Residue Catalyst Additives

The addition of residual fractions to gas oil feed results in an increase in the impurity content of the equilibrium FCC catalyst and causes a decrease in activity. Metal impurities exist as porphyrin complexes which crack and deposit metal residues on the catalyst surface, causing catalyst deactivation. The most serious effects on catalyst performance result from nickel and vanadium compounds. Sodium can also deactivate acid sites on the catalyst, but the effect is generally reduced by desalting erode oils and by absorption of small amounts of sodium on the matrix. Sulfur compoimds in the feed contaminate products and regenerator flue gas. 

Efforts have been made to develop additives that limit the effects of impurities in the feed. However, a practical way to counter the effect of metal impurities has been to increase the withdrawal and replacement of equilibrium catalyst with fresh catalyst, despite the increase in cost. Some of the ways in which metals and other impurities can be managed in modem FCC units are as follows  

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Of the three worldwide manufacturers of poly(ethylene oxide) resins. Union Carbide Corp. offers the broadest range of products. The primary quaUty control measure for these resins is the concentrated aqueous solution viscosity, which is related to molecular weight. Specifications for Polyox are summarized in Table 4. Additional product specifications frequendy include moisture content, particle size distribution, and residual catalyst by-product level. 

The mixture is kept for 3 hours at 105°C after the oxide addition is complete. By this time, the pressure should become constant. The mixture is then cooled to 50°C and discharged into a nitrogen-filled botde. The catalyst is removed by absorbent (magnesium siUcate) treatment followed by filtration or solvent extraction with hexane. In the laboratory, solvent extraction is convenient and effective, since polyethers with a molecular weight above about 700 are insoluble in water. Equal volumes of polyether, water, and hexane are combined and shaken in a separatory funnel. The top layer (polyether and hexane) is stripped free of hexane and residual water. The hydroxyl number, water, unsaturation value, and residual catalyst are determined by standard titration methods. 

The original recipe adopted by the U.S. Government Synthetic Rubber Program was known as the "Mutual Recipe" and is shown iu Table 4. As can be seen, the reaction temperature was set at 50°C, which resulted iu 75% conversion to polymer iu about 12 h. The reaction was then stopped by addition of a "shortstop," such as 0.1 parts hydroquinone, which destroyed any residual catalyst (persulfate), and generated quiuone, which helped inhibit any further polymerisation. 

In batch or semi-batch polymerization processes it is often desirable to add a "chaser catalyst" towards the end of the reaction to reduce the residual monomer concentration to acceptable levels. The ability of the catalyst to reduce the monomer concentraion to low levels (ca 0.10 vol%) is of considerable importance for economic, envirorunental and physiological reasons. The chaser catalyst addition reduces processing time and increases throughput (Kamath and Sargent (1987)). 

The most important undesired metallic impurities are nickel and vanadium, present in porphyrinic structures that originate from plants and are predominantly found in the heavy residues. In addition, iron may be present due to corrosion in storage tanks. These metals deposit on catalysts and give rise to enhanced carbon deposition (nickel in particular). Vanadium has a deleterious effect on the lattice structure of zeolites used in fluid catalytic cracking. A host of other elements may also be present. Hydrodemetallization is strictly speaking not a catalytic process, because the metallic elements remain in the form of sulfides on the catalyst. Decomposition of the porphyrinic structures is a relatively rapid reaction and as a result it occurs mainly in the front end of the catalyst bed, and at the outside of the catalyst particles. 

Transition metal catalysts and biocatalysts can be combined in tandem in very effective ways as shown by the following example (Scheme 2.21). An immobilized rhodium complex-catalyzed hydrogenahon of 46 was followed by enzymatic hydrolysis of the amide and ester groups of 47 to afford alanine (S)-9 in high conversion and enanhomeric excess. Removal of the hydrogenation catalyst by filtration prior to addition of enzyme led to improved yields when porcine kidney acylase 1 was used, although the acylase from Aspergillus melleus was unaffected by residual catalyst [23]. 

Additional support for our observations was found when catalysts A-1 to A-3 were stndied. Catalyst A-1 was developed according to the old recommendations for a residue catalyst with a moderate zeolite surface area and a large active matrix snrface area. The catalyst did not give as good naphtha selectivity as expected when the North Sea long residue feed was cracked. An attempt to improve this was made with catalyst A-2 where the matrix surface was lowered, while the zeolite surface area was kept the same. The naphtha selectivity was however not improved, and it was concluded that the zeolite surface area was too low. So in catalyst A-3 the zeolite snrface area instead was increased compared with the base catalyst A-1. Now the naphtha selectivity increased, but the gas yields also increased dramatically. This catalyst did indicate that a possible way to go could be to increase the zeolite surface... 

A wide range of plastics with different properties has been used in the construction of laboratory apparatus. In spite of the adsorption ability of the polymers and, therefore, the risk of analyte loss by adsorption on container walls, contamination arising from residual catalysts and additives used in their manufacture is the main problem. Among the most common plastics used in manufacturing laboratory containers are low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP) and polytetrafluoro-ethylene (PTFE). 

The second method is azeotropic condensation polymerization of lactic acid, which produces high-molecular weight PLA without using chain-extenders or esterification-promoting adjuvants. This type of polymerization needs high reaction rates and thus uses catalysts however, due to the use of catalysts, the PLA produced by this method is not suitable for some applications, such as medical, since any residual catalyst offers toxicity within the polymer, which is harmful for medical applications. In addition to toxicity, residual catalyst degrades PLA in further processing (39). On the other hand, the level of residual catalyst can be reduced with the use of sulphuric acid (55,56). 

HNO3 (90%, 2.45 g, 35 mmol) and dried zeolite beta (H ) (l.Og) were stirred together at OU for 5 min.. Addition of Ac,0 (5 mL. 53 mmol) resulted in an exothermic reaction, causing a temporary rise in temperature to ca. 10-15 C. After a further 5min, the aromatic substrate, e.g. 12 (35 mmol), was added dropwise and the mixture was then allowed to warm up to rt and stirred for a further 30 min. The product was obtained by direct vacuum distillation of the mixture, first at 30 Tort to give recovered AC2O. and then at 0.2 Torr to yield the nitro compound. The residual catalyst was then ready for reuse, with no additional treatment necessary. 

Aqueous catalysts offer facile catalyst separation for many homogeneous catalytic reactions [1] and several new processes have been commercialized (cf. Section 3.1.1.1). However, aqueous media cannot be used for chemical systems in which a component of the system undergoes undesired chemical reactions with water. Furthermore, the low solubility of many organic compounds in water could limit the applications of aqueous catalysts. Nonaqueous biphasic systems could overcome these limitations, provided the catalyst is preferentially soluble in the catalyst phase at the conditions under which the catalyst phase is separated from the product phase. It should be noted that there may be some catalyst loss into the product phase. The acceptable level of catalyst leaching depends on the quality specifications of the product, whether the residual catalyst could cause any health and/or environmental hazards, and the cost of the catalyst. When the leached catalyst has to be removed from the product phase, the cost of additional conventional catalyst separation and recycling must be considered also. 

Pyrolysis of dihalocyclopropanes was studied along with the effects of electrophilic reagents, and confirms the foregoing results (33-37). In many cases, those authors observed that polymeric residues, in addition to ally lie and diene-type products, were present at the end of pyrolysis. The formation of these polymers confirms the hypothesis that the dihalocyclopropanes are monomers that can be polymerized either by cationic processes or by the action of transition-metal complex catalysts. 

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