Method of removing oxygenated sulfur compounds from hydrocarbons

Abstract

A process for the removal of oxygenated sulfur compounds from a hydrocarbon stream, especially the effluent from a sulfuric acid alkylation reactor, in which the hydrocarbon stream is first subjected to deentrainment of any carryover liquid sulfuric acid and then passed over a sorbent which removes the oxygenated sulfur compounds.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the treatment of alkylate product from a process wherein normal olefins are reacted with isoalkanes in the presence of sulfuric acid to produce alkylate product. More particularly the invention relates to a process wherein sulfuric acid is mechanically removed from the effluent from the alkylation reactor and subsequently treated to remove residual oxygenated sulfur compounds. More particularly the invention relates to a process wherein the oxygenated sulfur compounds are removed by sorption.

2. Related Information

In the petroleum refining industry, acid catalyzed alkylation of aliphatic hydrocarbons with olefinic hydrocarbons is a well known process. Alkylation is the reaction of a paraffin, usually isoparaffins, with an olefin in the presence of a strong acid which produces paraffins, e.g., of higher octane number than the starting materials and which boil in range of gasolines. In petroleum refining the reaction is generally the reaction of a C₂ to C₅ olefin with isobutane.

In refining alkylations, hydrofluoric or sulfuric acid catalysts are most widely used under low temperature conditions. Low temperature or cold acid processes are favored because side reactions are minimized. In the traditional process the reaction is carried out in a reactor where the hydrocarbon reactants are dispersed into a continuous acid phase.

Although this process has not been environmentally friendly and is hazardous to operate, no other process has been as efficient and it continues to be the major method of alkylation for octane enhancement throughout the world. In view of the fact that the cold acid process will continue to be the process of choice, various proposals have been made to improve and enhance the reaction and to some extent moderate the undesirable effects.

In the past the alkylate product has been washed with water or treated with caustic to remove or neutralize any carryover sulfuric acid. Both methods of treatment have drawbacks. When a water wash is used, there is some carryover of water to the distillation columns used to separate the alkylate from unreacted materials. This water dilutes any acid left or dissolves any sulfonates or sulfonic esters which cause corrosion problems. The caustic tends to produce salts which can foul downstream heat exchangers, especially the reboiler in the recovery columns. Various solutions have been proposed for this problem. U.S. Pat. No. 5,220,095 disclosed the use of particulate polar contact material and fluorinated sulfuric acid for the alkylation.

U.S. Pat. Nos. 5,420,093 and 5,444,175 sought to combine the particulate contact material and the catalyst by impregnating a mineral or organic support particulate with sulfuric acid.

Various static systems have been proposed for contacting liquid/liquid reactants, for example U.S. Pat. Nos. 3,496,996; 3,839,487; 2,091,917; and 2,472,578. However, the most widely used method of mixing catalyst and reactants is the use of various arrangements of blades, paddles, impellers and the like that vigorously agitate and blend the components together, for example, see U.S. Pat. Nos. 3,759,318; 4,075,258 and 5,785,933.

SUMMARY OF THE INVENTION

In the present process oxygenated sulfur compounds are removed from a hydrocarbon stream comprising passing said hydrocarbon stream over a supported sorbent comprising a component selected from the group consisting of copper, zinc and mixtures thereof. Preferably the oxygenated sulfur compounds are present as a residual amount in the hydrocarbon stream, such as that present in a hydrocarbon stream separated and recovered from a sulfuric acid catalyzed paraffin alkylation. The residual amount is preferably less than 1000 wppm. Preferably the sorbent is regenerable.

In a preferred embodiment the invention comprises removing the sulfuric acid from the alkylate by mechanical means instead of water wash or caustic treatment product prior to treatment to remove oxygenated compounds by absorption. The preferred mechanical means comprises a vessel containing a coalescer material upon which the sulfuric acid impinges. The sulfuric acid, being much heavier than the hydrocarbon, falls out and may be removed by gravity. The alkylate product may then be treated to remove the oxygenated sulfur compounds by adsorption in any of several points in the process after the mechanical deentrainment. The adsorber may contain regenerable or nonregenerable sorbents and may be located directly after the coalescer to treat the entire stream or downstream on any of the other product streams. The sorbents may remove the oxygenated sulfur compounds from light (C₄ and lighter) and heavier (C₅ and heavier) components separately if desired.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified flow diagram of one embodiment of the invention.

FIG. 2 is a simplified flow diagram of the invention showing various placements of the sorber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The alkylate product to be treated may come from any cold acid alkylation process which uses sulfuric acid as the catalyst. Preferably, the fluid system comprises a liquid and is maintained at about its boiling point in the reaction zone.

The coalescer is a conventional liquid-liquid coalescer of a type which is operative for coalescing vaporized liquids and comprises demisters and co-knit structures which are catalytically inert or active. Demisters and co-knit structures are typically used for liquid-liquid coalescers and coalescing of mists. They are known as “mist eliminators” or demisters and are composed of one or more materials which are knit together to form a mesh. The stitched mesh is then crimped, stretched, and folded or bundled to provide the desired amount of surface area per volume ratio, and are commonly known as “mist eliminators” or “demisters” used to coalesce condensible vapors in gaseous streams. A suitable coalescer comprises a mesh such as a co-knit wire and fiberglass mesh. For example, it has been found that a 90 needle tubular co-knit mesh of wire and fiberglass such as manufactured by Amistco Separation Products, Inc of Alvin, Tex. or ACS Industries LLC of Houston, Tex., can be effectively utilized, however, it will be understood that various other materials such as co-knit wire and teflon (Dupont ™), steel wool, polypropylene, PVDF, polyester or various other co-knit materials can also be effectively utilized in the apparatus. Various wire screen type packings may be employed where the screens are woven rather than knitted. Other acceptable coalescers include perforated sheets and expanded metals, open flow cross channel structures which are co-woven with fiberglass or other materials, such as polymers.

Typically the alkylate from the alkylation process contains some sulfuric acid as well as sulfonates and sulfonic esters which must be removed. Referring now to FIG. 1 a simplified flow diagram of one embodiment is shown. The alkylate is taken from alkylation reactor 10 via flow line 101 and fed to deentrainment vessel 20. Deentrainment vessel 20 contains a coalescer material upon which the sulfuric acid droplets impinge and fall out. The sulfuric acid and hydrocarbons in the alkylate product are practically insoluble in one another. The sulfuric acid droplets are collected and recycled to the alkylation reactor 10 via flow line 104.

The liquid from the deentrainment vessel is passed via flow line 102 to absorption vessel 50 containing a bed 52 of sorbent material. Any material that will sorb the oxygenated sulfur compounds will suffice. One typical sorbent is Engelhard Cu-0226 14×28, 10% Cu on alumina. Another is BASF R3-12, 40% Cu/40% Zn on alumina. Substantially all of the oxygenated sulfur compounds are sorbed by the sorbent. Hydrogen is fed to the sorber as required via flow line 108 during the regeneration step. The liquid from the sorber is then fed via flow line 110 to a deisobutanizer 30 containing standard distillation structure 32 such as sieve trays, bubble cap trays and the like, where iC₄ and C₃'s and lighter are taken as overheads via flow line 109. The overheads containing the iC₄ and lighter material is then fed via flow line 109 to depropanizer 60 containing standard distillation structure 62 where C₃ and lighter is removed as overheads via flow line 111. The iC₄ is recycled to the alkylation reactor via flow line 104. The bottoms from the deisobutanizer containing the alkylate are fed via flow line 105 to debutanizer 40 containing standard distillation structure 42 where nC₄ is removed as overheads via flow line 106 and alkylate product is taken as bottoms via flow line 107. When the efficiency of the sorbent declines to a determined level, the alkylate feed is ended and the sorbent regenerated with hydrogen at 125 psig and 650° F., the hydrogen ended, the sorbent cooled, the alkylate feed restated and the steps repeated.

FIG. 2 shows alternate placements of the sorber 50 as indicated by the dashed lines and the reference numerals 50A-50G. The remaining vessels are numbered as in FIG. 1. As seen the sorber may be placed to remove the oxygenated sulfur compounds from any of the streams downstream of the deentrainment vessel such as the nC₄ stream, the feed to the depropanizer, the C₃ product, the feed to the deisobutanizer, the feed to the debutanizer or the alkylate product stream.

Although not shown there would be typically two, preferably three, sorbers in parallel use. One sorber would be in use, a second would be a back up and the third would be undergoing regeneration.

EXAMPLES

In the following examples hydrocarbon feeds treated to remove oxygenated sulfur compounds are simulated as C₄=about 95% isobutane or C₈=about 50% isooctane and 20% n-butane with sulfur esters added. In the initial run the sorber catalyst treatment was activation and in subsequent runs the treatment was regeneration. The sorbent unit was ⅜″ OD tubing containing 10 grams (11 ml) of the sorbent. The sorption took place at 125 psig and 150° F. to simulate conditions of the hydrocarbon stream entering a debutinizer column. The length of each run was determined by time to break through (Time to BT). Break through was defined as when the effluent from the sorber contained 15% of the sulfur of the feed stream.

Catalyst activation and regeneration procedure was as follows:

• 1. Purged with nitrogen −40 ccm for 20 minutes at 125 psig and 300° F.
• 2. Started hydrogen −30 ccm, 125 psig and ramped temperature to 650° F. (10° F./min). Held for 3 hours then cooled to 150° F. while flowing hydrogen. (6 hrs total).

The adsorption procedure was carried by the following procedure:

• 1. Purged with nitrogen (or He)—flowed 40 ccm for 30 min at 125 psig and kept temperature at 150° F. Shut off gas flow before starting hydrocarbons.
• 2. Hydrocarbon flow at 125 psig and 150° F.
• 3. After complete breakthrough occurred feed terminated.
• 4. Regenerated catalyst per procedure above.

Example 1

Engelhard Cu-0226 S 14×28, 10% Cu on alumina was used as sorbent to treat sulfur ester containing hydrocarbon feeds as described. The conditions, residual sulfur compound content (wppm), and results are shown in TABLE I.

TABLE I
Catalyst:	Engelhard Cu-0226 S 14 × 28, 10% Cu/Alumina
	grams	10
	ml	11
SORBENT TREATMENT STEP
Reduction	Run #1	Run #2	Run #3	Run #4	Run #5
H2 feed Ml/min	30	30	30	30	30
Temp ° F.	650	650	450	450	450
Pressure psig	100	100	100	100	100
Time hrs	4	4	4	4	4
HYDROCARBON PROCESSING STEP
Feed	C4	C4	C4	C8	C8
Flow rate: ml/min	3	3	3	2	2
WHSV: 1/hr	10.026	10	10	8.436	8.436
Density: g/cm3	0.557	0.557	0.557	0.703	0.703
Temp ° F.	100	100	100	325	325
Pressure psig	100	100	100	200	200
Time to BT hr	44	50	>70	24	29
S in Feed, wppm	14	14	7	23	18
Capacity gS/gcat	0.006176	0.007018	>0.005	0.004608	0.004524
Productivity: grams	441.144	501.3	NA	202.464	244.644
feed/g cat

Example 2

BASF R3-12, 40% Cu/40 Zn on alumina was used as sorbent to treat sulfur ester containing hydrocarbon feeds as described. The conditions, residual sulfur compound content (wppm), and results are shown in TABLE II.

	TABLE II
	Catalyst:	BASF R3-12, 40% Cu, 40% Zn/alumina
		grams	10
		ml	10.5
SORBENT TREATMENT STEP
	Reduction		Run #1	Run #2	Run #2
	H2 feed	ml/min	30	30	30
	Temp	° F.	450	450	450
	Pressure	psig	100	100	100
	Time	hrs	12	18	18
HYDROCARBON PROCESSING STEP
Feed		C4	C8	C8
Flow rate:	ml/min	6	2	2
WHSV:	1/hr	20.052	8.436	8.436
Density:	g/cm3	0.557	0.703	0.703
Temp	° F.	100	325	325
Pressure	psig	100	200	200
Time to BT	hr	74	23	14
S in Fd	wtppm	4.937163	16	23
Capacity	gS/gcat	0.007326	0.003036	0.002688
Productivity:	grams feed/	1483.848	194.028	118.104
	g cat

Claims

1. A process for the removal of oxygenated sulfur compounds from a hydrocarbon stream comprising passing said hydrocarbon stream over a supported sorbent comprising a component selected from the group comprising copper, zinc or mixtures thereof.

2. The process according to claim 1 wherein said sorbent is supported on alumina.

3. The process according to claim 1 wherein said oxygenated sulfur compounds are present as a residual amount.

4. The process according to claim 3 wherein said oxygenated sulfur compounds are the residual amount present in a hydrocarbon stream recovered from a sulfuric acid catalyzed paraffin alkylation.

5. The process according to claim 4 wherein said hydrocarbon stream is the alkylate product recovered from a sulfuric acid catalyzed paraffin alkylation.

6. The process according to claim 5 wherein said hydrocarbons comprise isooctane.

7. A process for the removal of residual amount of oxygenated sulfur compounds from a stream comprising hydrocarbons and sulfuric acid comprising mechanically separating sulfuric acid from said hydrocarbons, recovering the hydrocarbons containing a residual amount of oxygenated sulfur compounds and passing said hydrocarbon stream over a supported sorbent comprising a component selected from the group comprising copper, zinc or mixtures thereof.

8. The process according to claim 7 wherein said sorbent is supported on alumina.

9. The process according to claim 7 wherein said residual amount is less than 1000 wppm oxygenated sulfur compounds.

10. The process according to claim 9 wherein said oxygenated sulfur compounds are the residual amount present in a hydrocarbon stream recovered from a sulfuric acid catalyzed paraffin alkylation.

11. The process according to claim 10 wherein said hydrocarbon stream is the alkylate product recovered from a sulfuric acid catalyzed paraffin alkylation.

12. The process according to claim 11 wherein said hydrocarbons comprise isooctane.

13. The process according to claim 7 wherein said hydrocarbons comprise C4's.

14. The process according to claim 7 wherein said mechanical means comprises a coalescer.

15. A process for the treatment of the effluent from an alkylation reactor wherein a stream containing normal butene is contacted with a stream containing normal and isobutanes in the presence of liquid sulfuric acid under conditions of temperature and pressure to produce isooctane along with sulfonates and sulfonic esters, comprising the steps of:

(a) passing said effluent through a deentrainment device containing coalescer material wherein any entrained sulfuric acid is removed from the effluent; and

(b) passing the effluent from said deentrainment device to a sorber containing a sorbent which selectively sorbs oxygenated sulfur compounds from said effluent.

16. A process for the treatment of the effluent from an alkylation reactor wherein a stream containing normal butene is contacted with a stream containing normal and isobutanes in the presence of liquid sulfuric acid under conditions of temperature and pressure to produce isooctane along with sulfonates and sulfonic esters, comprising the steps of:

(a) passing said effluent through a deentrainment device containing coalescer material wherein any entrained sulfuric acid is removed from the effluent;

(b) passing the liquid effluent from the deentrainment device to a deisobutanizer;

(c) removing isobutane from the deisobutanizer as a first overheads;

(d) recycling the isobutane from the deisobutanizer to the alkylation reactor;

(e) removing normal butanes and alkylate from the deisobutanizer as a first bottoms;

(f) passing the bottoms from the deisobutanizer to a debutanizer;

(g) removing normal butanes from said debutanizer as a second overheads;

(h) removing alkylate from said debutanizer as a second bottoms; and

(i) passing said second bottoms to a sorber containing a sorbent which selectively sorbs oxygenated sulfur compounds from said effluent.

17. The process according to claim 16 further comprising passing said first overheads to a sorber containing a sorbent which selectively sorbs oxygenated sulfur compounds from said effluent.

18. The process according to claim 16 further comprising passing said second overheads to a sorber containing a sorbent which selectively sorbs oxygenated sulfur compounds from said effluent.

19. The process according to claim 16 wherein said sorbent is selected from the group consisting of copper and zinc supported on alumina.