PROCESS FOR DESULFURIZATION OF HYDROCARBONS

Abstract

A process for hydrodesulfurizing an olefinic naphtha feedstock while retaining a substantial amount of the olefins, which feedstock has a T.sub.95 boiling point below 250° C. and contains at least 50 ppmw of organically bound sulfur and from 5% to 60% olefins, the process including hydrodesulfurizing the feedstock in a sulfur removal stage in the presence of a gas including hydrogen and a hydrodesulfurization catalyst, at hydrodesulfurization reaction conditions, to convert at least 60% of the organically bound sulfur to hydrogen sulfide and to produce a desulfurized product stream wherein the gas to oil ratio and the pressure are configured for the selectivity slope, (% HDS−% OSAT)/(% OSAT*(100−% HDS)), to be above 0.55, and to provide a lower octane loss at all severities above 60% HDS, compared to compared to all prior reported processes with similar conversion of organic sulfur with a lower gas to oil ratio, as measured by the selectivity slope.

Claims

1) A process for hydrodesulfurizing an olefinic naphtha feedstock while retaining a substantial amount of the olefins, which feedstock has a T.sub.95 boiling point below 250° C. and contains at least 50 ppmw of organically bound sulfur and from 5% to 60% olefins, said process comprising: (a) hydrodesulfurizing the feedstock in a sulfur removal stage in the presence of a gas comprising hydrogen and a hydrodesulfurization catalyst, at hydrodesulfurization reaction conditions including a temperature from 200° C. to 350° C., a pressure from 2 barg 35 barg, and gas to oil ratio from 500 Nm.sup.3/m.sup.3 to 2500 Nm.sup.3/m.sup.3, to convert at least 60% of the organically bound sulfur to hydrogen sulfide and to produce a desulfurized product stream wherein the gas to oil ratio and the pressure being configured for the selectivity slope, (% HDS−% OSAT)/(% OSAT*(100−% HDS)), to be above 0.55.

2) A process according to claim 1 wherein the process severity is configured for converting at least 70% of the organically bound sulfur to hydrogen sulfide.

3) A process according to claim 1 wherein less than 50% of the sulfur in the feedstock directed to the sulfur removal stage is found in mercaptans.

4) A process according to claim 1 wherein the liquid hourly space velocity is from 1.1 hr.sup.−1 to 3 hr.sup.−1.

5) A process according to claim 1 further comprising the steps of: (b) separating the feedstock in at least a heavy naphtha stream and a light naphtha stream according to boiling point; (c) directing said heavy naphtha stream as the feedstock of said hydrodesulfurizing step, providing a desulfurized product stream; (d) optionally directing the light naphtha stream as the feedstock to a further sulfur removal stage, providing a light desulfurized naphtha stream; and (e) combining said desulfurized product stream and either said light naphtha stream or said light desulfurized naphtha stream to form a final product stream.

6) A process according to claim 1 in which said hydrodesulfurization catalyst comprises 0.5% to 5% cobalt and/or nickel and 3% to 20% molybdenum and/or tungsten, on a refractory support.

7) A process according to claim 6 in which said hydrodesulfurization catalyst comprises 0.5% or to 5% cobalt and 3% to 20% molybdenum.

8) A process according to claim 6 in which refractory said support comprises alumina, silica or silica-alumina.

9) A process according to claim 5, wherein said step (c) comprises the substeps: (x) directing said heavy naphtha stream as the feedstock of a first hydrodesulfurizing step in the presence of a catalytically active material, providing a desulfurized heavy product stream; (y) optionally separating the desulfurized heavy product stream into at least a desulfurized heavy naphtha stream and a gas stream; and (z) further desulfurizing the heavy desulfurized naphtha product stream in the presence of a catalytically active material, providing the desulfurized product stream wherein the conditions and catalytically active material of steps (x) and (z) may be similar or different.

10) A process according to claim 9 wherein said step (x) converts at least 75% of the organically bound sulfur to H.sub.2S.

11) A process according to claim 9, wherein said step (y) is present and involves the steps: (p) separating the desulfurized heavy product stream in a at least a desulfurized heavy naphtha stream, desulfurized intermediate naphtha stream and a gas stream, and one or both of the steps; (q) further desulfurizing the desulfurized intermediate naphtha stream, providing the intermediate desulfurized product stream; and (r) combining two or more of the intermediate desulfurized product stream, the heavy desulfurized product stream, said light naphtha stream and said light desulfurized naphtha stream to form a final product stream.

12) A process according to claim 1, wherein the process for hydrodesulfurizing the olefinic naphtha feedstock retains at least 20% of the olefins in the olefinic naphtha feedstock.

13) A process according to claim 1, further comprising a step of selective diolefin hydrogenation prior to said hydrodesulfurizing step.

14) A process according to claim 12, in which the reaction conditions of said selective diolefin hydrogenation involves a temperature from 80° C. to 200° C., a pressure from 5 barg to 50 barg, and a gas to oil ratio from 2 Nm.sup.3/m.sup.3 to 250 Nm.sup.3/m.sup.3 to convert at least 80% of the diolefins to alkanes or mono-olefins or by reaction with mercaptans to sulfides.

15) A process according to claim 12, in which the selective diolefin hydrogenation reaction conditions involves a temperature from 100° C. to 130° C., a pressure of 5 barg to 50 barg, and a gas to oil ratio of 250 Nm.sup.3/m.sup.3 to 2500 Nm.sup.3/m.sup.3 to convert at least 90% of the diolefins to alkanes or mono-olefins or by reaction with mercaptans to sulfides.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0066] FIG. 1 shows a simple process, implementing the present disclosure.

[0067] FIG. 2 shows an implementation of the present disclosure in a process involving pretreatment and separation.

[0068] FIG. 3 shows experimental data presented as olefin saturation vs. hydrodesulfurization.

[0069] FIG. 4 shows experimental data presented as selectivity vs. 100%−hydrodesulfurization, together with linear fits of the experimental data.

[0070] 102 Hydrocarbon feedstock [0071] 104 Stream of hydrogen containing gas [0072] 106 Combined feedstock [0073] 108 Material catalytically active in hydrodesulfurization [0074] 110 Desulfurized naphtha stream [0075] 202 Di-olefinic hydrocarbon feedstock [0076] 204 Hydrogen containing gas [0077] 206 Di-olefinic feedstock reaction mixture [0078] 208 Material catalytically active in diolefin saturation [0079] 210 Intermediate product [0080] 212 Separator [0081] 214 Light naphtha stream [0082] 216 Heavy naphtha stream [0083] 218 Hydrogen containing gas [0084] 220 Heavy naphtha reaction mixture [0085] 222 First material catalytically active in hydrodesulfurization [0086] 222 Material catalytically active in hydrodesulfurization [0087] 224 Partly desulfurized heavy naphtha [0088] 226 Further catalytically active material [0089] 228 Desulfurized heavy naphtha [0090] 230 Desulfurized naphtha product

DETAILED DESCRIPTION

[0091] FIG. 1 shows a process for removing organically bound sulfur from hydrocarbons. The process involves combining a hydrocarbon feedstock 102 containing organically bound sulfur and olefins with a stream of hydrogen containing gas 104 such that the ratio of hydrogen containing gas to feedstock is at least 750 Nm.sup.3/m.sup.3. The combined feedstock 106 is directed to contact a material catalytically active in hydrodesulfurization 108, such as 1% cobalt and 3% molybdenum, on an alumina support, at a temperature around 250° C. A desulfurized naphtha stream 110 is withdrawn from the catalytically active material.

[0092] In a further embodiment the catalytically active material may have a different composition such as 1% to 5% cobalt and 3% to 20% molybdenum or tungsten, on a refractory support, which may be alumina, silica, spinel or silica-alumina.

[0093] In a further embodiment the hydrogen containing gas may comprise significant amounts of other gases, e.g. more than 25%, 50% or even 75% nitrogen, methane, ethane or mixtures hereof.

[0094] FIG. 2 shows a process for removing organically bound sulfur from hydrocarbons comprising di-olefins. The process involves combining a di-olefinic hydrocarbon feedstock 202 containing organically bound sulfur, olefins and diolefins with a stream of hydrogen containing gas 204 such that the ratio of hydrogen containing gas to feedstock is around 5-10 Nm.sup.3/m.sup.3 providing a di-olefinic feedstock reaction mixture 206. The di-olefinic feedstock reaction mixture 206 is directed to contact a material catalytically active in diolefin saturation 208, such as 2% nickel or cobalt and 7% molybdenum or tungsten, on an alumina support, at a temperature around 100-200° C., to provide an intermediate product 210 comprising less than 0.1% or 0.3% di-olefins. Under such mild conditions, it is considered that the lighter sulfur components of the di-olefinic hydrocarbon feedstock do not react to release organic sulfur as H.sub.2S, but instead they may undergo recombination reactions with olefins to form heavier sulfides. The intermediate product 210 is directed to a separator 212, from which a light naphtha stream 214 and a heavy naphtha stream 216 are withdrawn. The heavy naphtha stream 216 is combined with a stream of hydrogen containing gas 218 such that the ratio of hydrogen containing gas to feedstock in the resulting heavy naphtha reaction mixture 220 is at least 750 Nm.sup.3/m.sup.3 and directed to contact a first material catalytically active in hydrodesulfurization 222, such as 1% cobalt and 3% molybdenum, on an alumina support, at a temperature around 250° C., providing a partly desulfurized heavy naphtha 224. The partly desulfurized heavy naphtha 224 may optionally be directed to a further catalytically active material 226 such as 12% nickel on an alumina support, typically operating at a temperature higher than the first material catalytically active in hydrodesulfurization 222, such as 300° C. to 360° C., providing a desulfurized heavy naphtha 228. The desulfurized heavy naphtha 228 is then combined with the light naphtha stream 214 to provide a desulfurized naphtha product 230. In FIG. 1 and FIG. 2 the temperature control of the reactions are not shown, but since the HDS reactions are exothermic, it is typical to add cold hydrogen containing gas or cold recycled product to maintain a low temperature increase. If the GOR is increased the requirement for using product recycle may be reduced, as more quench gas will be available.

[0095] In a further embodiment the light naphtha may also be desulfurized by contact with a material catalytically active in hydrotreatment, but typically at less severe conditions than the heavy stream(s).

[0096] In a further embodiment the partly desulfurized heavy naphtha may be directed to a separator to provide the heavy sulfurized naphtha fraction contacting the third catalytically active material and an intermediate naphtha fraction which may either be treated by contact with a further catalytically active material or be combined into the desulfurized naphtha product.

EXAMPLES

[0097] Two feedstocks of commercial, heavy catalyst cracked naphtha boiling between 60 and 200° C. were directed to hydrodesulfurization in an isothermal downflow pilot plant reactor. The feedstocks are characterized in Table 1 and Table 2. The hydrodesulfurization conditions in the reactor are further specified below.

[0098] The reactor effluent was cooled to ca. −5° C. to condense the treated naphtha product, which was separated from a remaining gas phase comprising H.sub.2S and unreacted Hz, and subsequently stripped using N.sub.2 to remove any dissolved H.sub.2S from the product. The catalyst used was a hydrodesulfurization catalyst comprising 1.1 wt % Co and 3.2 wt % Mo on alumina support. The catalyst was a 1/20 inch trilobe size in Example 1 and a 1/10 inch quadlobe size in the remaining examples.

[0099] The experimental results are listed in Table 3 to Table 6, and depicted in FIG. 3 and FIG. 4.

[0100] FIG. 3 plots % OSAT vs. % HDS. The attractive region of parameters of high % HDS and low % OSAT is proximate to the lower right corner.

[0101] FIG. 4 plots selectivity (% OSAT/% HDS) vs. 100−% HDS. Here the attractive region of parameters corresponds to the steepest line, especially to the top left. For each set of experiments a linear fit is made, with intercept forced to 1, corresponding to a selectivity of 1 for maximum severity. For each individual experiment the corresponding value of selectivity slope between the experimental point and the point ((% OSAT/% HDS), (100−% HDS))=(0,1) is calculated as (% HDS−% OSAT)/(% OSAT*(100−% HDS)) and included in the tables reporting the experiments.

Example 1

[0102] In Example 1 Feedstock 1 was treated under a GOR level of 500 Nm.sup.3/m.sup.3, with 100% hydrogen treat gas. The severity of hydrodesulfurization was controlled by varying the temperature from 200 to 280° C. and the gas to feedstock ratio (GOR) of 250 to 1400 Nm.sup.3/m.sup.3, with an inlet pressure of 20 barg. The liquid hourly space velocity (LHSV) was 2.5 1/hr (v/v/hr). Experimental results are shown in Table 3, and in FIGS. 3 and 4 using the symbol ‘x’.

Example 2

[0103] In Example 2 Feedstock 2 was treated under a GOR level of 1200 Nm.sup.3/m.sup.3 with 100% hydrogen treat gas with an inlet pressure of 20 barg. The severity of hydrodesulfurization was controlled by varying the temperature from 220 to 265° C. The liquid hourly space velocity (LHSV) was 2.5 1/hr (v/v/hr). Experimental results are shown in Table 4, and in FIGS. 3 and 4 using the closed circle symbol ‘.circle-solid.’.

Example 3

[0104] In Example 3 Feedstock 2 was treated under a GOR level of 1200 Nm.sup.3/m.sup.3 with a treat gas mixture of H2 and CH.sub.4 with a total inlet pressure of 20 barg. The severity of hydrodesulfurization was controlled by varying the H2 concentration in the treat gas from 42% to 75%. The temperature was 235° C. The liquid hourly space velocity (LHSV) was 2.5 1/hr (v/v/hr). Experimental results are shown in Table 5, and in FIGS. 3 and 4 using the closed triangle symbol ‘.box-tangle-solidup.’.

Example 4

[0105] In Example 4 Feedstock 2 was treated under a GOR level of 1200 Nm.sup.3/m.sup.3 with a 100% hydrogen treat gas with an inlet pressure of 8.3 barg. The severity of hydrodesulfurization was controlled by varying the temperature from 220 to 265° C. The liquid hourly space velocity (LHSV) was 2.5 1/hr (v/v/hr). Experimental results are shown in Table 6, and in FIGS. 3 and 4 using the open square symbol ‘□’.

[0106] Analyzing the experimental results by the direct inspection using FIG. 3 shows that Example 4 at low pressure and high GOR operate in the more desirable range of high % HDS and low % OSAT, while Example 1 according to the prior art at low GOR and high pressure is the least desirable. Examples 2 and 3 are similar to each other with a position between the other two experiments.

[0107] FIG. 4 shows a transformed representation of the experimental results, by plotting selectivity (% HDS/% OSAT) vs. % HDS for the experiments where % HDS is above 60. The parameters of the fitted lines are shown in Table 7, for a two-parameter fit of slope and intercept and for a linear fit with intercept forced to 1. In FIG. 4 the lines with intercept 1 is shown to benefit the comparison of lines.

[0108] The low conversion experiments (two experiments of Example 1) were omitted as they deviated from the linear trend, with a selectivity slope far below the other experiments of Example 1.

[0109] Example 3 indicate that keeping the absolute pressure, while reducing partial pressure has an effect upon selectivity similar to changing severity by changing temperature. A comparison of Example 3 and 4 indicate that for conditions with the same partial pressure of hydrogen (42% hydrogen at 20 barg vs. 100% hydrogen at 8.3 barg), selectivity slope is higher when the absolute pressure is lower.

[0110] Table 7 shows that for Examples 4 according to the present invention the slope is close to 1, and much higher than for Examples 1, 2 and 3. This documents that operation at high GOR and low pressure provides an optimal parameter space in which the desired selectivity for % HDS over % OSAT is possible, and furthermore that this optimal parameter space is conveniently identified by evaluating the slope of selectivity assuming an asymptotic selectivity of 1 at 100% HDS. The assumption of an asymptotic selectivity also has the convenience that a measure of the quality of conditions may be estimated from a single experiment and calculated as (% HDS−% OSAT)/(% OSAT*(100−% HDS)). From Tables 3 to 6 it is seen that the selectivity slope varies little with severity within similar experiments. The high intercept value for Example 3, is considered to an artefact due to statistical uncertainty, and as shown in Table 5 the selectivity slope values for the two experiments are consistent, confirming the appropriateness of using the selectivity slope parameter. It is seen that only experiments with low absolute pressure and elevated GOR have values above 0.7.

TABLE-US-00001 TABLE 1 Feedstock Property Method of Analysis Sulfur ASTM D 4294 250 ppmw SG 60/60° F. ASTM D 4052 0.7605 Olefin ASTM D 6839 35 w % RON ASTM D 2699 89.8   Boiling point ASTM D 7213 SimDist IBP 37° C.  5% 62° C. 10% 71° C. 50% 117° C. 95% 173° C. FBP 201° C.

TABLE-US-00002 TABLE 2 Feedstock Property Method of Analysis Sulfur ASTM D 4294 249 ppmw SG 60/60° F. ASTM D 4052 0.7517 Olefin ASTM D 6839 35 w % RON ASTM D 2699 90.7   Boiling point ASTM D 6729 DHA IBP −3.4° C. 10 wt % 49° C. 20 wt % 69° C. 50 wt % 115° C. 90 wt % 166° C. FBP 189° C.

TABLE-US-00003 TABLE 3 Temperature Pressure % Olefin Selectivity [° C.] (barg) GOR % H2 % HDS Saturation slope 200 20.0 502 100 41 4 0.14 210 20.0 502 100 61 7 0.20 230 20.0 502 100 88 18 0.32 240 20.0 502 100 92 24 0.37 250 20.0 502 100 95 34 0.41 260 20.0 502 100 97 47 0.36 280 20.0 502 100 99 75 0.38

TABLE-US-00004 TABLE 4 Temperature Pressure % Olefin Selectivity [° C.] (barg) GOR % H2 % HDS Saturation slope 220 20.0 1200 100 75 5 0.52 235 20.0 1204 100 90 12 0.62 235 20.0 1200 100 92 16 0.58 265 20.0 1200 100 98 39 0.61

TABLE-US-00005 TABLE 5 Temperature Pressure % Olefin Selectivity [° C.] (barg) GOR % H2 % HDS Saturation slope 235 20.0 1200 42 83 7 0.60 235 20.0 1200 63 88 10 0.67

TABLE-US-00006 TABLE 6 Temperature Pressure % Olefin Selectivity [° C.] (barg) GOR % H2 % HDS Saturation slope 220 8.3 1200 100 69 2 1.00 235 8.3 1200 100 86 6 0.98 245 8.3 1200 100 90 8 1.04 265 8.3 1203 100 95 16 1.00

TABLE-US-00007 TABLE 7 Slope Intercept Slope w. intercepts = 1 Example 1 0.320 1.2 0.345 Example 2 0.497 1.7 0.534 Example 3 0.417 4.1 0.622 Example 4 0.991 1.1 0.997