Extruded catalyst

Base Metal Catalyst - An alternate to a noble metal catalyst is a base metal catalyst. A base metal catalyst can be deposited on a monolithic substrate or is available as a pellet. These pellets are normally extruded and hence are 100% catalyst rather than deposition on a substrate. A benefit of base metal extruded catalyst is that if any poisons are present in the process stream, a deposition of the poisons on the surface of the catalyst occurs. Depending on the type of contaminant, it can frequently be washed away with water. When it is washed, abraded, or atritted, the outer surface is removed and subsequently a new catalyst surface is exposed. Hence, the catalyst can be regenerated. Noble metal catalyst can also be regenerated but the process is more expensive. A noble metal catalyst, depending on the operation, will typically last 30,000 hours. As a rule of thumb, a single shift operation of 40 hours a week, 50 weeks a year results in a total of 2,000 hours per year. Hence, the catalyst might have a 15 year life expectancy. From a cost factor, a typical rule of thumb is that a catalyst might be 10%-15% of the overall capital cost of the equipment. 

The reactor was packed with 2.30 kg of 3-mm diameter extruded catalyst particles. The composition of the commercial waste HBr feed used in this study is given in Table 1. 

Figure 6. XPS wide scans of a commercial copper/aluminum extruded catalyst obtained using silicon Ka x-radiation A. untreated catalyst B. following 200 C for 12 hours in 10% hydrogen/90% helium gas mixture.

Tronconi et al. [46] developed a fully transient two-phase 1D + 1D mathematical model of an SCR honeycomb monolith reactor, where the intrinsic kinetics determined over the powdered SCR catalyst were incorporated, and which also accounts for intra-porous diffusion within the catalyst substrate. Accordingly, the model is able to simulate both coated and bulk extruded catalysts. The model was validated successfully against laboratory data obtained over SCR monolith catalyst samples during transients associated with start-up (ammonia injection), shut-down (ammonia... 

Fig. 40. Typical deactivation curve for residuum hydroprocessing catalyst. Arabian Heavy atmospheric residuum desulfurized to 1.10 wt. % product sulfur with a iV-in. extrudate catalyst (Tamm ei al., 1981).

Fig. 45. Effect of hydrogen partial pressure on vanadium deposition for an Arabian Heavy atmospheric residuum at a reaction temperature of 371°C (700°F) using a -in. extrudate catalyst (Tamm et at., 1981).

Expanded-bed reactors normally operate with 1/32-in. extruded catalysts which require partial recycle of the liquid products to maintain the catalyst particles in an expanded and fluidized state. 

It is also possible to use finely divided catalyst in the expanded-bed reactor. If the catalyst is a suitable size (50 to 200 pm, i.e. 50 x 10 4 to 200 x 10 4 cm), it is possible to operate the expanded-bed reactor without recycling the liquid products to maintain the catalyst in the fluidized state. In addition, the finely divided catalyst has a relatively larger number of external pores on the surface than the extruded catalyst and is less likely to have metal contaminants plugging up these pores because of their size. The overall effect of a finely divided catalyst in this reactor is more efficient sulfur removal for a given set of process conditions. 

To obtain a correct grain size distribution for a catalyst, a proper sampling procedure should be adopted. For example, samples should be taken from various depths within a container in order to determine whether the batch has been rendered inhomogeneous by settling effects, and care must be taken to ensure that the sieving process itself does not cause attrition. In the case of tableted or extruded catalysts the process of attrition may be inhibited by binders used in their preparation. 

The ability of this technology to segregate catalyst at any desired length was demonstrated in a test performed on 1/32 inch diameter extruded catalyst. The spent catalyst was stripped of oil and then length graded into three fractions a short fraction of less than 1.5 mm in length, a mid-range fraction between 1.5 mm and... 

Figure 1. Method of test for radial crush strength of extruded catalyst shapes.

Cross-sectional shapes with a higher external surface per unit particle volume than cylinders (e.g. a clover leaf) can give even larger external specific areas on extruded catalyst these have been used in some hydrodesulfurization catalysts. 

Figure 7 Experimental friction factors obtained with strings of extruded catalyst particles.

The technology now exists to extrude catalyst supports directly in the OCFS form from any extrudable matrix. Thus in addition to standard support ceramics—cordierite, steatite. 

Cince the first commercial H-Oil unit came on-stream at Lake Charles in 1963, a variety of feedstocks have been processed, including heavy cycle oils, atmospheric bottoms, vacuum bottoms, and cutback propane deasphalter bottoms. The unit has operated successfully with both microspheroidal and extrudate catalysts and has been expanded to 6000 bbl/day. 

From 1963 to 1967 a 1/32 inch extrudate catalyst was used. In 1967 relatively minor modifications were made to accommodate a micro-spheroidal fine catalyst. This eliminated the need for the internal recycle pump previously required to supply the liquid velocity necessary for bed expansion. Operating and performance data have been described previously (3, 4). 

From 1967 through 1971 the unit operated with the fine catalyst. During this period the feed was West Texas sour vacuum bottoms cutback with 20% heavy cycle oil. In the last few months of operation with the fine catalyst, conversion of vacuum bottoms to distillate ranged from 55 to 75%, with 75-80% sulfur removal. The performance of the micro-spheroidal or fine catalyst was equivalent to the performance of the 1/32 inch extrudate. The unit capacity was expanded from 2500 to 6000 bbl/day. It was necessary to return to the extrudate catalyst at the higher feed rate to avoid excessive expansion of the catalyst bed. 

Catalyst. Microspheroidal and extrudate catalysts have been used commercially. These catalysts consist of a combination of metals such as cobalt and molybdenum or nickel and molybdenum on an alumina support. An earlier publication reported that a 1/32 inch extrudate performs (3) better than a 1/16 inch extrudate (5). The most active catalyst is the one with the greatest surface area (6, 7). 

The extrudate catalyst requires higher liquid velocities than the flne catalyst to maintain the desired bed expansion. The liquid velocity is provided by recycling a portion of the eflBuent back to the inlet. The recycle or ebullating pump can be located internal or external to the reactor. 

The particle size and form of cracking catalysts are varied, depending on the type of process in which they are used. Pelleted or extruded catalysts, employed in fixed- and moving-granular bed systems, are normally prepared in a cylindrical shape, with dimensions of about 4 mm. 

Fig. 6.3-20 Various shapes of extruded catalyst carriers (courtesy Bonnot, Uniontown, OH, USA)...

German Fixed-bed T3T>e (Early). The first commercial units built in Germany employed a fixed bed of granular or extruded catalyst. In order to provide adequate cooling surface for heat removal, the reactors were of a complex design and of low capacity. Different reactor designs were used for atmospheric- and medium-pressure (7-10 atm) operation. 

Extruded catalysts were made by means of a Winkworth extruder. This could produce a range of shaped (tri-lobe, quadri-lobe, star shapes etc) and cylindrical extrudates at 10 kg h scale with 1-4 mm diameter. A wide variety of lubricants and binding additives were investigated to aid the extrusion process and improve the crush strength of the resulting extrudates. Finding additives that improved the physical properties of the extrudate but did not interfere with the FT chemistry proved to be a challenge but eventually suitable additives were found. 

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