INDUSTRIAL A N D ELVGIJYEERINGCHEJIIXTRY
July, 1929
patent protection available, patents which norm:illy would be infringed and expired patents, the processes of which are feasible in the solution of the particular problem. Thus a search of this kind not only informs the research
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department of what has been done but also indicates what can be done without adverse legal consequences. Thereafter a research program may be planned and executed with a minimum of wasted effort and unnecessary expense.
The Refining of Light Oil with Silica Gel at Rochester, N. Ye1 Rufus E. Fulreader ROCHESTER G A S A Y D ELECTRIC CORPORATION. ROCHESTER. S-. Y
HE recovery of light oil as a by-product from the manufacture of coal gas and water gas was undertaken by the Rochester Gas and Electric Corporation during the war as a source of toluene for the manufacture of T.K.T. After the war the demand for toluene fell rapidly, but an outlet for the product was provided by the motor fuel market, since the merits of light oil as a fuel for internal-combustion engines had already been well established. The method of purification of the crude oil consisted in washing with sulfuric acid and a final distillation, prior to mixing with gasoline, to give a blended motor fuel. A satisfactory product was obtained by this treatment, but it gave a low yield of refined product. The acid used not only removed the undesirable gum-forming constituents from the oil but, in addition, any unsaturated compounds the percentage of which varied with the grade of light oil. Unsaturated compounds of the type occurring in light oil have been shown to have considerable value as a motor fuel, and it was with the idea of retaining these in the oil, resulting in a more desirable product and greater yield, that the silica gel process mas installed a t Rochester. The plant was originally designed for continuous operation with a daily capacity of 4000 gallons. The equipment is housed in a three-story steel-frame building with corrugated-iron siding situated adjacent to the light-oil recorery plant and covers a ground space of 550 square feet. There are two distinct units comprising the plant, the oil-treating unit and the activation unit, the two being separated by an 8inch tile fire wall. It is understood that in future installations the activating unit will not be included as an essential integral part of a silica gel plant. It is planned to have all spent gel returned to the Silica Gel Corporation a t Baltimore, where activation will be centralized, thus reducing initial plant costs and effecting an operating economy. The general layout of the plant is shown in the diagrammatic flow sheet.
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Crude Oil Cycle
The oil to be treated by silica gel is taken from the crude storage tanks of the light-oil recovery plant and pumped through a meter and then to a Venturi mixer where a small quantity of 66" B4. sulfuric acid is intimately mixed with the oil. The amount of acid used is never in excess of 0.05 pound acid per gallon of oil, this quantity being sufficient to.remove all moisture from the crude oil which cannot be completely removed by mechanical separation following the steam distillation of 75ash oil in the recovery plant. This pretreatment with acid is vital, since any moisture in the oil is selectively absorbed by the gel and impairs its refining action on the oil. The oil passes from the Venturi mixer to a settling tank, where any sludge that is formed by Received January 10, 1920.
the acid is allowed to settle out. Two settling tanks are provided so that acid can be mixed with the oil and sludge settled out in one tank n-hile the circulating pump is drawing acidulated clear oil out of the other. The circulating pump is of the piston type and maintains the pressure of the oil throughout the system between 100 and 175 pounds per square inch, this pressure being sufficient t o keep the oil in the liquid phase a t the temperatures required in the process. From the circulating pump the oil passes through a heat interchanger of the shell and tube type, the crude incoming oil passing through the tubes and recovering the heat from the outgoing refined oil. The crude oil then passes through a preheater, where it is heated by live steam to a temperature of 230" F. The crude oil is now properly conditioned for the gel treatment and passes on to the percolator. The percolator is conical in shape, 41/y feet high, and has a capacity of 26 cubic feet. A steam jacket cast as an integral part of the percolator and supplied with live steam allows for temperature control. A centrally guided stirrer for agitation is also provided. Two such percolators are necessary for continuous operation, one being in operation while the other is being charged or discharged. The acidulated oil passes from the preheater upward through the percolator containing a 300-pound charge of silica gel. The temperature of the oil and gel in the percolator is maintained a t 2iO" F. The percolator and circulating pump are of such capacity that the oil is in contact with the gel for one hour, the mixture being stirred constantly during this time. The oil leaves the percolator through two offtake pipes covered with monel metal screens of 350 mesh to prevent the escape of gel with the oil. The gum-forming constituents in the oil have now been removed by the gel and the hot treated oil passes over to the heat interchanger and thence to a cooler, where the temperature is reduced to cooling water temperature. The treated oil is then mashed free from all traces of acid by allowing it t o bubble through a solution of caustic soda and finally runs to the treated light-oil storage tank. The product is now given a final simple batch distillation, which is discontinued a t such a point that the resulting rectified light oil or motor benzene has an end point of 160" F. by the Engler test. Silica Gel Cycle
The chemical composition of silica gel is almost, exactly like that of sand or quartz, though its structure is entirely different. It is made by treating sodium silicate with sulfuric acid. The resultant product is a jelly-like mass which must be dried and crushed t o be used. A grain of 4 i c a gel contains a multitude of infinitesimal capillaries which exhibit a spongy appearance under a microscope. I t is estimated that
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Tewmo 0,' 70 Ncu~eaiizeewo tirrii
Flow Sheet for Light-Oil Treating Plant
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a cube of silica gel '/4 inch on a side has an exposed surface equivalent to 5000 square feet. It is this tremendous surface per unit volume that gives silica gel its property of absorbing liquids and catalyzing chemical reactions. The particular quality of gel used in refining motor benzene is so fine that 80 per cent passes a 250-mesh screen. The gel starts its cycle from the storage hopper located on the third floor of the plant. A screw conveyor measures and feeds the gel into an agitator, which is essentially a cylindrical tank equipped with a centrally guided stirrer for mixing the gel with sufficient oil to give a mixture that will readily flow to the percolator. As previously mentioned, the percolator holds a charge of some 300 pounds of gel and can be used until the oil leaving .the gel falls below a predetermined standard as to color and gum content after distillation. When the gel in one percolator is spent, the oil is directed to the second percolator containing a fresh charge of gel, in this way making the operation continuous. The spent gel containing considerable acidulated light oil is now drawn off into the decanting hopper located below the percolators. The decanting hopper is a steam-jacketed kettle similar in design t o the percolator but having pipe conneotions on the side a t various elevations and equipped with a stirrer. The mixture is allowed to settle in the decanting hopper and clear oil is drawn off through the offtake pipes and led to the recovered-oil tank. The gel remaining in the decanting hopper is then heated by steam on the jacket and live steam blown through the mass for the purpose of removing the greater portion of the oil in the capillaries of the spent gel. The steam carrying oil from the gel is conducted to a shell and tube condenser, the condensate running to the recovered-oil storage tank. The partially dried gel is discharged from the bottom of the decanting hopper with the aid of the spiral stirrer into a screw conveyor, which delivers it to a bucket elevator and then into a hopper. From the hopper it travels by a screw
conveyor a t a uniform rate through the tile fire wall separating the treating and activating units, directly into the primary activator. This activator consists of two hearths 4 feet 6 inches in diameter and constructed of '/r-inch steel plate welded a t the joints and heated indirectly with combustion gas. Superheated steam is admitted with the gel in the primary activator to remove the last traces of oil in the gel, the oil distilling being condensed and run to the recoveredoil tank. The gel in the primary activator is heated to 450' F. The activator is equipped with arms radiating from a centrally revolving vertical shaft, each arm carrying a number of teeth serving as revolving rakes to agitate the gel and direct its travel from the center to the outside of the activator, where it is taken in the dry state by a screw conveyor to the secondary activator located directly below the primary and of identical construction. Here the gel is heated indirectly t o a temperature of 550-600' F. The admission of air from an auxiliary fan supplies the oxygen for combustion of carbon and other ignitable substances in the gel. The gel leaves the secondary activator by a screw conveyor, which discharges into a 3-inch gel-lifting pipe through which air is blown a t the rate of 60 cubic feet per minute under 6 inches water pressure differential supplied by an auxiliary fan. The air carries the gel to a cyclone located above the storage hopper. A bag collector removes gel fines from the exit air of the gel-lifting system. The gel has now completed its cycle and is in the active condition ready to be charged into a percolator. Heat for the primary and secondary activators is supplied by a gas furnace consuming normally 2.6 cubic feet per minute of 540-B. t. u. illuminating gas. The flue system between the furnace and activators is so arranged that part of the gas goes directly to the primary and part to the secondary activator, or all the gas can be passed through the secondary and primary in series. An induced-draft fan having a capacity of 520 cubic feet per minute a t 800" F. with 3-inch water pressure differential is necessary to overcome friction in the flues.
July, 1929
I N D U S T R I A I , AaVD ENGIXEERING CHE,UIXTRY Operating Results
The silica gel plant has been in operation since March 1, 1927. It was designed t o treat an uncut crude light oil having an end point ranging from 428" to 536" F. (220' to 280' C.), which light oil has approximately 85 per cent distilling at 356" F. (180' c.). Originally the oil to gel ratio was 25 to 1, but this has been increased to as high as 200 to 1. The plant has never shown an oil loss in excess of 3 per cent, the average figure over the past twenty months being 1.4 per cent. The gel-treated finished product has a Saybolt color ranging from 19 to 25, and is stable over a considerable storage period. The sulfur content is within specification limits, and
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the gum content, as determined by copper dish test, ranges from 6 to 20 mg. and shows no corrosion by standard tests. Owing to the small amount of crude light oil production a t Rochester, averaging 1500 gallons per day, it has been the practice to accumulate 10,000 to 15,000 gallons of crude and put that quantity through the gel plant at one running. This can be accomplished in 36 hours, showing that the plant is capable of operating considerably over designed capacity. Inasmuch as this plant is operated under capacity and periodically, the cost per gallon of crude treated is somewhat higher than was the case with the old acid wash process. This differential, however, is considerably more than offset by the 15 per cent increase in yield of motor benzene directly attributed to the silica gel process.
Silica Gel as a Reagent for the Extraction of High-Sulfur Oils from Crude Petroleum Preliminary Paper'J Gladys E. Woodward3 CHEMICAL LABORATORY OF THE COLLEGE OF LIBERAL ARTS, XORTHWESTERN UNIVERSITY,
T HAS been known that silica gel has a high adsorptive power toward sulfur compounds. Through this means completely desulfurized gasolines have been obtained (I).* Waterman and his co-workers (2, 3) and later Wood, Sheeley, and Trusty (4) have shown that different types of sulfur compounds are removed to a different degree by this silica gel treatment. Silica gel has not heretofore been used for the purpose of concentrating the sulfur compounds that are found in the crude oil. Since such drastic heat treatment had to be applied to the gel in order to remove completely the adsorbed material, the use of silica gel as a reagent for extraction of the sulfur compounds in the form in which they originally existed did not a t first seem possible. However, since silica gel produced such a marked decrease in the sulfur content of a petroleum oil, it seemed advisable to investigate the possibilities of separating from the gel the high-sulfur material thus removed from the oil. Superheated steam had been tried by other workers (private communication), but the method did not seem favorable. In the present research it was found that certain organic solvents displaced the adsorbed material to a different degree. Thus, by washing first with the solvent removing the smallest amount of material and then with the more effecbive solvents in order, different fractions of oil were obtained. This process of washing removed a total of more than 90 per cent of the adsorbed material. The remaining small percentage was easily liberated by dissolving the gel in 10 per cent sodium hydroxide a t 30" C. In every fraction the oil obtained was considerably higher in sulfur than the original oil. The highest sulfur oils were those removed from the gel by benzene; oils containing 5.65 and 4.98 per cent sulfur were 1 Received March 19, 1929.
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2 This paper contains results of a n investigation carried o u t a s part of project No. l i of t h e American Petroleum Institute research program. Financial assistance in this work has been received from a research f u n d donated b y t h e Universal Oil Products Company. This fund is being administered b y t h e American Petroleum Institute with t h e cooperation of the Central Petroleum Committee of t h e National Research Council. F r a n k C. Whitmore is director of project N o . 17. 8 Research Fellow, American Petroleum Institute. Italic numbers in parenthesis refer t o literature cited a t end of article.
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EVANSTON, ILL.
obtained, while the original crude contained only 2.30 per cent sulfur. Thus, it may be seen that silica gel extracts a part of the oil which is considerably richer in sulfur compounds than the original oil. That an oil still richer in sulfur may be obtained from this high-sulfur extract seems promising, for in a small experiment on the 5.65 per cent oil a fraction was obtained containing 8.70 per cent sulfur. Two methods of treating the oil with the gel were employed. The first, filtration through a column of gel, was too slow. The best method was to dilute the oil with naphtha and stir with the gel until equilibrium was established. Using a solution of InglenTood crude petroleum4in naphtha, the reduction in sulfur content produced by a commercial silica gel5 was 18 per cent. Most of the work has been carried out with this gel. But a recent experiment with a sample of Holmes gel,$ which is much more porous, indicates that this is considerably more efficient in removing the high-sulfur constituents from the oil. The reduction of a solution of the Inglewood crude in this case was 37 per cent, twice as great as produced by the commercial gel: and the material recovered from the gel contained 6.84 per cent sulfur as against 3.98 per cent in a similar fraction from the commercial gel. Furthermore, it would seem that the material removed by Holmes gel would be easier to work with as it is a solid. No further experiments, honTever, have been performed in this connection. Another indication of the greater effectiveness of Holmes gel is that it removes almost all of the colored constituents of the oil. The black solid removed is apparently the cause of the color in the oil. Since it has now been shown that it is possible to recover the material adsorbed on the gel, and to make a further ex4 This oil was obtained from t h e Inglewood field in California through the courtesy of t h e Universal Oil Products Company. "This crude oil came from Standard Oil T a n k No 9461, h-ovember 19, 1926, and represents t h e regular pipe line r u n from t h e Inglewood field. This field was producing about 40,000 barrels per day a t t h a t time. T h e production come5 from a n average depth of about 2000 feet below surface. T h e producing formation is Pliocene marine sand, a n d t h e general structure is a n anticline faulted on one side." 3 200-mesh gel obtained from t h e Silica Gel Corporation of Baltimore. 8 Kindly furnished hy Harry N Holmes, Oberlin College, Oberlin, Ohio.
