Slurry phase catalyst testing

The catalyst itself was based on a nickel spinel (NiAl204) for stabilization. The active nickel was introduced as surplus of the stoichiometric content of the spinel to the catalyst slurry. The content of active nickel in the final catalyst could be adjusted via the pH during the precipitation. By XRD, a-alumina was identified as an additional phase in case the nickel was incompletely incorporated into the spinel. The sol-gel technique was then used to coat the plates with the catalyst slurry. Good catalyst adhesion was proved by mechanical stress and thermal shock tests. 

The various aspects that are to be considered to achieve a proper and efficient catalyst testing approach are presented. This applies to heterogeneous systems in which the catalyst is the solid phase and the reactants are in the gaseous and/or the liquid phase. The presence of a solid phase introduces complicating phenomena on which this chapter focuses. In this respect, homogeneous catalysis is a limiting case and does not need separate treatment. The solid catalyst can be present as either a packed bed of particles, a wash-coated monolith, a fluid bed, an entrained bed, or in a liquid-phase slurry. 

Support modification has been reported earlier in the open literature [5,6,7,8,9]. Zirconia modification of silica supports was used to prevent the formation of unreducible cobalt-silicates [5]. Zr, Ce, Hf, or U modification of titania supports was reported to prevent the formation of cobalt-titanates during regeneration [6]. To increase the porosity of titania supports, they were modified with small amounts of binders, e.g. silica, alumina or zirconia [7]. Lanthanum oxide promotion of alumina was reported to be beneficial for improved production of products with higher boiling points [8], and zirconia modification of alumina supports was carried out to decrease the interaction of cobalt with alumina [9]. All these modified supports were either used for fixed bed cobalt based Fischer-Tropsch synthesis catalysts or they were used for slurry phase cobalt catalysts, but not tested under realistic Fischer-Tropsch synthesis conditions in large scale slurry bed reactors. 

Laboratory Fischer-Tropsch synthesis tests were performed in a slurry-phase Constant Stirred Tank Reactor. The pre-reduced catalyst (20-30 g) was suspended in ca 300 ml molten Fischer-Tropsch wax. Realistic Fischer-Tropsch conditions were employed, i.e. 220 °C 20 bar commercial synthesis gas feed 50 vol% H2, 25 vol% CO and 25 vol% inerts synthesis gas conversion levels in excess of 50%. Use was made of the ampoule sampling technique as the selected on-line synthesis performance monitoring method [23]. 

Sasol R D has also being investigating the viability of slurry-phase reactors which are essentially fixed-fluidized beds with pdwdered catalyst suspended in a liquid of low volatility (in the Sasol pilot plant tests FT wax is used). 

At high temperatures Sasol tests have shown that the slurry bed has a lower conversion than the fixed fluidized-bed (FFB). At these high temperatures the wax is hydrocracked, ie, there is a negative wax production. To avoid this, the reactor temperature has to be lowered which, of course, means a further drop in conversion. It is not possible to load as much catalyst per unit reactor volume in a slurry phase reactor as in a normal FFB reactor. This gives the latter system an intrinsic advantage. (Increasing the catalyst content of a slurry increases its viscosity, hence the bubble size increases, resulting in a shorter gas residence time.)... 

In recent years, catalysts have been developed which give a non-Schulz-Flory product distribution in fixed beds. Such catalysts should be tested in slurry phase operation. 

The 60 A pore diameter catalyst used by Rebenstorf in the earlier mentioned experiments should therefore not be active in high-yield slurry polymerization. But its activity in low yield gas phase polymerization was almost comparable to the activity of a good catalyst tested in high-yield slurry polymerization. This activity lasted until a yield of approximately 0,3 g/g was reached. 

A single-step process for DME production from synthesis in which methanol is a co-product was also investi ted recently [8385]. The methanol synthesis, methanol dehydration, and water-gas shift reactions occur simultaneous in the reactor over mixed methanol and alcohol dehydration catalysts. The Air Products slurry-phase process has been tested over a wide range of operating conditions and offers the potential for both lower capital and operating costs compared with a multistep proeess in which methanol synthesis Irom synthesis is the first step of the process [83,85]. Most recently, a DME to methanol selectivity of 7624 mol% was claimed for a mixed-eatalyst system operated at 250°C and 65 mol% CO eonversion [84]. The productivity at these eonditions was 4.7 gmol/k of DME and 1.5 gmol/kgdi of methanol. These values compare with 95% DME selectivity and 51% methanol eonversion over a SAPO-16 catalyst at 425°C for the synthesis of DME from methanol [86]. 

Slurry bed reactors using heavy oil to support the catalyst have been tested and can operate over a wider range of operating conditions and feed gas compositions thm the fluid beds. Sasol has now developed an improved Sasol advanced Synthol (SAS) reactor to produce high-grade distillate. The Sasol slurry phase distillate process (SSDP) has been tested in a demonstration plant at Sasol 1 since 1993. The SAS reactor is said to use an iron-based catalyst similar to the one used in its original plants, whereas the SSDP process uses a cobalt catalyst. 

Dimethyl Ether. Synthesis gas conversion to methanol is limited by equiUbrium. One way to increase conversion of synthesis gas is to remove product methanol from the equiUbrium as it is formed. Air Products and others have developed a process that accomplishes this objective by dehydration of methanol to dimethyl ether [115-10-6]. Testing by Air Products at the pilot faciUty in LaPorte has demonstrated a 40% improvement in conversion. The reaction is similar to the Hquid-phase methanol process except that a soHd acid dehydration catalyst is added to the copper-based methanol catalyst slurried in an inert hydrocarbon Hquid (26). 

These reactors for hquids and liquids plus gases employ small particles in the range of 0.05 to 1.0 mm (0.0020 to 0.039 in), the minimum size hmited by filterability. Small diameters are used to provide as large an interface as possible since the internal surface of porous pellets is poorly accessible to the hquid phase. Solids concentrations up to 10 percent by volume can be handled. In hydrogenation of oils with Ni catalyst, however, the sohds content is about 0.5 percent, and in the manufacture of hydroxylamine phosphate with Pd-C it is 0.05 percent. Fischer-Tropsch slurry reac tors have been tested with concentrations of 10 to 950 g catalyst/L (0.624 to 59.3 IbiTi/fF) (Satterfield and Huff, Chem. Eng. Sci., 35, 195 [1980]). 

The semibatch model GASPP is consistent with most of the data published by Wisseroth on gas phase propylene polymerization. The data are too scattered to make quantitative statements about the model discrepancies. There are essentially three catalysts used in his tests. These BASF catalysts are characterized by the parameters listed in Table I. The high solubles for BASF are expected at 80 C and without modifiers in the recipe. The fact that the BASF catalyst parameters are so similar to those evaluated earlier in slurry systems lends credence to the kinetic model. 

The activity tests of liquid-phase oxidation of aqueous phenol solution were conducted in a semibatch slurry reactor at operating conditions given in the caption of Figure 1. The experimental apparatus, the procedure of these measurements and the analysis of the reaction samples are described in detail in a preceding paper [6]. Additional kinetic and mechanistic investigations were carried out in an isothermal, differentially operated "liquid-saturated" fixed-bed reactor [8, 9] which was packed with a pretreated EX-1144.3 catalyst (Sfld-Chemie... 

Finally, the chemical stability of the catalysts employed in this study was tested by means of XRD and EDXS analyses. The examination of fresh and used catalysts shows that during the reaction course metal ions are slowly leached into the aqueous solution, which can be attributed either to the temperature of operation or the presence of complexing carboxylic acids and benzoquinones in the liquid-phase. Contrary to the results obtained in continuous-flow fixed-bed reactors [8, 9], the extent of catalyst dissolution in the slurry reactor was considerable. This is probably due to the higher accumulation of benzoquinones which are known to form stable complexes with metal ions. Examination of the X-ray powder diffraction patterns of the molecular sieves before and after the liquid-phase phenol oxidation... 

In 1975, Chem Systems developed the liquid phase methanol (LPMeOH) process which is based on the low pressure synthesis technology except that the new process is carried out in an inert oil phase [79], The catalytic system used is Cu/Zn0/Al203, that is modified for slurry operation (i.e., attrition resistant, finely powdered, and leaching resistant). The S3.85 and S3.86 catalysts of BASF and EPJ-19 and EPJ-25 catalysts of United Catalysts Inc. were developed for this process [14,19]. The process has been tested for commercial feasibility at a demonstration scale by Air Products and Chemicals, Inc [79]. 

The setup for testing of catalysts has to be as close as possible to the technical conditions of catalyst application. Therefore, powder catalysts for liquid and gas-liquid reactions are usually tested in slurry reactors, which can be operated continuously, under semibatch conditions (constant pressure of the reaction gas, compensation of gas uptake) or in the complete batch mode (no compensation of gas uptake, record of pressure drop of the gas phase). In contrast, catalysts for continuous fixed-bed applications have to be tested in continuous lab-scale fixed-bed reactors. The latter can be operated under either steady-state or non-steady-state (transient) conditions. 

All olefin polymerization processes described in Section 2.5 have been tested, and some are being operated commercially with metallocene catalysts. Metallocenes can be used directly in solution processes but need to be supported to be used in slurry and gas-phase processes. In the latter case, the support of choice is Si02. There are several supporting techniques for metallocenes, but this subject is beyond the scope of this chapter [24]. 

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