Process For Production Of Olefins And Acetylene

Abstract

Ethylene, acetylene, and petroleum coke are manufactured by distilling a crude oil to produce a more volatile straight run naphtha and a less-volatile reduced crude oil; feeding the straight run naphtha to a hydrocarbon pyrolysis furnace to produce products comprising acetylene, ethylene, and hydrogen; coking the reduced crude to produce petroleum coke and a coker naphtha; separating a portion of the hydrogen from the hydrocarbon pyrolysis furnace effluent; using a portion of the hydrogen to hydrotreat the coker naphtha so as to produce hydrotreated oils having a substantially lower aromatic and olefin content than the coker naphtha; and feeding a portion of the hydrotreated oils into the hydrocarbon pyrolysis furnace.

Description

BACKGROUND OF THE INVENTION

Coker naphthas, derived from the coking of reduced crude, can be used as feedstocks in hydrocarbon pyrolysis furnaces but they are uneconomic, inferior feeds due to their high olefin content. They produce more polymers and tars than do paraffins, and correspondingly less ethylene and acetylene. This invention upgrades coker naphthas as commercial hydrocarbon pyrolysis feedstocks by hydrotreating to substantially saturate their olefin content, producing a stream with a paraffin content of about 90-95 percent. The paraffin feed causes less polymer and tar deposition in the pyrolysis furnace while it produces higher yields of acetylene and ethylene.

SUMMARY OF THE INVENTION

The operation of a hydrocarbon pyrolysis furnace is substantially improved by distilling a crude oil to produce a straight-run naphtha and a reduced crude, feeding the straight-run naphtha to the hydrocarbon pyrolysis furnace in order to produce products comprising ethylene, acetylene, or ethylene and acetylene, and hydrogen, coking the reduced crude to produce petroleum coke and a coker naphtha, separating a portion of the hydrogen from the hydrocarbon pyrolysis effluent, using a portion of the separated hydrogen to hydrotreat the coker naphtha so as to produce a hydrotreated oil having a substantially lower olefin content than the coker naphtha, and feeding a portion of the hydrotreated oils into the hydrocarbon pyrolysis furnace.

DESCRIPTION OF THE DRAWING

The drawing is a schematic representation of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the drawing, distillation unit 1, operating at atmospheric pressure, produces light petroleum ends boiling in the range of from about 40.degree. to about 85.degree. F. a light naphtha boiling in the range of from about 85.degree. to about 200.degree. F. and a heavy naphtha boiling in the range of from about 200.degree. to about 400.degree. F.

Hydrocarbon pyrolysis furnace 2 is any suitable pyrolysis furnace referred to in Acetylene, Its Properties, Manufacture and Uses by S. A. Miller, V. I, Chapter 5, pp. 383-448; 451-471. For instance, feed may be charged to a steam cracker to produce ethylene, or it may be thermally cracked in a Wulff furnace to produce ethylene or acetylene, or ethylene and acetylene. Any type of furnace which can be used to pyrolyze a distilled crude oil to obtain hydrocarbon gases is encompassed within the concept of the invention.

Operating temperatures for pyrolysis range from about 600.degree. to about 3,000.degree. F., depending upon the type of furnace used and the type of products desired with about 900.degree. to about 2,800.degree. F. being preferred. Pressures range from about 0.05 to about 50 atmospheres, but preferably are about 0.15 to about 5 atmospheres, and most preferably, about 0.4 to about 2.5 atmospheres.

Separations train 3 is a standard unit known to the art where the pyrolysis gases are separated through absorption, drying, partial condensation, and/or distillation into the desired products.

H.sub.2 purification unit 4 recovers hydrogen from stream F by various known techniques such as adsorption, distillation, or, by catalytically reacting the hydro carbon content of stream F with steam to convert the hydrocarbons into CO and H.sub.2. A representative physical separation technique is illustrated in "Hydrocarbon Processing," 46:11, (Nov., 1967), pp. 160, 190. A catalytic process for the recovery of hydrogen is well-explained in the work, Industrial Chemicals, 2nd Ed., by Faith, Keyes, and Clark, John Wiley & Sons, N.Y., Apr., 1961, pp. 440-449. CO.sub.2 may be removed from the crude hydrogen product by absorption with carbonates or alcohol amines. Any commercial H.sub.2 purification process which may be used to recover hydrogen from a mixed hydrocarbon stream is operable with the invention.

Hydrotreater 5 is any standard hydrotreater which may be equipped for a one- or two-stage operation. When two stages are used, the hydrotreater should operate at temperatures of from about 600.degree. to about 675.degree. F. in the first stage, and at pressures in the range of from about 350 to about 800 p.s.i.g. Preferred temperatures and pressures for the first stage of hydrotreatment are from about 620.degree. to about 660.degree. F. and from about 500 to about 800 p.s.i.g. In the second stage temperatures range from about 680.degree. to about 720.degree. F. and pressures range from about 350 to about 800 p.s.i.g.

If desired, the hydrotreatment can be done in a single stage if the coker naphtha is diluted with a straight-run naphtha. The operating conditions applied are those required in the second stage of a two-stage operation.

The ratio of hydrogen to hydrocarbon feed is about 1,000-4,000 standard cubic feet per barrel (s.c.f./b.), but preferably is about 2,500-3,500 s.r.f./b.

Catalysts for hydrotreatment are selected from the group consisting of cobalt, nickel, molybdenum, and combinations thereof.

The catalyst load is 1 to about 10 pounds of hydrocarbon feed per one pound of catalyst per hour, but preferably is 4 to about 7 pounds of hydrocarbon feed per pound of catalyst per hour for the first stage of hydrotreatment, and 2 to about 5 pounds of feed per pound of catalyst per hour for the second stage.

Coker 6 is a conventional delayed coker which operates at pressures of from 10 to about 70 p.s.i.g. but preferably operates at pressures of from 20 to 50 p.s.i.g., and at temperatures in the range of from about 800.degree. to about 1100.degree. F. but preferably at temperatures of from about 850.degree. to about 1050.degree. F.

Extractor 7 can be any solvent extraction system operable with the invention. Commercial solvents such as ethylene glycol, propylene glycol, dimethylformamide, n-methyl pyrrolidone, tetramethylene sulfone, sulfur dioxide, dicyanobutene, dimethylacetamide, furfural, furfuryl alcohol, tetrahydrofurfuryl alcohol, phenol, or the like, and/or mixtures thereof are appropriate. "Hydrocarbon Processing," 47:9, Sept., 1968, presents flow charts of two commercial extraction systems at pages 189 and 190 which can conveniently be employed.

Having described the apparatus of the invention, the preferred embodiment of the process may now be explained.

As depicted in the drawing, 100 pounds of crude oil are introduced into distillation unit 1 through line 20. 45.97 pounds of reduced crude and gas oil are withdrawn from distillation unit 1 and sent to coker 6 through line 11. 23.80 pounds of fuel oils are removed through line 10. 26.59 pounds of light and heavy naphthas are withdrawn from distillation unit 1 as stream A and 3.64 pounds of light ends are withdrawn as stream B. These streams enter hydrocarbon pyrolysis furnace 2 from which stream C is withdrawn and introduced into separations train 3.

5.21 pounds of C.sub.2 H.sub.2 are removed from separations train 3 as stream D, and 7.61 pounds of C.sub.2 H.sub.4 are removed as stream E. 8.12 pounds of aromatic oils and tars are removed from separations train 3 and introduced into coker 6 through line 30.

11.4 pounds of CO, H.sub.2 and CH.sub.4 are removed from separations train 3 and introduced into H.sub.2 purification unit 4, from which 9.12 pounds of fuel gas are removed as stream G. 2.28 pounds of H.sub.2 is withdrawn from H.sub.2 purification unit 4 through line 40 and introduced into hydrotreater 5, which receives 10.02 pounds of coker naphtha, stream H, from coker 6. 29.86 pounds of fuel oil are removed from coker 6 through line 60, 9.90 pounds of coke are withdrawn through line 62, and 4.31 pounds of fuel gas are removed from coker 6 through line 61.

2.10 pounds of fuel gas are withdrawn from hydrotreater 5 through line 50, and 10.20 pounds of hydrotreated oils are removed from the hydrotreater as stream I and introduced into hydrocarbon pyrolysis furnace 2, or, optionally, they are introduced into extractor 7 from which 1.35 pounds of aromatics are withdrawn through line 70, while the paraffins and naphthenes are removed as stream J which is sent to hydrocarbon pyrolysis furnace 2.

The composition of stream A through J are tabulated in table 1 . All values are in pounds per 100 pounds of crude oil feed. ##SPC1##

MODIFICATIONS OF THE INVENTION

For the sake of clarity, the invention has been described in terms of a preferred embodiment. It is not intended to limit the process to the particular operation shown. Rather, all equivalents obvious to those skilled in the art are to be included within the scope of the invention as claimed.

Claims

What is claimed is:

1. An improved process for the operation of a hydrocarbon pyrolysis furnace consisting essentially of

a. distilling a crude oil to produce a naphtha and a reduced crude, which is less volatile than said naphtha,

b. feeding at least a portion of said naphtha to said hydrocarbon pyrolysis furnace operating at about 900.degree. to about2800.degree. F. to produce products comprising ethylene and hydrogen,

c. coking said reduced crude to produce petroleum coke and a coker naphtha,

d. separating at least a portion of said hydrogen from said hydrocarbon pyrolysis furnace effluent,

e. utilizing at least a portion of said separated hydrogen to hydrotreat said coker naphtha to produce a hydrotreated oil having a lower olefin content than said coker naphtha,

f. feeding at least a portion of said hydrotreated oil into said hydrocarbon pyrolysis furnace.

2. The process of claim 1 wherein a portion of the aromatics contained in the hydrotreated oils withdrawn from the hydrotreater are removed in an extraction step prior to introducing said hydrotreated oils into said hydrocarbon pyrolysis furnace.

3. The process of claim 2 wherein aromatics are removed by extraction with a solvent selected from the group consisting of ethylene glycol, propylene glycol, tetramethylene sulfone, dimethylformamide, N-methyl pyrrolidone, sulfur dioxide, dicyanobutene, dimethylacetamide, furfural, furfuryl alcohol, tetrahydrofurfuryl alcohol, phenol, and mixtures thereof.

4. The process of claim 1 wherein the volatile straight run naphtha boils in the range of from about 85.degree. F. to about 400.degree. F.

5. The process of claim 1 wherein the less volatile reduced crude oil boils above 650.degree. F.

6. The process of claim 1 wherein the hydrocarbon pyrolysis furnace is operated at temperatures of from about 600.degree. to about 3,000.degree. F, and at pressures of from about 0.05 to about 50 atmospheres.

7. The process of claim 1 wherein the coker naphtha boils in the range of from about 100 to about 400.degree. F.

8. The process of claim 1 wherein the hydrotreater is operated at temperatures of from about 600.degree. to about 750.degree. F. and at pressures of from about 300 to about 1,500 p.s.i.g.

9. The process of claim 1 wherein the coker is operated at temperatures of from about 800.degree. to about 1,100.degree. F. and at pressures of from about 10 to about 70 p.s.i.g.

10. An improved process for the operation of a hydrocarbon pyrolysis furnace consisting essentially of

a. distilling a crude oil to produce a more volatile naphtha boiling at about 100.degree. to about 400.degree. F. and a less volatile reduced crude oil boiling above 600.degree. F,

b. feeding said naphtha to said hydrocarbon pyrolysis furnace operating at about 900.degree. to about 2,800.degree. F. to produce products comprising ethylene and hydrogen,

c. coking said reduced crude oil at from about 850.degree. to about 1,050.degree. F. to produce petroleum coke and a coker naphtha boiling in the range of from about 100.degree. to about 400.degree. F.

d. separating at least a portion of said hydrogen from said hydrocarbon pyrolysis furnace effluent,

e. utilizing at least a portion of said separated hydrogen to hydrotreat said coker naphthas at from about 600.degree. to about 750.degree. F. and at pressures of from about 300 to about 800 p.s.i.g, to produce a hydrotreated oil having a lower aromatic content and olefin content than said coker naphtha,

f. feeding said hydrotreated oils to an extractor wherein the aromatics are withdrawn, and

g. introducing at least a portion of said extracted, hydrotreated oils into said hydrocarbon pyrolysis furnace at from about 900.degree. to about 2,800.degree. F.