US2094485A - Process for sweetening hydrocarbon fluids - Google Patents

Description

Patented" Sept. 28, 1937 oFFICE mooass Fon SWEETENING n naocma- BON FLUIDS Albert E. Buell, Bartlesvllle, 10km" assignor to Phillips Petroleum Company, a corporation oi Delaware No Drawing. Application Januarym, 1937 Serial No. 121,908

8 Claims.

'Ehis application is a continuation in part of my copending application, May 12, 1934.

This invention relates to the refining of hydrocarbon products and particularly to the'refining of petroleum products containing malodorous sulfur compounds of the mercaptan type. More directly, it relates to sweetening sour petroleum hydrocarbon products by means of a moist solid 10 carriers. The invention is of special 'valueand application in the treatment of light petroleum distillates such as natural gasoline, refinery straight run and crackedgasolines, petroleum solvent naphthas, liquefied petroleum gases, and

the like.

Such unrefined petroleum products contain mercaptans, commonly called sour elements, which give the oil undesirable odor, and render it corrosive and unstable. These compounds are customarily removed, or altered, by the so-called doctor;process, a laborious, cumbersome and very unecon'omical chemical treatment with alkali plumbite and sulfur. In some instances, e. g., r, natural gasoline, the sweetening reaction has been accomplished through the use of alkaline hypochlorite solutions, but this method, too, has not proved satisfactory in most cases. Sometimes the sour" elements seem to be particularly-difficult to sweeten, thereby requiring large quantities of the reagent, and in other cases the treatment'seems to result in the introduction into the oil of undesirable constituents as bad as those originally present. Still other methods have been suggested for removal or conversion of the mercaptans but almost without exception these methods involve numerous treating steps which.

demand such close control of the operation that the operating costs are increased so much as to render such methods uneconomical.

One of the principal objects of the present invention is to provide a process for sweetening the mercaptan-bearing oils in'a far more efficient and inexpensive manner than practiced heretofore. ,5 Another object of the invention is to provide a processior converting the mercaptans in the oil to the disulfide form without the production of and the consequent introduction into the oil 50. of the various undesirable compounds which are formed as by-products in nearly all of the sweetening methods used heretofore.

Still another object of the invention is to prov vide a process wherein the sweetening reagent is '55 regenerated either continuously or intermittently.

Serial No. 725,405, filed.

reagent comprising copper chloride adsorbed on A further object of the invention is to provide a process and reagent which isso rapid in its sweetening reaction that the apparatus necessary for this refining step is very small and inexpensive as compared to that needed for any of the methods suggested heretofore.

-Other objects and novel features and advantages of this invention will be apparent from the following specification.

I have discovered that a solid treating agent comprising a 'ghly porous or adsorbent material such as fullers earth, charcoal and the like, impregnated .with a concentrated solution of cupric chloride, is an excellent reagent for rapidly and efficiently sweetening sour hydrocarbon oils. I

have found that during simple filtering of the oils in the liquid state at ordinary temperatures through a bed of'this reagent the mercaptans are converted to the disulfidesi" .The principal reactions are believed to be shown in the equations:

(1) 2CuCl +4RSI-I--- 2R-SCu+ Cupric Mer- Cuprous chloride captan mercaptide RSS-R+4HC1 v Alkyl Hydrochlodisulflde ric acid (2) 2RSCu+2( IuC1 RSS-R 4CuCl Cuprous Cupric Alkyl Cuprous mercaptide chloride disulfide chloride In the first step of the reaction, one-half of the mercaptan is converted to'the alkyl disulfide and the rest is left as cuprous mercaptide. The latter the'n reacts (as shown in Equation 2) with additional cupric chloride to give alkyl disul-flde and cuprous chloride, On'combining the two equationsintoone, the ultimat'e'reaction is:

Cupric Mer Alkyl chloride captan, disnlfi de 4CuCl 4HCl Cuprous Hydrochlochloride ric acid Since cuprous chloride and hydrochloric acid captan content is high the life of the reagent is quite short.

I have discovered that this spending of the reagent can be prevented and the activity maintained over long periods even when treating gasolines of extremely high mercaptan content, e. g.', those of west Texas origin, by dissolving air or an equivalent gas containing free oxygen in the gasoline previous to its passage thru the reagent bed. In this manner the cuprous chloride and hydrochloric acid, formed as shown above in the sweetening step, react with the oxygen in the air to give cupric chloride and water.

Theoretically only 8 volumes of air (gas) at 0 C.

- and 750 mm. is required for 100 liquid volumes of gasoline containing 0.01% mercaptan sulfur. The quantity of air needed for the west Texas gasolines, some of which contain as high as 0.04% mercaptan sulfur, is still quite low. I have found by experiment both in laboratory and in plant operations that a sufiicient quantity of air can be dissolved in the gasoline under the usual conditions of plant operation to keep a cupric chloride-fullers earth reagent regenerated. No loss of oil vapors is encountered in this regenerative process inasmuch as the quantity of air needed is so small as to cause no appreciable increase in the vapor pressure of the product during treatment. Any gas containing free oxygen and not detrimental to the copper treating reagent, may be used in conjunction with the hydrocarbon fluid so as to maintain the reagent in an active state.

For while it is possible to prepare the reagent in any one of a number of ways, a preferred way is to spray a concentrated solution containing cupric chloride onto the solid adsorbent material used for the carrier, thereby impregnating the adsorbent with an aqueous solution phase containing cupric ions and chloride ions. Fuller's earth is preferred as the solid adsorbent carrier material, but other materials such as charcoal, silica gel, alumina, pumice, etc., are suitable. It is understood, of course, that' the cupric chloride solution may be prepared not only from the salt itself, but also from other soluble copper salts with suitable soluble alkaline chlorides; copper sulphate and sodium chloride, for example, are a preferred combination. By the term aqueous solution phase I mean to imply that the interstices or pores of the adsorbent are partly or completely filledwith an aqueous solution containing copper chloride; obviously the quantity depends on the natureof-the' selected adsorbent, but, for example,'with 'fullers earth a preferred quantity of solution lies within the range whichfinished reagent. i

It is evident-that the 'best sweetening results will produce a content of'5 to 10% CuClz in the can be obtained by -ha'ving arelatively large volume of *a compar-atively concentrated solution adsorbed' in the carrier. However, in order to apply the solution uniformly to the carrier it is usually desirable to use a somewhat more dilute solution than that desired in the finished reagent,

water of solution from the impregnated adsorbent, thus concentrating the solution. after it has been adsorbed; but, if desired, the volume and concentration of the solution used for impregnation of a unit quantity of adsorbent may be controlled to give a finished reagent of the desired composition without removal or addition of Water to it before use.

In the operation of the process as stated, hydrogen sulfide if present is removed by any desired means from the sour gasoline before treatment with the above described sweetening reagent. The requisite quantity of air is then dissolved in the gasoline, preferably using some excess air over the theoretical amount to take care of normal fluctuations in operation. The air may be added to the stream of sour gasoline flowing to the treater in any suitable manner; the amount may be automatically controlled in proportion'to the flow of gasoline if desired, and the air may be introduced thru a porous tube or plate to break it up into small bubbles to insure rapid solution. The gasoline is then contacted with the reagent, preferably by filtration thru a bed disposed in a suitable closed treating vessel. Flow rates of 10-20 volumes of gasoline per hour per volume of reagent are generally satisfactory, but higher or lower rates may be used, depending mainly on the mercaptan content of the gasoline or other hydrocarbon fluid treated.

Under normal conditions of continuous use the reagent has an indefinitely long life, averaging from six to twelve months, or longer. The principal change tending to occur is in the water content. In some instances this is due to accumulation of water of reaction, or removal of water present in the gasoline by the reagent, resulting in dilution of the solution with which the carrier is impregnated. In other cases the gasoline being treated may contain little or no dissolved water, particularly where it has been previously carefully fractionated for removal of excessively volatile hydrocarbons such as propane, and water steps, as outlined below, to maintainthe volume within theseand concentration of the solution limits.

Where, after a considerable period of operafl tion, the reagent has accumulated water beyond-,

that originally present, the reagent may be:: ;re'=- stored to substantially its original-elfectiueness; by removal of the accumulated .excessl'awatelli this may be done, for example;byvblovqtngcthe reagent bed with air, preferably heated to F. or so; or by removing the ireagentIrom-the treating vessel and then zre'movi-ng :the excess moisture. Under .nocircumstances, however, should the water be removedtoaipointwhere the aqueous solution phase is destroyed, for it is essential to the conduct of the process covered by this application that an aqueous phase containing cupric ions and chloride ions b maintained on the carrier, since without itthe acid formed in the first step of the reaction (Equation 1) is not held by the reagent, and thus it cannot be regenerated, and the treated oil will contain acid and the very objectionable copper mercaptide.

By removing accumulated water at intervals, and taking the necessary precautions to prevent introduction of water into the reagent by the gasoline, other than reaction water, the life of 5 the sweetening agent may be considerably prolonged.

Where the tendency is toward the reverse condition, that is, removal of water from there- 'agent by gasoline which is not saturated with water, the aqueous'phase may be maintained on the carrier by adding water to the gasoline before treatment, so that the added water plus that formed in the reaction will balance the water content of the treated gasoline. One convenient way of accomplishing this is by introduction of a controlled small quantity of steam into the sour gasoline; the condensed steam is'thoroughly dispersed and dissolved. Insome cases the reagent life has been prolonged in this way to an indefinite period, compared with a period of only a few days without the addition of moisture before the reagent became dehydrated to the extent that the sweetening and regenerating reactions would not proceed.

In either case, therefore, whether the reagent tends to accumulate or to lose water, the life may be greatly prolonged by maintaining the aqueous solution phase with which the adsorbent is impregnated within the limits specified; in most cases, however, normal conditions are such that .the solution concentration remains at substantially its original value, and the reagent requires attention only at infrequent intervals, as illus- 'trated by the following examples:

Example I A very sour west Texas gasoline, containing about 0.05% mercaptan sulfur, is treated by .adding air and then passing it thru a bed of about 40 2,000 pounds of sweetening reagent at a flow rate of about 15,000 gallons per day. At approximately 100 day intervals accumulated water is removed from the reagent by taking the reagent out of the treating vessel and exposing it to the atmosphere until the water content is reduced to the original value. Meanwhile, a second treater is used to sweeten the gasoline. This reserve treater contains only 185 pounds of sweetening reagent, but can be operated at the 15,000 gallon flow rate for 30 day periods, if desired, before it accumulates sufiicient excess water to prevent sweetening. The reagent was originally prepared by" spraying 15-30 mesh fullers earth with solution containing copper chloride prepared from copper sulfate and an excess of sodium chloride, to produce a reagent comprising about 75 parts by weight fullers earth, and about 25 parts solution containing about 14% copper and 20% chloride ions.

Example II A sweetening reagent was prepared by uniformly spraying each 1,000 pounds of 15-30" mesh fullers earth with about 40 gallons of a (35 solution containing about 10% chloride and about 7% cupric copper, made from copper sulfate and sodium chloride, and then concentrating the adsorbed solution to about 15% chloride content. The reagent was then used to treat a Mid-Continent gasoline with alow mercaptan sulfur content at a flow rate of about five volumes of gasoline per volume of reagent per hour, air in the proper proportion being added to the gasoline stream entering the treater. The gasoline was stabilized before treating to remove norsorbed in the carrier at approximately its original Patent is:

mally gaseous hydrocarbons and was substantially" dehydrated by this fractionation. The dry gasoline removed water from the sweetening reagent to such an extent that complete sweetening was not obtained after several days opera- 5 tion. Steam was then added to the gasoline stieam. before treatment to replace the water removed from the adsorbed solution phase; the product became completely sweet. Thereafter a controlled amount of steam was continually 10 added to the gasoline to maintain the solution at substantially its original concentration, and

the reagent has. continued to be used since.

During the first year of operation about million gallons of gasoline were treated, with 19,000 15 pounds of reagent present. in the treater.

Example III gallons of reagent prepared as in Example 11 was used to sweeten 10,000 gallons daily of 20 north central Texas natural gasoline for a period of sixteen months. Normal conditions of operation were .such as to maintain the solution adconcentration, during this period, without addi- 25 tion or removal of water from the reagent by the means described in the above examples. Cost of the chemicals used in preparation of the reagent amounted to about 6 mills per 1,000 gallons of 30 gasoline treated during this period, compared with an average of about 16 cents per 1,000 gallons by the method formerly used.

What I claim and desire to secure by Letters 1. A process for sweetening mercaptan-bearing 35 hydrocarbon oil, comprising contacting said oil, in admixture with a gas containing free oxygen, with an adsorbent material impregnated with a maintained aqueous solution phase containing 40 cupric ions and chloride ions.

2. A process for sweetening mercaptan-bearing petroleum oil, comprising contacting said oil, in

admixture with air, with an adsorbent material impregnated with a maintained aqueous solution 45 phase containing'cupric ions and chloride ions.

3. A process for sweetening mercaptan-bearing petroleum oil, comprising adding air to said petroleum oil, and contacting the mixture of said oil and air with a sweetening agent consisting of an 50 adsorbent material impregnated with a maintained aqueous solution of a soluble copper salt and a soluble chloride, whereby the said petroleum oil is sweetened and the sweetening agent is maintained active. 55

4. A process for sweetening mercaptan-bearing gasoline, comprising contacting said gasoline, in the presence of a small proportion of air, with a sweetening agent consisting of an adsorbent material impregnated with a maintained aqueous 0 solution of a soluble copper salt and a soluble chloride, whereby the said gasoline is sweetened and the sweetening agent is maintained active.

5. A process for sweetening mercaptan-bearing petroleum oil, comprising adding, air to said oil, 65

through a body of sweetening agent consisting of fullers earth impregnated with a maintained aqueous solution of a soluble copper salt and a soluble chloride, whereby the said gasoline is sweetened and the sweetening agent is maintained active.

7. A process as in claim 3 in which the soluble copper salt is copper sulfate and the soluble chloride is sodium chloride.

ALBERT E. BUELL.