US 3803259 A
Description (OCR text may contain errors)
US. Cl. 260-683 R 7 Claims ABSTRACT OF THE DISCLOSURE In a procses for cracking a petroleum derived naphtha having a boiling range of 90 to 400 F. and a specific gravity of 0.65 to 0.78 to alkenes and alkanes; the instant invention relates to an improvement comprising admixing about 1.0 to 35 parts by weight of H 8 (or an amount of a compound which yields an SH radical in the cracking environment sufficient to yield that amount of H 5) per 100 parts by weight of alkane and H 8 (or a precursor thereof) in the mixture consisting essentially of H 8 (or the precursor thereto) and the naphtha to be cracked, and then passing the resulting mixture through a reactor maintained at a temperature of about 1100 F. to about 2000 F. with a residence time of about 0.25 to about 2.0 seconds and a pressure of about 0 to about 65 p.s.i.g. Steam is also employed.
BACKGROUND OF THE INVENTION This invention relates to an improvement in the cracking of naphtha.
Tremendous quantities of lower alkenes are used and needed by modern chemical process industries. Thus, huge quantities of propylene are polymerized to polypropylene and are employed to produce acrylonitrile, cumene, isopropanol, plasticizer alcohols, propylene oxide, oxo alcohols, and other chemicals. Lower alkenes are much used to alkylate aromatic compounds and to alkylate paraflins to form high octane components of motor fuel.
A considerable need exists for improved methods of producing such alkenes which are used and needed in huge and ever increasing quantities. In particular, it is anticipated that the need for propylene will greatly increase in the near future.
One means for obtaining such lower alkenes is by cracking naphtha derived from petroleum. Any improvement in such a cracking process whereby the yield of alkenes is improved or whereby the relative selectivity of propylene to ethylene is improved is of considerable benefit to the industry and constitutes a significant advance in the art.
OBJECTS OF THE INVENTION One object of the invention is to provide an improvement in the process for cracking naphtha to produce alkenes whereby the selectivity to the alkene product or the alkene product having the greater number of carbon atoms is increased.
Another object of this invention is to provide an improvement in the process for cracking naphtha whereby the conversion to alkenes is improved.
These and other objects and advantages will appear from the following description of the embodiments of the invention, and the most novel features will be particularly pointed out hereinafter in connection with the appended claims.
SUMMARY OF THE INVENTION In one aspect, this invention discloses an improvement in a process for cracking naphtha having a boiling range of 90 to 400 F. and a specific gravity of 0.65 to 0.78 to alkenes and alkenes; wherein the improvement comprises United States Patent 0 admixing about 1.0 to 35 parts by weight of H S (or an amount of a compound which yields SH radicals in the cracking environment sufiicient to yield that amount of H S) per 100 parts by weight of H 8 (or the precursor thereto) with the naphtha to be cracked to form a mixture comprising H 8 (or a precursor thereof) and the naphtha, and then passing the mixture through a reactor maintained at a temperature of 1100 F. to about 2000 F. with a residence time of about 0.25 to about 2.0 seconds, and a pressure of about 0 to about 65 p.s.i.g.
DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention is based upon the discovery that introduction of H 8 into the reaction environment of certain naphtha cracking reactions in the quantities and under the conditions specified increases conversion and increases the selectivity to, and thereby the production of, alkene reaction products having a greater number of carbon atoms in preference to alkene reaction products having a lesser number of carbon atoms. Thus, addition of H 8 to a reaction environment wherein naphtha is cracked increases conversion and the proportion of propylene to ethylene produced. Particularly desirable results are obtained when steam and H S are concurrently employed.
The naphtha which is cracked according to the process of this invention can include any naphtha product having the following properties:
Boiling range -400 F. (D-86). Specific gravity 0.65-0.78.
It is presently preferred to employ a highly paraflinic naphtha derived from petroleum.
The mixture comprising naphtha and H 8 (or a precursor thereof) is passed to the cracking environment at a pressure of about 0 to about 65 p.s.i.g. for a residence time of about 0.25 to 2.0 seconds. If the residence time is too long, particularly at relatively low pressure, undesirable side reactions occur which militate against the beneficial effect of adding H S (or a precursor thereto) to the naphtha to be cracked.
Preferably, the cracking conversion is conducted continuously. When the cracking conversion is conducted continuously, a gas hourly space velocity of about 400 to about 22,000 cc. of gaseous feed volume per cc. of reactor volume per hour at STP (standard temperature pressure) is most preferably employed. At significantly higher space velocities insufficient reaction occurs to be commercially desirable, and at significantly lower space velocities an undue amount of deleterious side reactions occur.
The reaction environment is often preferably maintained at a temperature of about 1300 to about 1800" F. Below 1100 F., insufficient conversion occurs, and above 2000 F, undesirable side reactions occur. The range between 1300 and 1800 F. is the most commercially feasible region wherein side reactions are minimal but adequate conversion is yet obtained. Still more preferably, the improved cracking conversion is optimumly conducted at a temperature of about 1400 to 1700 F. when the preferred naphthas are employed as feedstock.
It is often advantageous to employ the shorter residence times of the invention when the higher reaction temperatures are employed in order to avoid side reactions which militate against the beneficial effects of employing H 3 (orda precursor thereof) in admixture with the naphtha fee According to the improvement in the cracking of naphtha of this invention, often, about 1.0 to 35 parts by weight of H 8 per parts by weight of the naphtha plus 'I-I S of the feed passed to the cracking reactor are employed. Levels of H 8 below about 1.0 parts by weight are not effective, and levels above about 35 parts by weight are not economical. Often, the feed mixture consists essentially of naphtha and H 5, or in lieu of all or part of the H 8, an equivalent amount of a compound which yields H 8 in the cracking environment. Steam should also be employed to mitigate coking.
More preferably, about 2.0 to 20 parts by weight of H 5 (or an amount of a compound which yields H 5 in the cracking environment sufficient to yield that amount of H 8) per 100 parts by weight of H S (or a precursor thereof) plus the naphtha to be cracked are employed. Such levels are most commercially feasible. Examples of materials which yields H 8 in the cracking environment include: mercaptans, mercaptides, thioethers, carbon disulfide, ammonium sulfide, polysulfides such as disulfide oils, sulfur, and the like. Essentially any substance which will yield H 8 under the reaction conditions specified otherwise can be employed in lieu of any proportion of the H 8 specified. Which compounds will yield H 8 under the cracking environment specified are well known to the art or can readily be determined by simple experiment not amounting to invention. Mixtures of H 8 and an in situ H 8 precursor can be employed if desired.
Gaseous diluents which are substantially entirely inert to the reaction environment can be employed if desired. Some examples of such diluents include: nitrogen, helium, neon, steam, methane, ethylene, and the like. A purpose of the diluent is to lower the partial pressure of the hydrocarbon and to minimize coking. Generally less than 1 part of diluent per part of feed is suitable.
Steam should be employed to mitigate coking. About 0.5 to 0.75 pound of steam per pound of naphtha charged is most suitable.
The H 8 (or precursor thereof) can be admixed with the naphtha and with the other components of the feedstock, if any, by any means heretofore known to the art for admixing fluids. Often, a conventional proportionator is advantageously employed.
Often the improved cracking process of the instant application is advantageously conducted in a reaction chamber which is packed with a suitable particulate packing material which can be, but is not limited to, a heterogeneous catalytic material. Examples of suitable particulate packing materials include: alumina, kaolin, magnesium oxide, silicates, and the like. Suitable packing material for a packed bed often has the greatest dimension of particles in the range of inch to inch. Also, presently preferred is a packing material comprising particulate alumina having a particle size of about 70 to 400 U .S. sieve employed as a fluidized bed.
The H 8 (or precursor thereof) of the instant invention is believed to function as a reaction directing agent or catalyst. Thus, the eifect noted differs from mere metal or catalyst passivation. The system of the instant invention is a homogeneous system wherein reaction is efiected upon contact of the gaseous H 8 molecules plus generated radicals and the gaseous naphtha molecules plus generated radicals.
The following examples are presented so that the invention can be more clearly understood. These examples should not be interpreted as limiting the invention.
4 EXAMPLE 1 A cracking feedstock was prepared by admixing 50 weight percent Kuwait light distillate and Kuwait natural gasoline. Chemical analysis of the mixture indicated that the molecular weight ranged from C to C hydrocarbons. Results of ASTM distillation and gas chromatog raphy of the mixture are given in the following Table I. As indicated in the table, the feedstock has a boiling point range which is representative of naphthas.
TABLE I AS'IM method Test Results D4298- Specific gravity at 60 F./60 F 0. 6849 D4298. API gravity at 60 F 75. 1. D-86. Distillation:
0. initial boiling point 42 C. at which 2 volume percent recovered. 46 C. at which 5 volume percent recovered--- 50 C. at which 10 volume percent recovered.. 54 C. at which 20 volume percent recovered. 57 C. at which 30 volume percent recovered. 62 C. at which 40 volume percent recovered. 68 C. at which 50 volume percent recovered- 77 C. at, which 60 volume percent; recovered- 9 C. at which volume percent recovered. 10 C. at which 80 volume percent recovered. 12 0. at which volume percent recovered. 135 C. at which volume percent recovered. 14 C. final boiling point 15 Percent volume recovery at 70 0..... 4 Percent volume recovery at 0.... 6 Percent volume recovery at 140 C 91. 5 Percent volume residue. 1. 0 Percent volume ioss.--... 1. 0
D4266- Total sulfur, wt. percent 0. 028 D-323. Reid vapor pressure, lb./sq. in- 8. 5 Color LP. (Lovinbond 18 cell) 0.25
D-156--- Color (Seybolt) Butanes, percent volume- Lead content, parts/billio 13-1319. Hydrocarbon types (FIA) Aromatics/olefins/saturates 4.1/0/95.Q
Chromatographic analysis, approximate Wt. percent Compounds:
H35. 2. 7 I- 3. 9 GIS. 18. 7 C 8 15. 5 Gas 47. 6 C S. 9.2 "Ram one 1. 89 Toluene. 0. 80 Xylenes- Trace A tube reactor fabricated of stainless steel having an internal diameter of 0.305 inch and a reaction length of 2 feet was continuously charged with the above feedstock, with steam, and with a hydrogen sulfide precursor in the form of a 22 percent by weight aqueous solution of ammonium sulfide (except in the control runs) under conditions and with results as indicated in the following Table II. Pressure ranged from 15 to 18 p.s.i.g. Contact time ranged from 0.23 to 0.30 second. Approximately 0.75 pound of steam was employed for each pound of naphtha charged.
TABLE II Run number Na hth feed to, 259 282 270 273. 1 268. 6 276. 0 262. 7 267. 1
ste m fe ed rat: 174. 4 214 169. 6 165. 1 166. 7 214 169. 1 212. 0
(NH4)2S solution feed rate, g [hr 43. 6 0 42. 4 43. 9 44. 3 0 44. 9 0
Furnace temperature, C 845 848 860 890 930 940 9.65 970 Total feed rate, l./h1'-- 616. 8 594. 9 605. 7 615. 9 640. 1 623. 1 678. 9 661. 5
Wt 1. .9.? 5. 3 5. 5 6. 9 8. 5 10. 3 13. 2 l4. 9 12. 8 Cl! 7. 8 10. 0 8. 6 l0. 7 13. 6 21. 1 18. 1 22. 4 (QT-h 4. 7 2. 8 5. 9 6. 2 6. 0 3. 9 5. 9 3. 3 (HR- 9. 4 9. 2 11. 1 12. 5 13. 7 11. 1 11. 3 8. 8 (1H- 1. 4 0. 4 g g 2 i i H 0. 2 Trace 391% 10. s 8.4 12. 5 1a. 4 13. 5 8.0 7.1 e. 7 Oil 54. 7 59. 9 46. 1 40. 1 33. 1 35. 1 36. 3 38. 5
Norn.Reaction gas temperature is approximately 80 0. lower than furnace temperature.
These data clearly demonstrate that use of a hydrogen sulfide precursor such as ammonium sulfide improves the yield of propylene as compared to control runs wherein a hydrogen sulfide precursor is not employed.
EXAMPLE 2 The runs of Example 1 are repeated except that an equivalent amount of hydrogen sulfide is employed in lieu of the hydrogen sulfide precursor, ammonium sulfide. Similar results are obtained.
EXAMPLE 3 The runs of Example 1 are repeated except that no steam is employed, a pressure of 65 p.s.i.g. is employed, a residence time of 0.25 second is employed, a temperature of 2000 F. is employed, and 35 parts by weight of H 8 per 100 parts by weight of naphtha are employed. Similar results are obtained to those of Example 1.
1. In a process for cracking naphtha having a boiling range of 90 F. to 400 F. and a specific gravity of 0.65 to 0.78 to alkenes and alkanes, the improvement comprising admixing about 2.0 to about 20 parts by weight of H 8, or an amount of a compound which yields an SH radical in the cracking environment sufficient to yield that amount of H 8, per 100 parts by weight of naphtha and H 8, or the precursor thereof, in the mixture comprising H S, or the precursor thereof, and the naphtha to be cracked and then passing the resulting mixture through a reactor maintained at a temperature of about 1300 to 1800" F. with a residence time of 0.25 to 2.0 seconds and a pressure of 0 to 65 p.s.i.g., and wherein 0.5 to 0.75 pound of steam per pound of naphtha is charged to the reactor, said improvement providing an increase in selectivity of propylene in the al'kenes.
2. The improved process of claim 1 wherein the naphtha is a petroleum derived naphtha.
3. The improved process of claim 2 wherein CS or (NH S is employed as an H 5 precursor.
4. The improved process of claim 1 wherein H 8 is employed per se.
5. The improved process of claim 1 wherein the cracking reaction is carried out continuously; and wherein the reaction is carried out at a gas hourly space velocity of about 400 to 22,000 cc. of gaseous feed volume per cc. of reactor volume per hour at standard temperature and pressure; and wherein the temperature is 1400 F. to 1700 F.
6. The improved process of claim 1 wherein CS or (NHQ S is employed as an H S precursor.
7. The improved process of the claim 1 wherein H 8 is employed per se.
References Cited UNITED STATES PATENTS 2,415,477 2/1947 Folkins et a1 260-683 2,361,149 10/1944 Perquin 208106 2,168,840 8/1939 Groll 260683.3 3,641,190 2/1972 Kivlen et a1. 260683 DELBERT E. GANTZ, Primary Examiner C. E. SPRESSER, JR., Assistant Examiner US. Cl. X.R.