Disposal of spent catalyst

The high quality achieved by the modem technologies of off-site regeneration often allows to perform more than one cycle with the same catalyst batch. In addition to this economic incentive for regeneration, more and more stringent environmental regulations for disposal of spent catalysts encourage their reuse. 

Another use of vanadium is as a catalyst in a variety of reactions. Vanadium pentoxide, ivhen placed on an inert support material, is the principal catalyst used in the oxidation of SO2 to SO3 in the production of sulfuric acid, and for the conversion of naphthalene into phthalic anhydride during the formation of plastics. In addition, vanadium oxychloride, tetrachloride and triacetylacetonate are used as polymerization catalysts in the production of soluble copolymers of ethylene and propylene. In the reaction vessels, these polymers are viscous liquids, which can trap the vanadium catalysts and result in a vanadium content of up to 500 mgkg in products used for the packaging of food and pharmaceuticals. The disposal of spent catalysts could also be a point source for a contamination of the biosphere and of food with vanadium (Byerrum 1991). Furthermore, vanadium is used for the production of yellow pigments and ceramics. 

Recently, selective synthesis of / -cymene from toluene and propane or isopropanol over zeolite catalysts has been thoroughly investigated. Zeolite-based processes avoid the disposal of spent catalyst, product contamination by the catalyst, separation of the catalyst from the product and corrosion of the reactor and tubes. The results using various zeolite types were promising. However, the formation of undesired -propyl toluene is observed particularly in the presence of MFI type zeolites, whereas large pore zeolites yield significant amounts of m-and o-cymene besides the desired / -cymene. However, low conversion and relatively low selectivity are the drawbacks of these investigations. 

Transport and disposal of spent catalyst on-site acid regeneration High isobutane/olefin ratio Fast catalyst deactivation... 

Catalysts new zeolites, improved texture, combination of different catalyst types, regeneration or rejuvenation techniques, disposal of spent catalysts ... 

In the conventional ethylbenzene technology, an aluminum chloride —hydrogen chloride combination is the most widely used catalyst. The highly corrosive nature of aluminum chloride requires special resistance materials in the construction of the reaction vessel and product handling equipment. The polluting nature of aluminum chloride further necessitates treatment of the product for disposal of spent catalysts. 

Although the catalyst was very effective for the conversion of carbonyl sulfide, carbon disulfide, and mercaptans, it was ineffective for thiophene. Other problems with the process were the low space velocities required and the need to remove and dispose of spent catalyst containing all of the collected sulfur as sodium sulfate. 

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. 

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. 

We need to keep in mind the disposal costs in all of the mechanisms for solidification. With the first method, keep in mind that free liquids are typically not allowed in most disposal scenarios. And adding too much adsorbent can substantially add to disposal costs. Make this point clear to your field people. As far as using polymerization catalysts and chemical reagents, keep in mind disposal costs. Ensure that you are cognizant of disposal costs of spent catalyst prior to using this scenario. As far as freezing is concerned, consider the cost to keep the contaminants frozen and what the downsides are. The downsides besides cost include measures in case of power failure and use of freezing equipment after wastes have been disposed. 

Activated Raney nickel is pyrophoric and should never be allowed to become dry. Thus decanting is preferred to filtration, and when decanting, a small amount of solvent must always be left behind to cover the catalyst powder. For safe disposal, the spent catalyst should be slurried in water and flushed down the drain under running water. 

Catalytic processes (finid catalytic cracking, catalytic hydrocracking, hydro-treating, isomerization, ether manufacture) also create some residuals in the form of spent catalysts and catalyst fines or particulates. The latter are sometimes separated from exiting gases by electrostatic precipitators or filters. These are collected and disposed of in landfills or may be recovered by off-site facilities. The potential for waste generation and hence leakage of emissions is discussed below for individual processes. 

In the demetallization catalyst test run. the fresh catalyst makeup to the unit was reduced to 8.5 TPD. Ten TPD of equilibrium catalyst were sent to the Meraux plant for demetallization. This catalyst was then returned to the refinery where ii was added to the cal cracker along with the fresh catalyst. During the DEMET test run. losses were running at 1.5 TPD total so that it was necessary to withdraw 7 TPD of spent catalyst and dispose of this to landfill. The equilibrium catalyst produced during the DEMET test run contained about 2 tHK) PPM of nickel and about 450 PPM of vanadium and the surface area remained at 128 mVgrn,... 

Chromium(III) was also effective in several selective reductions, although with lesser yields. The chromium ion is also undesirable from the standpoint of spent catalyst disposal. 

The disposal of spent hydrotreating catalysts is not an insignificant problem. This may involve recovery of metals for environmental and r economic reasons. Solutions to this problem still have to be improved upon, especially in reducing the cost of the operation. The amounts of catalyst involved are large and will increase rapidly in the coming years. 

Due to these disadvantages, research on the transesterification reaction using heterogeneous catalysts for biodiesel production has increased over the past decade (Lee and Wilson, 2014). Fig. 6.9 summarizes the classification of catalysts. Zhang et al. (2003) argued there is a considerable incentive for the substimtion of liquid bases by solid bases for the following reasons (1) energy intensive product/catalyst separation, (2) corrosiveness, and (3) the costs associated with the disposal of spent or neutralized caustics. 

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. 

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. 

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... 

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. 

In the context of sustainable development, all spent catalysts should be recycled as far as possible, or properly disposed off in an environmentally friendly manner, in case recycling is not possible (NFESC, 1996). 

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. 

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