Catalyst

Abstract

The present invention provides a Fischer-Tropsch catalyst comprising greater than about 40% by weight of cobalt, and having a packed apparent bulk density greater than about 1.30 g/mL.

Claims

1. A Fischer-Tropsch catalyst comprising greater than about 40% by weight of cobalt, and having a packed apparent bulk density greater than about 1.30 g/mL.

2. The catalyst according to claim 1 wherein the catalyst has a packed apparent bulk density of cobalt greater than about 0.60 g/mL, or greater than about 0.65 g/mL, or greater than about 0.70 g/mL, greater than about 0.75 g/mL, or greater than about 0.80 g/mL.

3. The catalyst according to claim 1 wherein the catalyst comprises greater than about 45% by weight, or greater than about 50% by weight, of cobalt.

4. The catalyst according to claim 1 wherein the catalyst has a packed apparent bulk density greater than about 1.35 g/mL, or greater than about 1.40 g/mL, or greater than about 1.45 g/mL, or greater than about 1.50 g/mL, or greater than about 1.55 g/mL, or greater than about 1.60 g/mL.

5. The catalyst according to claim 1 wherein the catalyst has an average cobalt particle size of from about 5 nm to about 20 nm.

6. The catalyst according to claim 1 wherein the catalyst comprises less than about 3% by weight, or less than about 1% by weight, or less than about 0.5% by weight, of noble metals.

7. The catalyst according to claim 6 wherein the noble metals comprise rhenium and/or platinum.

8. The catalyst according to claim 1 wherein the catalyst comprises a catalyst support.

9. The catalyst according to claim 8 wherein the catalyst support comprises silica.

10. The catalyst according to claim 8 wherein the catalyst support comprises an oxide, optionally titania oxide.

11. The catalyst according to claim 10 wherein the catalyst support comprises up to about 30% by weight of the oxide.

12. The catalyst according to claim 8 wherein the catalyst support is absent of alumina.

13. The catalyst according to claim 1 wherein the catalyst exhibits a rate of CO hydrogenation greater than about 55 mmol, or about 60 mmol, or about 65 mmol, or about 70 mmol, or about 75 mmol, or about 80 mmol, or about 85 mmol, or about 90 mmol, CO per gram of cobalt per hour after at least about 48 hours of operation at about 180° C., with a feed stream of about 10 mol % inert tracer gas, a H.sub.2/CO ratio of about 10 at an absolute pressure of about 354.6 kPa (3.5 atm) and a flow rate such that CO conversion is between about 18.0% and about 22%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments of the invention are described below by way of example only with reference to FIGS. 1 to 3 of the accompanying drawings, wherein;

(2) FIG. 1 illustrates the effect of increasing the level of impregnation on the number of synthetic steps required to reach a certain cobalt loading.

(3) FIG. 2 illustrates the time required for two catalysts to lose activity when exposed to the same burden of the regenerable poison NH.sub.3.

(4) FIG. 3 illustrates CO conversion versus flux of H.sub.2S for three different catalysts.

DETAILED DESCRIPTION

(5) Catalyst Synthesis

(6) The synthesis of comparative catalyst 1 in Table 3 is outlined below. Catalysts 1 to 11 in Tables 3 and 4, which fall within the scope of the invention, were made in a similar way, but with varying amounts of Co, Ti and Re, and on both PD12058 and LC150 (which are different batches of silica).

(7) Materials

(8) Table 2 outlines the materials used in the synthesis of the catalysts.

(9) TABLE-US-00002 TABLE 2 Materials Purity/Concentration Supplier Silica (LC150/PD12058) — Grace/PQ Titanium(IV) bis(ammonium 50% Sigma lactato)dihydroxide (TALH) Citric acid monohydrate 99 wt. % Sigma Cobalt nitrate hexahydrate 98 wt. % Sigma HReO.sub.4 sol. 75 wt. % Sigma Pt(NH.sub.3).sub.4(OH).sub.2 sol. 9.96 wt. % Alfa Aesar

(10) Preparation of Modified Support

(11) 16 g of PD12058 was weighed out and placed in a fan oven at 100° C. for 2 hours to dry. 11.66 g of the hot silica was immediately weighed into an alumina bowl, covered and allowed to cool to room temperature. 2.5 g of citric acid was weighed out and mixed with 1.2 mL of deionized water under heat to 50° C. until fully dissolved. 11.54 g of TALH was then weighed and added to the cooled citric acid solution and mixed until homogeneous. The mixture was poured into a graduated cylinder, the beakers rinsed out with 1 mL of deionized water and the volume adjusted to 25.2 mL. The solution was added to cooled silica in 4 aliquots with stirring after each addition until the mixture was homogeneous and the liquid absorbed. After the final addition, the impregnated silica was transferred to a weighed crucible and spread evenly over the crucible surface, so that material did not exceed 10 mm depth. The crucible was transferred to a muffle furnace and dried/calcined using the following program: 2° C./min to 100° C. and hold for 5 hours, then 2° C./min to 250° C. and hold for 5 hours. Once material was calcined and cooled to below 50° C. the weight of the sample was taken and compared to the expected material weight to calculate the purity of the support.

(12) Catalyst Synthesis

(13) 9.1 g of the modified support material from the previous step was weighed out into an alumina bowl. 12.47 g of cobalt nitrate hexahydrate was weighed, 3.1 mL of deionized water added, and the mixture heated to 50° C. on a hotplate with stirring until fully dissolved. 0.2698 g of perrhenic acid was weighed out and added to the cobalt nitrate solution with stirring. The solution was poured into a graduated measuring cylinder and the volume adjusted to 11.5 mL with deionized water. Once cool to room temperature the solution was added to the modified support in 4 aliquots with stirring after each addition until the mixture was homogeneous and the liquid absorbed.

(14) After the final addition, the impregnated support was transferred to a weighed crucible and spread evenly over the crucible surface so that material did not exceed 10 mm depth. The crucible was then transferred to a muffle furnace and dried/calcined using the following program: 2° C./min to 100° C. and hold for 5 hours, then 2° C./min to 200° C. and hold for 3 hours, followed by 1° C./min to 250° C. and hold for 3 hours. Once calcined and cooled, the cobalt impregnation described above was repeated with the addition of 1.79 g of citric acid to the cobalt nitrate solution prior to impregnation. The calcination program of this additional step was: 2° C./min to 100° C. and hold for 5 hours then 2° C./min to 250° C. and hold for 3 hours.

(15) The final step of the synthesis was the addition of platinum as a promotor. 0.4518 g of tetraamine platinum hydroxide was weighed out and rinsed into a graduated cylinder, and the solution topped up with water to 10.7 mL. The solution was then added to the dried and calcined material from the last step in 4 aliquots with stirring after each addition until mixture was homogeneous and the liquid absorbed.

(16) After the final addition, the impregnated support was transferred to a weighed crucible and spread evenly over the crucible surface so that material did not exceed 10 mm depth. The crucible was then transferred to a muffle furnace and dried/calcined using the following program: 2° C./min to 100° C. and hold for 5 hours, then 2° C./min to 250° C. and hold for 3 hours. Once cool the finished catalyst was weighed and transferred to a labelled bottle.

(17) Excess Wetness Impregnation

(18) For the drying of excess wetness impregnated catalysts, a rotary evaporator was adapted into a rotary drying unit. This allowed the impregnated catalyst to be dried under heating and mixed in a rotary paddle flask broadly simulating the action of an industrial paddle drying. To prevent reflux, a vacuum tube was held at the base of the neck inside the vessel creating airflow into the open vessel and out the vacuum tube, along with any evaporating moisture. Mineral oil was used as the heating medium in the heating bath to allow for a greater range of temperatures than would be allowed by water.

(19) By way of an example, a catalyst according to the invention (42.0% Co, 0.2% Re, 0.03% Pt on 10% TiO.sub.2/AGC) was prepared by impregnating the support with excess liquid impregnation followed by drying in the simulated-paddle drying apparatus to reduce the solution volume to such a point that the impregnated material was free flowing within the paddle flask. Tests were conducted on 75 mL of support to give enough material to allow for appropriate mixing by the paddles. For the drying, the oil bath was preheated to 60° C. For each step, the catalyst support was impregnated in the drying flask to minimize losses during transfer. The flask was then attached to the setup, rotated at 20 rpm, airflow started, and the oil bath was heated to 90-95° C. at approximately 1° C./min and held until the impregnated catalyst became free flowing, typically taking 15-30 minutes while at temperature. The dried impregnated catalyst was then calcined in a muffle furnace using the heating procedure described above.

(20) Measuring Packed Apparent Bulk Density

(21) Packed apparent bulk density (PABD) is measured in a graduated cylinder of 5 mL volume. However, a graduated cylinder of any reasonable volume (for example 5 mL, 25 mL, 100 mL, or 250 mL) can be used without any significant difference in result (i.e., no more than 1% difference). The cylinder is filled with catalyst and hand tapped to settle the solid and more material added, tapped, etc. until the amount just approaches 5 mL. The graduate is then fitted onto a Quantachrome Autotap DAT-4 instrument and subjected to 1500 taps. The settled volume of the catalyst is determined and then the catalyst mass is determined. The packed apparent bulk density is calculated by dividing the weight of catalyst in grams by the volume in mL after 1500 taps. The packed apparent bulk density of cobalt is calculated by multiplying the packed apparent bulk density of the catalyst by the weight % of cobalt in the catalyst.

(22) The above method is generally in accordance with the procedures of ASTM D7481-09 (i.e., D7481 approved or reapproved in 2009): Standard Methods for determining loose and tapped bulk densities of powders using a graduated cylinder.

(23) Preferably, the measured catalyst mass is a dry mass. Since the tapping process takes time, the catalyst will collect moisture from the atmosphere to varying extents, depending on relative humidity, prior exposure, and time of exposure. If an “undried” mass is measured, the packed apparent bulk density of cobalt will be overestimated. This is because accumulated moisture increases the mass of a given volume of catalyst by the amount of water collected, resulting in an inflation of the packed apparent bulk density of cobalt by the relative moisture content. Therefore, to ensure accurate and consistent results, it is preferable for measurements to be made on a “dry” basis. The dry mass may optionally be measured using a moisture balance, which includes a heating stage for removing adsorbed moisture.

(24) Within a microchannel reactor, the packed apparent bulk density of cobalt may optionally be determined by densifying the charge within the microchannels of the reactor using a suitable method (such as those disclosed in WO2013013077, in the name of the present applicant, which is incorporated herein by reference), determining the total mass of catalyst charged, and from this deriving the charged reactor packed apparent bulk density of cobalt.

(25) Catalysts and Fixed Bed Reactor Test Results

(26) Table 3 illustrates nine catalysts that were synthesized according to the invention, as well as a comparative catalyst known in the art. The weight percent of cobalt in the catalysts of the invention varied from 43% to 53%, with a packed apparent bulk density of at least 1.32 g/mL.

(27) For the fixed bed reactor test, a catalyst sample of volume of 0.1285 mL was diluted with 2.184 mL of SiC (1:18 volume ratio) and loaded into a reactor. The catalyst was activated by flowing H.sub.2 at 400° C. for two hours, at atmospheric pressure and a GHSV of 15000 hr.sup.1. After activation, the reactor was cooled to 165° C. and the gas flow switched to synthesis gas (H.sub.2:CO 2:1, 5% N.sub.2 diluent) before holding at this temperature for 2 hours. The pressure was then increased to 2000 kPa (20 bar), and the reactor temperature was then ramped to the target test temperature of 205° C. The test was run for 140 hours. Deactivation was measured in the periods of from 0 hours to 24 hours and from 116 hours to 140 hours, with the conversions and selectivities noted at 24 and 140 hours.

(28) As can be seen from the fixed bed reactor test results in Table 3, all of the catalysts according to the invention exhibited a significantly higher CO conversion than the comparative example. The highest CO conversation was observed with catalyst #9, which contains 53% by weight of cobalt, and has a packed apparent bulk density of 1.63 g/mL and a packed apparent bulk density of cobalt of 0.86 g/mL. Furthermore, all of the catalysts according to the invention exhibited a lower deactivation rate than the comparative example and, as such, can be used for a longer period of time in a Fischer-Tropsch reaction before regeneration is required.

(29) Table 4 illustrates two catalysts that were synthesized according to the invention, as well as a several comparative catalysts. C2-C14 represent ActOCat 1200, which is a catalyst known in the art. The reference catalyst (#C2) has a PABD of cobalt of 0.426 g/ml, comparative catalysts #C3-C14 have a PABD of cobalt of 0.596 g/ml and the catalysts according to the invention (#10-11) have a PABD of cobalt of 0.784 g/ml.

(30) The final column in Table 4 is the cobalt time yield (CTY), which is the moles of CO converted per mole of cobalt in the sample per unit time, and is representative of the efficiency of the catalyst.

(31) Comparing C2 with C3-C14 in Table 4, as expected it can be seen that increasing the catalyst PABD, and thus increasing the PABD of cobalt, increases the moles of CO converted per mL of catalyst, per hour (from 29 mmol CO ml.sup.−1 h.sup.−1 to 37-44 mmol CO ml.sup.−1 h.sup.−1). However, the efficiency of the catalyst (the CTY) does not increase and remains approximately the same (1.1 mmol CO mol Co.sup.−1 s.sup.−1 compared to 1.00-1.2 mmol CO mol Co.sup.−1 s.sup.−1).

(32) However, comparing #10-11 with C2-C14 in Table 4, it can be seen that increasing the catalyst PABD, and thus increasing the PABD of cobalt, increases both the moles of CO converted per mL of catalyst per hour, and the efficiency of the catalyst. The efficiency (CTY) increases from to 1.00-1.2 mmol CO mol Co.sup.−1 s.sup.−1 in the comparative catalysts to approximately 1.5 mmol CO mol Co.sup.−1 s.sup.−1 in the catalysts according to the invention. Therefore, the catalysts of the invention not only increase the PABD of cobalt in the catalyst, such that the moles of CO converted increases, but do so in a way that is considerably more efficient than catalysts of the art.

(33) This is achieved through use of the method of making a Fischer-Tropsch catalyst according to the invention. Catalysts #12-13 were made using AGC silica and the excess liquid impregnation method, wherein the support is impregnated 130% of the pore volume of the support. Therefore, the method of making a Fischer-Tropsch catalyst according to the invention results in catalysts which are more efficient than catalysts of the art.

(34) TABLE-US-00003 TABLE 3 Catalyst composition Fixed bed reactor test resuits Co Ti Re Pt No. PABD ρ Co XCO XCO Deactivation C5+ C5+ CH4 CH4 # Catalyst ID Silica wt. % wt. % wt. % wt. % steps (g/mL) (g/mL) (t1) (t2) Rate (%/day) (t1) (t2) (t1) (t2) C1 1401-28-009-1 PD12058 33 6.5 0.2 0.03 4 0.67 0.22 34.48 29.76 −0.86 87.1 84.92 7.29 8.03 1 1402-17-013-1 LC150 2 48 5.5 0.3 0.015 8 1.32 0.63 71.8 69.3 −0.56 87.3 85.3 9.1 9.1 2 1402-21-051-1 LC150 2 48 5.5 0.1 0.045 8 1.33 0.63 69.94 70.57 0.04 85.1 85.02 9.25 9.01 3 1402-21-051-2 PD12058 43 6.5 0.2 0.03 8 1.49 0.64 67.03 70.27 0.56 84.93 83.89 10.32 9.94 4 1403-27-009-1 LC150 1 48 5.5 0.1 0.015 8 1.37 0.65 76.7 74.9 −0.45 87.1 85 9.6 9.4 5 1402-07-009-2 LC150 1 48 5.5 0.3 0.045 8 1.42 0.68 77.27 75.27 −0.38 85.86 84.32 10.45 10.1 6 1402-17-013-2 LC150 1 48 7.5 0.3 0.015 8 1.44 0.69 68.4 67.9 −0.25 84.3 83 11.6 11 7 1403-26-009-3 LC150 1 48 7.5 0.1 0.045 8 1.45 0.69 71.6 71.8 −0.16 84.9 83.1 11 10.7 8 1403-26-009-2 LC150 2 48 7.5 0.1 0.015 8 1.45 0.69 68.4 70.4 0.1 86.1 84.3 9.9 9.8 9 1402-07-009-1 PD12058 53 6.5 0.2 0.03 8 1.63 0.86 80.76 79.03 −0.35 86.77 84.59 9.84 10.1 PABD = Packed apparent bulk density

(35) TABLE-US-00004 TABLE 4 Catalysts Methanation Results PABD g Co mmol CO mmol CO mmol CO # Catalyst Cat. ID (g ml.sup.−1) ml.sup.−1 ml.sup.−1 h.sup.−1 gCo.sup.−1 h.sup.−1 mol Co.sup.−1 s.sup.−1 C2 Reference 1412-03-003-2 0.99 0.426 29.153 68.434 1.101 C3 ActOCat 1200 + 3 w/o Pt 1609-27-059-4 1.25 0.596 37.268 62.530 1.006 C4 ActOCat 1200 + 3 w/o Pt 1609-27-059-4 1.25 0.596 37.306 62.594 1.007 C5 ActOCat 1200 + 3 w/o Pt 1609-27-059-4 1.25 0.596 37.412 62.773 1.010 C6 ActOCat 1200 + 3 w/o Pt 1609-27-059-4 1.25 0.596 37.549 63.003 1.013 C7 ActOCat 1200 + 3 w/o Pt 1609-27-059-4 1.25 0.596 40.100 67.282 1.082 C8 ActOCat 1200 + 3 w/o Pt 1609-27-059-4 1.25 0.596 41.552 69.718 1.121 C9 ActOCat 1200 + 3 with Pt 1611-28-059-4 1.25 0.596 41.397 69.459 1.117 C10 ActOCat 1200 + 3 with Pt 1611-28-059-4 1.25 0.596 41.937 70.364 1.132 C11 ActOCat 1200 + 3 with Pt 1611-28-059-4 1.25 0.596 42.576 71.435 1.149 C12 ActOCat 1200 + 3 with Pt 1611-28-059-4 1.25 0.596 42.959 72.079 1.159 C13 ActOCat 1200 + 3 with Pt 1611-28-059-4 1.25 0.596 44.530 74.715 1.202 C14 ActOCat 1200 + 3 with Pt 1611-28-059-4 1.25 0.596 44.589 74.815 1.203 10 Present Invention 1504-30-055-1 1.48 0.784 72.516 92.447 1.487 11 Present Invention 1504-30-055-1 1.48 0.784 73.284 93.427 1.503

(36) Poisoning Resistance

(37) Poisoning by reactive nitrogen compounds is unusual in that they are not “fatal”, but rather produce a deactivation of the catalyst which eventually saturates at a non-zero catalyst activity. The exact saturation activity is dependent on both the catalyst and reactor type being used, but is typically in the region of 30% to 50% of the fresh catalyst activity.

(38) FIG. 2 compares the poisoning resistance of catalyst #9 with comparative example ActOCat 1200, which is a catalyst known in the art having 43% by weight of cobalt. Catalyst #9, with 53% by weight of cobalt, has roughly 184% the PABD of cobalt in the reactor compared to the comparative example.

(39) As can be seen in the figure, the ActOCat 1200 catalyst experiences saturated deactivation after about 250 hours of exposure. In contrast, catalyst #9 does not reach saturated deactivation until about 640 hours of exposure, or about 2.5 times as long, with the same NH.sub.3 feed level. This illustrates the vastly improved poisoning resistance of the catalysts of the invention compared to those in the art.

(40) FIG. 3 demonstrates the improved resistance to sulfur poisoning of the catalysts of the invention. The average amount of sulfur exposed to the catalyst is approximately 2.9×10.sup.−3 molsS/molCo (which is about the same exposure expected at a dosing of 5 ppbv for a 2 yr life).

(41) As can be seen in the figure, at the same flux of H.sub.2S, the rate at which CO conversion declines is significantly less for the high cobalt-containing catalyst of the invention compared to the comparative ActOCat 1200 catalyst. The catalysts of the invention can accommodate H.sub.2S better than the comparative catalyst because of the higher cobalt surface area per packed volume of catalyst in the reactor.

(42) Operating Temperature

(43) Catalyst #9 in Table 3 was used in a Fischer-Tropsch reaction and compared to ActOCat 1200. Catalyst #9 contains 53% by weight of cobalt, whereas ActOCat 1200 contains 43% by weight of cobalt, and thus has a lower PABD of cobalt.

(44) The reaction conditions were as follows: Feed H.sub.2:CO=1.77, 32% inerts, 290 ms contact time, 2.461 MPa (357 psig) inlet pressure. C15 and C16 both used ActOCat 1200, but with a slightly different average reactor temperature.

(45) TABLE-US-00005 TABLE 5 ActOCat 1200 Catalyst # 9 C15 C16 Hours on stream 214 215 217 Avg. reactor T (° C.) 202.5 212 210 CO conversion 74.0% 73.0% 73.9% CH.sub.4 selectivity 6.4% 6.6% 6.4% CO.sub.2 selectivity 0.0% 0.4% 0.4% C2 selectivity 0.6% 0.8% 0.6% C3 selectivity 1.8% 2.1% 1.8% C4 selectivity 2.0% 2.4% 2.3% C5+ selectivity 89.2% 87.8% 88.5% Wax alpha 0.943 0.933 —

(46) As can be seen from Table 5, the comparative data indicates that catalyst #9 uses a reactor temperature that is lower by approximately 8-10° C. for an identical performance (i.e. identical activity) under the same operating conditions.

(47) Furthermore, the lower operating temperature used with catalyst #9 provides an alpha number improvement of approximately 0.07-0.10, as analyzed for the C25-C90 wax carbon number range. As discussed earlier, this advantageously increases the economic value of the products of the reaction.

(48) A further consequence of the lower operating temperature used by catalyst #9, compared to catalysts of the art, is a longer time before regeneration is required, thus increasing the economic value of the reaction process.