Patent Application
20060278568
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.
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.
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
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.
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.
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:
The adsorption procedure was carried by the following procedure:
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.
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.
