Finishing, catalyst

Curing Catalysts for A Methylol Agents. Many acid-type catalysts have been used in finishing formulations to produce a durable press finish. Catalyst selection must take into consideration not only achievement of the desked chemical reaction, but also such secondary effects as influence on dyes, effluent standards, formaldehyde release, discoloration of fabric, chlorine retention, and formation of odors. In much of the industry, the chemical suppher specifies a catalyst for the agent so the exact content of the catalyst may not be known by the finisher. 

In many cases drying operations are critical to the production of successful commercial catalysts. Close control of the drying process is necessary to achieve the proper distribution of the catalyst precursor within the pore structure of the support. Drying also influences the physical characteristics of the finished catalyst and the ease with which subsequent pelleting or extrusion processes may be carried out. 

The high specific surface area supports (10 to 100 m2/g or more) are natural or man-made materials that normally are handled as fine powders. When processed into the finished catalyst pellet, these materials often give rise to pore size distributions of the macro-micro type mentioned previously. The micropores exist within the powder itself, and the macropores are created between the fine particles when they... 

Although a carrier is often the major constituent of a catalyst pellet, one often finds that there are materials that are added in small amounts during catalyst preparation in order to impart improved characteristics to the finished catalyst. These materials are referred to as promoters. They may lead to better activity, selectivity, or stability. The manner in which promoters act is not well understood, although a number of plausible explanations have been set forth. They remain one of the reasons for the black magic aura of catalysis. 

This method involves the repeated dipping of porous support materials into a solution containing the desired catalytic agent. It is then dried and calcined to transform the metal into insoluble form. The agent must be applied uniformly in a predetermined quantity to a preset depth of penetration. The metal loading in the finished catalyst is typically 1-5%, Fig. 6.5. 

This technique was successfully used to monitor the deposition of catalyst within a support pellet and clearly distinguish the amount of penetration there was into the pellet. Therefore, one can quickly obtain a time required to produce a catalyst pellet that is of the egg-shell type or completely saturated. Moreover, it is possible to very finely resolve the thickness of the catalyst penetration into the particle, resulting in good control of the finished catalyst. 

Figure 2. Compositional diagram for the preparation of bismuth molybdate catalysts using the HI AD process configuration shown in Figure 1 at 900°C using air as make up gas. Plot is of concentrations of bismuth used in the reacting solution vs arc plasma analyzed concentrations of the finished catalysts directly fi-om HTAD reactor Circles Co-precipitation prepared materials. Triangles Up flow prepared aerosol materials. Squares. Down flow prepared aerosol materials.

The secrecy of the manufacturing processes is maintained partially by discouraging outside investigators through patent protection. However, the most important aspect of the protection is probably that examination of the finished catalyst offers little information on how it was prepared and no information on why a particular preparation procedure was used. 

The finished catalyst consists of irregular pieces of a narrow range of sizes. 

Impregnated catalysts are prepared by impregnating a metal salt on a porous support. The metal loading in the finished catalyst is typically 1-5 %. 

For optimal performance of dual function isomerization catalysts based on zeolite Y or mordenite, extensive removal of sodium is necessary. The finished catalyst must be highly crystalline, and the finely dispersed metallic hydrogenation function should be well distributed throughout the catalyst particles. The proposed mechanism explains the stabilizing influence on conversion and the suppression of cracking reactions by addition of the metallic hydrogenation function to the active acidic catalyst base. 

Table II provides another illustration of this effect. In these experiments analysis was done by mercury intrusion, which is sensitive to a broader range of pores. In this series of experiments, samples of hydrogel were washed in various alcohol-water mixtures to yield pore volumes ranging from high, for the sample washed in pure alcohol, to low, for the sample washed in pure water. This procedure does not affect the surface area, which remained constant at 375 m2/g The activity of the finished catalyst increases with the pore volume. Notice that all samples have about the same volume inside...

The advantage of using a phosphine complex is that it contains no chloride, and the counter-ion is easily decomposed or eliminated. The complex has to be synthesised (not easy or cheap), and nonaqueous solutions are needed, which means that the support must be dehydrated, the solvent dried, and the finished catalyst stored in ampoules sealed under vacuum. 

The preparation of a successful supported bimetallic catalyst is quite a difficult proposition. The main problem is to ensure that the two components reside in the same particle in the finished catalyst, and to know that it is so. The main physical techniques to characterise bimetallic particles are hydrogen chemisorption, XRD, TEM, EDX, XPS, XAFS,197Au Mossbauer (Section 3.3) and CO chemisorption coupled by IR spectroscopy (Section 5.3). The characterisation of bimetallic catalysts is not always thoroughly done, and there is the further complication of structural changes (particularly of the surface) during use. In situ or post-operative characterisation would reveal them, but it is rarely done. 

The method of preparation plays a dominant role in determining the structure and composition of the finished catalyst, and in the COPPT method the support is formed during the preparation. We now examine how the method adopted controls the structure of the catalyst, and hence its activity... 

When multicomponent solid systems are used to prepare a catalyst, homogenization of the precursors (mixing at the molecular level) is extremely important The activity of the finished catalyst should not differ in the different parts of a catalyst charge, or from batch to batch of it. Two fundamental aspects of solid-state reactions involved in the preparation of catalysts are nuclcation and the growth from solution of the nuclei or elementary particles into distinct solid phases in the... 

These catalysts were modified by adding non-volatile inorganic acids and their salts, namely orthophosphoric acid, boric acid, barium sulfate, sodium silicate, barium nitrate, and hydrofluoric acid. The additives were added to the finished catalyst by direct impregnation from solution. The presence of the additives did not alter the specific surface or the geometric structure of the final preparations. 

In mid 1959 a significant decision was made, with the sales manager and me dissenting, not to enter the finished catalyst business at that time with our new isomerization catalyst, and to concentrate instead on the adsorbent portion of the molecular sieve business. Accordingly, a major reduction was made in the level of our catalytic studies with zeolites shortly thereafter. 

Sample Solution Fill a 100-mL porcelain crucible halffull of ashless filter paper pulp. Place 2 g of the finished catalyst, in droplet or flake form and accurately weighed, on top of the paper pulp. Transfer the crucible to a muffle furnace set at room temperature, and slowly raise the temperature to 650° so that the stearine melts into the paper, and the organic mass bums and chars slowly. Continue heating at 650° for 2 h or until the carbon is burned off. Cool, add 20 mL of hydrochloric acid, quantitatively transfer the solution or suspension into a 400-mL beaker, and carefully evaporate to dryness on a steam bath. Cool, add 20 mL of hydrochloric acid, warm to aid dissolution (catalysts containing silica will not dissolve completely), transfer into a 500-mL volumetric flask, dilute to volume with water, and mix. Allow any solids to settle, pipet a clear, 50-mL aliquot into a 400-mL beaker, and dilute to 250 mL with water. (If there is suspended matter in the volumetric flask, filter a portion through a dry, medium-speed filter paper into a dry receiver, and pipet from the receiver.)... 

As might be expected, finished catalyst shapes are dictated by the process for which they are used fixed bed, moving bed, or fluidized bed. Each process type has its own physical performance requirements of hardness, abrasion resistance, pressure drop, flow characteristics, pore size distribution, surface area, shape, etc., and these are generally supplied by the support. The active component is primarily responsible for the catalytic performance, when it is properly dispersed throughout the support. 

Limitations of Quality Control. Quality control by detection is based on the inspection of finished catalyst before it is being shipped to the customer. 

In working with catalyst suppliers ve are led to the understanding that SPC procedures and control charts can be applied to the preparation o smaller batches o finished catalysts such as used in chemical industries. 

Alumina promoted FCC catalysts are commercially viable if, and only if, the alumina component produces the desired properties without detrimentally affecting the attrition resistance and the cracking activity of the finished catalyst particle. Previous work (8.9.11) indicated that attrition resistant catalysts containing alumina could be formed only if a highly dispersed, pseudoboehmitic alumina was used. Other studies have demonstrated catalytic performance improvement without determining the attrition character of the catalyst (1-7). 

Precipitation is usually understood as obtaining a solid from a liquid solution. In the production of precipitated catalysts, the first step is the mixing of two or more solutions or suspensions of materials, causing the precipitation of an amorphous or crystalline precipitate or gel. The wet solid is converted to the finished catalyst by filtration, washing, drying, forming, calcination and activation. Adjusting production conditions can vary cristallinity, particle size, porosity, and composition of the precipitate or gel. 

Typical metallic monoliths in use today, illustrated in Fig. 10, have cell densities in the range 15-78 cells cm (100-500 cells inch ), corresponding to individual cell dimensions of 1.1-2.5 mm. To minimize additional back pressure due to the catalyst formulation, it is essential that the eoating be applied in a controlled manner. It is difficult to define a typical thickness of the catalyst layer (often referred to as washcoat layer ), since this inevitably differs from one catalyst manufacturer to another, depending upon the precise processing techniques used and the application for the finished catalyst. However, usually it is about as thick as the metal foil, typically 0.04-0.05 mm. 

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