US3457165A - Treatment of hydrocarbon distillates to remove acidic organic material employing a fixed bed containing a solid alkali metal hydroxide - Google Patents

Description

United States Patent US. Cl. 208-263 9 Claims ABSTRACT OF THE DISCLOSURE Concerns a cyclic process for treating a hydrocarbon distillate containing acidic organic materials in order to remove these materials therefrom The reagent employed is a fixed bed containing solid alkali metal hydroxide. Principal problem encountered is the build-up of a flocculent material in the bed with the resultant deactivation of the bed. Solution disclosed herein encompasses the use of a cyclic process having a treating cycle state and a reactivation cycle state. Treating cycle state involves contacting the acidic hydrocarbon distillate with the bed of alkali metal hydroxide at conditions effective to form salts of acidic organic materials and to adsorb the soformed salts on the bed. Reactivation cycle state utilizes a hydrocarbon solvent at a temperature greater than 150 F. to dissolve the salts of acidic organic materials in conjunction with cooling of the resultant salt-containing hydrocarbon solvent to precipitate and recover the salts of acidic organic materials.

The present invention relates to .a cyclic process for treating a hydrocarbon distillate containing acidic organic materials in order to efiect removal of these materials therefrom. In one aspect the present invention encompasses a method for recovering valuable acidic organic materials such as naphthenic acids and phenols, from a hydrocarbon distillate containing the same. In a second aspect, the present invention comprehends a treating method for a hydrocarbon distillate containing acidic organic materials for the purpose of effecting one or more of the following: improved corrosion characteristics, increased response to oxidation inhibitors, improved odor, decreased tendency to form emulsions, improved color stability, etc. In another aspect, the present invention is directed at the acquisition of improvements in subsequent processes operating on the treated distillate produced by the present inventionparticularly, a subsequent sweetening process.

The concept of the present invention resulted from my work with a solid bed of alkali metal hydroxide during which I noted that the decay in the ability of the bed to remove acidic organic materials from a hydrocarbon distillate was paralleled by a build-up of flocculent materials in the bed. Infrared inspection of this material indicated it primarily consisted of phenolates, naphthenates and mercaptides. Attention was then focused on finding a workable means of removing these materials, and, quite surprisingly, I found that by raising the temperature of the distillate being treated to about 176 F., the fiocculent materials would dissolve, and upon cooling the resulting salt-containing distillate a precipitate would form. Moreover, this procedure effected the reactivation of the bed of alkali metal hydroxide. Based on these facts the present invention was then formulated as a process involving a repetitive sequence of cycles through a treating operation with a bed of solid alkali metal hydroxide and a reactivation operation for this bed.

3,457,165 Patented July 22, 1969 Treating processes directed at the removal of acidic organic materials are widely used in commercial refining operations. These acidic organic materials are commonly thought to be of three general types. Ranked in order of decreasing acidity, these are: carboxylic acids such as aliphatic and naphthenic acids; phenolic materials such as phenol, cresol, and other alkyl and polyalkyl phenols; and mercapto compounds such as alkyl mercaptans, thiophenols, etc. The reason for desiring the removal of these materials are manifold. One prominent reason is associated with the fact that these materials, or salts thereof, find use in a wide variety of industrial chemical products. For example, the metallic naphthenates and phenolates have been found to be highly desirable as components of detergents, dryers for paint, in the manufacture of resins, in the preparation of disinfectants, as treating agents for cloth, as lubricating oil additives, .and in like applications well known to those skilled in the art. Still other reasons have to do with a desire to produce a product distillate having certain preferred characteristics. For instance, removal of these materials can improve one or more of the following properties of the distillate: corrosion characteristics, response to oxidation inhibitors, offensive odor, emulsion-forming tendencies, color stability, etc. Yet other reasons emanate from the fact that removal of these materials can effect substantial improvement in subsequent processes to which the product distillate is subjected-most significantly in a subsequent sweeting operation.

Perhaps the most popular commercial treating processes designed to perform the above-mentioned tasks employ an aqueous solution of alkali metal hydroxide. In these processes the oil-soluble, acidic organic materials react with the .alkali solution to form oil-insoluble salts which are readily separable from the hydrocarbon distillate. Because the solubility of the organic portion of these materials in the hydrocarbon phase shifts saltforming reaction equilibrium, difliculty is commonly experienced when the distillate contains high molecular weight organic materials This problem can be somewhat minimized, but not eliminated by the addition of solutizerssuch as isobutyric acid, tannic acid, methanol, various aliphatic alkanolamines, etc.in order to increase the extratcion capabilities of these solutions. Yet another problem associated with these processes is the almost inevitable requirement for .a water-wash step on the efiluent side of the treating process. This water-wash step is employed to remove residual suspensions or emulsions of treating solutions and dissolved organic salts. Likewise, in most cases utilization of the alkali metal hydroxide contained in these solutions is relatively low with a substantial amount of unused alkali being rejected in the spent treating solution.

Considering these disadvantages, it was not unexpected that attention in the art has been directed to treating processes employing a solid bed of alkali metal hydroxide. This type of process offers the following advantages over liquid alkali treating: (1) no subsequent drying step is required, (2) works equally as well on high molecular weight acidic materials, and (3) potentially can result in more efficient utilization of the alkali metal hydroxide. Despite these advantages, development in this area has not been rapid primarily because of the generally imposed requirement of using reasonably large particles of alkali metal hydroxide in order to reduce the pressure-drop across the treating bed, coupled with the commonly observed increase in the rate of deactivation of the bed due to the rapid coating of these large particles with salts of acidic organic materials.

As a result of my investigations in this area, I have now found that this problem can be readily transformed into a desirable feature of a cyclic process. Considering for the moment the situation that would exist if the adsorp- 1 tion of salts did not take place, it is evident that these salts would appear in the efliuent. from the treating zone and would necessitate additional processing stepssuch as, a washing step, a settling step, or an adsorption step in order to separate the salts from the treated distillate. Taking advantage of this adsorption phenomenon, the cyclic process of the present invention eliminates any requirement for these subsequent processing steps to obtain a distillate substantially reduced in acidic organic material content.

' Essential to the cyclic process of the present invention ismy discovery that by regulating the temperature of contact of the distillate with the solid alkali metal hydroxide bed, the bed can be made to oscillate between adsorption and desorption of these materials. Consequently, the present invention involves a cyclic treating process having a first portion of each process cycle devoted to forming and adsorbing salts of acidic organic materials and a second portion of each process cycle devoted to removal and recovery of these salts. By means of this cyclic process the hereinbefore mentioned advantages of solid bed treating are realized.

It is, accordingly, an object of the present invention to provide a workable and convenient process for removing acidic organic materials from a hydrocarbon distillate containing the same. Another object of the present invention is to realize the potential advantages of solid bed alkali metal hydroxide treating. Yet another object of the present invention is to provide a convenient and simple procedure for reactivating a bed. of solid alkali metal hydroxide that has accumulated substantial quantities of salts of acidic organic materials.

In a broad embodiment, the present invention encompasses a cyclic process for treating a hydrocarbon distillate containing acidic organic materials in which process a treating cycle state alternates with a reactivation cycle state. During the treating cycle state, the process comprises the steps of: (a) contacting the hydrocarbon distillate with a fixed bed containing solid alkali metal hydroxide maintained in a treating zone, at conditions, in cluding a temperature less than about 100 F., etfective to form salts of acidic organic materials and to adsorb the so-formed salts on the bed; and (b) recovering from the efiiuent from the treating zone a treated distillate substantially reduced in acidic organic material content. During the reactivation cycle state, the process comprises the steps of: (a) contacting the resultant bed of solid alkali metal hydroxide containing salts of acidic organic materials with a hydrocarbon solvent at conditions, including a temperature greater than 150 F., effective to dissolve salts of acidic organic materials; and (b) cooling the effluent from the treating zone during this portion of the cycle to precipitate salts of acidic organic materials.

A preferred embodiment of the present invention comprehends a cyclic process for treating a kerosine distillate containing naphthenic acids, phenolic materials, and mercapto compounds, in which process a treating cycle state alternates with a reactivation cycle state. The treating cycle state comprises the steps of: (a) contacting the kerosine distillate with a fixed bed, containing a mixture of solid sodium hydroxide and polypropylene granules, maintained in a treating zone at conditions, including a temperature of less than 100 F., effective to form sodium naphthenates, phenolates, and mercaptides and to adsorb the so-forrned sodium salts on said bed; (b) recovering from the effluentfrom the treating zone, a treated distillate substantially reduced in content of naphthenic acids, phenolic materials and mercapto compounds. The reactivation cycle state comprises the steps of: (a) contacting the resultant bed containing sodium naphthenates, phenokites, and mercaptides with the kerosine distillate at conditions, including a temperature greater than 150 F., sutficient to effect removal of these sodium salts, and (b) cooling the effiuent from the treating zone to precipitate sodium naphthenates, phenolates, and mercaptides.

Other embodiments and objects of the present invention encompass: various kinds of hydrocarbon distillates that can be treated thereby, types of alkali metal hydroxides and adsorbent materials that can be employed in the treating bed, various kinds of hydrocarbon solvents that can be used in the reactivation portion of the cycle, discrete values of process parameters and operating conditions that govern the actual operation of the process, and the like particulars, all of which are hereinafter disclosed in the discussion of each of these facets of the present invention.

The cyclic process of the present invention is especially advantageously used in the treatment of heavier hydrocarbon distillates containing acidic organic materials and particularly, kerosines and jet fuels. Typically, kerosines boil within the range of from about 350 F. to about 600 F., whereas jet fuels commonly boil in the range of 350 F. to about 500 F. Other heavy hydrocarbon distillates treatable by the process of the present invention include fuel oils, light gas oils, heavy gas oils, diesel fuels, lubricating oils, and the like high boiling distillates. While the present invention is particularly applicable to the treatment of heavier hydrocarbon distillates, it is understood that the process may also be used for the treatment of other acidic organic material-containing streams including: cracked and straight run gasolines, light naphthas, heavy naphthas, etc. The special applicability of the present invention to hydrocarbon distillates boiling above the gasoline range is primarily a consequence of the almost inevitable presence of significant quantities of acidic organic materials in these streamsparticularly, naphthenic acids and phenolic materials. For example, excellent results are obtained with the present invention when processing a kerosine distillate as will be shown in the examples.

At this point it is to be noted that the cyclic process of the present invention has the capability to remove varying quantities of the acidic organic materials in the hydrocarbon stream being treated. Paralleling the classification hereinbefore given with reference to the acidity of these materials, the cyclic process of the present invention will easily remove substantially all of the aliphatic and naphthenic acids, a major portion of the phenolic materials, and a significant portion of the mercapto compounds. That is to say that the naphthenic and aliphatic acid materials are most easily removed, followed by the phenolic materials, with the mercapto compounds being most difficult of all to remove. The exact proportion of each of the various classes of materials that will be removed by the process of this invention is governed principally by the contacting time of the distillate with the bed of solid alkali metal hydroxide. Since the contact time scales as a function of some constant times the inverse liquid hourly space velocity (LHSV), it is evident that the most acidic materials will be removed at high space velocity with very little removal of the weakly acidic materials, and on the other hand, the weakly acidic materials will be removed, along with the highly acidic materials, at relatively low space velocity. In this context, LHSV is defined as the liquid volume of the distillate charged per hour to the treating zone divided by a total volume of the treating zone containing the bed of solid alkali metal hydroxide. Balancing all of these considerations, I have found for kerosine distillates that an LHSV of about 1.0 yields substantially complete removal of naphthenic materials and phenolic materials, coupled with the 40 to 60% removal of mercapto compounds. Similar relationships govern other boiling range distillates, and can be easily ascertained by methods familiar to those skilled in the art. It is to be noted that this sequen- According to the present invention, the treating portion of the cyclic process involves contacting the dis tillate to be treated with a fixed bed containing solid alkali metal hydroxide. Although in theory, any solid alkali metal hydroxide could be employed in the present invention, in actual practice either sodium hydroxide or potassium hydroxide or mixtures of these is preferred, primarily because of their ready availability and relatively modest cost. Despite the teachings of the prior art in this area that the size of the particles is a critical parameter, I have found for my purposes that the exact size of the particles is not controlling. For instance, as will be shown in an example, I have obtained useful results with solid caustic of -20 mesh on a Tyler standard screen scale. In some cases it may be advantageous to use particles of alkali metal hydroxide from inch in diameter up to about 1.0 inch in diameter or larger. It is to be understood that the size of the particles used in the cyclic process of the present invention is slowly decreasing during the course of operation of the process, necessitating periodic replacement and/or replenishment of this material.

In a preferred embodiment of the present invention, the particles of solid alkali metal hydroxide are employed in a treating zone in admixture with particles of a lipophilic solid adsorbent. In this context lipophilic refers to an adsobent having an aflinity for fats and oils. Any suitable lipophilic adsorbent may be employed such as granular polypropylene, activated charcoal, soft coal, granular polyethylene, granular polystyrene, etc. Excellent results are obtained with granular polypropylene. These materials are preferably utilized in approximately the same sized particles as the initial size of the solid alkali metal hydroxide particles. Furthermore, these particles are preferably utilized in a weight ratio of about 10% to about 50% of the total Weight of the resulting treating bed.

The treating portion of the cyclic process of the present invention is accomplished by passing the distillate to be treated through a treating zone containing a bed of solid alkali metal hydroxide. The distillate may pass in either upward or downward flow. In view of the hereinbefore mentioned capability of the hot distillate to remove adsorbed salts of the acidic organic materials, it is essential that a temperature of less than about 100 F. be maintained in the treating zone. The pressure utilized in this zone is subject to a wide range of choice, normally being chosen to insure that the hydrocarbon distillate remains in the liquid phase and to sustain the desired flow rate through the bed. Likewise, the LHSV, as pointed out hereinbefore, is subject to a wide variation depending on the particular results sought. I have found that good results are obtained for most distillates with a LHSV of about 0.5 to about 5.0 with a value of about 1.0 giving excellent removal of naphthenic acids and phenolic materials. Furthermore, I have found it to be a good practice to condition the bed with a light alcohol such as methanol, ethanol, etc., in order to aid in the initial attack of the solid alkali metal hydroxide upon the distillate. For example, I have found improved results with the addition of methanol at a rate of about 1 cc. per liter for about the first 20 volumes of the distillate being treated based on the volume of the caustic bed. After this initial treatment of the bed with the alcohol further addition of the alcohol is not necessary.

The duration of the treating portion of the process cycle can be selected according to a number of difierent methods. According to one method, it is selected as a function of the concentration of acidic organic materials in the efiluent from the treating zone. In another method, it is selected on the basis of the increase of the pressure drop across the bed caused by the build-up of flocculent material in the bed as previously explained. Still another method of selecting this parameter involves the selection of a time interval which is substantially less than the time required for deactivation of the solid alkali metal hydroxide-that is before significant build-up of fiocculent material in the bed is observed. Although each of these methods is acceptable, it is preferred to operate in the treating mode of the process until a significant build-up of flocculent material in the bed is observed. Since this period depends on a number of factors which are unique for each distillate being treated, such as concentration of acidic organic materials in the distillate, the size of the particles used in the treating bed, the liquid hourly space velocity, etc., it is most convenient to determine this as a function of the build-up of pressure drop across the bed for each particular distillate. Therefore, in the preferred mode of operation, when the pressure drop across the bed becomes unacceptable, the reactivation of the cycle will commence.

According to the present invention, the reactivation portion of the cycle is commenced by passing a hydrocarbon solvent at a temperature greater than F. through the bed of solid alkali metal hydroxide having salts of acidic organic materials adsorbed therein. This hydrocarbon solvent can be any hydrocarbon solvent effective to remove these undesired salts, and it, in a preferred embodiment, comprises the hydrocarbon distillate which is being treated during the treatment portion of the cycle. That is when a kerosine distillate is being treated, a portion of it is heated to a temperature of about 150 F. to about 200 F. and contacted with the deactivated solid alkali metal containing bed. However, in some cases, it is advantageous to employ a different boiling range distillate in the reactivation portion of this cyclefor example, when treating a gas oil fraction it is convenient to use a kerosine fraction. Similarly, when treating a kerosine it is sometimes convenient to use a gasoline fraction as the hydrocarbon solvent.

Regardless of what type of hydrocarbon solvent is used, a hydrocarbon efliuent, containing dissolved salts of acidic organic materials, is recovered from the treating zone during this portion of the cycle. Upon cooling of this effluent, a precipitation of the salts is observed. This fact facilitates separation of the hydrocarbon solvent from the salts since any convenient procedure for separating a solid particle from a liquid can be employed. Good results are obtained merely by injecting the effluent into a settling zone wherein the salts of acidic organic materials rapidly separate from the hydrocarbon solvent.

Aside from the temperature, the other conditions such as pressure and LHSV utilized in the reactivation portion of the cycle need not vary from those employed during the treatment portion of the cycle. Likewise, the duration of this portion of the cycle can be set by a number of methods which are analogous to those previously mentioned for the treating portion of the cycle. However, the preferred method involves monitoring the amount of salts of acidic organic material contained in the effiuent from the treating zone during the reactivation cycle and stopping this portion of the cycle when this quantity drops to a predetermined level.

In any event, at the end of the reactivation cycle state, the treatment portion of the cycle is once again commenced and the process continues to operate in this fashion until replenishment or replacement of the solid alkali metal hydroxide is necessary, at which point fresh treating agent is added and the process continued. It should be noted that combinations of two or more treating beds may be used in a treatment system so that continuous processing of the hydrocarbon distillate is achieved. The procedures for doing this and the necessary piping arrangements are well-known to those skilled in the art and will not be repeated here.

The following examples are introduced to illustrate further the novelty, utility, and mode of operation of the present invention but not with the intention of unduly restricting the present invention.

Example I A treating zone is loaded with 83 grams of 10-20 mesh particles of solid sodium hydroxide. A kerosine distillate having 114 p.p.m. of mercapto sulfur, an acid number of 0.007, a phenolic content of 100 p.p.m., a 41.9 API gravity at 60 F., and a boiling range of about 372 F. to about 497 F., is then charged to the treating zone, in downflow fashion at a temperature of 70 F., a pressure adequate to sustain a flow rate of 100 cc. per hour through the zone, and a LHSV of 1.0 based on the volume occupied initially by the solid caustic. During the first hours of operation of the process, methanol is added to the feed stock at a rate of 0.1 ml. per hour in order to facilitate attack of the caustic on the distillate as explained hereinbefore.

A treated kerosine is Withdrawn from the treating zone and its mercapto sulfur content, phenolic content, and acid number are determined at the end of each 20 hour interval. Results of these measurements are in accordance with the data reported in Table I.

TABLE I.-RESULTS on TREATING PORTION OF CYCLE Mercapto S, p.p.m 114 72 75 85 92 102 At the end of interval 5, a build-up of a flocculent material in the treating bed was noted with resulting increase in the pressure drop across the bed. At this point, the reactivation portion of the cycle is commenced and the same kerosine distillate is charged to the treating zone at a temperature of 190 F. and a LHSV of 2.0. Immediately, sodium salts of phenolic materials and naphthenic acids are detected in the ellluent from the treating zone and upon cooling of this eflluent formation of a precipitate is noted. The kerosine is separated from the precipitate in a settling zone and recycled to the treating zone. After about one hour of this treatment, it is noted that the amount of precipitate being recovered is negligible. At this point, the temperature in the treating zone is reduced to 70 F. a second cycle commences. It is found that the initial activity of the solid caustic is restored and the pressure drop across the bed is approximately equal to its initial value. Cyclic operations are continued in this fashion for a substantial number of cycles, with good recovery of the salts of the acidic organic materials and successful reactivation of the caustic bed.

Example II Another kerosine distillate, having 710 p.p.m. of mercapto sulfur, an acid number of 0.019, a 38.0 API gravity at 60 F., and a boiling range of about 400 F. to about 525 F., is charged to a treating zone containing a fixed bed comprising 80 grams of a 12 to 30 Tyler mesh caustic particles. The treatment portion of the cycle is conducted at conditions identical to those reported in Example I. The mercapto sulfur content of the effluent from the treating zone is 184 p.p.m. at 20 hours, 184 p.p.m. at 40 hours, and builds to 374 p.p.m. at 200 hours. During the first 40 hours, methanol is admixed with the feed stock at the rate of 1 ml. of methanol per liter of kerosine. The acid number of the etfiuent remains constant at about 0.005 throughout the 200 hours. However, at the 200 hour point, the effects of a build-up of a flocculent material in the treating bed are manifested in the decline in activity of the bed for mercapto sulfur removal. The reactivation portion of the cycle is, consequently, started by heating the kerosine distillate to about 200 F. and passing it through the clogged bed at a LHSV of 1.0. An eflluent rich in salts of organic materials is withdrawn from the treating zone, cooled to 70 F., and injected into a settling zone where a precipitate settles out. A substantially salt-free kerosine is withdrawn from the settling zone, heated to about 200 F. and recycled to the treating zone. This portion of the cycle continues for about 2 hours until the concentration of salts of acidic organic materials in the kerosine effluent drops to a negligible value. The second cycle is then started by passing the kerosine distillate at a temperature of F. through the treating zone. Restoration of extraction activity is noted and the process continues in this fashion through subsequent cycles with efiicient utilization of the caustic materials to extract acidic organic materials.

Example HI Yet another kerosine distillate, having 720 p.p.m. of mercapto sulfur, an acid number of 0.03, a phenolic content of 250 p.p.m., an API gravity of 41.8 and a boiling range of 297 F. to 506 F is admixed with 0.1 volume percent of methanol and charged to a treating zone containing a fixed bed of 35 grams of a 10-20 mesh solid particles of potassium hydroxide in admixture with sufficient granules of 30-40 mesh activated carbon to result in a bed occupying a 100 cc. volume. Once again conditions employed here are identical to those reported in EX- ample I. Results of the first portion of the cycle are: at 40 hours, a mercapto sulfur content in the effluent of 132 p.p.m.; at 60 hours235 p.p.m.; at hours-305 p.p.m.; and at hours390 p.p.m. During the entire 100 hours the acid number of the effluent is substantially constant at about 0.002 and the phenolic content is constant at about 10 p.p.m. At the 100 hour point, the bed is clogged with flocculent material and reactivation is started by heating the kerosine distillate, to a temperature of about 180 F. and passing it through the bed at a LHSV of 1.0. Reactivation is complete in about 3 hours and the treatment portion of the cycle restarted as previously explained. Operation is continued for about 10 cycles and results similar to those reported for the first cycle are obtained for each of the subsequent cycles.

Example IV Example III is repeated with the same kerosine and conditions except that the treating bed comprises 30 grams of l020 mesh caustic in admixture with commercial available polypropylene granules or 12 mesh such that the resultant mixture occupies a volume of 100 cc. Results here for the first cycles are: at 20 hours, 150 p.p.m. mercapto sulfur in the efiluent from the treating zone; at 40 hours, 55 p.p.m.; at 60 hours, 94 p.p.m.; at 80 hours, 94 p.p.m.; and at 100 hours p.p.m. Once again, the acid number remained at 0.002 throughout this period. At this point, the reactivation portion of the cycle is commenced in the manner reported in Example IH. Operation is continued for 15 cycles with good results being continuously achieved.

I claim as my invention:

1. A cyclic process for treating a hydrocarbon dist1llate containing acidic organic materials, said cyclic process comprising the steps of:

(a) contacting, during a first portion of the process cycle, the hydrocarbon distillate with a fixed bed containing solid alkali metal hydroxide maintained in a treating zone, at conditions, including a temperature less than 100 F., effective to form salts of acidic organic materials and to absorb the so-formed salts on said bed;

(b) recovering, during this first portion of the process cycle, from the effluent from the treating zone, a treated distillate substantially reduced in acidic organic material content;

(c) thereafter, during a second portion of the process cycle, contacting the resulting bed of solid alkali metal hydroxide containing salts of the acidic organic materials with a hydrocarbon solvent at conditions, including a temperature greater than F., effective to dissolve salts of acidic organic materials;

(d) cooling the effluent from the treating zone, during 9 the second portion of the cycle, to precipitate salts of acidic organic materials, and,

(e) thereafter, repeating steps (a) through (d).

2. The cyclic process of claim 1 further characterized in that said hydrocarbon solvent is said hydrocarbon distillate.

3. The cyclic process of claim 1 further characterized in that said alkali metal hydroxide is selected from the group consisting of sodium hydroxide, potassium hydroxide, and mixtures thereof.

4. The cyclic process of claim 1 further characterized in that said hydrocarbon distillate is a kerosine.

5. The cyclic process of claim 1 further characterized in that said hydrocarbon distillate is a gasoline.

6. The cyclic process of claim 1 further characterized in that said hydrocarbon distillate is a gas oil and that said hydrocarbon solvent is a kerosine.

7. The cyclic process of claim 1 further characterized References Cited UNITED STATES PATENTS 2,600,537 6/1952 Honeycutt 19614.40 1,728,156 9/1929 Wheeler 208-263 2,321,540 6/1943 Atwood 208263 DELBERT E. GANTZ, Primary Examiner J. M. NELSON, Assistant Examiner US. Cl. X.R. 208-283