NANOSCALE NICKEL PHOSPHIDE CATALYSTS FOR HYDROTREATMENT
This present disclosure is directed to methods for the preparation of a hydrotreatment catalyst, such as nanoscale nickel phosphide (i.e., Ni2P) particles supported on high-surface area metal oxides (e.g., silica, alumina, amorphous silica-alumina), in a manner that is compatible with conditions employed in commercial hydrotreating units. The catalyst synthesis includes impregnation, drying, and in situ reduction, and can provide highly active catalysts for the removal of S and N impurities from crude oil fractions.
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This application claims the benefit of U.S. Patent Application No. 62/151,890, filed Apr. 23, 2015, the disclosure of which is hereby incorporated by reference in its entirety.
BACKGROUNDThe removal of sulfur and nitrogen impurities from fossil fuel feedstocks is a critical processing step in producing ultralow sulfur transportation fuels. The removal of organonitrogen compounds is necessary to achieve the ultralow sulfur levels since these compounds inhibit sulfur removal. In addition, organosulfur and organonitrogen compounds poison catalysts used in down-stream refinery processes such as hydrocracking, catalytic cracking and reforming. While sulfided Co—Mo/Al2O3 and Ni-Mo/Al2O3 hydrotreatment catalysts are the workhorses of commercial hydrotreating processes, a considerable research effort is ongoing to assess the potential of alternate catalytic materials for hydrotreatment, such as metal phosphides for the hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) reactions. A number of laboratories have investigated the HDS properties of the monometallic phosphides of the first-row transition metals (e.g., Ni2P), of MoP (molybdenum phosphide), and WP (tungsten phosphide) on supports such as silica, as well as the HDS properties of bimetallic phosphide materials. Among the monometallic phosphides, Ni2P has generally been identified as being the most active hydrotreatment catalyst for HDS of thiophene, dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). Some bimetallic phosphide catalysts, Ni2P containing a second first-row metal (e.g., Fe0.03Ni1.97P/SiO2), for example, have exhibited HDS activities that are higher than those of the binary phosphides of the same metals, as well as different product selectivities.
There is a need for Ni2P hydrotreatment catalysts having superior HDS and HDN activities, as well as having improved selectivity for certain hydrotreatment products compared to existing hydrotreatment catalysts. For example, Ni2P hydrotreatment catalysts having higher HDS and HDN activities relative to conventional Co-Mo/Al2O3 and Ni-Mo/Al2O3 sulfide catalysts are desirable. There is also a need for Ni2P hydrotreatment catalysts that can be readily and easily synthesized at low temperatures (T 400° C.). The present disclosure seeks to fulfill these needs and provides further related advantages.
SUMMARYThis summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
In one aspect, the present disclosure features a method of preparing a hydrotreatment catalyst including nanoscale Ni2P particles on a support. The method includes the steps of
(a) providing an impregnation solution comprising nickel hydroxide in hypophosphorous acid;
(b) impregnating the support with the impregnation solution;
(c) drying the impregnation solution to provide Ni(H2PO2)2 on the support; and
(d) reducing the Ni(H2PO2)2 on the support in a hydrogen environment, a sulfiding environment or an inert gas environment and at a temperature of 300-500° C. to provide a hydrotreatment catalyst comprising nanoscale Ni2P particles on the support.
In another aspect, the present disclosure features a method of hydrotreating a petroleum feedstock. The method includes hydrotreating the petroleum feedstock in a reactor using a hydrotreatment catalyst prepared according to the methods described herein.
In yet another aspect, the present disclosure features a hydrotreatment catalyst including nanoscale Ni2P particles on a support, prepared according to the methods described herein.
The foregoing aspects and many of the attendant advantages of this disclosure will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings.
This present disclosure is directed to methods for the preparation of a hydrotreatment catalyst, such as nanoscale nickel phosphide (i.e., Ni2P) particles supported on high-surface area metal oxides (e.g., silica, alumina, amorphous silica-alumina, titania, zirconia), in a manner that is compatible with conditions employed in commercial hydrotreating units. The catalyst synthesis includes impregnation, drying, and in situ reduction, and can provide highly active catalysts for the removal of S and N impurities from crude oil fractions.
Referring to
In some embodiments, the Ni(H2PO2)2 impregnation solution has a phosphorus-to-nickel mole ratio (P/Ni) of 2.0, of 1.0 to 2.0, or greater than 2. In some embodiments, the Ni(H2PO2)2 impregnation solution has a phosphorus-to-nickel mole ratio of 1.0 to 2.0. The phosphorus-to-nickel ratio can be adjusted to lower or higher values by adding a metal salt (e.g., Ni(NO3)2, NiCl2, NiSO4, NiCO3) or more H3PO2, respectively. The Ni(H2PO2)2 impregnation solution can be maintained at a temperature of 20° C. or more (e.g., 40° C. or more, 50° C. or more, 60° C. or more, or 70° C. or more) and/or 75° C. or less (e.g., 70° C. or less, 60° C. or less, 50° C. or less, or 40° C. or less), to decrease the likelihood or prevent the precipitation of dissolved materials. In some embodiments, the Ni(H2PO2)2 impregnation solution is maintained at a temperature of 70° C. or less.
The Ni(H2PO2)2 impregnation solution can be applied (e.g., impregnated) onto a high surface area metal oxide support, and the Ni(H2PO2)2 solution impregnated support can be dried to provide Ni(H2PO2)2 impregnated on the support using either the incipient wetness or equilibrium adsorption method. In some embodiments, drying the Ni(H2PO2)2 solution-impregnated support can include heating the impregnated support, for example, to a temperature of 70° C. (e.g., 60° C., 50° C., or 40° C.). For example, heating the impregnated support can be to a temperature of 40° C. or more (e.g., 50° C. or more, 60° C. or more) and/or 70° C. or less (e.g., 60° C. or less, 50° C. or less). The dried Ni(H2PO2)2-impregnated support (i.e., the catalyst precursor) can have 20 wt % or less of water.
In some embodiments, the dried Ni(H2PO2)2-impregnated support is then heated and reduced in a reducing atmosphere to provide nanoscale Ni2P particles on the support. During the heating and reduction step, the nickel hypophosphite on the support is converted to nanoscale Ni2P particles. The nanoscale Ni2P particles can be relatively phase pure. As used herein, a “phase pure” nanoscale Ni2P particle denotes that the only phase identified by X-ray diffraction or transmission electron microscopy is Ni2P. The heating and reduction can include loading the dried Ni(H2PO2)2-impregnated support into a reactor system, purging the reactor system at room temperature using an inert gas (e.g., nitrogen or argon), and then heating the dried Ni(H2PO2)2 impregnated support in flowing hydrogen (H2) gas, or a sulfiding gas, to an elevated temperature. The sulfiding gas can include a sulfiding agent, such as a flowing gaseous mixture of hydrogen sulfide in hydrogen (e.g., 3-10 mol % H2S/H2).
In some embodiments, during the heating and reducing step, the hydrogen gas or sulfiding gas is flowed at a rate of 50 mL/min or more (e.g., 60 mL/min or more, or 70 mL/min or more) and/or 80 mL/min or less (e.g., 70 mL/min or less, or 60 mL/min or less). In some embodiments, the gas is flowed at a rate of 50 mL/min, 60 mL/min, 70 mL/min, or 80 mL/min. In some embodiments, the gas is flowed at a rate of 60 mL/min.
In some embodiments, during the heating and reducing step, the elevated temperature for the reduction reaction is 300° C. or more (e.g., 350° C. or more, 400° C. or more, or 450° C. or more) and/or 500° C. or less (e.g., 450° C. or less, 400° C. or less, or 350° C. or less). For example, the elevated temperature for the reduction is 300° C. to 500 ° C. (e.g., 300° C. to 450° C., 300° C. to 400° C., 350° C. to 500° C., 350° C. to 450° C., or 400° C. to 500° C.). In some embodiments, the dried Ni(H2PO2)2-impregnated support is heated and reduced for a duration of about 30 minutes or more (e.g., 1 hour or more, 2 hours or more, 3 hours or more) and/or 4 hours or less (e.g., 3 hours or less, 2 hours or less, or 1 hour or less). For example, the dried Ni(H2PO2)2 impregnated support can be heated and reduced for 1 hour, 2 hours, 3 hours, or 4 hours. In certain embodiments, the dried Ni(H2PO2)2-impregnated support is heated and reduced for 2 hours.
The synthetic procedure of the present disclosure presents numerous advantages. For example, the nanoscale Ni2P particles produced using the synthetic procedure of the present disclosure do not need to be washed with water, since the synthesis does not produce salts that must be removed. For example, when a hydrogen atmosphere is used for the reduction step, the reaction proceeds as follows:
12 Ni(H2PO2)2+35 H2→6 Ni2P+14 PH3+32 H2O+4 H3PO4. (Eq. 1)
As can be seen from Equation 1, the reaction does not produce any salt by-products. The synthesis of the nanoscale Ni2P particles is relatively easy, and can be carried out directly in a hydrotreatment reactor (i.e., in situ preparation) at low temperatures (T≤400° C.) and without the need of a washing step to remove salt by-products, using a reducing agent (e.g., H2 or H2S/H2).
The synthetic procedure of the present disclosure provides nanoscale Ni2P particles having desirable physical and catalytic properties, as will be detailed infra.
SupportThe support for the nanoscale Ni2P particles can include a variety of metal oxides, such as alumina (Al2O3), silica (SiO2), or amorphous silica-alumina (ASA). In some embodiments, the support can have Brunauer-Emmett-Teller (BET) surface areas of 25 m2/g or more (e.g., 50 m2/g or more, 100 m2/g or more, 200 m2/g or more, 300 m2/g or more, or 400 m2/g or more) and/or 500 m2/g or less (e.g., 400 m2/g or less, 300 m2/g or less, 200 m2/g or less, 100 m2/g or less, or 50 m2/g or less). In some embodiments, the support can have BET surface areas of 500 m2/g or more.
In some embodiments, the support can have pore volumes of 0.1 cm3/g or more (e.g., 0.3 cm3/g or more, or 0.7 cm3/g or more) and/or 1.0 cm3/g or less (e.g., 0.7 cm3/g or less, or 0.3 cm3/g or less). In some embodiments, the support can have average Barrett-Joyner-Halenda (BJH) pore sizes of 1 nm or more (e.g., 5 nm or more, 15 nm or more, 25 nm or more) and/or 30 nm or less (e.g., 25 nm or less, 15 nm or less, or 5 nm or less). In some embodiments, the support can have BJH pore sizes of 30 nm or more.
In some embodiments, the metal oxide support includes a surface layer of P2O5, B2O3, or both. The surface layer can have an average thickness of 0.1 nm or more (e.g., 0.5 nm or more, 1 nm or more, 2 nm or more, 3 nm or more, or 4 nm or more) and/or 5 nm or less (e.g., 4 nm or less, 3 nm or less, 2 nm or less, 1 nm or less, or 0.5 nm or less).
In some embodiments, the surface layer of the support has an average thickness of 5 nm or less (e.g., 4 nm or less, 3 nm or less, 2 nm or less, or 1 nm or less). In some embodiments, the average thickness of the surface layer is measured using X-ray photoelectron spectroscopy. In some embodiments, the surface layer is continuous. In certain embodiments, the surface layer is non-continuous. Without wishing to be bound by theory, it is believed that the surface layer is associated to the bulk of the support via a combination of covalent and ionic bonds.
The surface layer of P2O5, B2O3, or both, on the metal oxide support can be deposited onto the support prior to impregnating the support with Ni(H2PO2)2. For example, to prepare a B2O3 and/or P2O5 surface layer on the support (e.g., silica, alumina, or amorphous silica-alumina), selected amounts of boron and/or phosphorus-containing compounds such as H3B03, H3PO4, and/or an ammonium phosphate salt such as NH4H2PO4 and/or (NH4)2HPO4, and water can be impregnated onto the support until incipient wetness is achieved. After impregnation using the boron and/or phosphorus compounds, the impregnated support can be dried, then calcined to provide a metal oxide support having a P2O5 and/or B2O3 surface layer.
Drying of the boron- or phosphorus-impregnated support can occur at 70° C. or more (e.g., 80° C. or more, 100° C. or more, or 110° C. or more) and/or 120° C. or less (e.g., 110° C. or less, 100° C. or less, 80° C. or less), for a duration of 24 hours or more (e.g., 36 hours or more, 48 hours or more, or 60 hours or more) and/or 72 hours or less (e.g., 60 hours or less, 48 hours or less, or 36 hours or less). Calcining the dried impregnated support can be conducted in an oxygen-containing atmosphere (e.g., air) or pure oxygen at a temperature of from 400° C. or more (e.g., 425° C. or more, or 450° C. or more) and/or 500° C. or less (e.g., 450° C. or less, or 425° C. or less), for a duration of 2 hours or more (e.g., 3 hours or more, or 4 hours or more) and/or 5 hours or less (e.g., 4 hours or less, or 3 hours or less).
The supports of the present disclosure can be characterized using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, BET surface area, and BJH pore size measurements.
Catalyst CharacteristicsIn some embodiments, the nanoscale Ni2P particles on the support synthesized by the methods of the present disclosure have a relatively uniform diameter. As used herein, “uniform diameter” refers to a diameter that does not vary by more than 20% compared to an average diameter of the nanoscale Ni2P particles. In some embodiments, the nanoscale Ni2P particles are in the form of a plurality of Ni2P crystallites on a surface of the support, as identified and characterized using X-ray diffraction and transmission electron microscopy. The crystallites can have an average diameter of 3 nm or more (e.g., 5 nm or more, or 10 nm or more) and/or 15 nm or less (e.g., 10 nm or less, or 5 nm or less). In some embodiments, the crystallites have an average diameter of 3 nm to 15 nm. In certain embodiments, the crystallites have an average diameter of 3 nm to 5 nm. In some embodiments, the crystallites have an average diameter of 3 nm or less (e.g., 3 nm, 2 nm, or 1 nm).
Without wishing to be bound by theory, it is believed that smaller particles can result in increased dispersion of the active Ni2P phase and thereby provide a higher active catalytic site density. It is also believed that uniformly-sized particles can allow for better control of catalytic activity and product selectivity.
The nanoscale Ni2P particles can have a surface that is relative rich in phosphorus, compared to the bulk of the nanoscale Ni2P particles. The composition of the surface and bulk of the nanoscale Ni2P particles can be determined using X-ray photoelectron spectroscopy (which can provide a quantitative measure of surface composition) and energy dispersive X-ray spectroscopy (EDX) (which can provide a semi-quantitative measure of bulk composition), respectively. Without wishing to be bound by theory, it is believed that a surface enrichment in phosphorus can provide increased stability to the Ni2P catalyst (e.g., provide better resistance to sulfur poisoning or bulk sulfide formation) and provide desirable catalytic activity and selectivity properties.
In some embodiments, using X-ray photoelectron spectroscopy, the composition of the surface of a nanoscale Ni2P particle can be measured to a depth of 3 to 10 nm. In some embodiments, the surface composition of the nanoscale Ni2P particles includes a mole ratio of P/Ni of 1.0 or more (e.g., 2.0 or more, 3.0 or more, 4.0 or more, 5.0 or more) and/or 6.0 or less (e.g., 5.0 or less, 4.0 or less, 3.0 or less, or 2.0 or less), as determined by X-ray photoelectron spectroscopy. In some embodiments, the surface composition of the nanoscale Ni2P particles includes a mole ratio of P/Ni of 1.0 to 6.0 (e.g., 1.0 to 5.0, 2.0 to 6.0, 2.0 to 5.0, or 2.0 to 4.0), as determined by X-ray photoelectron spectroscopy.
In some embodiments, the nanoscale Ni2P particles have a bulk portion, below the surface layer, the bulk portion has a mole ratio of P/Ni that is less than that of the surface layer. For example, the bulk portion can have a mole ratio of P/Ni of 0.5 or more (e.g., 1.0 or more, 2.0 or more, 3.0 or more, 4.0 or more) and/or 5.0 or less (e.g., 4.0 or less, 3.0 or less, 2.0 or less, or 1.0 or less), provided that the bulk portion P/Ni mole ratio is less than the P/Ni mole ratio of the surface layer of the nanoscale Ni2P particles.
The nanoscale Ni2P particles can be 5 wt % or more (e.g., 8 wt % or more, 10 wt % or more, or 15 wt % or more) and/or 25 wt % or less (e.g., 15 wt % or less, 10 wt % or less, or 8 wt % or less) of the total weight of the hydrotreatment catalyst, which includes the nanoscale Ni2P particles and the support. In some embodiments, the nanoscale Ni2P particles are 5 wt % to 25 wt % (e.g., 5 wt % to 15 wt %, 5 wt % to 10 wt %, or 10 wt % to 25 wt %) of the total weight of the hydrotreatment catalyst. The Ni2P wt % is calculated based on the amount of Ni and P that is impregnated into the support.
In some embodiments, the hydrotreatment catalyst of the present disclosure has a BET surface area of 75 m2/g or more (e.g., 100 m2/g or more, 150 m2/g or more, or 200 m2/g or more) and/or 250 m2/g or less (e.g., 200 m2/g or less, 150 m2/g or less, or 100 m2/g or less). In certain embodiments, the hydrotreatment catalyst of the present disclosure has a BET surface area of 75 m2/g to 250 m2/g (e.g., 100 m2/g to 200 m2/g or 150 m2/g to 250 m2/g). In some embodiments, the hydrotreatment catalyst of the present disclosure has a BET surface area of 250 m2/g or more. Without wishing to be bound by theory, it is believed that a higher BET surface area provides better catalytic properties.
Catalyst Evaluation—HydrodenitrogenationThe catalytic activity of the hydrotreatment catalysts of the present disclosure can be evaluated using a hydrodenitrogenation test. As used herein, the hydrodenitrogenation test can include exposing the hydrotreatment catalyst to 1000 ppm carbazole and 3000 ppm benzothiophene in a 60 wt % decane and 39.55 wt % p-xylene solvent mixture at a rate of 5.4 mL/min, a H2 flow rate of 50.0 mL/min, at a temperature of about 267 to 407° C., and at a pressure of 3.0 MPa.
In some embodiments, the hydrotreatment catalyst of the present disclosure, i.e., the nanoscale Ni2P particles on the support, have a carbazole hydrodenitrogenation turnover frequency of 0.0001/s or more (e.g., 0.0002/s or more, 0.0003/s or more, 0.0004/s or more, or 0.0005/s or more) and/or 0.0006/s or less (e.g., 0.0005/s or less, 0.0004/s or less, 0.0003/s or less, or 0.0002/s or less), at 350° C., over a time period of 24 hours to 120 hours, when subjected to a hydrodenitrogenation test. For example, the hydrotreatment catalyst can have a carbazole hydrodenitrogenation turnover frequency of 0.0001/s to 0.0006/s (e.g., 0.0001/s to 0.0005/s, 0.0002/s to 0.0006/s, or 0.0002/s to 0.0004/s) at 350° C., over a time period of 24 hours to 120 hours, when subjected to a hydrodenitrogenation test. Without wishing to be bound by theory, it is believed that a high turnover frequency is indicative of highly active catalytic sites. A superior catalyst can have a high turnover frequency and/or a high chemisorption capacity, which is a measure of active sites.
In some embodiments, when the nanoscale Ni2P particles are 5 wt % to 25 wt % (e.g., 5 wt % to 20 wt %, 10 wt % to 20 wt %, 10 wt % to 15 wt %, 15 wt % to 20 wt %) of the hydrotreatment catalyst (i.e., 5 wt % to 25 wt % of the total combined weight of the nanoscale Ni2P particles and the support), the hydrotreatment catalyst is capable of providing a carbazole hydrodenitrogenation conversion of 1% to 97% (e.g., 1% to 95%, 1% to 90%, 90% to 97%, 80% to 97%), at 350° C. over a time period of 24 hours to 120 hours, when subjected to the hydrodenitrogenation test.
In some embodiments, when subjected to carbazole and benzothiophene (for example, in a hydrodenitrogenation test), the hydrotreatment catalyst of the present disclosure provides higher proportions of a cyclohexylbenzene product, compared to a sulfided nickel-molybdenum catalyst on alumina. For example, the hydrotreatment catalyst can provide 20% to 50% more of a cyclohexylbenzene product, compared to a sulfided nickel-molybdenum catalyst on alumina having a composition of 4 wt % NiO, 19.5 wt % MoO3, and 8 wt % P2O5 (in its oxidic form).
Catalyst Evaluation—HydrodesulfurizationIn some embodiments, the catalytic activity of the hydrotreatment catalysts of the present disclosure can be evaluated using a hydrodesulfurization test. As used herein, the hydrodesulfurization test includes exposing the hydrotreatment catalyst to 1000 ppm of 4,6-dimethyldibenzothiophene in decalin, a H2 flow rate of 50.0 mL/min, at a temperature of about 257 to 327° C., and at a pressure of 3.0 MPa.
In some embodiments, when the nanoscale Ni2P particles are 5 wt % to 25 wt % (e.g., 5 wt % to 20 wt %, 10 wt % to 20 wt %, 10 wt % to 15 wt %, 15 wt % to 20 wt %) of the hydrotreatment catalyst (i.e., 5 wt % to 25 wt % of the total combined weight of the nanoscale Ni2P particles and the support), the hydrotreatment catalyst is capable of providing a 4,6-dimethyldibenzothiophene hydrodesulfurization conversion of 1% to 65% (e.g., 1% to 50%, 5% to 65%, 10% to 65%, or 50% to 65%), at 300° C., over a time period of 24 hours to 120 hours, when subjected to a hydrodesulfurization test.
In some embodiments, nanoscale Ni2P particles on an alumina support that has a P2O5 and/or B2O3 surface layer can have good 4,6-dimethyldibenzothiophene hydrodesulfurization conversion. In some embodiments, the alumina support can have a phosphorus content of from 1 wt % to 2 wt %. In certain embodiments, the alumina support can have a boron content of from 0.6 wt % to 1.2 wt %.
Hydrotreatment of Petroleum FeedstockIn some embodiments, the hydrotreatment catalyst of the present disclosure is used to hydrotreat a petroleum feedstock (e.g., a petroleum distillate). The hydrotreatment of petroleum feedstock can occur in a reactor using the hydrotreatment catalyst. The hydrotreatment can include one or more of hydrodenitrogenation (HDN), hydrodesulfurization (HDS), hydrodeoxygenation (HDO), hydrodemetallation (HDM), and hydrogenation (HYD).
In some embodiments, the hydrotreatment catalyst is prepared in situ in the reactor by reducing the Ni(H2PO2)2 that is impregnated on the support in a reducing atmosphere in the reactor, to provide nanoscale Ni2P particles on the support, prior to hydrotreating the petroleum feedstock. The reduction of the Ni(H2PO2)2 can include heating to a temperature below a temperature limit of the reactor, for example, heating to a temperature of 400° C. or less in the reactor. An in situ reduction of the hydrotreatment catalyst can be more convenient, cost-effective, and can provide greater amounts of active catalyst, when compared to a hydrotreatment catalyst prepared via an ex situ reduction. In some embodiments, the hydrotreatment catalyst is prepared ex situ (i.e., in a separate reactor different from the hydrotreatment reactor), and then placed in the reactor prior to hydrotreating the petroleum feedstock. An ex situ preparation of the hydrotreatment can allow for the identification of an active catalytic phase, and can allow for quantification of the number of active sites and other properties.
As discussed above, the synthesis of the nanoscale Ni2P particles does not require a step of washing the hydrotreatment catalyst prior to hydrotreating the petroleum feedstock, since the synthesis does not produce salts that must be removed.
The following example is included for the purpose of illustrating, not limiting, the described embodiments. Example 1 describes a method for preparing nanoscale Ni2P particles on supports and characterization of the resulting materials. Example 2 describes the synthesis and characterization of nanoscale Ni2P particles on P2O5— or B2O3-modified supports.
EXAMPLES Example 1. Synthesis and Characterization of Ni2P Supported on silica, alumina, or ASAThis example describes a method for synthesizing metal phosphide catalysts (e.g., Ni2P) supported on high surface area metal oxides (e.g., silica, alumina, amorphous silica-alumina) in a manner that is compatible with conditions employed in commercial hydrotreating units. The catalyst synthesis includes impregnation, drying and in situ reduction (i.e., reduction within the hydrotreatment reactor) and yields highly active catalysts for the removal of S and N impurities from crude oil fractions.
Catalyst Preparation
A metal hydroxide, such as nickel hydroxide (Ni(OH)2), was dissolved in hypophosphorous acid (H3PO2, 50 wt % aqueous solution). The resulting solution had a phosphorus-to-nickel mole ratio (P/Ni) of 2.0, the solution was maintained at an elevated temperature 70° C.) to avoid precipitation of solid material. The solution was impregnated onto a high surface area metal oxide support and dried at 70° C. The dried catalyst precursor was loaded into the reactor system, purged at room temperature in an inert gas, and then heated in flowing hydrogen (H2) or hydrogen sulfide/hydrogen to a temperature in the range 300-500° C. During the heating step, the nickel hypophosphite on the oxide support was converted to phase-pure Ni2P.
Catalyst Characterization
For sufficiently high loadings, Ni2P was identified on the support material using X-ray diffraction (XRD). XRD patterns for Ni2P on silica (SiO2), alumina (Al2O3) and amorphous silica-alumina (ASA) are shown in
The BET surface areas and chemisorption capacities (CO, O2) for the in situ prepared Ni2P catalysts are given in Table 1 along with comparison data from ex situ prepared catalysts from phosphate- and hypophosphite-based precursors. The in situ prepared Ni2P catalysts were reduced within the hydrotreatment reactor. In contrast, the ex situ prepared Ni2P catalysts were reduced in a reactor separate from the hydrotreatment reactor, then the reduced catalysts were loaded into the hydrotreatment reactor. The in situ prepared catalysts had high surface areas, but there were no clear trends in chemisorption capacities that would predict high catalytic activity.
For Ni2P/SiO2, the catalyst prepared ex situ from a phosphate-based precursor had higher chemisorption capacities than the in situ and ex situ catalysts prepared from the hypophosphite-based precursors. The opposite trend was observed for the alumina- and ASA-supported Ni2P catalysts.
A comparison of the bulk precursor compositions for phosphate- (“phos”) and hypophosphite- (“hypo”) based Ni2P catalysts supported on SiO2 and Al2O3, as well as the surface compositions (determined by XPS) for the reduced Ni2P/SiO2 and Ni2P/Al2O3 catalysts is shown below, in Tables 2 and 3.
Catalyst Activity
A schematic representation of the high pressure reactor studies of Example 1 is shown in
Referring to
The carbazole HDN activities (on a mass catalyst basis) are plotted in
As is clear from the results shown in
An additional feature of the catalyst of Example 1 is that the catalyst precursors could be reduced in situ using a sulfidation pretreatment (3 mol % H2S/H2) to give highly active Ni2P catalysts, as shown in
Example 1 demonstrates the preparation of metal phosphides (e.g., Ni2P) supported on high surface area metal oxides (silica, alumina, amorphous silica-alumina) in a manner that is compatible with conditions employed in commercial hydrotreating units. Hypophosphite-based precursors could be reduced in situ in a reactor using either H2 or H2S/H2 at 300-500° C. to give highly active Ni2P catalysts as demonstrated by HDN and HDS activity measurements using a mixed carbazole/benzothiophene feed.
Example 2. Ni2P on P2O5— or B2O3-Modified SupportsThis example describes a method for preparing metal phosphides (e.g., Ni2P) supported on high surface area P2O5— or B2O3-modified Al2O3 supports (P-Al2O3 and B—Al2O3, respectively) in a manner that is compatible with conditions employed in commercial hydrotreating units. The catalyst synthesis includes impregnation, drying and calcination of the P— or B-impregnated Al2O3 supports, followed by impregnation, drying and in situ reduction (i.e., reduction within the hydrotreatment reactor) of the Ni2P catalyst precursor to yield highly active catalysts for the removal of S and N impurities from crude oil fractions.
An aqueous solution of H3BO3, H3PO4, and/or an ammonium phosphate salt such as NH4H2PO4 and/or (NH4)2HPO4, was impregnated onto the Al2O3 support until incipient wetness. The resulting P-Al2O3 and B-Al2O3 supports had loadings of 0-5 wt % P and 0-2 wt % B, respectively. A metal hydroxide, such as nickel hydroxide (Ni(OH)2), was dissolved in hypophosphorous acid (H3PO2, 50 wt % aqueous solution). Ni(NO3)2 or another Ni salt may or may not be added to the impregnation solution to adjust the P/Ni mole ratio. The resulting solution had a phosphorus-to-nickel mole ratio (P/Ni) of 1.5-2.0, the solution was maintained at an elevated temperature 70° C.) to avoid precipitation of solid material. The solution was impregnated onto the P-Al2O3 or B-Al2O3 support and dried at 70° C. The dried catalyst precursor was loaded into the reactor system, purged at room temperature in an inert gas, and then heated in flowing hydrogen (H2) or hydrogen sulfide/hydrogen (H2S/H2) to a temperature in the range 300-500° C. During the heating step, the nickel hypophosphite on the oxide support was converted to phase-pure Ni2P.
Referring to
While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.
Claims
1-28. (canceled)
29. A hydrotreatment catalyst comprising nanoscale Ni2P particles on a support, wherein the nanoscale Ni2P particles are in the form of a plurality of Ni2P crystallites on the support, and the plurality of crystallites has an average diameter of 3 nm to 15 nm; and
- wherein the support is selected from the group consisting of silica, alumina, and amorphous silica-alumina; the support optionally comprising a surface layer comprising P2O5, B2O3, or a combination thereof.
30. The hydrotreatment catalyst of claim 29, wherein the hydrotreatment catalyst does not comprise an inorganic salt.
31. The hydrotreatment catalyst of claim 29, wherein the hydrotreatment catalyst does not include impurities.
32. The hydrotreatment catalyst of claim 29, wherein the impurities comprise Ni12P5.
33. The hydrotreatment catalyst of claim 29, wherein the plurality of crystallites has a diameter that does not vary by more than 20% compared to the average diameter.
34. The hydrotreatment catalyst of claim 29, wherein the nanoscale Ni2P particles are 5 wt % to 25 wt % of the hydrotreatment catalyst and wherein the nanoscale Ni2P particles have a surface composition comprising a mole ratio of P/Ni of 1.0-6.0.
35. The hydrotreatment catalyst of claim 34, wherein the nanoscale Ni2P particles have a bulk portion below the surface composition, having a mole ratio of P/Ni that is less than that of the surface composition.
36. The hydrotreatment catalyst of claim 29, wherein the surface layer of the support, when present, has a thickness of 5 nm, and wherein the catalyst has a BET surface area of from 75 m2/g to 250 m2/g.
37. The hydrotreatment catalyst of claim 29, having a carbazole hydrodenitrogenation turnover frequency of from 0.0001/s to 0.0006/s at 350° C. over a time period of 24 hours to 120 hours, when exposed to 1000 ppm carbazole and 3000 ppm benzothiophene in a 60 wt % decane and 39.55 wt % p-xylene solvent mixture at a rate of 5.4 mL/min, and a H2 flow rate of 50.0 mL/min, at a temperature of about 267° C. to 407° C. and a pressure of 3.0 MPa.
38. The hydrotreatment catalyst of claim 29, wherein when the nanoscale Ni2P particles are 5 wt % to 25 wt % of the hydrotreatment catalyst, the hydrotreatment catalyst is capable of providing a carbazole hydrodenitrogenation conversion of 1% to 97% at 350° C. over a time period of 24 hours to 120 hours, when exposed to 1000 ppm carbazole and 3000 ppm benzothiophene in a 60 wt % decane and 39.55 wt % p-xylene solvent mixture at a rate of 5.4 mL/min, and a H2 flow rate of 50.0 mL/min, at a temperature of about 267° C. to 407° C. and a pressure of 3.0 MPa.
39. The hydrotreatment catalyst of claim 29, wherein when the nanoscale Ni2P particles are 5 wt % to 25 wt % of the hydrotreatment catalyst, the hydrotreatment catalyst is capable of providing a 4,6-dimethyldibenzothiophene hydrodesulfurization conversion of 1% to 65% at 300° C. over a time period of 24 hours to 120 hours, when exposed to 1000 ppm of 4,6-dimethyldibenzothiophene in decalin, and a H2 flow rate of 50.0 mL/min, at a temperature of about 257° C. to 327° C. at a pressure of 3.0 MPa.
40. The hydrotreatment catalyst of claim 29, wherein the hydrotreatment catalyst provides higher proportions of cyclohexylbenzene when exposed to carbazole and benzothiophene, compared to a nickel-molybdenum catalyst on alumina.
41. A method of hydrotreating a petroleum feedstock, comprising hydrotreating the petroleum feedstock in a reactor using a hydrotreatment catalyst according to claim 29.
42. The method of claim 41, wherein the hydrotreatment catalyst is prepared in situ in the reactor prior to hydrotreating the petroleum feedstock, by:
- (a) providing an impregnation solution comprising nickel hydroxide in hypophosphorous acid;
- (b) impregnating the support with the impregnation solution;
- (c) drying the impregnation solution to provide Ni(H2PO2)2 on the support; and
- (d) reducing the Ni(H2PO2)2 on the support in a hydrogen environment, a sulfiding environment or an inert gas environment, and heating at a temperature below a temperature limit of the reactor to provide the hydrotreatment catalyst.
43. The method of claim 42, wherein reducing the Ni(H2PO2)2 comprises heating to a temperature of 400° C. or less in the reactor.
44. The method of claim 41, wherein the method does not include a step of washing the hydrotreatment catalyst prior to hydrotreating the petroleum feedstock.
45. The method of claim 41, wherein the hydrotreatment catalyst is prepared ex situ and then placed in the reactor prior to hydrotreating the petroleum feedstock.
46. The method of claim 41, wherein hydrotreating the petroleum feedstock comprises a reaction catalyzed by the hydrotreatment catalyst that is selected from the group consisting of hydrodenitrogenation; hydrodesulfurization; and hydrogenation; and a combination thereof.
47. The method of claim 41, wherein the petroleum feedstock is a petroleum distillate.
Type: Application
Filed: Jul 24, 2019
Publication Date: Nov 14, 2019
Applicant: Western Washington University (Bellingham, WA)
Inventor: Mark E. Bussell (Bellingham, WA)
Application Number: 16/520,988