US3280211A - Hydrofluoric acid alkylation with intermittent olefin feed - Google Patents

Description

United States Patent Ofiice 3,2802 ll Patented Oct. 18, 1966 3,280,211 HYDROFLUORIC ACID ALKYLATION WITH INTERMITTENT OLEFIN FEED David A. McCaulay, Hcmewood, Ill., assignor to Standan! Oil Company, Chicago, Ill., a corporation of Indiana No Drawing. Filed Aug. 20, 1965, Ser. No. 481,394 8 Claims. (Cl. 260-68148) This application is a continuation-in-part of my cpending application, Serial No. 330,269, filed December 13, 1963, now abandoned and entitled Process.

This invention relates to an improvement in the process of alkylating isoparaflins with olefins, using hydrofluoric acid as the alkylation catalyst.

The HP alkylation process was commercialized during World War II, and has been extensively used in many refineries during the past 20 years. Many publications have described the process, such as Hydrofluoric Acid Alkylation, published in 1946 by the Phillips Petroleum Company; Advances in Catalysis, volume 1, pages 27-64, especially pages 59-63 (Academic Press, Inc., 1948); Advances in Petroleum Chemistry and Refining, volume III, chapter 6 (Interscience Publishers, Inc., 1960); and, particularly, Catalytic Alkylation, by Cupit et al. in Petroleum Management, volume 33 (December 1961), pages 203-215 and volume 34 (January 1962), pages 207-217. The disclosure in the foregoing references, and in other references cited later in this application, are incorporated herein.

The HF alkylation process is suitable for alkylating isobutane and isopentane with olefins having from 3 to 5 carbon atoms per molecule. As most frequently practiced, the process is used to alkylate isobutane with mixed butylenes to make an alkylate having predominantly dimethyl hexanes and trimethyl pentanes. When the process was first developed, the alkylate so produced was of great value as a motor fuel component because of its relatively low boiling range, its relatively high, in the range of 93-96, unleaded research octane, and its octane response to tetra-ethyl lead. As refining procedures and techniques have advanced, the 93-96 clear octane of alkylate no longer has its former superiority relative to other motor fuel components in respect of clear octane rating. However, the relatively low boiling range of alkylate and its favorable tetra-ethyl lead response still make it a desirable component of motor fuel. The problem now is to develop improvements in the process whereby an alkylate of increased clear octane rating may be obtained.

I have now discovered an improvement in the HF akylation process whereby the octane number of the alkylate may be increased to about 99-100 or slightly higher. In my improvement, the fresh olefin to be charged to the HF alkylation reaction zone is first treated to separate branched-chain olefins from straight-chain (or normal) olefins, and the latter only injected into the reaction zone at a localized point at or near that point at which the isoparafiin and the HF are introduced into the reaction zone. The injection of the straight-chain olefins is done in a pulsating or intermittent manner rather than in a continuous constant-rate manner. The fraction of the time during which the olefin is injected into the reaction zone may vary from less than down to about 1%, advantageously about 5 to 10%. The injection of the straightchain olefins preferably is done at relatively uniform intervals. The reaction zone is maintained at a low temperature, not above about 0 C., and preferably below l0 C.

The isoparafi'in feedstock of the process comprises isobutane or isopentane (Z-methylbutane) or mixtures thereof. Other C and C parafiins, such as normal butane, normal pentane and neopentane may, and normally do,

accompany the isoparaffin, but are not alkylated, and are discharged from the alkylation plant system in the distillation train downstream from the reaction zone. The nonreactive parafiins may be separated from the isobutane or isopentane prior to the charging of the latter to the reaction zone, but this is not necessary, since their presence in the reaction zone is not a significant disadvantage in operating the system.

The olefin feedstock of the process comprises propylene, the two normal 'butene isomers and the two normal pentene isomers. Inasmuch as the olefin charged to the reaction zone is characterized by a substantial absence of isoolefins, it is necessary to separate the latter from the normal olefins. Although this may be done by distillation, the boiling points of the C -C olefin isomers are such that a distillation separation is difficult and costly. A preferred method of removing isoolefins is by sulfuric acid extraction as described by Valet et al. in their article titled New Low Cost Isobutylene Process, appearing in Petroleum Refiner, volume 41, No. 5 (May 1962) pages 119-123. The charge to such process may be a stream consisting essentially of olefins, or, more usually, a stream containing olefins and paraflins. The process is operable on a C stream, a C stream or a combined C -C stream. The use of such process permits the recovery therefrom of a raffinate having less than about 2% iso-olefins and containing normal olefins and any parafiins in the charge. The rafiinate from the extraction may be dried to remove Water or treated to remove traces of sulfuric acid, but these steps are not essential.

Because the octane of the alkylate produced by alkylating isobutane with butylenes is superior to that derived from alkylating other combinations of the foregoing feedstocks, most commercial HF alkylation plants are designed to operate using as the feed a C fraction, With only minor amounts of C and C hydrocarbons, either paraffinic or olefinic, therein, and further description of this improvement will be in terms of using a C hydrocarbon feed. It is to be understood, however, that the process is operable when the reactive isoparaffin portion of the feed comprises, in part or entirely, isopentane, and the olefinic portion of the feed likewise comprises, in part or entirely, propylene or normal pentenes.

After the isobutylene has been removed as aforesaid the stream containing the normal butenes (and, generally, normal butane and isobutane also) is injected into the alkylation zone. The injection is done in an intermittent or pulsating manner at a fairly high frequency, in the range of about 30 to 60 injections per hour. The duration of each injection is relatively short, desirably in the range of from about 1 to 10 seconds per injection, with the longer periods being used with the lower frequencies. The objective is to increase, contrary to practice heretofore, the localized concentration of the olefin in the acid to promote the formation of the fluoride of the olefin, e.g., a butyl fluoride.

For convenience and to facilitate understanding, I shall consider the addition of olefin to my process in terms of liquid hourly space velocity. The liquid hourly space velocity of a hydrocarbon stream may be defined as' the volume of hydrocarbon per hour per volume of catalyst used and may be calculated by dividing the hydrocarbon feed rate, expressed as volume per hour, by the volume of catalyst employed. Hereinafter, where an instantaneous olefin feed rate is used to calculate the liquid hourly space velocity, the resulting value of the liquid hourly space velocity is referred to as the instantaneous space velocity. On the other hand, where the overall ole:

fin feed rate, i.e., the average feed rate over the entire run,

is used to calculate the liquid hourly space velocity, the resulting value is referred to as the overall space Velocity. in the case of the continuous addition of olefin feed to the alkylation process, the values of the instantaneous space velocity and the overall space velocity are quite similar; whereas in the case of the intermittent or pulsating addition of olefin feed to the process, the values of the instantaneous space velocity and overall space velocity are quite different. It should be noted, however, that if the same amount of olefin feed is charged by each method of addition and the same amount of catalyst is used, the resulting values of overall space velocity will be the same.

The instantaneous space velocity of the olefin being injected should be high, relative to prior practice, above about 30 volumes of olefin per hour per volume of HF in the reaction zone, and preferably above about 50 volumes of olefin per hour per volume of HF. Values much larger than the latter figure may be used, for example, 600 volumes of olefin per hour per volume of HF. The olefin'contain-ing stream is injected either into the recycled isobutane stream or directly into the reaction zone through a single inlet, or a plurality of relatively closely spaced inlets. This olefin injection pattern is to be distinguished from the multiple olefin injection points previously used in alkylating isoparafiins.

Other process variables, except for temperature, are substantially those heretofore practiced commercially. The external ratio of isoparafiin to olefin is generally in the range from about 3:1 to 12:1, frequently about :1. The overall space velocity of the olefin feed is generally in the range of about 0.1 to about 0.4, preferably about 0.15 to 0.30. Residence time in the reaction zone of the HF and hydrocarbons may be in the range of to 60 minutes, preferably at least minutes. HF purity is desirably maintained above 80%, e.g., about 90%.

The equipment used to contain the reaction zone may be any of those various reactors, referred to in the referenees cited above, developed heretofore for HF alkylation. The reaction zone may be mechanically stirred, but this is not necessary inasmuch as the high velocity of the olefin stream, as it is injected into the reaction zone, will provide sufiicient turbulence for satisfactory operations in which 250 grams (450 cc.) of isobu-tane and 250 grams (250 cc.) of HF were mixed in an autoclave and cooled. Thereafter, the olefin was added at either a continuous rate of about 0.24 volume of olefin per hour per volume of HF for one hour with continuous rigorous stirring, or at the rapid rate of about 216 volumes of olefin per hour per volume of HF, followed by stirring for one hour, after which the product alkylate was recovered and analyzed. The hydrocarbons and the HF were all obtained commercially, the HF being anhydrous and 99.9% pure, and the hydrocarbons either C.P. grade or designated as the suppliers Pure grade. The temperatures recorded were those maintained in the course of each run when the olefin was added at a slow rate, or the temperature maintained during the stirring period followed rapid olefin addition. In the rapid olefin addition runs, the HF-isobutane mixture in the autoclave was first precooled to a temperature about 1'01S C. below the temperature maintained during the subsequent stirring following the olefin addition.

The following table summarizes the results obtained, using the CFRR clear octane number of the C -C alkylate fraction as the criterion of effectiveness. The table reports the corn-position of the olefin feed, the olefin feed rate in terms of overall space velocity and instantaneous space velocity, and the temperature maintained during the alkylation period. Each of Runs 1, 4 and 7 is a run made at conventional alkylation conditions. Runs 1, 2 and 3 used an olefin feed containing isobutylene as well as butene-l and butene-Z. Runs 4, 5 and 6 used butene-Z as the olefin feed, while Runs 7, 8 and 9 used butene-l as the olefin feed. Runs 2, 5 and 8 show the effect of adding the olefin on an intermittent basis at a rapid instantaneous space velocity. At the low tem perature employed, -15 C., and in the absence of isobutylene, the octane number of the alkylate obtained from butene-l olefin feed was significantly increased. This was shown by the result of Run 8. As indicated by Run 9, the reduced temperature in the absence of the intermittent addition of olefin feed did not provide the octane-number increase of the alkyl-ate.

TABLE Run No 1 3 2 4 I 6 5 7 9 8 lefin:

Isobutylene 34 53 O 0 0 0 0 0 Butene1 23 14 0 0 0 100 100 100 Butane-2- 43 33 100 100 100 0 0 0 Overall Space Velocity, Vol. 0lefin/hr./Vol. HF 0. 24 0. 28 0. 24 0. 24 0. 28 0. 24 '0. 24 0. 28 Instantaneous Sgace Velocity, Vol. olefin/hr.Nol. HF-.- 0. 24 216 0. 24 0.24 216 O. 24 O. 24 216 Temperature, 15 23 -18 15 20 15 Alkylate Octane N0., CFR-R clear 95. 4 95. 9 95. 0 96. 0 101. 9 100. 1 92. 1 87. 1 97 ject any normal butane from the system, and recovery product alkylate.

If desired, the isobutylene removed from the olefin feedstock may be injected into the reaction zone at one or more points distantly removed from the point of injection of the normal butenes.

A number of laboratory runs have been conducted to demonstrate the process.

These were batch alkyla In a specific continuous embodiment of the process, a refinery butane-butylene stream is extracted at C. with sulfuric acid to remove therefrom isobutylene. Three thousand barrels per day of the resulting rafiinate, comprising 35 isobutane, 13% normal butane, 27% butene-1, 21% butene-2, 1% isobutylene, and less than 3% of C s and C s, including traces of butadiene, is chilled to --10 C. and then injected into the first stage of an alkylation reaction zone having an elfective volume of 500 barrels and contained in a reactor of the cascade type. The rafiinate is injected in substantially equal increments at a frequency of times per hour, each increment being of 6 seconds duration. Eight thousand b./d. of recycle isobutane oommingled with 7 200 b./ d. of recycle and fresh HF are chilled to 10 C. and continuously pumped into the reaction zone at a point adjacent to and above the incoming olefin stream.

In the settling zone, which is integral with the reactor and follows the reaction zone, the HF is allowed to separate from the lighter hydrocarbon phase, and then withdrawn and recycled. The hydrocarbon phase is withdrawn from the settling zone, stripped of any residual HF, and then distilled to recover as a distillate fraction the recycle isobutane stream and, as bottoms, 2500 b./d. of C C alkylate having an octane of 99.5 CFR-R clear and being commingled with the normal butane from the incoming feed.

Having thus described the invention, I claim:

1. In a process for the alkylation of isoparafiins having from 4 to 5 carbon atoms per molecule with a feed stock comprising terminal olefins having from 4 to 5 carbon atoms per molecule and being substantially free of branched-chain olefins in a reaction zone using lhydrofluoric acid as an alkylation catalyst and being maintained at a temperature below about C., the improvement which comprises introducing said olefins into said reaction Zone intermittently at at least one point and at an instantaneous space velocity which has a value of at least about 30 volumes of olefin per hour per volume of hydrofluoric acid.

2. The process of claim 1 wherein said isoparaflins comprise isobutane.

3. The process of claim 1 wherein said feed stock comprising terminal olefins contains, on an olefin basis, less than about 2 weight percent of branched-chain olefins and said terminal olefins comprise normal butenes.

4. The process of claim 1 wherein said isoparaflEins comprise isobutane, said feed stock comprising terminal olefins contains, on an olefin basis, less than about 2 weight percent of branched-chain olefins, and said terminal olefins comprise normal butenes.

5. In a process for the alkylation of isoparaflins having from 4 to 5 carbon atoms per molecule with a feed stock comprising terminal olefins having from 4 to 5 carbon atoms per molecule and being substantially free of branched-chain olefins in a reaction zone using hydrofiuoric acid as an alkylation catalyst and being maintained at a temperature below about 0 C., the improvement which comprises introducing said olefins into said reaction zone intermittently at at least one point and at an instantaneous space velocity which has a value of at least about 30 volumes of olefin per hour per volume oij hydrofluoric acid and at an overall space velocity which is in the range of about 0.1 to about 0.4 volume of olefin per hour per volume of hydrofluoric acid.

6. The process of claim 5 wherein the overall space velocity is within the range of about 0.15 to 0.3.

7. In the alkylation of isoparafiins having from 4 to 5 carbon atoms per molecule with an olefin feed stock comprising butene-l in a reaction zone using hydrofluoric acid as an alkylation catalyst at a temperature below about 0 C. during the alkylation reaction, said olefin feed stock being substantially free of branched-chain olefins, the improvement which comprises introducing the olefins into said reaction zone intermittently at at least one point and at an instantaneous space velocity which is at least about 30 volumes of olefin per hour per volume of hydrofluoric acid.

8. In a continuous process for alkylating isobutane with an olefin feed stock comprising butene-l in a reaction zone using hydrofluoric acid as the alkylation catalyst at a temperature in the reaction zone below about 0 C., said olefin feed stock being substantially free of branchedchain olefins, the improvement which comprises injecting said olefin feed stock into a hydrofluoric acid-containing reaction zone intermittently at at least one point and at an instantaneous space velocity which is at a value of at least about 30 volumes of olefin per hour per volume of hydrofluoric acid.

References Cited by the Examiner UNITED STATES PATENTS 2,434,000 1/1948 Matuszak 260683.48 2,594,343 4/1952 Pines 260--683.49 2,603,591 7/ 1952 Evans 260-6852 2,916,444 12/1959 Vernon 260-680 OTHER REFERENCES Kobe and McKetta: Advances in Petroleum Chemistry, and Refining, vol. I, pages 369-371, Interscience Pub lishers, Inc., N.Y., 1948.

DELBERT E. GANTZ, Primary Examiner. R. S HUBERT, Assistant Examiner,

Claims (1)

1. IN A PROCESS FOR THE ALKYLATION OF ISOPARAFFINS HAVING FROM 4 TO 5 CARBON ATOMS PER MOLECULE WITH A FEED STOCK COMPRISING TERMINAL OLEFINS HAVING FROM 4 TO 5 CARBON ATOMS PER MOLECULE AND BEING SUBSTANTIALLY FREE OF BRANCHED-CHAIN OLEFINS IN A REACTION ZONE USING HYDROFLUORIC ACID AS AN ALKYLATION CATALYST AND BEING MAINTAINED AT A TEMPERATURE BELOW ABOUT 0*C., THE IMPROVEMENT WHICH COMPRISES INTRODUCING SAID OLEFIN INTO SAID REACTION ZONE INTERMITTENTLY AT AT LEAST ONE POINT AND AT AN INSTANTANEOUS SPACE VELOCITY WHICH HAS A VALUE OF AT LEAST ABOUT 30 VOLUMES OF OLEFIN PER HOUR PER VOLUME OF HYDROFLUORIC ACID.