METHOD FOR DENITROGENATING CRUDE FRACTIONS

Abstract: The present invention relates to a process for denitrogenating a distillate stream by contacting an organic nitrogen-containing petroleum distillate feed in the presence of an aqueous base selected from Group IA and IIA hydroxides and ammonium hydroxide and mixtures thereof, a phase transfer agent at a temperature and pressure effective to produce a treated petroleum feed having a decreased organic nitrogen content.

Description: METHOD FOR DENITROGENATING CRUDE FRACTIONS FIELD OF THE INVENTION The present invention relates to a method for denitrogenating certain refinery streams. BACKGROUND OF THE INVENTION Refinery streams that contain nitrogen compounds are typically problematic in refineries because the nitrogen components contained therein can have a negative impact on certain refinery operations. Currently there exists a need to significantly decrease the sulfur and aromatics content of crude fractions such as diesel, vacuum gas oil, light catalytic cycle oil and gasoline. However, the catalysts used to accomplish these goals are adversely affected by the presence of nitrogen compounds in the feed. Thus it would be desirable to develop a process that would permit the pre-treatment of nitrogen containing feeds in order to decrease their nitrogen content. Applicants' invention addresses these needs. SUMMARY OF THE INVENTION The present invention provides for a method for decreasing the nitrogen content of refinery streams by contacting a petroleum distillate stream in the presence of an effective amount of water, a base selected from Group IA and IIA hydroxides and ammonium hydroxide and a phase transfer agent at an effective temperature (i.e., at which the water is liquid to 180°C) for a time sufficient to produce a treated petroleum feed having a decreased nitrogen content. Optionally, the process can be carried out in the presence of an oxygen containing gas, although this is not required. The present invention may suitably comprise, consist or consist essentially of the described elements and may be practiced in the absence of an element not disclosed. DETAILED DESCRIPTION OF THE INVENTION The present invention provides for a method for decreasing the nitrogen content of organic-nitrogen-containing hydrocarbonaceous feedstreams by contacting the stream (also referred to herein as a fraction, feedstream or feed) containing the nitrogen to be removed with an effective amount of aqueous base selected from Group IA and IIA hydroxides and ammonium hydroxide, and at least one phase transfer agent at an effective temperature at which the aqueous phase remains liquid, typically up to 180°C to produce a treated petroleum stream having a decreased nitrogen content. The contacting is carried out at a pressure that corresponds to the reaction temperature and is typically from zero to less than 10,000 kPa. Lower pressures are preferred because this can minimize the need for high-pressure treatment process units. The nitrogen containing species that are most desirably removed by the process of the present invention are organo-nitrogen, non-basic heterocyclic, nitrogen containing species, e.g., carbazoles, indoles and pyrroles. Bases preferred are strong bases, e.g., NaOH, KOH, ammonium hydroxide, sodium and potassium carbonates. These may be used as an aqueous solution of sufficient strength, typically at least 20 wt% of the aqueous phase or as a solid in the presence of an effective amount of water to produce an aqueous solution of the foregoing strength. The phase transfer agent is present in a sufficient concentration to result in a treated feed having decreased nitrogen content. The phase transfer agent may be miscible or immiscible with the stream to be treated. Typically, this is influenced by the length of the hydrocarbyl chain in the molecule; and these may be selected by one skilled in the art. While this may vary with the agent selected typically concentrations of 0.05 to 10 wt%, preferably 0.1 to 5 wt% are used. Examples include quaternary ammonium salts, quaternary phosphonium salts, crown ethers, and open-chain polyethers such as polyethylene glycols, and others known to those skilled in the art either supported or unsupported. Process temperatures at which the aqueous phase remains liquid are used typically up to 180°C are suitable; however, temperatures of less than 150°C, less than 120°C can be used depending on the nature of the feed and phase transfer agent used. Examples of streams that may be treated according to the process of the present invention are nitrogen containing carbonaceous and hydrocarbona- ceous processed/distilled streams such as diesel, gasoline, vacuum gas oils (VGO) and light catalytic (cat) cycle oils (LCCO). These are typically 232- 566°C (450°F to 1050°F) fractions. The feed to be treated can have a range of nitrogen content. The average will vary by the feed but is typically about 50 ppm to 5000 ppm. The feed to be treated preferably should be in a liquid or fluid state at process conditions. This may be accomplished by heating the material or by use of a suitable non-interfering solvent as needed. These may be selected by those skilled in the art. Preferably the oil droplets should be of sufficient mean droplet size to enable the nitrogen containing components to achieve intimate contact with the aqueous phase. Oil droplet particles having a mean droplet size of about 1 to 100 microns (diameter) should be typical, and 1 to 20 are preferably; larger droplet sizes of greater than 100 microns are not preferable. Contact can be achieved, e.g., by vigorous mixing for the components of the mixture. Desirably the process should be carried out for a time and at conditions within the ranges disclosed sufficient to achieve a decrease, preferably a maximum decrease, in nitrogen content of the nitrogen containing petroleum stream. Reaction temperatures will vary with the particular stream to be treated due to its viscosity. An increase in temperature may be used to facilitate removal of species. Within the process conditions disclosed a liquid or fluid phase or medium should be maintained. Treatment typically removes the nitrogen containing species from the petroleum fraction into an aqueous base phase or a third phase containing the phase transfer agent. Following treatment, the treated stream has a decreased content of nitrogen. Optionally, a nitrogen recovery or extraction step may be added, as needed to recover the nitrogen containing species removed from the treated distillate stream from the aqueous phase. The nature of any such step(s) depends on the nature of the bed/reactor, solubility or insolubility of the removed nitrogen containing species in the aqueous phase. For separation/extraction purposes at least two phases are present, into at least one of which the nitrogen containing species are removed or extracted. The phase into which extraction occurs can be the second phase, i.e., the phase containing transfer agent and aqueous base or a third phase containing primarily aqueous base, with the second (intermediate) phase containing primarily phase transfer agent. The first phase is the treated (denitrogenated) distillate stream. The nature and amount of the phase transfer agent and may be chosen by one skilled in the art. The nitrogen decreased (i.e., upgraded) product may be used in refining operations using catalysts that are adversely affected by higher levels of nitrogen. A benefit to the present invention is that the process may be operated under mild temperatures and pressures resulting in a minimization of undesirable side reactions and an enhancement of yield also may be achieved as needed. The invention may be demonstrated with reference to the following examples: EXAMPLE 1 One hundred grams of a Baton Rouge Refinery virgin LCCO was combined with 400 ml of 50 wt% sodium hydroxide and 25 grams of 40 wt% tetrabutylammonium hydroxide. This mixture was subjected to homogenization/ dispersion (10,000 rpm) in a one liter glass flask using a Beckman Model 300 homogenizer, fitted with a standard generator with saw teeth. The solution warmed from 25°C to 65°C due to frictional heating of the rotor/stator. Homogenization was stopped after fifteen minutes. The LCCO and the aqueous caustic phase were separated by use of a separatory funnel. Between the top LCCO phase and the bottom caustic phase, a third phase was observed, the volume of which corresponded to the volume of tetra butyl ammonium hydroxide added. This phase was also highly colored (dark green) and was allowed to separate overnight. Elemental analysis by combustion showed the following results N = 0.24 (starting) to N = 0.00 (Atlantic Microlab). EXAMPLE 2 In a second experiment, 5 ml of a 100 ppm carbazole in xylene solution was shaken for thirty seconds at room temperature with 5 ml of 50 wt% sodium hydroxide solution and 1 ml of tetrabutylammonium hydroxide (40 wt% in water). Immediately a slight reddish color was evident in the third phase between the top xylene layer and the bottom aqueous caustic layer (both of which were colorless). A control experiment was conducted which was identical to the previous experiment, except that no tetrabutylammonium hydroxide was added. No third phase formed and no color change was noted. After allowing the phases to separate, the xylene layers were analyzed by gas chromatography. These are the carbazole peak areas relative to the initial 100 ppm carbazole stock solution. Feed NaOH alone 1.00 NaOH and tetrabutyl ammonium hydroxide 0.19 From these results, it is apparent that simply contacting the petroleum stream with strong caustic is insufficient to deprotonate and extract a significant quantity of carbazole. However, with the aid of a phase transfer catalyst such as tetrabutylammonium hydroxide, significant extraction of carbazole can be achieved. EXAMPLE 3 A low sulfur (hydrotreated) diesel oil was treated with three different aqueous solutions in separate experiments. The aqueous solutions differed in their sodium hydroxide concentrations, of 25, 33 and 50 wt%. These were prepared by adding the appropriate quantity of sodium hydroxide solid to 100 grams of distilled water and stirring until completely dissolved. To each of these caustic solutions was added 25 grams of polyethylene glycol ("PEG") 400. Separately, 50 mis of diesel were added to each of these aqueous solutions and homogenized at 6000 rpm for 15 minutes to ensure good contacting. Then the mixtures were transferred to glass separatory funnels and allowed to phase separate. The top layer was isolated and washed with equal volumes of distilled water, 2% HC1 in water and with distilled water again. Five grams of magnesium sulfate was added to treated diesel and stirred. After filtration, samples were submitted for nitrogen determination by gas chromatographic analysis using a nitrogen analyzer (Antek). A control sample was also prepared by subjecting the initial feed only to the washing and drying steps. The following results were obtained: Caustic Concentration ppm Nitrogen Feed 72, 71 (repeat) Wash only 52 25% NaOH 22 33% NaOH 16 50% NaOH 10 EXAMPLE 4 The same procedure as detailed in Example 3 was repeated, except that, after preparing the 50 wt% caustic solution, the PEG 400 was added and then the aqueous solution was stirred and bubbled with nitrogen for thirty minutes to drive air from the solution. Previously nitrogen-sparged low-sulfur diesel was then added and nitrogen-sparged for an additional thirty minutes. After all of the air had been sparged from the system, the two phases were mixed thoroughly by homogenization at 6000 rpm for 15 minutes. The product (treated) diesel was worked-up as described in Example 3. The nitrogen content of the product diesel was found to be 10 ppm. This experiment demonstrates that the nitrogen removal does not require oxygen. EXAMPLE 5 In two separate experiments, 100 wppm solutions of carbazole and 3-methylindole in toluene were treated with a 50 wt% potassium hydroxide solution in water to which had also been added 800 wppm of cetyltrimethyl- ammonium bromide. Equal volumes of the aqueous caustic solution and organic solution were mixed by magnetic stir bar for thirty minutes at room temperature. After the stirring ceased, the two phases were allowed to separate and the organic phase was analyzed by gas chromatography. The carbazole and 3methylindole contents were reduced by 54% and 47%, respectively.

Claims: CLAIMS: 1. A process for decreasing the organic nitrogen content of petroleum distillate stream, comprising: contacting an organic nitrogen-containing petroleum distillate stream in the presence of an effective amount of water, inorganic base selected from Group IA and IIA hydroxides and ammonium hydroxide and mixtures thereof, and a phase transfer agent at an effective temperature for a time sufficient to produce at least a treated petroleum distillate stream having a decreased organic nitrogen content. 2. The process of claim 1 wherein the base is selected from NaOH and KOH and mixtures thereof. 3. The process of claim 1 wherein the temperature is up to 180°C. 4. The process of claim 1 wherein the phase transfer agent is selected from tetraalkylammonium salts, quaternary phosphonium salts, crown ethers and open-chain polyethers. 5. The process of claim 1 wherein the phase transfer agent is selected from tetraalkylammonium hydroxide and polyethylene glycols and tetraalkylammonium salts. 6. The process of claim 1 wherein the contacting is carried out in the presence of an oxygen containing gas. 7. The process of claim 1 wherein the inorganic base is present in an amount of at least 20 wt%. 8. The process of claim 1 wherein the phase transfer agent is present in an amount of 0.1 to 10 wt%. 9. The process of claim 1 wherein the nitrogen-containing petroleum distillate stream has a mean droplet size of 1-100 microns.

Inventors: GREANEY MARK ALAN, REBICK CHARLES, GREANEY, MARK, ALAN, REBICK, CHARLES
Applicants: EXXONMOBIL RES & ENG CO, EXXONMOBIL RESEARCH AND ENGINEERING COMPANY
Application year: 2001
Main classification: C10G19
IPC codes: C10G19, C10G27