GB2105742A - Hydrocarbon sweetening process - Google Patents

Abstract

A sour hydrocarbon sweetening process for converting mercaptans in the sour hydrocarbon to disulfides comprises contacting the sour hydrocarbon in the liquid phase with a particulate catalyst containing copper metal, copper oxide and/or copper sulfide supported on a porous refractory inorganic carrier, such as alumina, in the presence of a gas containing sufficient molecular oxygen to react with the mercaptans in the hydrocarbon and convert them to disulfides.

Description

SPECIFICATION Hydrocarbon sweetening process This invention relates to hydrocarbon refining. More particularly, it concerns a process for sweetening hydrocarbon feedstocks using a certain copper-containing sweetening catalyst.

Many hydrocarbon feedstocks contain minor amounts of mercaptans that impart an objectionable odor and corrosiveness to the feedstock. Such feedstocks are commonly called "sour" and are usually treated to convert the mercaptans to nonodiferous, non-corrosive disulfides. Under proper conditions the overall chemical reaction involved in the conversion is 2RSH+1/2 O2eRSSR+H2O wherein R is a hydrocarbon radical, typically an alkyl radical. Such treatment is commonly called "sweetening" and a sweetened hydrocarbon feedstock will normally contain less than about three wppm mercaptan sulfur. The sweetening reaction is normally catalyzed by a sweetening catalyst and, as indicated, requires molecular oxygen to proceed.

Copper chloride and copper sulfate-sodium chloride complexes are among the more widely used sweetening catalysts. These catalysts are effective but they have several shortcomings. Firstly, they are generally not suitable for sweetening feedstocks that contain significant amounts of unsaturated (cracked) hydrocarbons because they tend to form gums with such feedstocks. They are also usually limited to use with feedstocks with neutralization numbers above 0.005 mg KOH/g due to the formation of copper naphthenates that cause thermal instability and increase the likelihood of gum formation. Secondly, these catalysts are highly corrosive and must be contained in lined reactors. In addition to being expensive, such reactors usually have a restricted operating temperature range.

Lastly, when spent, these catalysts contain water soluble copper compounds which make them difficult and expensive to dispose of in areas that do not have access to a Class A chemical dump.

U.S. Pat. No. 3907666 describes a sweetening catalyst composed of a Cu/Fe/O spinel optionally supported on a refractory metal oxide. The alleged advantage of this catalyst over copper chloride catalyst is increased throughput life.

U.S. Pat. No. 2361651 describes a vapor phase naphtha sweetening process in which the sulfur compounds in the naphtha are oxidized to sulfur dioxide at elevated temperatures. The patent indicates that this reaction is catalyzed with copper oxide supported on clay and that the sweetened naphtha yield could be increased by including a Group II metal oxide, hydroxide or carbonate in the catalyst.

U.S. Pat. No. 3454488 describes a sweetening process using a catalyst made by ionically binding a copper salt onto an ion exchange material having a high base exchange capacity such as a zeolite or a sulfonate resin and converting the bound salt to the elemental metal, sulfide, or oxide.

A principal object of this invention is to provide an alternative catalyst to the copper chloride and copper sulfate/sodium chloride catalysts for liquid phase sweetening of hydrocarbons at mild temperatures that can be used in existing equipment, lessens operating expenses, and does not require special disposal facilities.

In accordance with the invention there is provided a process for sweetening a sour hydrocarbon comprising contacting the hydrocarbon in the liquid phase under sweetening conditions and in the presence of a gas containing molecular oxygen with a catalyst comprising at least one member of the group consisting of copper metal, copper oxide, and copper sulfide, said member being supported on a refractory porous inorganic carrier, whereby the mercaptans in the sour hydrocarbon are converted to disulfides.

The sour hydrocarbon feedstocks that may be sweetened using the invention process are typically of petroleum, oil shale, coal, or tar sand origin. These feedstocks will usually have a boiling range of about 1 00C to about 3500C at 760 mm Hg, more usually 300C to 3000C at 760 mum Hg.

Petroleum fractions falling in this range include gasoline, light and heavy naphthas, gasoline, kerosene, jet fuel, diesel fuel and light fuel oils. These fractions may be straight-run or cracked. These sour feedstocks normally contain between about 10 and 500 wppm, more usually 50 to 300 wppm, mercaptan sulfur.

The catalyst that is used in the invention process is currently used as a sorbent or scavenger to remove mercaptans and other sulfur-containing compounds from naphtha, petroleum distillates or other hydrocarbons. Its use as a sulfur scavenger is taught in U.S. Pats. Nos. 4163708 and 4259213.

The catalyst may be used fresh, after regeneration as a sulfur sorbent or after being spent as a sulfur sorbent. In other words the catalyst that is used in the current sweetening process is the fresh, regenerated or spent sulfur sorbent of U.S. Pats. Nos. 4163708 and 4259213. The copper component of the catalyst is copper metal and/or copper oxide in the case of fresh or regenerated material and copper sulfide (primarily cupric sulfide) in the case of spent material. Accordingly, the copper component of the catalyst used in this invention may be copper metal, copper oxide, copper sulfide or mixtures thereof. The copper component will constitute about 5% to about 50%, preferably 10% to 40%, by weight of the catalyst calculated as copper metal.The copper component is supported and dispersed in finely divided form on a natural or synthetic refractory oxide of a Group II, III, or IV metal or mixtures thereof. There is generally no substantial ionic binding between the copper component and the refractory oxide support. Examples of such oxides are alumina, silica, silica-alumina, boria, attapulgite clay, kieselguhr, and pumice. The supports that are used in the catalyst do not have high base exchange capacities although some may have limited ion exchange capacity. The support is not activated. Preferably, the porous support constitutes the remainder of the catalyst. The catalyst is in a particulate, e.g. pellet or extrudate, form and will usually have a specific surface area (measured by the B.E.T. method) in the range of about 30 to 300 m2/g, preferably 50 to 200 m2/g.The average size of the catalyst pellets will usually be in the range of about 0.08 to about 0.3 cm in diameter and about 0.3 to about one cm in length.

The catalyst is made by either (a) impregnating the carrier with an aqueous solution of a watersoluble copper salt, the anionic portion of which may be readily removed or converted to the oxide form upon drying and calcining or (b) comulling an appropriate copper compound with peptized carrier, extruding the comulled mixture in particle form, and calcining the extruded particles. These techniques for making the catalyst are described in detail in U.S. Pats. Nos. 4163708 and 4259213.

The oxidative sweetening process may be carried out in either upflow or downflow fixed bed reactors by passing the sour feedstock through one or more beds of the catalyst. A gas containing molecular free oxygen, such as air or other mixtures of oxygen with nitrogen or other inert gases, is normally mixed with the feedstock in amounts that provide at least a stoichiometric amount of oxygen relative to the mercaptan content of the sour feedstock. Less than stoichiometric amounts of oxygen will result in conversion of a less than desirable portion of the mercaptans to disulfides. Preferably the mol ratio of oxygen to mercaptan sulfur is in the range of about 1:4 to about 10:1. In other words 1 to 40 times the stoichiometric amount of oxygen will normally be used.Even greater excesses of oxygen may be used but are not necessary and may cause an undesirable amount of oxidation of the hydrocarbon stock itself. The amount of oxygen in the gas component of the reaction mix may vary greatly (e.g. from a few percent to 100% by volume). However, for convenience, air is preferred.

Mild reaction temperatures are used that typically range between about 35"C to 2000C, preferably 500C to 150"C. The pressure should be such as to maintain the hydrocarbon feed in a liquid state at a given reaction temperature. Normally pressures in the range of atmospheric to 300 psig, preferably 25 to 100 psig, will be used. The space velocity is generally between about 1 to 10, preferably 1 to 5. The sweetening process of the invention will typically produce a sweetened hydrocarbon that contains less than about 3 wppm mercaptan sulfur. It is noted that the process does not remove any significant amount of sulfur from the hydrocarbon but merely converts mercaptans to disulfides.

The performance of the catalyst may be monitored by determining the amount of mercaptans in the process effluent using conventional analytical methods. These include the DOC test, ASTM D484, or more complex analytical procedures which determine complete breakdown of sulfur types as shown below in Tables 1 and 2. When the amount of mercaptan sulfur in the effluent exceeds about 3 wppm the temperature can be raised to regain activity. However, eventually the catalyst may become so inactive that it must be replaced or regenerated.

Carbon is believed to be the primary deactivation agent that affects the performance of the catalyst. Accordingly, when the catalyst is spent, it may be regenerated by removing residual carbon with an oxidizing medium, e.g. air, at elevated temperatures.

The following Examples further illustrate the invention process. These examples are not intended to limit the invention in any manner.

Example 1 A sour Arabian middle distillate (boiling range 300--5000F) having the total sulfur content of 2600 wppm (0.26%) and a mercaptan sulfur content of 134 wppm was sweetened using a catalyst made by the comulling process of U.S. Pat. No. 4259213. The catalyst composition and properties were as follows: CuO 32.5% by weight calculated 26% as Cu metal Alumina 67.5% by weight Pore Volume 0.50 cc/gm Average Pore Size 100 AO Average Particle Size 1/16"x1/4" length pellets For test purposes the catalyst was crushed to 1 6-32 mesh and twenty cubic centimeters of this catalyst was installed into a fixed bed downflow nanoreactor. The distillate, mixed with air at the air flow rates indicated in Table 1, was run through the catalyst-filled nanoreactorfor a total of 1044 hr.

The LHSV was 3.0, pressures ranged from 60-85 psig, and temperatures ranged from 2250F to 2600 F. The sweetened product was analyzed periodically for sulfur and mercaptan content. Table 1 summarizes the process conditions and sour feed and sweetened product analyses.

Table 1 Run, Hours Feed 141 285 727 852 948 1044 Run Conditions Feed Rate, cc/hr 60 60 60 60 60 60 Temperature, OF 250 250 250 230 260 225 Pressure, psig 50 50 85 85 85 88 Air Flow Rate, SCF/hr 0.5 0.2 0.2 0.02 0.02 0.02 Catalyst Volume, cc 20 20 20 20 20 20 Product Inspection Doctor Test (ASTM D484-1 7) Sour Sweet Sweet Sweet Sweet Sweet Sour Mercaptans, ppm 134 0.16 0.2 < 0.1 < 0.1 0.3 14 H2S, ppm Free Sulfur, ppm 0.63 1.04 1 Thiophanes, ppm 1825 1825 2275 Sulfides, ppm Disulfides, ppm 4.5 1 75 200 Total Sulfur, ppm 2600 2700 2600 2600 2500 2500 2600 Example 2 A second run was made on the same mid-distillate feed of Example 1. The same catalyst and apparatus used in Example 1 were also used in this second run. Table 2 reports the process conditions and results of this second run.

Table 2 Run, Hours Feed 144 240 336 888 1320 1680 1824 2060 2401 Run Conditions Feed Rate, cc/hr 60 60 60 60 60 60 60 60 60 Temperature, F 175 200 250 250 250 250 250 305 330 Pressure, psig 85 85 85 85 85 85 85 85 85 Air Flow Rate, SCF/hr 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.01 0.01 Catalyst Volume, cc 20 20 20 20 20 20 20 20 20 Product Inspection Doctor Test (ASTM D484)17) Sour Sweet Sweet Sweet Sweet Sweet Sweet Sour Sweet Sour Mercaptans, ppm 134 < 1 < 1 < 1 - - < 1 H2S, ppm - < 1 Free Sulfur, ppm 0.63 < 1 Thiophanes, ppm 1825 2480 Sulfides, ppm - 100 Disulfides, ppm 4.5 120 Total Sulfur, ppm 2600 2600 2600 2600 2600 2600 2600 2600 2600 Compared to sweetening of comparable feedstocks under comparable conditions with a copper sulfate/sodium chloride catalyst sold by Perco, the results of Example 2 indicate the catalyst life, on the basis of barrels of throughput per pound of catalyst, of the catalyst of the invention process is at least about two-fold greater than that of the Perco catalyst.

Example 3 A sour Arabian light straight-run (LSR) naphtha (boiling range 95-280 F, 500-600 wppm total sulfur and about 50-300 wppm mercaptan sulfur) was sweetened using the catalyst and apparatus described in Example 1. The pressure was 60 psig and the LHSV was 3. Other process conditions are reported in Table 3 below. Samples of the feed and product were taken periodically and analyzed for mercaptan content. Table 3 reports the results of these analyses. At the end of this run, the catalyst was not spent and was still performing satisfactorily.

Table 3 Afr rate Mol ratio Mercaptan Mercaptan Run hrs. Temp ( F) (SCCM) [O2]/[RSH] in feed wppm in product wppm 0-1170 200#150 5#1 14-1.8 140-240 0.2-0.5 1170-1700 150 0.5#0.25 .75 290#122 1-6 1700-2100 175 0.4 -2.0 80 4-6 2100-2500 190 0.4 1.0 190-130 0.4-0.8 2500-3700 170 0.40.2 2.5-1.2 54-76 0 4 3700-3800 170 0.2 0.4 200 63-100 3700-4400 165 0.5 1.2e2.5 200e80 < 1 4400-4570 150 0.5 2.5 80 0.5 4570-4680 150 0.5 1.0 190 1.2 4680-4727 136 0.5 1.0 180 3.0 Compared to sweetening LSR with Perco catalyst, the results of Example 3, for which the catalyst was not yet spent and may well have had thousands of hours of service left, indicate that the catalyst of this invention has at least a two-fold greater catalyst life.

Example 4 The sour Arabian light straight-run (LSR) naphtha of Example 3 was sweetened using a catalyst of the same original composition as Example 1 but which had been used previously to remove mercaptans from hydrocarbon feedstocks in a commercial sulfur-sorbing operation. This previously used sulfur sorbent contained 3.9% by weight sulfur and 6.0% by weight residual carbon. The same apparatus and pressure were used as were used in Example 3. Other operating conditions as well as the feed and product analyses are reported in Table 4 below.

Table 4 Mercaptan/H2S Mercaptan Air rate Mol ratio in feed, in product, Run hrs. Temp (0F) LHSV (SCCM) [02]ffRSH] wppm wppm 0-75 143 3 0.51 0.80 240/- < 1 75-184 150 3 0.51 0.85 150/80 < 1 184-290 150 3 0.51 0.65 300/10 < 1 290-350 132 3 0.51 0.65 290/8 < 1 350-665 138 3 0.51 0.85 140/85 < 1 665-710 123 3 0.51 0.65 310/- 8-10 710-860 133 3 0.51 0.60 350/40 3-4 860-980 132 6 1.0 0.72 270/10 50+25 980-1220 148 4.5 .76 0.95 130/80 10-30 1220-1750 160 3 .52 0.72 275/- 1-3 1750-1840 160 3 .52 0.97 130/80 25-14 1840-1960 175 3 .52 0.92 140/80 < 1 The data reported in Table 4 indicate that it is feasible to use a material that was often heretofore discarded as a catalyst to effectively sweeten sour hydrocarbon feedstocks.

The above examples evidence that the present invention provides longer catalyst life than competitive sweetening processes using the Perco catalyst. Also, as indicated previously there are less disposal problems with the present process and the catalyst used in it is not corrosive.

Claims (11)

Claims

1. A process for sweetening a sour hydrocarbon comprising contacting the hydrocarbon in the liquid phase under sweetening conditions and in the presence of a gas containing molecular oxygen with a particulate catalyst comprising at least one copper component selected from copper metal, copper oxide and copper sulfide, said copper component being supported on a refractory porous inorganic carrier, whereby mercaptans present in the sour hydrocarbon are converted to disulfides.

2. A process according to Claim 1, wherein the sour hydrocarbon has a boiling range lying within the range from 1 00C to 3500C at 760 mm Hg and contains from 10 to 500 wppm mercaptan sulfur and the sweetened hydrocarbon contains less than 3 wppm mercaptan sulfur.

3. A process according to Claim 1 or 2, wherein said copper component constitutes from 5% to 50% by weight of the catalyst.

4. A process according to Claim 1, 2 or 3, wherein the catalyst has a specific surface area in the range from 30 to 300 m2/g.

5. A process according to Claim 1, 2, 3 or 4, wherein the amount of molecular oxygen is at least stoichiometric relative to the mercaptan sulfur content of the sour hydrocarbon.

6. A process according to any preceding claim, wherein the mol ratio of oxygen to mercaptan sulfur is in the range from 1:4 to 10:1.

7. A process according to any preceding claim, wherein the gas containing molecular oxygen is air.

8. A process according to any preceding claim, wherein the inorganic carrier is alumina.

9. A process according to any one of Claims 1 to 7, wherein the carrier is attapulgite clay.

10. A process according to any preceding claim, wherein there is no substantial ionic binding between the copper component and the inorganic carrier.

11. A process in accordance with Claim 1 for sweetening a sour hydrocarbon, substantially as described in any one of the foregoing Examples.