Ni/Cu Absorbent/Catalyst for Desulfurization and Isomerization of N-Paraffins

A conventional isomerization catalyst designated as "HS-10" and commerically available from the Linde Division of the Union Carbide Corporation is contacted in 7 separate runs with a hydrocarbon feedstock consisting of equimolar mixture of n-pentane and n-hexane and doped with thiophene in concentrations varied as hereinafter described.

During start-up of the process, hydrogen gas contacts the isomerization catalyst for 4 hours at 300.degree. C. and the feedstock contacts the isomerization catalyst in the presence of hydrogen in a stainless steel reactor (designated as R-2 herein) in each run for 24 hours under the conditions in Table I:

In run numbers 2 and 3 a catalytic absorbent, designated as Catalyst A (containing a nominal 20 weight percent of copper oxide, calculated as CuO, on gamma alumina), is contacted with the feedstock in an upstream separate stainless steel reactor (designated as R-1 herein) under the above mentioned conditions in Table I. In these runs the feedstock is passed serially over the materials in R-1 and R-2 and the effluent from R-1 analyzed for sulfur content and the effluent from R-2 analyzed for octane rating and for the products set forth in Table II:

In runs 6 and 7, R-1 contains Catalyst DF, a dual-function catalyst containing a nominal 15.0 weight percent of nickel oxide, calculated as NiO, 68 weight percent of LZ-210 zeolite (having a silica-to-alumina ratio of 9.0), and 17 weight percent of alumina. Catalyst DF is prepared by comulling the LZ-210 zeolite with sufficient alumina hydrogel. The comulled paste is extruded in particulate form having a cross-sectional cylindrical shape. The particulates are of a length between about 1/4 and 1/2 inch, are dried and calcined in air. The extrudates are then impregnated with sufficient aqueous solution of nickel nitrate. In runs 8 and 9, Catalyst DF is contacted with the feedstock in R-2.

The following Table III summarizes (1) the sulfur content of the feedstock (doped with n-butyl mercaptan) or effluent from R-1 for each run and (2) the isomerized products and octane values obtained from the effluent of R-2. Note that in runs 1, 4, 5, 8 and 9, the feedstock is passed through only one reactor vessel, R-2, and contacts either the catalytic absorbent or dual-function catalyst as shown in Table III.

The data in Table III demonstrate that in run no. 4, 5 ppmw of sulfur causes a substantial decline in isomer product yields as compared to the yields in run nos. 1, 2 and 3 from the sulfur-free feedstocks. The process of the invention in run no. 3 provides a sulfur-free feedstock contacting the isomerization catalyst and results in isomerization products of essentially the same yields as in run nos. 1 and 2 wherein the sulfur-free feedstocks also contact the isomerization catalyst.

In run no. 5, a feedstock containing 100 ppmw of sulfur contacting the isomerization catalyst in R-2 also causes substantial decline in the activity of the isomerization catalyst as compared to that when a sulfur-free feedstock contacts the catalyst (see run nos. 1-3). However, when the dual-function Catalyst DF is utilized in the upstream reactor, R-1, in the process of the invention (run nos. 6 and 7), a substantial increase in isomerization results in the products from R-2 as compared to that in run no. 5. Such an increase in isomerization occurs when 0 or 100 ppmw of sulfur are contained in the feedstock supplied to R-1. It is clearly shown in run no. 7 that the dual-function catalyst provides substantial desulfurization.

Furthermore, the dual-function catalyst (run nos. 6 and 7) also provides substantial isomerization. In runs nos. 6 and 7 the mole percent of pentane isomer product (i-C.sub.5) is more than doubled and the mole percent of n-hexane product remaining (n-C.sub.6) is essentially reduced by at least a factor of two, when compared against run nos. 1-3 wherein sulfur-free feedstocks also contact the isomerization catalyst in R-2. Thus, isomerization occurs in both R-1 and R-2 in run nos. 6 and 7 whereas in run nos. 1-3 isomerization only occurs in R-2.

In run nos. 8 and 9 wherein the dual-function Catalyst DF is employed in R-2 as the only catalyst in the process, the yield of isomerization products is at least equivalent, or in the case of n-hexane isomerization, substantially greater than that in respective run nos. 1 and 5. In the comparison of run no. 8 with run no. 1, both the isomerization catalyst, HS-10, and the dual-function catalyst are contacted with the sulfur-free feedstock to produce similar yields of isomerized products. However, when the feedstock is doped with 100 ppmw of sulfur in run nos. 9 and 5, the process of the invention (employing Catalyst DF in run no. 9) produces a substantially increased yield of isomerized hexane compounds and improved product octane compared to run no. 5 employing the conventional catalyst. Catalyst DF is clearly more sulfur tolerant than Catalyst HS-10.

Two catalysts, one designated as "DFNi" and the other as "DFCu/Ni" are prepared in a similar manner to Catalyst DF of Example I, except Catalyst DFNi contains a nominal 11.0 weight percent of nickel oxide, calculated as NiO, and Catalyst DFCu/Ni contains a nominal 11.0 weight percent of nickel oxide (as NiO) and 8.1 weight percent of copper (II) oxide, calculated as CuO, with both catalysts having the balance of the composition with a support containing LZ-210 zeolite (having a silica-to-alumina ratio of 12.0) in an 80/20 weight ratio to alumina.

Each catalyst is contacted in the R-2 reactor of Example I in separate 70-hour runs with the hydrocarbon feedstock of Example I, doped with thiophene to an initial concentration of 15 ppmw, calculated as S. The catalysts are initially contacted with hydrogen gas for 48 hours at 375.degree. C. and 300 p.s.i.g. and then contacted by the feedstock under the same conditions as Example I for 70 hours, except the temperature is increased to 270.degree. C. for the run employing Catalyst DFNi and to 285.degree. C. for the run employing Catalyst DFCu/Ni, the initial temperatures being selected to provide each catalyst with the same initial isomerization activity for each run.

In accordance with the same designations as indicated for the R-2 hydrocarbon products in Table II of Example I, the following Table IV summarizes the isomerized products obtained from the effluent of each run. Throughout each run the effluent is observed to have a nil sulfur concentration.

The data in Table IV demonstrate that the Catalyst DFCu/Ni has much more isomerization stability than Catalyst DFNi over the course of each run. For example, the decrease in the mole percent of pentane isomer product in the total pentane product (i-C.sub.5) over the last 50 hours of each 70 hour run is only about 12.5 mole percent (37.5-25.0) for the nickel/copper containing catalyst compared to about twice that amount, i.e., 23.5 mole percent, (36.0-12.5) for the nickel-only catalyst. Also, the decreases in the mole percentage of methyl pentane (MP) and dimethyl butane (DMB) product and the increases in the mole percentages of the normal hexane (n-C.sub.6) product over each run are much less sharp for the nickel/copper catalysts than for the nickel-only catalyst.

In view of the foregoing description of the invention including the Examples thereof, it is evident that many alternatives, modifications, and variations can be made by those skilled in the art without departing from the concept of the present invention. Accordingly, it is intended in the invention to embrace all such alternatives, modifications, and variations as may fall within the scope of the appended claims.