Patent Application
20080067109
The instant invention is a method for removing nitrogen from diesel boiling range feedstreams containing both nitrogen and sulfur contaminants. The present method involves contacting, preferably by a non-dispersive method, a diesel boiling range feedstream containing both nitrogen and sulfur contaminants with a sulfuric acid solution thus producing a diesel boiling range product. The contacting of the diesel boiling range feedstream with the sulfuric acid solution reduces the nitrogen content of the diesel boiling range product by at least 85 wt. %. The resulting diesel boiling range product is then hydrotreated. It should be noted that hydrotreating and hydrodesulfurization are used interchangeably herein, and the phrase “diesel boiling range feedstream” is meant to refer to a diesel boiling range feedstream containing both nitrogen and sulfur contaminants and possessing a Total Acid Number (“TAN”). TAN is a measurement of the acidic content of an oil and is determined experimentally by titration of the oil with an appropriate base, as described for example in ASTM method number D664.
Feedstreams suitable for treatment with the present method boil within the diesel range. The diesel boiling range includes streams boiling in the range of about 300° F. to about 775° F., preferably about 350° F. to about 750° F., more preferably about 400° F. to about 700° F., most preferably about 450° F. to about 650° F. These include diesel boiling range feedstreams that are not hydrotreated, are a blend of non-hydrotreated diesel boiling range feedstreams, previously hydrotreated diesel boiling range feedstreams, blends of hydrotreated diesel boiling range feedstreams, and blends of non-hydrotreated and hydrotreated diesel boiling range feedstreams.
The diesel boiling range feedstreams suitable for treatment with the present method also contain nitrogen. Typically, the nitrogen content of such streams is about 50 to about 1000 wppm nitrogen, preferably about 75 to about 800 wppm nitrogen, and more preferably about 100 to about 700 wppm nitrogen. The nitrogen appears as both basic and non-basic nitrogen species. Non-limiting examples of basic nitrogen species may include quinolines and substituted quinolines, and non-limiting examples of non-basic nitrogen species may include carbazoles and substituted carbazoles.
In practicing the instant invention, the above-defined feedstream is intimately contacted with a sulfuric acid solution. The sulfuric acid solution used herein contains at least about 75 wt. % sulfuric acid, based on the sulfuric acid solution, preferably greater than about 75 wt. %, more preferably about 75 wt. % to about 88 wt. %. The sulfuric acid solution may be obtained through any means known. It is preferred that the sulfuric acid solution be the spent acid from an alkylation process unit having a sulfuric acid concentration within the above-defined ranges. A typical alkylation process involves combining an olefinic hydrocarbon feedstream containing C4 olefins with isobutane to produce a hydrocarbonaceous mixture. This hydrocarbonaceous mixture is subsequently contacted with sulfuric acid. The sulfuric acid used for contacting the hydrocarbonaceous mixture is typically reagent grade sulfuric acid having an acid concentration of at least about 95 wt. %. Preferably the sulfuric acid has a sulfuric acid concentration of greater than about 97 wt. %. The hydrocarbonaceous mixture is contacted with the sulfuric acid under conditions effective at producing at least an alkylate and sulfuric acid solution. The sulfuric acid solution so produced comprises at least about 75 wt. % sulfuric acid, based on the sulfuric acid solution, preferably greater than about 75 wt.% more preferably about 75 wt. % to about 92 wt. %, about 0.5 to about 5 wt. % water, with the remaining balance being acid soluble hydrocarbons. It is more preferred that the effective conditions be selected such that the sulfuric acid solution so produced comprises between about 82 and 92 wt. % sulfuric acid, about 1 to about 4 vol. % water, with the remaining balance being acid soluble hydrocarbons. However, it is most preferred that the effective conditions be selected such that the sulfuric acid solution so produced comprises between about 85 and 92 wt. % sulfuric acid, about 1.5 to about 4 vol. % water, with the remaining balance being acid soluble hydrocarbons.
It should be noted that it is within the scope of the present invention to dilute the sulfuric acid obtained from the alkylation unit, or otherwise, with a suitable diluent, preferably water, in order to provide a sulfuric acid solution having the above-described concentration of sulfuric acid, i.e. at least about 75 wt. % sulfuric acid, based on the sulfuric acid solution, preferably greater than about 75 wt. %, more preferably about 75 wt. % to about 88 wt. %. In order to determine the sulfuric acid concentration once the diluent has been added to the sulfuric acid solution, the sulfuric acid content and water content are measured by standard analytical techniques. The equivalent acid strength can then be calculated with the following formula: equivalent wt % sulfuric acid=wt % sulfuric acid/(wt % sulfuric acid+wt % water). In this formula, the acid soluble hydrocarbon content of the spent alkylation acid is treated as an inert diluent with respect to the sulfuric acid and water content.
The diesel boiling range feedstream is contacted with the sulfuric acid solution at an acid volumetric treat rate of greater than about 0.5 vol. %, based on the diesel boiling range feedstream, preferably about 0.5 to about 20 vol. %, and more preferably 0.5 to about 5 vol. %. The contacting can be achieved by any suitable method including both dispersive and non-dispersive methods. Non-limiting examples of suitable dispersive methods include mixing valves, mixing tanks or vessels, and other similar devices. Non-limiting examples of non-dispersive methods include packed beds of inert particles and fiber film contactors such as those sold by Merichem Company and described in U.S. Pat. No. 3,758,404, which is hereby incorporated by reference, which involve contacting along a bundle of metallic fibers rather than a packed bed of inert particles. Preferred contacting methods are non-dispersive, and more preferred contacting methods are those that are classified as dispersive.
The contacting of the diesel boiling range feedstream with the sulfuric acid solution occurs under effective conditions. By effective conditions, it is to be considered those conditions that allow the present method to achieve a reduction of nitrogen of greater than about 80 wt. %, preferably greater than about 85 wt. % more preferably greater than about 92 wt. %. Effective conditions are also to be considered those conditions that minimize yield losses during the sulfuric acid solution treatment to about to about 0.5 to about 6 wt. %, preferably about 0.5 to about 4 wt. %, more preferably about 0.5 to about 3 wt. %.
The contacting of the diesel boiling range feedstream with the sulfuric acid solution produces at least a diesel boiling range product that is sent to suitable aromatics and sulfur removal processes. Thus, the used sulfuric acid solution, which now contains the removed nitrogen species, must be separated from the diesel boiling range product. The used sulfuric acid solution and the diesel boiling range product can be separated by any means known to be effective at separating an acid from a hydrocarbon stream. Non-limiting examples of suitable separation methods include gravity settling, electric field induced settling, centrifugation, microwave induced settling and settling enhanced with coalescing surfaces. However, it is preferred that the diesel boiling range product and the used sulfuric acid solution be separated, or allowed to separate, into layers in a separation device such as a settling tank or drum, coalescer, electrostatic precipitator, or other similar device. It is more preferred that the above-described fiber-film contactors be used for separating the used sulfuric acid solution and the diesel boiling range product produced by the present process. The diesel boiling range product can then be withdrawn from the separation device and passed to a suitable hydrotreating process.
The diesel boiling range product thus obtained by the present method will contain substantially less nitrogen, both basic and non-basic, than the initial diesel boiling range feedstream. By substantially less, it is meant that the nitrogen content of the diesel boiling range feedstream is reduced by at least about 80%, preferably at least about 85%, more preferably at least about 90%. Thus, it can likewise be said that the diesel boiling range product will have a nitrogen level about 80%, preferably at least about 85%, more preferably at least about 90% lower than that of the diesel boiling range feedstream. This will typically result in a diesel boiling range product having a nitrogen level of less than about 200 wppm, preferably less than about 100 wppm, more preferably less than about 50 wppm, and most preferably less than about 20 wppm. The contacting of the diesel boiling range feedstream with the sulfuric acid solution also typically results in a diesel boiling range product having a TAN that is higher than the TAN of the diesel boiling range feedstream.
The diesel boiling range product will also typically have a sulfur concentration lower than that of the nitrogen-containing diesel boiling range feedstream. Thus, the contacting of the diesel boiling range feedstream with the sulfuric acid solution also reduces the sulfur content of the diesel boiling range product. The diesel boiling range product will therefore have a sulfur content lower than the diesel boiling range feedstream. However, it is desirable to minimize the reduction of sulfur to minimize yield losses. Typically the diesel boiling range product will have a sulfur content about 0.1 to about 25% lower than the diesel boiling range feedstream, preferably about 0.1 to about 15% lower, more preferably about 0.1 to about 10% lower, and most preferably about 0.1 to about 5% lower.
The diesel boiling range product is then hydrotreated to reduce sulfur levels. Any suitable hydrotreating catalyst can be used to hydrotreat the diesel boiling range product. Non-limiting examples of suitable hydrotreating catalysts are those that are comprised of at least one Group VIII metal oxide, preferably an oxide of a metal selected from Fe, Co and Ni, more preferably Co and/or Ni, and most preferably Co; and at least one Group VI metal oxide, preferably an oxide of a metal selected from Mo and W, more preferably Mo, on a high surface area support material, preferably alumina. These catalysts can be arranged in any suitable manner such as, for example, fixed beds. It is also contemplated that more than one hydrotreating catalyst can be used, and more than one bed of catalysts can be used, e.g. a stacked bed configuration. The diesel boiling range product is contacted with the hydrotreating catalysts under conditions effective at removing at least a portion of the sulfur contained in said diesel boiling range product. Preferably, that amount of sulfur necessary to meet current environmental regulatory standards is removed during the hydrotreating. As previously mentioned, the contacting of the diesel boiling range feedstream with the sulfuric acid solution typically results in a diesel boiling range product having a TAN that is greater than the TAN of the diesel boiling range feedstream. Thus, one embodiment of the instant invention involves contacting the diesel boiling range product, prior to hydrotreating, with an effective amount of a material selected from caustic and water, preferably water. By an effective amount of material, it is meant that amount of material that reduces the TAN of the diesel boiling range product. The diesel boiling range product is contacted with the caustic or water under effective conditions. By effective conditions, it is meant those conditions, that when selected, allow for the reduction of the TAN of the diesel boiling range product. Preferably the effective amount of material and the effective conditions are selected such that the TAN of the diesel boiling range product is equal that of the diesel boiling range feedstream. More preferably the effective amount of material and the effective conditions are selected such that the TAN of the diesel boiling range product is lower than that of the diesel boiling range feedstream.
The above description is directed to preferred embodiments of the present invention. Those skilled in the art will recognize that other embodiments that are equally effective could be devised for carrying out the spirit of this invention.
The following examples will illustrate the improved effectiveness of the present invention, but is not meant to limit the present invention in any fashion.
Two 10 ml samples of a virgin diesel, referred to herein as feed #1, were pipetted into two glass vials. One sample was combined with 0.1 ml (1 vol. % treat rate) of a reagent grade sulfuric acid solution having a sulfuric acid concentration of 96.1 wt. %, and the other sample was mixed with the same sulfuric acid solution but with 0.2 ml (2 vol. % treat rate). The mixtures were shaken by hand for 60 seconds and then allowed to separate at room temperature. The two phases, i.e. the diesel boiling range product and the sulfuric acid solution, separated and the diesel product layers were removed. The diesel products were weighed and analyzed by ANTEK for nitrogen and sulfur contents. The results of this experiment are contained in Table 1 below.
A second diesel boiling range feedstream, referred to herein as feed #2, was also treated according to the method outlined in Example 1 above. The second diesel feedstream, however, contained about one-third cracked stock, i.e light cat cycle oil and coker gas oil. A 2 liter sample of feed #2 was also treated in glass separatory funnels with the sulfuric acid solution described above in Example 1 at a 5 vol. % treat rate. The results of these experiments are contained in Table 1 below.
As can be seen in Table 1, both feeds responded well to treatment with the acidic solution, with nearly quantitative nitrogen removal. Low feed losses were also observed. The feed recovered was calculated by dividing the volume of diesel product recovered by the volume of the diesel feedstream and then multiplying by 100. It was also noted that the acidic solution by product from feed #2 became more fluid with increased acidic solution treat rates.
The experiments contained in Examples 1 and 2 above were repeated with spent sulfuric acid solution obtained from an alkylation unit. The composition of the spent alkylation acid was 90 wt % sulfuric acid, 4 wt % water and 6 wt % acid soluble hydrocarbon (by difference). The equivalent sulfuric acid concentration is 96 wt. %. The results of these experiments are contained in Table 2 below.
As can be seen from Table 2, similar results are obtained by using the spent alkylation unit acid as are obtained using reagent grade sulfuric acid.
Twenty milliliters of a virgin diesel was equilibrated to 120° F. in a water bath. The 20 ml sample was combined in a glass centrifuge tube with 0.2 ml (1 vol. % treat rate) of reagent grade sulfuric acid having an acid concentration of 96.1 wt. %. This mixture was shaken for 60 seconds and then subjected to ten minutes of cetrifugation at 1500 rpm. The diesel and the sulfuric acid solution separated rapidly, and the diesel layer was removed and analyzed by ANTEK for nitrogen and sulfur content.
This procedure was repeated at several acid concentrations. The acid concentration was reduced by adding distilled water to the reagent grade sulfuric acid.
The results of these experiments are contained in
Since one of the objects of the instant invention is to remove as much of the nitrogen as possible from the feed while minimizing yield losses,
Twenty milliliters of a diesel boiling range feedstream containing about one third cracked stock, i.e., light cat cycle oil and coker gas oil, was equilibrated to 120° F. in a water bath. The 20 ml sample was combined in a glass centrifuge tube with 0.8 ml (4 vol. % treat rate) of reagent grade sulfuric acid having an acid concentration of 96.1 wt. %. This mixture was shaken for 60 seconds and then subjected to ten minutes of cetrifugation at 1500 rpm. The diesel and the sulfuric acid solution separated rapidly, and the diesel layer was removed and analyzed by ANTEK for nitrogen and sulfur content.
This procedure was repeated at several acid concentrations. The acid concentration was reduced by adding distilled water to the reagent grade sulfuric acid to dilute the acid concentration.
100 milliliters of virgin diesel having a total acid number (“TAN”) of 0.26 mgKOH/g, a nitrogen concentration of 105 wppm, and a sulfur concentration 1.36 wt. % of was treated with sulfuric acid solution having a sulfuric acid concentration of 96 wt. %. The virgin diesel was treated by adding 1 ml of the sulfuric acid solution to the virgin diesel at room temperature, and shaking this mixture by hand in a separatory funnel for one minute. The mixture was then allowed to settle for 10 minutes and the spent acid solution and diesel boiling range product were decanted to recover the respective products.
The diesel boiling range product so recovered was separated into equal portions that were placed into 50 ml centrifuge tubes. The tubes were placed in a centrifuge operated at 1500 rpm for ten minutes. Acid sludge was observed at the bottom of the centrifuge tubes. One of the four samples was set aside and marked “acid treated, centrifuged only”, referred to herein as “Sample #1” for comparison with the other three samples.
25 ml of diesel boiling range product from each respective centrifuge tube was pipetted into separate 50 ml centrifuge tubes for further treatment. To the first 25 ml sample, referred to herein as “Sample #2”, 5 ml of distilled water was added. To the second and third samples, referred to herein as “Sample #3” and “Sample 4”, respectively, was added 2.5 ml of a 5 wt. % NaOH solution. Samples 2, 3, and 4 were each shaken for 60 seconds, and then centrifuged for ten minutes at 1500 rpm. Sample #4 was then further treated by adding 5 ml of distilled water with subsequent shaking and centrifugation as defined above.
All of the Samples were submitted Galbraith Analytical Laboratories for TAN analysis. Sample 2 was observed to have a TAN of 0.37 mg KOH/g, illustrating that the sulfuric acid treatment increases the TAN of the diesel boiling range products. Sample #2 had a TAN of 0.25 mg KOH/g, illustrating that simple water washing was sufficient to lower the TAN to at least the level in the feedstream.
Sample #3 had a TAN below detection limits, which may be an erroneous reading due to caustic carryover. Sample #4 had a TAN of 0.03 mg KOH/g, essentially zero. It should be noted that water washing after caustic treating should minimize or eliminate caustic carryover, and that the nitrogen concentration of the diesel boiling range products was not reduced by the caustic and water washing.
Thus, Example #6 illustrates that simple water washing after sulfuric acid treatment is effective at lowering the TAN of the diesel boiling range product to at least that of the diesel boiling range feedstream, overcoming corrosion problems associated with typical acid treating processes.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US04/40095 | 12/1/2004 | WO | 00 | 10/24/2007 |
| Number | Date | Country | |
|---|---|---|---|
| 60527257 | Dec 2003 | US |
