Disposal of catalyst

Nonhazardous spent catalysts can be also reused in the production of bricks. Specifically, catalysts are crushed and decreased in size to form alumina/silica sand that can replace the sand used in the manufacture of bricks. Moreover, spent fluidized-bed catalysts can be reused as cement components. Specifically, the catalyst is used to replace clinker in the final grinding (Cardenosa el al., 1992). For the disposal of catalysts, the techniques presented in Section 4.3 can be largely applied. 

Establishing the reaction network, using the wealth of techniques at the disposal of catalyst researchers, gives insight into how the catalyst works and provides the basis for the kinetic modeling studies. 

The new generations of zeolites and other microporous materials will start a new era for the petroleum processing, petrochemical, and chemical industries. These developments will also benefit our environment. Regenerable molecular sieves will replace corrosive and difficult-to-dispose-of catalysts. Shape selective processes can also generate less low-value byproducts and thus help us using our available resources more efficiently. Future shape selective catalysts and processes will be based on one or more of the foUowing ... 

A new type of materials has been developed by delaminating the lamellar precursors of some zeolites. These materials show external surface areas > 600 m. g from where active sites can be accessible to very large molecules. If on one hand delamination eliminates geometrical shape selective properties of zeolites, it allows on the other hand to dispose of catalysts with the good reactant accessibility of mesoporous materials, but with the stability and active sites characteristics of zeolites. The very large and well structured external surface area can be specially suited for supporting different catalytic functions, which include, among others, metals, transition metal complexes and enzymes. 

Selection or development of a phase transfer catalyst often plays the most important role in developing a new PTC system. Two main factors considered in selecting a PTC catalyst are the ability to transfer one of the reactants into the normal phase of the other reactant and the ability to activate the transferred species to facilitate the chemical reaction. In practice, other features of PTC catalysts considered by chemists or engineers in developing a PTC process include the stability, cost and availability, toxicity, recovery, recycling, and disposal of catalysts. 

Waste solvent and oils can be used, where applicable, as cracker feedstock or as fuel. In some cases, concentrated polymer waxes can be sold as a by-product to the wax industry. Polymer scrap can be recycled. The usage of purification agents should be minimised through onhne regeneration and extended hfetime. Typically with the new generation of catalysts the efficiency is sufficiently high that catalyst residues can remain in the polymer, thus avoiding a catalyst wash step and the need to dispose of catalyst residues. 

To solve some of the environmental problems of mixed-acid nitration, we were able to replaee sulfuric acid with solid superacid catalysts. This allowed us to develop a novel, clean, azeotropic nitration of aromatics with nitric acid over solid perfluorinated sulfonic acid catalysts (Nafion-H). The water formed is continuously azeotroped off by an excess of aromatics, thus preventing dilution of acid. Because the disposal of spent acids of nitration represents a serious environmental problem, the use of solid aeid eatalysts is a significant improvement. 

If a waste sulfuric acid regeneration plant is not available, eg, as part of a joint acrylate—methacrylate manufacturing complex, the preferred catalyst for esterification is a sulfonic acid type ion-exchange resin. In this case the residue from the ester reactor bleed stripper can be disposed of by combustion to recover energy value as steam. 

Disposal of spent hydrogenation catalyst requires a special chemical waste landfill because of its nickel content and the fact that oil-soaked catalysts tend to be pyrophoric. Compared to disposal costs, reprocessing to recover the nickel may become economically viable. 

Arsenic Peroxides. Arsenic peroxides have not been isolated however, elemental arsenic, and a great variety of arsenic compounds, have been found to be effective catalysts ia the epoxidation of olefins by aqueous hydrogen peroxide. Transient peroxoarsenic compounds are beheved to be iavolved ia these systems. Compounds that act as effective epoxidation catalysts iaclude arsenic trioxide, arsenic pentoxide, arsenious acid, arsenic acid, arsenic trichloride, arsenic oxychloride, triphenyl arsiae, phenylarsonic acid, and the arsenates of sodium, ammonium, and bismuth (56). To avoid having to dispose of the toxic residues of these reactions, the arsenic can be immobi1i2ed on a polystyrene resia (57). 

Commercially, a small amount of the 4,4 -MDA is isolated by distillation from PMDA. Depending on the process employed, the removal of MDA can be partial (as is done with the isocyanates) or total. Partial removal of MDA gives some processiag latitude but yields of 4,4 -MDA are reduced. Distillation residues from PMDA manufacture that contain less than 1% MDA pose a disposal problem. Processes for the regeneration of MDA by heating these residues ia the presence of aniline and an acid catalyst have been patented (33—35). Waste disposal of PMDA is expensive and reclamation processes could become commercially viable. The versatility of the isocyanate process, however, can be used to avoid the formation of low MDA content distillation residues. 

SoHd by-products include sludge from wastewater treatment, spent catalyst, and coke from the EDC pyrolysis process. These need to be disposed of in an environmentally sound manner, eg, by sludge digestion, incineration, landfill, etc. 

Undercharge of catalyst. Potential for accumulation of reactants and subsequent runaway reaction. Possibility of no reaction resulting in a waste disposal issue. 

They may require pH adjustment and settling. These effluents should preferably be recycled or reused. Spent catalysts are usually sent for regeneration or disposed of in a secure landfill. Air emissions should be monitored aimually, except for nitrate acid plants, where nitrogen oxides should be monitored continuously. 

Despite all the advantages of this process, one main limitation is the continuous catalyst carry-over by the products, with the need to deactivate it and to dispose of wastes. One way to optimize catalyst consumption and waste disposal was to operate the reaction in a biphasic system. The first difficulty was to choose a good solvent. N,N -Dialkylimidazolium chloroaluminate ionic liquids proved to be the best candidates. These can easily be prepared on an industrial scale, are liquid at the reaction temperature, and are very poorly miscible with the products. They play the roles both of the catalyst solvent and of the co-catalyst, and their Lewis acidities can be adjusted to obtain the best performances. The solubility of butene in these solvents is high enough to stabilize the active nickel species (Table 5.3-3), the nickel... 

Very few data [47] relating to the disposal of used ionic liquids are available. In Difasol technology, the used ionic liquid is taken out of the production system and the reactor is refilled with fresh catalyst solution. 

To reduce pollution, Dow developed a new catalyst system from the mor-denite-zeolite group to replace phosophoric acid or aluminum chloride catalysts. The new catalysts eliminates the disposal of acid wastes and handling corrosive materials. 

The most widely used homogeneous catalysts are simple acids and bases which catalyse well-known reactions such as ester and amide hydrolysis, and esterification. Such catalysts are inexpensive enough that they can be neutralized, easily separated fi om organic materials, and disposed of. This, of course, is not a good example of green chemistry and contributes to the huge quantity of aqueous salt waste generated by industry. 

These three steps all produce significant amounts of waste. First, as discussed earlier, the nitration process results in the production of spent sulfuric acid. In the past the company had been able to sell much of this material to the coke and steel industries but declining demand meant that the acid now required disposing of, at additional cost. At the time green catalytic nitration technology was becoming available with clay, zeolite and lanthanide catalysts all providing possible alternatives to the use of sulfuric acid (see below). Improved selectivity to the desired para-isomer is an added benefit of some of these catalytic systems. However on the... 

The production of biodiesel from low quality oils such as animal fats, greases, and tropical oils is challenging due to the presence of undesirable components especially FFA and water. A pre-treatment step is required when using such high fatty-acid feedstock. Generally, this esterification pre-treatment employs liquid sulfuric acid catalyst which must subsequently be neutralized and either disposed of or recycled. However, requirement of high temperature, high molar ratio of alcohol to FFA, separation of the catalyst, enviromnental and corrosion related problems make its use costly for biodiesel production. 

The first step on transfer of the sythesis is to evaluate the discovery route, looking particularly at overall yield and purity, as well as parameters such as cost of production (cost of starting materials, solvents, labor and overhead, and disposal of waste stream), ease of removal of impurities or catalyst from products, and the degree of hazard associated with solvents, reactants, intermediates, and products. The route used in discovery is... 

In many cases, the comparison of a reaction accelerated by microwave irradiation has been made with the same reaction in an oil bath at the same bulk temperature. Unfortunately, there have been quite a few reports in the chemical literature that have not been conducted with such proper control of conditions and consequently a fair comparison is not possible. Nevertheless, using this MW approach, the problems associated with waste disposal of solvents that are used several fold in chemical reactions, and excess usage of chemicals are avoided or minimized. The discussion pertaining to the preparation of supported reagents or catalysts has not been included in this chapter because numerous review articles are available on this theme [14—22],... 

Also, by the very nature of chemical transformations, there are almost always unused chemicals remaining. These chemical leftovers include contaminants in the raw materials, incompletely converted raw materials, unavoidable coproducts, unselective reaction by-products, spent catalysts, and solvents. There have long been efforts to minimize the production of such waste products, and to recover and reuse those that cannot be eliminated. For those that cannot be reused, some different use has been sought, and as a last resort, efforts have been made to safely dispose of whatever remains. The same efforts apply to any leftovers from the production of the energy from the fuels produced or consumed by the processing industries. Of particular immediate and increasing concern are the potential detrimental effects of carbon dioxide emissions to the atmosphere from fossil fuel combustion, as discussed further in Chapters 9 and 10. 

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