US1839087A - Process of desulphurizing hydrocarbons - Google Patents

Description

Dec. 29, 1931.

J. L. COOLEY ET AL. 1,839,087

PROCESS OF DESULPHURIZING HYDROCARBONS Filed NOV. 30, 1927 2 Sheets-Sheet 1 STORRGE TAN K COOLER TOWER runrmez HERTER EXPAN SIOII TRHK 31M: tow

Dec. 29, 1931. J. 1.. COOLEY ET AL 1,339,087

PROCESS OF DESULPHURIZING HYDROCARBONS Filed Nov. 30. 1927 2 Sheets-Sheet 2 gwvento'ag T vmcm am Patented Dec. 29, 1931 UNITED STATES PATENT OFFICE JOHN L. COOLEY, OF BERKELEY, CALIFORNIA, AND LEONARD C. MCCLOUD, OF COLORADO, TEXAS, ASSIGNORS TO STANDARD OIL COMPANY OF CALIFORNIA, OF SAN FRANCISCO, CALIFORNIA, A CORPORATION OF DELAWARE PROCESS OF DESULPHURIZING HYDROCAR-BONS Application filed November 30, 1927. Serial No. 236,617.

This invention relates to a method for the removal of hydrogen sulphide and low boiling point sulphur compounds encountered in the distillation and refining of petroleums and hydrocarbons of low boiling point. In particular, this invention relates to the removal of such sulphur compounds as are found present in motor fuels produced by pyrogenetic cracking of hydrocarbons.

An object of the present invention is to disclose a process of removing hydrogen sulphide and low boiling point sulphur com pounds from hydrocarbons, particularly from cracked distillates.

Another object is to disclose a process of removing low boiling point sulphur compounds from cracked distillates without the use of expensive treating agents and the loss of valuable hydrocarbons incidental to the use of said agents. Another object is to produce a purified cracked distillate which is capable of giving increased yields of motor fuel distillates upon further treatment.

Low boiling point hydrocarbons are generally produced frompetroleum oil in one of two ways, namely, by fractional distillation at substantially atmospheric pressure, or by destructive distillation at high temperature and at a pressure above atmospheric. The first method is known as straight running and the second as cracking. Along with the low boilng point oil produced by either of these methods there is produced a considerable quantity of hydrogen sulphide and volatile sulphur compounds. These sulphur compounds may be partially in the form of gas and partially in solution in the oil. In either case their presence is detrimental. They have a corrosive action on metals, especially when they occur in oils used as fuel in motors. This corrosive action is likewise very injurious to storage tanks and other equipment with which it comes in contact. Such compounds have disagreeable odors and frequently discolor the oil in which they are found, hence, it is of the greatest importance to the refiner that they be removed. One way of doing this is to wash the oil with caustic for removal of H 8. This is usualy followed by treatment with sulphuric acid and subsequent neutralization and washing. It has been noted that on standing in contact with hydrogen sulphide some hydrocarbons have a tendency to combine with the sulphur to form more or less stable hydrocarbon-' sulphur compounds which resist the refining action of sulphuric acid and other treating agents, and so increase the cost of refining. This combining action is more rapid, and the resulting compounds are more refractory when air is present during the period of contact, therefore it is evident that it is to the interest of the refiner to remove the sulphur compounds soon after their appearance and as thoroughly as possible. The amount of sulphur compounds present depends largely upon the sulphur content of the crude from which the oil was originally obtained. The greater the amount of sulphur in the crude the more serious will be the matter of sulphur removal in the case of any distillate obtained from that crude. It is also a fact that oils produced by pyrogenetic cracking processes contain exceptionally large amounts of hydrogen sulphide and other sulphur compounds. This is to be expected because the charging stock to the process is usually a heavy distillate having a high sulphur content and the process is operated under conditions favorable to the decomposition of any sulphur compounds present. Removal of sulphur compounds is costly not only because treating reagents are expensive, but also because chemical treatment involves loss of valuable hydrocarbons along with impurities.

In substance, the process of the present invention consists in receiving the oil as it is condensed in a cracking process (such oil is commonly called cracked naphtha), while under the pressure maintained in said process, partially reducing this pressure, then, by means of a pump, injecting the oil under higher pressure into a tower so designed as to thoroughly sift the naphtha, exposing large surfaces, and thus allowing the escape of entrained volatile or gaseous sulphur com pounds. The naphtha may be heated in its passage to the tower and additional heat supplied at or near the base of the tower. This heating is for the purpose of vaporizing and evolving from solution the sulphur compounds and necessarily results in the vaporization of a certain amount of the more volatile hydrocarbons. To prevent the escape of valuable hydrocarbon compounds pressure above atmospheric is maintained on the tower, and in addition a cooling element in the top of the tower reduces the temperature of such compounds as reach this point, thus causing a return of all products condensable under the imposed conditions. The sulphur compounds released from the body of the naphtha escape beyond the cooler, while the pressure naphtha now substantially freed of the undesirable hydrogen sulphide and volatile sulphur compounds, is withdrawn from the base of the tower.

In order that the operation of this process may be more easily understood attention is called to the attached drawings, Figures 1 and 2, which show diagrammatically and in cross section two forms of apparatus which may be used. The apparatus shown is illustrative only and it is to be understood that various other forms may be used without departing from the spirit of this invention.

In Figure 1, 1 represents the pressure naphtha receiving drum attached to a pyrogenetic cracking process apparatus. The receiving drum may be provided with a vapor outlet line 50 having a pressure release valve 51 therein. The naphtha is drawn from this receiver through valve 2 and line 3 to a second drum 4 which acts as a partial separator for the gaseous and liquid compounds. At this point pressure may be partially released if desired through line 5 and valve 6. The degree to which pressure is released at this oint will depend upon the pressure of the crac ing system and the degree to which presure may be released without a material loss of hydrocarbon compounds with the gases. From this receiver 4 a liquid pressure naphtha is drawn through line 7 by pump 9 which pump raises the pressure to the desired degree and forces the pressure naphtha through heating element 10. This element may be heated either by fire or steam. From this heating element the naphtha then passes through line 11 to tower 12. The elevation at which this naphtha enters may be varied, to suit the special conditions in any case. This tower is provided with bafiies or bubble plates, or other means for exposing large surfaces of the pressure naphtha. The lower part of the tower represented by 13 may be enlarged for the purpose of providing necessary heating surface and set into a furnace such as 14. By means of this furnace the temperature of the naphtha is further raised.

15 represents a cooling coil or planer to prevent the escape of desirable hydrocarbon compounds, while the non-condensable gases including the hydrogen sulphide and other volatile sulphur compounds escape through line 16 and valve 17 by the means of which any desirable pressure is maintained upon the tower. From the base of the tower naphtha substantially free of the undersirable sulphur compounds passes through line 18, cooler 19, line 20, and pressure release valve 25 to desirable storage represented by 26.

The tower 12 may, if desired, be provided With one or more decanters of the form indicated by 43. The plate 44 is a solid gastight diaphragm or partition. Line 45 is a vapor by-pass allowing vapors from the portion of the tower below the partition 44 to pass into the upper part of the tower. Liquid reflux collecting on the top of 44 flows through line 46 to a small compartment or drum 43 whence it may be all or in part withdrawn through valve 48 to a storage tank not shown. The overflow from 43 through line 47 (which comprises a U-bend to act as a seal to prevent the entrance of vapors into 43) enters the tower just below the plate 44. The purpose of this decanter is to remove water from the system or to take off intermediate distillate. The latter use becomes an advantage in certain cases where the quantity of intermediate boiling-point stock in the oil being desulphurized is such that it is difficult to maintain a balance between the temperature of the oil in the base of the tower and the desired boiling-point stock leaving the tower.

Another means for carrying out this invention is represented in Figure 2. Numbers in Figure 2 which correspond to numbers in Figure 1 represent parts having identical functions and similar construction. Pressure cracked naphtha is received in drum 1 and flows through line 3 having valve 2 into a second drum 4 where the liquid and vapor are separated. The vapors so released flow through line 27 into a larger drum 30. This drum 30 contains suitable baflies or bubble-cap plates 31 to insure thorough dephlegmation of ascending vapor. At the top of the drum 30 is a gas release line 5 controlled by valve 6, by means of which the pressure is reduced substantially below that on drum 1. The naphtha from the drum 4 flows through line 29 into the drum 30 at a point above the entrance of the vapor line 27 This is to provide means of extracting all mechanically carried mist from the vapors. Liquid oil from drum 30 flows through line 7 to a pump 9 whereby it is forced into a fractionating tower 12. Between the pump 9 and the tower 12 the line 7 passes through a heat exchanger 10 wherein the naphtha is preheated by hot oil from the tower. This tower 12 is essentially the same as that illustrated in Figure 1 except that it is not set over a furnace. The oil reaching the lower part of the tower is withdrawn by a pump 32 through line 33 which communicates with a coil 37 placed in a furnace 38. The oil flowing through this coil is heated to the desired degree and returned to the lower part of the tower by means of line 39. This portion of the tower may be divided, as shown, by a transverse plate 40 through which runs one or more short pipes 41 to permit the oil which collects above the plate or diaphragm to overflow into the space below the plate. Likewise plate 40 is provided with one or more pipes 42 which permit the vapor to escape from the space below to the space above the plate. The treated naphtha from the base of tower 12 is withdrawn by means of line 18 through heat exchanger 10 and cooler 19 into storage tank 26 by line 24 and pressure release valve 25.

Following is an example of the operation of this process in the apparatus described above in Figure 1. Cracked naphtha from any cracking process, such as a liquid phase process, is received in drum 1 under the pressure employed on the cracking apparatus, for example 275 lbs. per sq. in. The flow of the naphtha through the line 3 is regulated by the valve 2 so as to maintain the desired liquid level in the drum 1. The pressure is reduced to 100 lbs. on the drum 4 by operation of the valve 6. The upper part of drum 4 is loosely packed with brick or tile to prevent valuable constituents being carried out as mist with the released gas. The gas so released carries but a small amount of condensable hydrocarbons. For the most part it is made up of very light hydrocarbon gases, hydrogen sulphide and low boiling point sulphur compounds. The flow of naphtha through line 7 is regulated by control of the speed of the pump 9 thus maintaining the desired level in the drum. By means of the pump 9 the naphtha is forced into tower 12 on which is held a pressure of about 350 lbs. per sq. in. Before entering the tower the oil is preferably passed through a preheater 10 where its temperature is raised to approximately 280 F. In the base 13 of the tower the oil is further heated to about 425 F. There will then be a progressively decreasing temperature at ascending points in the tower. In a specific instance when the temperature in 13 was 425 F. the temperature just below the planer 15 was 128 F. and the planer was 0perated so as to cause the gas to leave the top of the tower, through line 16 and valve 17, at F. This exitgas consists of very low boiling point, low specific gravity hydrocarbone and sulphur compounds. The condensate obtainable from this exit gas with solid CO and ether at F. (below zero) amounted to only about 2.8 gal. per 1000 cu. ft. The valve 17 is a pressure release valve set to operate, in this instance, at 350 lbs. The naphtha withdrawn from 13 through line 18, and cooler 19 is finally collected in receiver 26.

The desulphurized naphtha collected in the receiver 26 may then be further refined or treated as the refiner sees fit. In the case of ordinary naphtha the next step may be chemical treatment, as by sulphuric acid. The results of such treatment will indicate the advantage accruing from this method of sulphur removal in that from 20-30% less acid will be required to produce an oil of given quality than would be the case if the method were not used. After chemical treatment it is customary to distill the naphtha at low temperature, as by steam, to produce motor gasoline. Oil which has been processed in accordance with our invention suffers much lower losses during both chemical treatment and distillation than would otherwise be the case.

An example of the actual results obtained by the operation of our invention is afforded by the following data taken from a run made on naphtha produced b a commercial liquid phase pyrogenetic crac 'ng system:

The example described in detail above had particular reference to the form of apparatus shown in Figure 1. The process might be .carried out in the apparatus shown in Figure 2 without materially altering the conditions as stated or the results obtained. In some respects the latter apparatus would be preferable. The release of gas in the first stage of the process is effected in a more efficient manner, i. e. with less likelihood of loss of valuable hydrocarbons. The method of heating the oil from the base of the tower 12 by circulating through a coil is also more efficient and practical than that described in Figure 1.

It will be seen from the above that by this process the volatile sulphur compounds occurring in cracked naphtha are substantially eliminated and this is done with a very small loss of valuable hydrocarbons.

The pressures and temperatures mentioned in the example given are by no means applicable to all oils desulphurized by the process, nor is it essential that they be used as stated in the particular instance of the cracked naphtha of the above example. The choice of operating conditions is partly a matter of economy. The lower the pressure on the tower 12 the lower will be the temperature required in the naphtha at the base of the tower to effect the desired amount of vaporization.

,Thus, if a pressure of 100-150 lbs. be held within the tower, about 350 F. will be needed in the liquid naphtha. However, in this case the temperature of the exit gases must not exceed about 20 F. if loss of valuable constituents is to be avoided. Ordinarily it will be a more economical policy to carry higher pressure and supply additional heat to the system than to refrigerate the exit gases.

Much the same reasoning applies to the preliminary partial release of gas from the naphtha in drum 4 in Figure l or 30 in Figure 2. It has been found that the pressure on the crude naphtha may be released to a certain point without serious loss of valuable constituents. In the case of the cracked naphtha mentioned above this critical pressure was about 100 lbs. In other words, if a curve is drawn through points whose abscissae are pounds pressure on the release drum and whose ordinates are gallons of gasoline per 1000 cu. ft. of gas released at the different pressures, the point of origin being zero, we find an upward break at about 100 lbs. This means that in this instance the richness of gas released at pressure over 100 lbs. is low, but that the richness of the gas released at pressures less than 100 lbs. is high, and increases very rapidly as lower pressures are used. This gas released at 100 lbs. or more, as has been shown, contains a very small percentage of hydrocarbons heavy enough to be recoverable as gasoline and yet it does contain a substantial quantity of objectionable sulphur compounds and sufiicient uncondensable hydrocarbons to make it valuable as a gaseous fuel.

The advantage to be derived from a preliminary release of gas lies in this, that if the entire amount of gas is released in the tower the problem of avoidance of gasoline loss becomes much more serious. This is because of the high volume ratio of gas to liquid which would exist in the desulphurizing tower, and also because by its partial pressure effect such gas tends to increase the vaporization of the liquid hydrocarbons within the tower. There is a definite relation between the pressure to which the crude naphtha is reduced in the preliminary step with its consequent volume of gas released and the cooling temperature of condensation in the final step. The smaller the amount of gas which must be handled by the tower, the higher may be the temperature carried at the vapor outlet of the tower. However, the capacity and efficiency of the tower have a direct bearing upon this gas balance.

It is evident that the preliminary reduction of pressure to 100 lbs. in the case of a certain cracked naphtha might not be the optimum in the case of other refinery distillates. The amount of gas and very volatile hydrocarbons produced along with and in solution in a particular oil and the initial pressure will determine, to a large extent the critical pressure under which this preliminary release is carried out. The same is true of other operating conditions, such as the pressure on the tower 12, the temperature to which the oil in the bottom of the tower is raised, the temperature of the planer 15, etc. Moreover, for any given charging stock, the selection of operating conditions will be the result of an economic balance, as has been previously explained. This process, as described, is, therefore, subject to wide variations without departing from the spirit of the invention, which is the desulphurization of volatile oils by volatilization of sulphur compounds, the separation of such voiatilized compounds from the desirable constituents of the oil, and the prevention of loss of desirable constituents. The process may be operated with the pressure on the tower 12 no higher than that in the preliminary release drum 4, so long as the necessary cooling takes place in the vapors at the outlet of the tower to prevent the escape of desirable constituents.

What we claim is:

1. A process of removing volatile sulphur compounds from cracked pressure naphtha, which consists in releasing from the condensed naphtha in gaseous form the more volatile sulphur-compounds of the mixture of gases and vapors from a cracking operation while maintaining sutficient superatmospheric pressure of the cracking operation to prevent the escape of desirable naphtha constituents, and then passing the condensed naphtha to a rectifying column held under superatmospheric pressure in which the temperature and pressure are co-ordinated to separate additional volatile sulphur bodies from the naphtha without the loss of desirable naphtha constitutents by discharging the former from the top and the latter from the bottom of said rectifying column.

2. A process of removing volatile sulphurcompounds from cracked pressure naphtha, which consists in releasing from the condensed naphtha in gaseous form the more volatile sulphur-compounds of the mixture of gases and vapors from a cracking operation while maintaining sullicient superat-mospheric pressure of the cracking operation to prevent the escape of desirable naphtha constituents, increasing the pressure and passing the condensed naphtha under the increased pressure to a rectifying column held under superatmospheric pressure in which the temperature and pressure are co-ordinated to separate additional sulphur bodies from the naphtha without the loss of desirable constituents by discharging the former from the top and the latter from the bottom of said rectifying column.

3. A process of removing volatile sulphurcompounds from cracked naphtha condensed under the superatmospheric pressure of a cracking operation, which consists in reducing the pressure on the condensed naphtha to permit the release of part of the dissolved sulphur-compounds but maintaining a suit cient superatmospheric pressure to prevent the loss of desirable naphtha constituents, and then passing the condensed naphtha to a rectifying column held under superatmospheric pressure in which the temperature and pressure are co-ordinated to separate additional volatile sulphur bodies from the naphtha without the loss of desirable naphtha constituents by discharging the former from the top and the latter from the bottom of said rectifying column.

4. A process of removing volatile sulphurcompounds from crackednaphtha condensed under the superatmospheric pressure of a cracking operation, which consists in reducing the pressure on the condensed naphtha to permit the release of dissolved sulphurcompounds but maintaining a suflicient superatmospheric pressure to prevent the loss of desirable naphtha constituents, increasing the pressure and passing the condensed naphtha under the increased pressure to a rectifying column held under superatmospheric pressure in which the temperature and pressure are co-ordinated to separate additional sulphur bodies from the naphtha without the loss of desirable constituents by discharging the former from the top and the latter from the bottom of said rectifying column.

5. A process of removing volatile sulphurcompounds from cracked pressure naphtha condensed under a pressure of the order of 275 pounds which consists in reducing the pressure on the condensed naphtha to a pressure of the order of pounds to permit the release of dissolved sulphur-compounds without loss of desirable naphtha constituents, increasing the pressure and then passing the condensed naphtha under the increased pressure to a rectifying column held under superatmosphericpressure in which the temperature and pressure are co-ordinated to separate additional sulphur bodies from the naphtha without loss of desirable con-' stituents by discharging the former from the top and the latter from the bottom of said rectifying column.

Signed at Berkeley, Calif, this 16 day of September, 1927.

JOHN L. COOLEY. Signed at Colorado, Texas, this 16 day of October, 1927.

LEONARD G. MoCLOUD.

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