INDUSTRIAL AND ENGINEERING.CHEMISTRY
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peroxides, although less reactive toward lead than either dihydroxy dialkyl or acyl peroxides, are likely to be much more damaging from a corrosion standpoint since they possess greater stability toward heated oil. If nonperoxidic oxidizing agents other than oxygen were present in oils, they would prove to be much more damaging than peroxides because of their high stability with respect to heated oil, Although hydroperoxides and oxygen are the oxidizing agents most likely to be present in oils, there is a possibility that nonperoxidic oxidizing agents may form from (a)oxidation of nitrogen containing inhibitors and natural nitrogen compounds in the oil, (b) oxidation of oil, (c) reaction of nitrogen oxides produced in the combustion of engine gases with the heated oil, or ( d ) nitrobenzene not completely removed following solvent extraction of the oil. At low temperatures insoluble soap films formed on the lead surface are very effective in slowing the corrosion rate. A film formed slowly appears to be more protective than one formed rapidly.
Vol. 37, No. 10
ACKNOWLEDGMENT
The authors are pleased to extend their appreciation to the Lubri-Zol Corporation, sponsors of this work, for permission to publish the resufts. They are also grateful to Gus Abood, George J. Dlouhy, and Marjorie Palenschat for assistance in running many of the tests. They are indebeted to Paul F. Hart,man who synthesized many of the peroxides used. LITERATURE CITED
(1) Conant and Luta, J. Am. Chem. Soc., 46, 1254 (1924).
Denison, IND. ENQ. CHEM.,3 6 , 4 7 7 (1944). Donath, J . SOC.C h a . I d . , 14,283 (1895). Ehlers, Petroleum Z.,28, No.43 (1932). (6) Zbid., 31, No. 16 (1936). ( 8 ) Fischer and Pfleiderer, 2.unorg. allgem. Chem., 124, 6 1 (1922). (7) Fox, Analyst, 8, 110 (1883). (8) Graefe, Petroleum Z., 28, No.23 (1932). (9) Pomeroy, J. Inat. Petroleuk, 30, 96 (1944). (10) Prutton et al., IND. ENQ.CHEM.,37, 90 (1945). (11) Wheeler, Oil & Soup, 9, 89 (1932). (2) (3) (4)
Alkylation of Isoparaffins bv Olefins in Presence of Hydrogen Fluoride J
CARL B. LINN AND ARISTID V. GROSSE' Universal Oil Products Company, Riverside, Ill.
E
YDROGEN fluoride is widely used as a catalyst for the interaction of olefins and isobutane to produce highly branched liquid paraffins (I, 7,IO), a process which has a n important place in the aviation gasoline program, The liquid product of the alkylation process, known as alkylate, consists of highly branched-chain paraffins and has superior antiknock properties both with and without added tetraethyllead, The amount of alkylate being regularly incorporated in aviation gasoline blends runs from about 25 to 40%. The discovery that isoparaffins would react with olefins in the presence of a catalyst (14, 16, 26) overthrew the classical concept of the chemical inertness of the paraffins and opened extensive new fields for research. It has been found that alkylation of isoparaffin hydrocarbons can be catalyzed by numerous compounds including metal halides such as aluminum chloride (14,16, 17, $I), zirconium chloride, etc. (8),sulfuric acid (3,4, 1@,WO), boron fluoride (Zb), hydrogen fluoride (IO), and others. Of these, hydrogen fluoride, sulfuric acid, and aluminum halides are being used commercially. The alkylation processes are of great commercial importance and our HF alkylation process is of particular interest a8 a chemical and engineering development (7). Anhydrous hydrogen fluoride catalyzes various reactions,
including the polymerization of olefins ( O ) , the alkylation of cyclic compounds such as aromatic hydrocarbons (6, 9, 2 4 , as well as other condensation reactions (2.9, 94). Materials which may be used with hydrogen fluoride under suitable conditions for alkylating cyclic compounds include alcohols, olefins, oxides such as ethylene oxide, ethers, organic acids, unsaturated alcohols, and alkyl halides (6, 86). Alkylating catalysts are effective over a wide range of temperatures; many of them function best at temperatures from about 0" to 50' C., although by proper correlation of operating conditions the range can be extended above and below these values. ADVANTAGES OF HYDROGEN FLUORIDE AS CATALYST
Hook, Pa.
Hydrogen fluoride has a number of advantages which recommend its use a a catalyst, particularly in the process for alkylating isoparaffins with olefins. Among these are the following physical properties: molecular weight, 20.01; specific gravity, 0.988; melting point, -83" C.; boiling point, 19.4' C. Hydrogen fluoride is one of the most stable compounds; it can be subjected to high temperatures and pressures and to the action of other catalytic agents without being broken down. Many of its organic compounds decompose either by heat alone or in the presence of catalysts to regenerate hydrogen fluoride,
Hydrogen fluoride catalyzes the interaction of olefins and ieoparafitins to form saturated products consisting of highly branched paraffinic hydrocarbons. The alkylation was carried out in the laboratory, both by continuous and batch operation, in apparatus of simple design. The effects of temperature, contact time, ratio of isoparaffin to olefin, and catalyst concentrationin water are described.
Runs involving the paraffins isobutane and isopentane, and the olefins, propene, isobutylene, 1-butene, and 2butene, are reported, as well as the production of alkylate from a butane-butene mixture. Normally the fluorine content of the alkylate is low and can be reduced further by treatment with certain materials such as calcium fluoride and aluminum fluorides at elevated temperatures.
1 Pnvlent
addrw. Houdry P r o w Corporation of Pennsylvania, Marc-
October, 1945
INDUSTRIAL AND ENGINEERING CHEMISTRY
an important factor from a commercial standpoint since it makes possible low catalyst consumption. Substantially all of the combined fluorine in the alkylation reaction products is recoverable as hydrogen fluoride. I n this respect it is unlike many other catalysts which are less chemically stable and undergo reaction with one or more of the materials in the system being catalyzed. Hydrogen fluoride is stable toward both oxidizing and reducing conditions; this' makes for low catalyst consumption and prevents loss of reactants occasioned by oxidation reactions. Hydrogen fluoride may, under alkylation conditions, form alkyl fluorides with olefins (9). As long as sufficient hydrogen fluoride is present, the alkyl fluoride formed reacts with isoparaffin to form alkylate (18). Under optimum conditions of operation, the organically bound fluorine in the paraffinic reaction product is usually less than 0.01%. Even such small amounts of fluorine may be objectionable, both because of increased catalyst consumption and contamination of the finished product with fluorine. The bound fluorine may be readily decomposed by passing the alkylate over a catalyst such as calcium fluoride or aluminum fluoride at an elevated temperature, usually about 100" C. The hydrogen fluoride resulting from this decomposition can be subsequently separated and recovered. If the amount of fluorine present is so low that its recovery is not essential to the economical operation of the process, it can be removed by treatment with lime, bauxite, or alkaline materials such as sodium hydroxide, usually at a slightly elevated temperature or with a sulfuric acid wash. Even under optimum conditions for the alkylation of isoparaffins with olefins, undesirable side reactions occur to a minor extent and result ip the formation of certain high-boiling materials not utilizable as motor fuel, which are soluble in hydrogen fluoride. Because of its low boiling point the hydrogen fluoride can be recovered by simple distillation with little or no loss other than that occasioned by handling. The sludge, as formed, contains fluorine in combination with hydrocarbons, but these compounda can easily be broken down by heating to drive off and recover hydrogen fluoride. This is the basis for the catalyst regeneration in the hydrogen fluoride alkylation process (7). An important advantage for hydrogen fluoride is that, by virtue of its chemical stability and low freezing point, it may be employed over a wide range of operating conditions. Conditions can &e employed which are most satisfactory thermodynamically or economically, without limitations due to catalyst properties. For example, in the alkylation reaction, atmospheric or slightly superatmospheric temperatures may be used with hydrogen fluoride; hence it is unnecessary to utilize refrigeration a8 is the case when certain other isoparaffins are the alkylation catalysts. The vapor pressure of hydrogen fluoride makes i t unnecessary to resort to extreme pressures to maintain the catalyst in liquid phase. Its freezing point permits its use a t temperatures much lower than is possible with most catalysts, which either freeze or become highly viscous a t low temperatures. Although, in the alkylation of isobutane with olefins to produce aviation blending fuel, the usual operating conditions are of the order of 30' C., there are catalytic reactions which are favored by low
925
temperatures. Since hydrogen fluoride catalyzes such reactions, it has a distinct advantage because of its physical properties. Conversely, since hydrogen fluoride is thermally stable, it can be employed a t much higher temperatures than those of alkylations with other catalysts. This is a unique property of hydrogen fluoride. Anhydrous hydrogen fluoride does not corrode ordinary iron equipment under most conditions. It is undesirable to have large percentages of water present, both because of the corrosion rate and the alkylation reaction; hence in the hydrogen fluoride alkylation process, steps are taken to maintain it practically anhydrous. Hydrogen fluoride cannot be separated by simple distillation because it forms a constant-boiling mixture with water. In the isoparaffin alkylation process the alkylate is substantially insoluble in hydrogen fluoride. The hydrogen fluoride has a relatively low solubility in the hydrocarbon product, of the order of 1% or less. This is an important property of an alkylation catalyst, since it simplifies the separation and recovery of the catalyst and the product. Hydrogen fluoride may be readily dissolved from the reaction products by distillation which is similar to the separation of dissolved water from hydrocarbons, described by Hachmuth (la) and commercially practiced for many years. Figure 1 is a flow sheet of a commercial plant in which the hydrogen fluoride and part of the hydrocarbon are taken overhead from the hydrogen fluoride stripper column and HF-free hydrocarbon is
taken as bottoms. The overhead vapor from the column coutains a concentration of hydrogen fluoride in excess of the amount which can be held dissolved in the hydrocarbon and hence separates into a two-phase system on condensation. The hydrocarbon phase is returned to the fractionation system, and the hydrogen fluoride is recovered for re-use. The workability of this system can be established by calculations based on the vapor pressures of pure hydrogen fluoride and the pure hydrocarbon, and on the solubility of the hydrogen fluoride in the hydrocarbon (7). EXPERIMENTAL PROCEDURE
SOURCEOF REAGENTS. Hydrogen fluoride (Harshaw Chemical
Company) was water-white and contained less than 1% water, and the residue left u n eva oration was less than 0.04%. Isobutane, obtainefirom fihillips Petroleum Company, waa more than 99 0 pure. Propylene, rom the Matheson Company, Inc., was 99% pure.
s
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INDUSTRIAL AND ENGINEERING CHEMISTRY
pruduvt. Moreover,. it could be used to determine that the catalyd had a long life although the values obtained were necessarily not the best since there was no ?ion for recovering and recycling the hydrogen fluoride disso ved in the effiuent from the set,tler. DETERMINATION OF ORGANIC FLUORINE. The procedure used to analyze for fluorine in the liquid alkylate was a modification of that employed to determine sulfur in gasoline ( 8 ) . The techniques used in the combustion of the sample and the absorption of the combustion products were identical with the sulfur method; the same solution, 0.06 N sodium carbonate was used in the scrubber. The fluoride present was determined by titration with standard thorium nitJrate in tho presence of alizarin sulfonate as indicator ($3). The data are largely taken from early experiments on the investigation of hydrogen fluoride as a catalyst. Recent data, which cannot be reported because of censorship restrictions, have extended the knowledge of the reaction and of the operating variables.
U
Figure 2.
TABLEI. IWBUTANE-ISOBUTYLENE ALKYLATION
Setup for Continuous Alkylations
Isobutylene and n-butenes were prepared by dehydration of tert-butanol and sec-butanol, respectively, over alumina (13). These olefins were fractionated and finally analyzed as 98% pure isobutylene and n-butene. Isopentane, C.P. material from Phillips Petroleum Company, was 99% pure. 1-Butene and 2-butene were the technical grade (Phillips Petroleum Company), analyzing 95'% pure. BB fraction was a commercial cut obtained from the Sun Oil Company. The alkylation may be carried APPARATUS AND PROCEDURE. out in any suitable reaction vessel which permits efficient contacting of the catalyst phase and the hydrocarbon phase. The reactor used for batch operations was a 1200-cc. Allegheny metal autoclave having a close-fitting nickel liner and a pressure-sealed mechanical stirrer turning a t 600 r.p.m. It carried a thermocouple well, pressure gage, and line runnin to the bottom for introducing or removing liquids, and c o u d be immersed in a cooling bath. T o start the operation the bomb was evacuated and cooled in ice water, and then charged with a weighed amount of li uid anhydrous hydrogen fluoride from a duralumin bomb. Wjen aqueous hydragen fluoride was used, it was weighed in the liner. After the reactor and catalyst were brought to the desired temperature, the stirrer was started and a mixture of olefin and isoparaffin was added over a period of 2-3 hours from a pressure charger equipped with a graduated gage glass. After the desired time the autoclave contents were slowly purged through a copper line into a 1500-cc. cop er flask containing 100 grams of water and immersed in a bat\ of solid carbon dioxide and acetone. (At room temperature anhydrous hydrogen fluoride reacts violently with water, but at low temperatures the reaction is moderate.) The material in the copper receiver, consisting of dilute hydrogen fluoride, alkylate, and unreacted isoparaffin, was allowed to come t o room temperature. The alkylate wv&srapidly separated from the hydrofluoric acid in a glass separatory funnel, washed several times with ice water, and dried with otassium carbonate. The liquid product was distilled throu a hightemperature Podbielniak column, and the condensabfe gas fraction was analyzed in a low-temperature Podbielniak apparatus. Figure 2 shows an apparatus for continuous experiments. The reactor had a capacity of 25 cc. and was agitated by a mixer turning at 1700 r.p.m. Hydrogen fluoride was added t o the reactor before the run began. After the run started, a mixture of olefin and isoparaffin was continuously pumped into the reactor. The reaction mixture passed from the reactor into a settling chamber from which the catalyst layer was recycled. The hydrocarbon layer was forced into a receiver, and the pressure released to atmospheric; the alkylate was then debutanized and waterwashed. A small amount of hydrogen fluoride was continuously lost from the Bystem due to its so!ubiljty in h drocarbons; this could be readily determined by titration. Tlis apparatus was well adapted to the preparation of considerable amounts of
1
Temperature ' C. Ratio, hydro6arbon/HF, by voi. Charge, grams Iso-C4Hs 1.0-CIHIO Butane-free roduct grams Properties o?produ& Bromine number Fluorine, % Engler distilla$ion 50% point, C. % over at 205O C. (end point) Octane No.. A.S.T.M. motor method
- 24
0.8
0.2
32
60 0.8
177 420 351
344 56 1 670
168 397 298
0 0.4
