Titania catalysts, their preparation and use in fischer-tropsch synthesis

Preparation of titania catalysts and their use in synthesis processes using the Fischer-Tropsch method

Fischer-Tropsch catalysts

Full description

Background of the invention

This invention relates to carrier materials containing titania, their preparation and use as catalysts (with added metal(s)) in the hydrocarbon synthesis of Fischer-Tropsch catalysts. This invention relates very specifically to a material that can withstand the high partial pressures of water often encountered in hydrocarbon synthesis processes such as slurry-based processes.

US Patent No. 5,140,050 describes advances in the preparation of carrier materials useful in the preparation of Fischer-Tropsch catalysts, and unexpected results obtained from the use of those catalysts in the Fischer-Tropsch catalysts process. As useful as these catalysts and carriers are, the operating conditions for the synthesis of Fischer-Tropsch catalysts, especially the relatively high partial pressures of water that occur as a result of Fischer-Tropsch catalyst reactions, lead to weakening of the catalysts and the formation of excess fines in the mixture. Interaction. Fine materials have harmful effects, including clogging of lines, reduced catalyst effectiveness, loss of catalyst through filters, and clogging of filters. Therefore, there is a need to develop a catalyst that can maintain its consistency. And thus its effectiveness... under evaporation conditions such as those that exist during the Fischer-Tropsch process

Fischer-Tropsch catalysts. The intensity of slurry operations, combined with the steam conditions in particular, requires a catalyst with high corrosion resistance. General description of the invention

According to this invention, both silica and alumina are used as binders for a carrier containing titania to achieve the required cohesion of the catalyst used in the synthesis of Fischer-Tropsch catalysts. The catalyst is formed by dispersing one or more active metals for Fischer-Tropsch catalysts, such as Group 8 metals such as cobalt or ruthenium, onto the surface of the carrier material. Thus, a catalyst is created with a high resistance - as measured by corrosion resistance - that maintains its consistency under conditions of relatively high partial pressure of water at high temperatures, such as 175 - 400 C, used in the Fischer-Tropsch processes.

Fischer-Tropsch catalysts.

US Patents No. 5,140,050 and No. 4,992,406 disclose improvements in the porosity of carrier materials containing titania due to the use of binders such as alumina, zirconia, or silica - in that order of preference. However, the invention herein disclosed reveals that the use of silica, a less preferable substance than alumina as a binder, with alumina produces a titania containing substance with resistance to corrosion, whether in the dry state or under evaporative conditions, more than Either alumina or silica alone. Thus, there is an apparent anomaly in the fact that adding

A less favorable material is a composition containing titania and alumina and results in a strong carrier as well.

The mechanism by which alumina and silica synergistically produce a material containing titania with high strength has not been clarified. However, without wishing to be attached to any particular mechanism, we see that small silica particles in the finished roasted carrier occupy positions at the interface between the large alumina particles and the very large titania particles and act as a kind of chemical docking agent. Thus, silica crystalline grains can be partially combined with both alumina and titania crystalline grains to form an essentially continuous crystalline phase. Silica acts as a bonding agent between alumina and titania. Steam, either during roasting or the synthesis of Fischer-Tropsch catalysts, can also form these mixed marginal phases of silica with alumina and silica with titania. Moreover, alumina itself does not mix well with titania and only physical forces are used to bind the particles. Steam can break down these physical forces well by agglomerating the alumina anyway and creating large alumina particles that are less able to provide binding properties. Silica itself is not a good binder because of its affinity for titania, which causes silica to lose much of its separation.

Brief explanation of the drawings

Figure (1): It is a graph of ultrasonic frictional wear for different samples, where the vertical coordinate represents fine materials by weight percentage with a value less than 25 microns, and the ordinate is

The sigmoid is the time in minutes in the ultrasound bath. Curves A, B, C, and D represent titania carriers with evaporated alumina, new alumina, evaporated silica-alumina, and new silica-alumina binders, respectively.

Detailed description:

A carrier containing titania is a particulate material that preferably contains at least about 50% by weight titania, very preferably at least 80% by weight titania, and preferably has a rutile:anatase ratio of approximately 1:9. . This material is mixed with appropriate amounts of silica and alumina that act as binding materials, where the binding material constitutes 3 to less than 30% by weight, preferably 3-20% by weight, and very preferably also 4-15% by weight, and very preferably also 5 - 10% by weight of the total carrier material. The mixture of silica and alumina binder contains 3-50% by weight silica, and very preferably 5-35% by weight silica.

The carrier is usually formed into porous particles with spherical or cylindrical shapes mainly by well-known methods such as extrusion, filamentation, agglomeration, spray drying, etc. A preferred method is spray drying, in which an aqueous slurry suitable for titania and binders are sprayed in a purged chamber with heated air. Spray drying produces a spherical carrier material with a size range of about 20-120 microns, which is well suited for use in Fischer-Tropsch process slurries.

Fischer-Tropsch catalysts

To achieve the benefits of porosity and strength, the binder components are mixed with titania primer prior to the forming process. They can be added in several forms, preferably as salts or as suspensions or colloidal solutions. For example, alumina solutions formed from aluminum chloride or acetate and nitrate are preferred sources of the alumina component. Ready-to-use silica solutions are preferred sources of the silica component. However, care should be taken in each case to avoid contamination of these binding solutions with elements that are harmful to the Fischer-Tropsch catalysts. For example, alkali cations, earth alkalis, and sulfur-containing anions such as carbonates are strong cobalt poisons under Fischer-Tropsch catalyst conditions and should therefore be minimized when preparing cobalt catalyst carriers.

The titania carrier material is usually baked after forming to plasticize the binders and optionally convert the anatase phase of titania to the rutile phase. This roasting is usually performed in air at temperatures ranging from 500 to 1000 C. When Fischer-Tropsch catalysts are prepared from this carrier, catalytically active cobalt metals are combined to create Fischer-Tropsch catalysts with the carrier. Enhancers such as zirconium, titanium, ruthenium, hafnium, cerium, thorium, uranium, and others that are well known to those skilled in this field can also be used. The metal or metals are present in amounts that are catalytically effective for Fischer-Tropsch synthesis

Fischer-Tropsch catalysts vary depending on the metal being chosen. Cobalt is preferably used in amounts of approximately 2-40% by weight, very preferably 5-30% by weight, and very preferably 10-25% by weight.

When boosters are used, they are used in smaller quantities of the active catalytic metal, in weight ratios for example from about 1/20 to 1/10 depending on the active metal. (This invention also foresees the use of ruthenium as an enhancer in combination with cobalt as an effective primary catalytic metal.) The preferred catalysts are often those containing cobalt and rhenium, cobalt and ruthenium, cobalt and thoria, and especially those containing cobalt and rhenium.

The catalyst can be prepared by various methods well known to those skilled in the art, including impregnation (either co-impregnation with enhancers or successive impregnation by either spray-drying or first-wetting methods). The preferred catalyst for fixed-bed Fischer-Tropsch catalysts is one in which the catalytic metals are located on the outside of the catalyst particle, i.e. in a layer no thicker than 250 microns, and preferably no more than 200 microns, and the preferred method for preparing the catalyst is It is the spraying method mentioned in US Patent No. 5,140,050, which is incorporated herein by reference, or in European Patent No. 0,266,898, which is incorporated herein by reference. For Fischer-Tropsch catalysts using slurry, the catalysts are preferably made by impregnation using the initial wetness of spray-dried carrier materials.

Measuring the strength of particles containing titania is not an easy task as the finely divided products of frictional wear have a tendency to adhere to the original surfaces and are not detectable by conventional methods such as the well-known Davison frictional wear test or Microtrac or Malvern diffractometers. Therefore, a new accelerated friction wear test has been developed, the results of which are reproducible and are believed to work based on micro-optical SEM images of friction wear products in a wear or grinding medium similar to the medium found in large slurry bubble column units.

The test consists of treating a small sample such as about 0.5 to about 3 g of catalyst or carrier suspended in acetone and subjecting it to an ultrasonic bath for the period of time mentioned, followed by filtration to determine the amount of fine material, i.e. producing particles with an average diameter of less than 25 microns. Therefore, 2.5 g of the sample is filled, after sieving it to a size of +45 microns, and suspending it in 12 ml of acetone in a 0.5 ounce (14 g) vial. After exposure to ultrasound in a Branson Model 2200 sonicating bath, usually for 30 minutes or longer, the mixture is filtered through a 500-mesh strainer (with 25-micron openings) onto a 0.02-micron filter membrane (Whatman Anodisc). The solids are then washed with acetone, dried, and weighed to determine a yield with a weight percentage of less than 25 microns. The synthesis of Fischer-Tropsch catalysts is a well-known process and the reaction conditions are mentioned in the available references. For example, temperatures may range from 175-400°C soon, and preferably from 180-250°C soon, while pressures may range from 1-100°C soon, and preferably from 15-40 bar soon. Hydrogen/CO ratios may range from 0.5/1 to

Approximately 1/4, preferably from 1.7/1 to approximately 2.5/1, and preferably an amount according to the chemical equation equal to approximately ± 3%. It is preferable to use the catalyst made from the carrier material of this invention in a slurry: such as a column-shaped reactor with a slurry through which bubbles pass, where the vacuum gas velocities per hour may range from 4,000 - 20,000. A slurry column process through which bubbles pass is described in U.S. Pat. No. 5,348,982, which is incorporated herein by reference.

Examples:

12 titania carrier materials were prepared by spray-drying mixtures of different binders with Degussa P-25 Tio2. The dried carriers were roasted between 700°C and 1000°C in rotary roasters. The amount and source of alumina binder and silica binder, the weight percentage of solids in the spray dryer feed, and the final baking temperature used in each of these twelve carrier materials are summarized in Table (1). Alumina chiorhydrol solution was made by GRACE Davison, named 100-CX and contains about 23.5% by weight A1203. Analytical inspections are also presented in Table 1, including data from 30-minute ultrasonic friction wear tests. The rutile content refers to the weight percentage of the rutile phase in titania, with the remainder being the anatase phase, as determined by X-ray diffraction (ASTMD 78-3720). SA refers to the surface area of the BET, and PV refers to the pore volume of pores less than about 5000 angstroms in diameter, measured with a mercury porosimeter (using a mercury contact angle of 125 degrees).

Examples (1 and 2) represent the case of the base with a titania binder, which here has reasonably good resistance and lacks resistance upon evaporation, as will be explained later. Examples (3-5) with silica solutions from different commercial suppliers produced very weak particles with a large fraction of fine material after baking, showing that using a silica binder alone is not a viable option. Example (6) illustrates this invention with the inclusion of a binder consisting of a mixture of alumina and silica solutions in a weight ratio of 9 to 1. This carrier material already shows the lowest value for ultrasonic frictional wear, and therefore the best resistance, among the unknown examples of steam.

Examples (7-12) in Table (1) were calcined at 700 C and therefore have a lower rutile titania content, large surface area, and large pore volume compared to examples (1-6). The large pore size is an important property in particular, as more active metal can be deposited with each initial wetting as the pore size increases. Figure (7) shows that, using the same mixture of alumina and silica binders as in Example (6), a significant improvement in pore volume gain can be achieved at the low baking temperature with only a small loss in particle strength. Comparing example (8) with (7) shows that changing the ratios of alumina to silica from 9:1 to 2:1, in a fixed composition of 6% by weight, can lead to a good pore size. However, a high binder concentration with a total value of 12 wt% versus 6 wt% gives a lower pore volume as shown by examples (8), (9) and (12). Examples (11) and (12) show that similar results are also obtained using aluminum nitrate

Aluminum nitrate instead of alumina chiorhydrol solution as a source of alumina bonding material.

Table 2 summarizes the minimum results obtained when silica is added to alumina-bound carrier materials after spray drying. Silica was added by impregnating tetraethyl silicate from a methanol solution, followed by drying and roasting at 800 C for 3 hours in a laboratory oven. As shown in the table, a lot of the added silicas are lost by volatilization during drying or roasting, which appears to be a serious problem for this method. Also importantly, the silica that remained on the carrier did nothing to improve the particle's resistance. In Example (13), adding silica to the carrier material of Example (1) failed to significantly improve the resistance. Example (14) used a carrier material with the same composition as Example (1), but it was a very weak starting material as a result of baking it at 850°C in a static oven. Example (15) used a very weak carrier material prepared by spray drying for an experimental deposited image of titania instead of 25-Degussa P. In both examples (14) and (15), the carrier materials also became weak after adding silica, and the bonded alumina may also be weakened by steam in the roasting step. It is clear from these examples that silica must work with alumina as an improved binder, and both must be present in the initial spray drying step. To also determine the balances for the new Sio2-A1203 binders, the two CO-Re catalysts were prepared: a base case with a titania carrier containing 6% of the A1203 binder. An example of this invention includes a titania carrier with 6% of the A1203 binder. Sio2 with a ratio of 9:1. Spray-dried carrier materials were created similarly to examples (1) and (6), but

On a larger scale. Each catalyst was then made by first impregnating aqueous solution of cobalt nitrate and perrhenic acid, followed by air roasting at approximately 400°C in a rotary roaster. Double impregnations/bakings were used to achieve the final metal loadings. The catalysts were tested using H2/CO synthesis gas at a 2:1 ratio in a small fixed bed reactor after reduction at 375°C. All catalysts were highly effective and selective in forming hydrocarbons, as shown in Table 3.

The final test for maximum critical resistance comes when the catalyst is subjected to high vapor partial pressure at a moderate temperature, such as that produced in hydrocarbon synthesis. To excite this medium, portions of each catalyst were packed into a fluidized bed reactor and treated with pure steam at approximately 250 °C and a pressure of 6.8 atm for a period of up to 6 days. New and steam-containing models were then evaluated for resistance to frictional wear using an ultrasonic friction wear test with a range of ultrasonic waves and multiple times. The results are summarized in examples (16-19) in Table (4) and shown graphically in Figure (1). Referring to Figure (1), it is clear that the amount of fine materials produced in the friction wear test increases with the increase in the number of times the ultrasonic waves are performed for all materials. Steam weakens the alumina bond, as shown in line A of the data. The silica-alumina binder of this invention (line C) weakens only very slightly upon evaporation, while it still maintains its balance in the case of alumina that is not exposed to steam as well (line B). A noticeable improvement in initial resistance and vapor stability was achieved with the use of the developed binder.

Table (1): Spray-dried titania carrier materials

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