US2344910A - Method of sweetening hydrocarbon oils - Google Patents

Description

March 21, 1944. s, w|NDLE I 2,344,910

METHOD OF SWEETENING HYDROOARBON OILS Filed March 4, 1941 (500/ 0/7 SWEETEN (Used fieqqenf) & STORAGE com/m WITH DOCTQR sownon H SWEETE'N l I (Llseo! Aeagenfl} (Your 01/ STORAGE I I CONTACT WITH I i DOCTOR SOLUTION Y L i z f zflfluui J ,Fz'g. 2

5 SULFUR CONTACT WITH '9" DOCTOR SOLUTION poducf) STORAGE (Used Reagem) I LA Fly;

' Inventor Attorney GEORGE s. wmoua Patented Mar. 21, 1944 METHOD OF SWEETENING HYDRO- CARBON OILS George S. Windle, El Paso, Tex., assignor to Standard Oil Company of California, San Francisco, Calif., a corporation of Delaware Application March 4, 1941, Serial No. 381,616

6 Claims, (Cl. 196-33) This invention relates to an improvement in the art of refining oils. It has particular reference to such oils as it is desired to sweeten, i. e., render nonreactive, or negative, to the well-known doctor test. The oils which it is generally desired to refine in this respect are the lighter fractions, such as gasoline, naphtha, kerosene, etc; i

- The impurities which render such oils sour are known to be certain sulfur compounds, principally hydrogen sulfide and mercaptans. The object of sweetening treatment in current use is to remove these reactive sulfur compounds, or to convert them to compounds which are relatively unreactive and harmless when the oil is used as a motor fuel, solvent, burner fuel, or the like. Practical methods are in wide use which accomplish this at low cost, but these methods are attended by certainrdisadvantages which it is the object of this invention to overcome.

The most widely used method of sweetening at present is the Well-known doctor treatment. This method involves, as a final step, the addition of sulfur for the purpose of precipitating lead sulfide. In order to obtain'a commercially practicable precipitation, it is necessary to add a small excess of sulfur above that theoretically required for the reaction. Since sulfur is readily soluble in oil, and since only a very small amount of dissolved sulfur will render the. oil corrosive, it is necessary to exercise extreme and constant control of this factor in order to avoid any more than the absolute minimum required for practical sweetening. Even if this minimum is maintained, the resultant sweetened oil tends to lack color stability, and tends to possess other objectionable properties which will be referred t below.

Another widely used sweetening process consists in treating the sour oil with a suspension of lead sulfide in caustic soda solution. This process does not require the addition of free sulfur, but in the case of most sour oils, it leaves much to be desired with respect to color stability, a tendency to form haze on exposure to sunlight and/ or to form gum in storage, and so on.

These and other sweetening processes which function by reason of a conversion of the sour or corrosive sulfur compounds to disulfides are all attended by the same disadvantages in greater or less degree depending on quantity of objectionable compounds in the untreated oil.

It is the object of this invention to overcome these disadvantages and specifically (as compared with sweetening treatments of the class mentioned) to produce a sweetened oil product possessing improved color stability, increased reslstance to haze formation, improved octane number, increased tetraethyl lead susceptibility, and improved response to the action of oxidation inhibitorsr Briefly stated, the process of my invention consists in blending oil which has been sweetened by the doctor-and'sulfur method, by the lead sulfide method, or by other chemically analogous method, with a regulated quantity of sour oil which has been contacted with doctor solution. After a period of time, which may be eight hours or more, the blend will be found to be sweet and to have attained a ,highjquality with respect to color stability, inhibitor response, etc. as noted above.

The simplicity of the process is, such that it may easily be operated continuously, and it requires no special equipment of any kind. The reagents may of course be recirculated and regenerated in the usual manner.

I have further found that it is particularly desirable, from an operating standpoint, to employ forthe two components of the blend above described, two portions of the same stream of feed stock entering the treating plant. When this is done I have found that the operator has only to maintain a constant volumetric split of the said stock in order to provide the proper reaction. In. other words, th desired results, in terms of quality, will then be obtained regardless of variations the, amount of undesired sulfur compounds in the feed. This is contrary to the situation, for example, in the: conventional doctorsweetening process where it is vitally important to maintain the addition of sulfur as nearly as possible at the minimum amount required to sweeten the stock, and this minimum rate depends entirely on the amount of objectionable sulfur compounds present in the stock.

For best results I have found that in my above described process the sweetened and the doctorcontacted stocks, when obtained by a split of the feed to the plant, should be mixed in the proportion, by volume, of to 77% of the sweetened stock to 23 to 25% of the doctor-contacted stock. This relationship holds good in the event the sweetening is done by means of lead sulfide, cupric chloride, or the like. It also holds good when the sweetening is done with doctor solution and sulfur, provided only the minimum of sulfur has been used to insure practical operation (it being necessary to use somewhat more than theoreticaliy required to satisfy the chemical reaction).

In the event, as frequently happens, more than the practical minimum amount of sulfur has been used, it will be necessary (in order to realize the full benefits of my process) to increase the relative proportion of doctor-contacted stock. The amount of this increase can best be determined by sample tests.

In applying my process to the case where it is desired to use the doctor treatment on both portions of the blend, it is convenient to contact the entire feed with doctor solution, then divide;

the stock in the proper portion, and subject one portion to sulfur treatment.

After separating in each diagram the components of the blend are the precipitate from the latter, the two stocks are blended. It might be expected that this split doctor treatment would produce the same results as if the same feed stock and the same quantities of doctor solution and sulfur had been used in a unified operation without the split. I have found, however. that oil produced by the split treatment, as described. will be of higher quality with respect to color stability, oxidation inhibitor response, etc.

In the event my process is applied to sweetening agents other than the doctor-and-sulfur agent, it is necessary that the split be made in the feed stock before it contacts the reagents. The sweetening reagent is then separated from the sweetened oil before the same is blended with the doctor-contacted reagent. On the other hand, separation of the doctor solution from the portionof oil with which it has been contacted may be made before or after the blend. It is usually convenient to allow the doctor solution to flow along with the blended oil into the rundown tankage. Since the blend must be stored for some hours in order to permit the reaction to be completed, this affords an opportunity to settle the doctor solution and reaction products completely out of the stock. and no special settling and separating apparatus is required.

As stated above, I prefer, when splitting the feed .to my process. to apportion the split at the rate of about 25% by volume to the doctor-contacting side and about 75% to the sweetening side. Some variation in this ratio is permissible, however. For convenience let the doctor-contacted component be designated as A, and the sweetened component as B. I have found that. when operating with split feed, best results are obtained by the use of a volumetric ratio of A to B of approximately one to three. I have also foundhowever. that very good results may still be realized even though the amount of B in the blend is increased, as, for example, a ratio of one to five. but I prefer to avoid a reluction of B below about one to three. In other words, a ratio of one to two is not advisable unless, in the case of doctor sweetening, a considerable xcess of sulfur has been applied in order to obtain rapid precipitation or break.

In the event the split treatment is not used, i. e., when my process is practiced bysimply blending a doctor-contacted stock with another stock which has been sweetened, the optimum ratio of-A to B in the blend will depend on the amount and nature of the sour compounds originally present in each of these stocks, and. also upon the sweetening reagent which has been used on stock B (and if this was doctor-and-sulfur, thenupon' the amount of sulfur used), and this is best determined by sample treatment. In any case. as stated above, it is preferable to use too much rather than too little of the component B.

Inasmuch as no special form of apparatus is essential to the practice of my process, it is un- 75 designated as follows: A refers to the doctorcontacted stock, and B to the sweetened stock.-

These diagrams are merely for the purpose of illustrating in a general way the flow line of my process. It is to be understood that they do not show all the possible ways in which it might be conducted,

The addition of small amounts of various chemicals to light oils for the purpose of retarding color degradation and gum formation is a well-known practice. In some cases the use of such inhibitors takes the place, in part, of some of the chemical refining of theoil. One of the advantages of my process is that it increases the beneficial effect of inhibitors on color stability and rate of gum formation. This fact may be used, of course, to reduce the amount of inhibitor or to improve the quality of the inhiibted oil when using the same amount of inhibitor.

An example of the operation of my process follows: The stock treated was a cracked gasoline obtained by distillation of a cracked naphtha which had been acid treated and neutralized. This gasoline was very sour (positive) to the doctor test. -It was pumped continuously into a treating plant at the inlet to which the feed stream was divided, 75% by volume flowing to a lead sulfide treater and the remaining 25% to a doctor treater. The 75% stream was mixed in a line with the lead sulfide reagent (2. suspension of PbS in NaOH solution). The mixture flowed through a tortuous line and discharged into the lower part of a vertical vessel having a cone bottom. A gravity separation took place in this vessel, the gasoline forming an upper layer and the reagent the lower layer. Gasoline flowed out of the'top of this vessel into and through a second settler to insure complete removal of reagent. From this second vessel the substan tially dry gasoline flowed to a storage tank.

The 25% portion of the feed stream was in- J'e'cted by means of a pump into the lower part of a third vessel. To the suction side of this pump there was connected a pipe supplying doctor solution (sodium plumbite). These two. liquids separated by gravity in this vessel, the gasoline flowing from the top of the vessel through a line connected to the aforesaid line carrying the lead sulfide treated gasoline to the storage tank. These two 7 oils were thus thoroughly blended by the time they entered the storage tank. The plant was operated continuously. Flow meters in the lines from the lead sulfide treater and doctor-contactor respectively enabled the operators to maintain the division of the feed at a constant ratio. Suflicient run-down tankage was provided so that the blended oil was allowed to stand for a period of at least eight to sixteen hours before being removed for marketing. Sampies taken from the lead sulfide side of the system were found to be doctor sweet. Samples taken from the doctor-contactor side of the system were, of course, sour to the doctor test. Samples gang-01o oi the: blend flowing to storage were likewisesour tothe'doctor. test. Samples taken from the run down tank eight to: sixteen hours after filling weredoctor sweet.

That this finished oil was of materially higher quality than that sweetened in the ordinary way with lead sulfide is shown by comparison with a sample of the sweet stream from the lead sulfide 'sideof the plant (1. e.,' a sample taken from the sweet lineand therefore not blended with-doctor contacted stock). In this table (a) represents the oil treated in the usual way with the lead sulfide reagent alone, and (b) the oil treated as described above, according to the process of my invention.

Contains inhibitor .c .No Yes No Yes Induction time "hours" 2. 25 4.50 4. 12. 00 Haze time .minutes... 50 80 100 400+ l-day gum (in sun). Slight Heavy None None Color after 3 months (dark) +23 +30 +30 +30 Color after 48 hours 140 +21 +26 +27 +29 Octane No 67.0 67. 1 67. 6 67. 7

The induction time mentioned above refers to an accelerated test to determine relative tendency to oxidize. the less the sample is subject to air oxidation. Haze time refers to exposure to sunlight in half-filled vented bottles.

In another case sour cracked oil was sweetened by the conventional doctor-and-sulfur method, enough sulfur being used to give a-fast "break between the reagent and the gasoline. This oil, following removal by settlement of reagent and precipitate was mixed with a portion of the same oil which had been contacted with doctor solution only, without addition of sulfur, in the proportion of three volumes of the former to one volume of the latter, and the mixture allowed to stand. Inhibitor was added, and the oil was found to have an induction period of 9.5 hours with time to haze formation 165 minutes. By comparison, a sample of the doctor sweetened stream. alone, containing the same inhibitor had an induction period of 8.25 hours and a haze time of 60 minutes.

The process of my application is applicable to any oil containing mercaptans. it is desired to sweeten are, as a. rule, the light distillates such as kerosene, naphtha. and gaso line.

The sweetening reagents to which my invention is applicable are those of the class which react principally by forming disulfides. That is, reagents such as lead sulfide, cupric chloride, doctor-and-sulfur which sweeten largely by converting odoriferous and sour sulfur compounds, rather than by removing the same.

There is no need to specify the amount and strength of the reagents used on the A and B components of the blend. As in the case of conventional sweetening processes, an excess above the theoretical requirement is used in order to facilitate contacting and to assure complete reaction-with the objectionable sulfur compounds. This is usually done in commercial plants by recirculating reagent.

Although I have referred throughout the above description to the preparation of the A component of the blend by contact with doctor solution (sodium plumbite), I wish to make it clear that, while this is usually the most convenient agent to be used in the said step of my process, it is The longer the induction time 1 The oils which not the only one which. may be so used. The beneficial results which are obtained by my mac'- esscan also berealized by the use of other. agents which perform the same function as the doctor solution, namely, which convert the mercaptans contained in the sour oil to oil soluble metallic mercaptides. V

Oils are frequently encountered which contain hydrogen sulfide, aswell as'mercaptans. Such oils are usually treated with caustic-soda solution in order to remove hydrogen sulfide before the oil is passed to the sweetening process. Likewise sour oils are sometimes treated with caustic soda or with an agent of the type commonly referred to as solutizer, in order to reduce the mercaptan content before the sweetening operation prop er. Obviously the process of my invention is applicable to such oils whether or not they have been subjected to pretreatment.

Various types of mixing, separating,.recirculating, etc. may be used in practicing my invention, and although a particular arrangement of apparatus has been described with reference to an example of the invention given above, it will be understood that the invention is not limited thereto.

I claim:

1. A method of sweetening sour oil continuously comprising dividing the sour oil in a predetermined ratio, sweetening one part by treatment with an agent which converts mercaptans principally to oil-soluble disulfides, separating the sweetened oil from the agent and insoluble reaction products, contacting the other part with an agent which converts mercaptans to mercap tides, thereby producing a sour oil containing dissolved mercaptides, blending the two parts in such relative proportions that the blend will be initially sour but will upon standing become sweet.

2. A method of sweetening sour oil continuously comprising dividing the sour oil in a predetermined ratio, sweetening one part by treatment with an agent which converts mercaptans to oilsoluble disulfides, separating the sweetened oil from the treating agent and insoluble reaction products, contacting the other part with doctor solution, blending the two parts in such relative proportions that the blend will be initially sour but will upon standing become sweet.

3. A method of sweetening sour oil continuously comprising dividing the sour oil in a volumetric ratio of to volumes for one part to 30 to 25 volumes, respectively for the other part, sweetening the larger part by treatment with an agent which converts mercaptans principally to oil soluble disulfides, separating the sweetened oil containing disulfides from the agent and insoluble reaction products, contacting the smaller part with sodium plumbite solution, blending the two parts in the aforesaid volumetric ratio, thereby producing a sour oil and allowing the blend to stand until it has become sweet.

4. A process of improving an oil containing disulfides which has been sweetened by means of a reagent which converts mercaptans to oil-soluble disulfides, comprising mixing with such sweetened oil a sour oil containing mercaptides which has been treated to convert mercaptans to oilsoluble mercaptides, using such relative volume of said sour oil containing mercaptides that the mixture will at first be sour but that on standing without further treatment it will become sweet.

5. A method of producing an improved doctorsweet oil comprising treating a quantity of sour oil containing mercaptans to convert-mercaptans 4 V to oil-soluble disulfides, thereby producing a sweet oil containing oil-soluble disulfides, treating another quantity of sour oil containing mercaptans to convert mercaptans. to oil soluble mercaptides,

7 thereby producing a sour oil containing mercap tides, and mixing a portion of said sour oil containing mercaptides with a portion of said sweet oii containing ,disulfides in such ratio that the mixture will, be sour initially, but will become sweet upon standing.

6. A method of producing an improved doctorsweet oil comprising treating a, quantity of sour

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