Deactivation mineral processing

The recovery, regeneration, and repeated reuse of the active catalyst are of prime importance in substantially reducing the overall cost of coal liquefaction. The used catalysts usually remain in the bottoms products, which consist of nondistillable asphaltenes, preasphaltenes, unreacted coal, and minerals. The asphaltenes and preasphaltenes can be recycled with the catalyst in bottoms recycle processes. However, unreacted coal and minerals, if present in the recycle, dilute the catalyst and limit the amount of allowable bottoms recycle because they unnecessarily increase the slurry viscosity and corrosion problems. Hence, these useless components should be removed or at least reduced in concentration. If the catalyst is deactivated, reactivation becomes necessary before reuse. Thus, the design of means for catalyst regeneration and recycle is necessary for an effective coal liquefaction process. Several approaches to achieving these goals are discussed below. 

It seems that fluid-bed cracking reactor (thermal or catalytic) is the best solution for industrial scale. However, regeneration and circulation of so-called equilibrium cracking catalyst is possible for relatively pure feeds, for instance crude oil derived from vacuum gas oils. Municipal waste plastics contain different mineral impurities, trace of products and additives that can quickly deactivate the catalyst. In many cases regeneration of catalyst can be impossible. Therefore in waste plastics cracking cheap, disposable catalysts should be preferably applied. Expensive and sophisticated zeolite and other molecular sieves or noble-metal-based catalysts will find presumably limited application in this kind of process. The other solution is thermal process, with inert fluidization agent and a coke removal section or multi-tube reactor with internal mixers for smaller plants. 

Desalting is a water-washing operation performed at the production field and at the refinery site for additional crude oil cleanup (Fig. 13.2). If the petroleum from the separators contains water and dirt, water washing can remove much of the water-soluble minerals and entrained solids. If these crude oil contaminants are not removed, they can cause operating problems during refinery processing, such as equipment plugging and corrosion as well as catalyst deactivation. 

The heteroatom reactants do not themselveB deactivate the catalyst the catalyst deactivates due to coke formation from hydrocarbons and metal deposition from the mineral in coal. The commercial HT process cannot be easily carried out on a bench scale, because of materials handling and pressure pioblenis however, the process is carried out on a demonstration scale at the Advanced Coal Lique ction Research and Devdopment Facility at Wilsonville, AL. Small portions of the catalyst are removed at various deactivation levels, quantified as the weight of product per weight of catalyst, with the metals and coke deposits on the removed solid being characterized. 

The pK found in this way may be directly compared with Forster-cycle calculations. However, straightforward utilization of the fluorescence titration method is usually limited to moderately strong photoacids due to partial deactivation processes of the photoacid occurring in very concentrated mineral acid solutions. The most accurate method of finding the pK of a photoacid is by direct kinetic measurements of the excited-state proton dissociation and recombination rates °. However, these measurements are not trivial and are limited to a relatively small number of photoacids where accurate measurement of the excited-state reversible dynamics of the proton-transfer reaction is possible. 

Table 6 shows the effect of traces of mineral acid concerning the hydrolytic behaviour of PA-6 during processing. Active mineral acids catalyse the hydrolysis. It is assumed for sample 4 and 8 that during the water treatment, traces of phosphoric acid were absorbed by PA-6, which then became active during processing. If bases (NaHCOs) were added for neutralisation and deactivation of the acid... 

A deactivating agent for copper-activated sphalerite is any species that has sufficient affinity for copper(I) or (II) to compete for it with sulfide ions in the surface lattice of the mineral, thus removing it from the surface. Ligands such as cyanide or ethylenediamine, which coordinate strongly to copper, have therefore been found to be the most effective. A knowledge of the stability of the species present in a system composed of H+, Zn +, Cu +, and CN ions has enabled the extent of deactivation Ijy cyanide ion to be predicted the results of these predictions are compared with experimental observations in Figure 2. This approach has been successfully extended to the effects of pH and the presence of other ions such as carbonate on the activation and deactivation processes, and is a pertinent example of the quantitative application of coordination chemistry to complex systems. 

If these crude oil contaminants were not removed, they would cause operating problems during refinery processing. The solids (dirt and silt) would plug equipment. Some of the solids, being minerals, would dissociate at high temperature and corrode equipment. Still others would deactivate catalysts used in some refining processes. 

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