to form them; or, in other words, the maintenance of conditions under which the vapors tend to cool from the moment they leave the surface of the oil body. In the present process, the

the 'process whereby, due tothe balancing them from the locus of vaporization to a locus of condensation. None of the va rs need travel for a substantial distance 1ncontact with the flm of oil on the tubes and there is no 'substantial pressure drop between the locus of formation of the vapors and the outlet la or j.

It should be understood, however, that the maintenance ofthe very high vacuum specified, while preferential in all the vaporizers of a series, is essential only in that vaporizer or those vaporizers wherein the higher or highest boiling point fractions are evaporated.

It is probable that even if the temperature of condensation of the mercury vapor in any I i given vaporizer be well within the cracking ran e, there is no 'cracking whatever of the oil cause of the lack of direct heat exchange between the heating medium and the oil vapors and because of the extreme speed and short distance of travel of the oil vapors from the surface of the oil to the vapor outleta. speed which is proportionate to the intensity of the vacuum, and a distance which isv so short that no substantial pressure drop can be established between the vapor exit and,r

the surface of the liquid oil. By reason of the last mentioned conditions, the factor of time which is one of the factors of cracking) is virtually absent.

We have not herein claimed the feature of columns of mercury 1n the tank y andboiler u, on the onehand, and in the columns 10 and 11 on the other hand, and to the manipulation of the valves w, different pressures/may be established in the boiler and in themercury vapor chambers of the'vaporizer, the same being 4claimed vin connection with the disclosure of a much superior arrangement, proved to be commercially o rative, set forth in applications filed by us ay 9, 1926, which are continuations in part of this application, atents on said applications having issued ay 29, 1929, No. 1,714,811 and 1,714,812. l

Nor have we herein claimed broadly important features of the process of distillation of lubricating oil bymeans of a heating medium, such as mercury vapor; the same claimed broadly in an application filed by us March 5, 1925, Serial No. 13,040, which is a continuation in part of thel present application. f f

Having now f ully described our invention, what we claim and desire to protect by Letters Patent is:

1. The process of distilling lubricating oil which comprises flowing a stream of oil continuously into, through and out of a confined space and while the oil is progressively trav eling through said space distributing the oil over a surface adapted to be heated, generating mercury vapor from a body of liquid merthan 25 millimeters mercury,

eilig curyy and flowing such va or into heat ei:-l

contact, with the regenerating it into vapor, removing t e oil' vapors and condensing them, and minimizing cracking during the vaporization of the oil by maintaining in said confined space an absolute pressure on the oil of less than milli meters mercury, bv maintaining so thin a layer of oil on the heated surface as to substantially eliminate hydrostatic pressure and thereby cause the entire body of oil to be under the specified high vacuum, and by limit-A ing the pressure and temperature of condensation of the mercury Vapor at the locus of '2. The process of distilling lubricating oil which comprises fiowing a stream of oil contin'uously into, through and out of a confined space and while the oil is eling through said space distributing the oil over a surface adapted to be heated, generating mercury vapor from a body of liquid mercury and flowing such vapor into heat exchange relation,'but out of contact, with the oil that is so distributed and flowing over said surface, effecting, by heat exchange and condensation of such vapor, the vaporization of the desired oil fraction,` returning condensed mercury to said body of liquid mercury and regenerating it into vapor, removing the oill vapors and condensing them, and minimizing cracking during the va orization of the oil by maintaining in sai confined space an absolute pressure on the oil of less by maintaining so thin a layer of oil on the heated surface as to substantially eliminate hydrostatic pressure and thereby cause the entire body of oil to be under'the specified high vacuum, b lim`- heat exchange.

iting the pressure and temperature o con densation of the mercury vapor at the locus of heat exchange, and by maintaining the part of said confinedspace occupied by vapor out of heat exchange relation with the surface heated by thefheating medium.

3. The process of distilling oil which comprises flowing a stream of oil continuously lnto, through and out of a Series spaces and while the voil is traveling through said spaces distributing the oil over surfaces adapted to be heated, generating mercury vapor from a body of liquid mercury and flowing such vapor in paths arranged in m'ultiple into heat exchange relation, but out of contact, with the oil that is so distributed and flowing over said surface, effecting, exchange and condensation of such vapor, the vaporization, in each confinedl space, of the desired oil fraction, returning condensed mercury to said body of liquid mercury and by heat progressively travr of confined regenerating in into vapor, removing the oil 'the yaporization of the oil vapors from each co ed space and condensing them, and minimizing cracking during b' maintainin in one or more of said confine spaces an a solute pressure on the oil oi less than 25 millimeters mercury, by maintaining so thin a layer of oil on the heated surface as to sub.- t

stantially eliminate hydrostatic pressure and thereby cause the entire body of oil to be under substantially the same absolute pressure, and by regulating the pressure and temperature of condensation of the mercury vapor at each locus of heat exchan eindependently.

4. The process of disting oil which comprises iowing a stream of oil continuously into, through and out of a series of confined spaces and while the oil is traveling through said spaces distributing the oil over surfaces adapted to be heated, generating vapor from 'a body of a liquid heating medium which is adapted to condense, at a given pressure, at the desired temperature of the oil distillation and is stable against decomposition at such temperature, flowing such vapor in paths arranged in multiple into heat exchange relation, but out of contact, with the oil that is so distributed and lowing over said surface while maintaining the vapor at the locus of heat exchangelat such pressure, effecting, by heat exchange and condensation of said vapor, the vaporization, in each conned space, of the desired oil fraction, returning the condensed heating medium to said liquid body and regenerating it into vapor, removing the oil vapors from each confined space and condensing them, maintaining in one or more of said confined spaces an absolute pressure on the oil ofless than 25 millimeters mercury, maintaining so thin a layer of oil on the heated surface as to substantially eliminate hydrostatic pressure and thereby cause the entire body of oil to be under substantially the same absolute pressure, and in each confined space independently regulating the pressure and temperature of condensation of the vaporous heating medium.

In testimony of which invention,

hereunto set our hands, at Philadelphia,

-Penna., on this 7th day of March, 1924.

ART

HUR E. PEW JR. HENRY THOMA.

we have

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