Resins deactivation

The main cause of resin deactivation is, however, the neutralization of acidic sites due to interaction with the contaminants present in the feed. The neutralization may be due to ... 

In 2005, Bornscheuer s group studied the DKR of acyloins, which constitute important building blocks in organic synthesis e.g. for the total synthesis of epothilones). " No combination of base and solvent was found that could selectively racemise the acyloins or the corresponding esters under the conditions needed for a DKR. In contrast to bases, an acidic resin such as Amberlyst 15 was found to racemise the acyloins selectively in n-hexane and in water. Unfortunately, the acidic resin deactivated the lipase Candida antarctica lipase... 

The paper-impregnation drying oven exhausts contain high concentrations (10—20% LEL) of alcohols and some resin monomer. Vinyl resins and melamine resins, which sometimes also contain organic phosphate fire retardants, may be used for air filters. The organic phosphates could shorten catalyst life depending on the mechanism of reduction of catalyst activity. Mild acid leaching removes iron and phosphoms from partially deactivated catalyst and has restored activity in at least one known case. 

By deactivating the active weak link. For example, commercial polyacetal (polyformaldehyde) resins have their chain ends capped by a stable grouping. (This will, however, be of little use where the initiation of chain degradation is not at the terminal group.)... 

After deactivation and removal of the initiating system, the eoumarone-indene resin is separated from solvent and low moleeular weight materials by vacuum distillation. The removal of the low moleeular weight materials is important beeause they produce strong odour, they aet as softeners and they eause an undesirable deerease in softening point. Therefore, at this stage the softening point of the eoumarone-indene resins is adjusted. Finally, stabilizers are added to the liquid resin while it is still hot to inhibit further oxidation (whieh eauses diseolouration and odour). 

Polybutene resins. These liquid resins are obtained by cationic polymerization of petroleum C4 streams in the presence of AICI3 at relatively low temperature. Temperature and AICI3 concentration are important factors as they influence the molecular weight and viscosity of the final resin. After reaction, the mixture is deactivated with water, methanol, ammonia or aqueous sodium hydroxide. The organic layer is separated and distilled to remove solvent and unconverted material. 

Both sulfuric acid and hydrofluoric acid catalyzed alkylations are low temperature processes. Table 3-13 gives the alkylation conditions for HF and H2SO4 processes. One drawback of using H2SO4 and HF in alkylation is the hazards associated with it. Many attempts have been tried to use solid catalysts such as zeolites, alumina and ion exchange resins. Also strong solid acids such as sulfated zirconia and SbFs/sulfonic acid resins were tried. Although they were active, nevertheless they lack stability. No process yet proved successful due to the fast deactivation of the catalyst. A new process which may have commercial possibility, uses... 

Another example of enzyme- and acid-catalyzed DKR has been reported by Bornscheuer [45]. Acyloins were racemized by using an acidic resin through the formation of enol intermediates. The enzymatic resolution was catalyzed by CALB. Since deactivation of this enzyme occurred in the presence of the acidic resin, they designed a simple reactor setup with two glass vials cormected via a pump to achieve a spatial separation between the acidic resin and the enzyme (Figure 4.20). 

Several palladium catalysts for formation of aryl sulfides from aryl halides have been investigated more recently. A combination of Pd2(dba)3 and DPEphos catalyzed the formation of a broad range of diaryl sulfides in the presence of 1 mol.% palladium and NaO-t-Bu base in toluene solvent.12,rThe highest yields of alkyl aryl sulfides were obtained from aryl triflates and n-butyl thiol catalyzed by a combination of palladium acetate and BINAP. However, these reactions contained 10 mol.% catalyst, were long, and required deactivated aryl triflates. A combination of Pd2(dba)3 and DPPF catalyzed the coupling of thiols with resin-bound aryl halides.121... 

The isolation of product is usually possible after evaporation of the solvent and extraction with hexane, ether, or toluene. Supported versions, for example on polystyrene grafted with PPh2 groups, have proved unsatisfactory because the rate of deactivation is greatly enhanced under these conditions [37]. Asymmetric versions exist, but the ee-values tend to be lower than in the Rh series [38]. With acid to neutralize the basic N lone pair, imine reduction is fast. Should it be necessary to remove the catalyst from solutions in order to isolate a strictly metal-free product, a resin containing a thiol group should prove satisfactory. A thiol group in the substrate deactivates the catalyst, however. 

Several strategies were developed to prevent the formation of unreactive dimers [86], with one of the more successful methods being immobilization of the catalyst on solid support. Whereas normally, most immobilized catalysts lose activity in comparison to their soluble analogues, in this case the rate increased, due to the prevention of deactivation by dimerization. Even more convincing, there was a negative correlation between the loading on the resin and the rate of the reaction (Fig. 44.12). 

Other materials that have been investigated include sulfated zirconia, Br0nsted and Lewis acids promoted on various supports, heteropolyacids, and organic resins, both supported and unsupported. On the whole, these materials also deactivate rapidly, and some of them also exhibit environmental and health hazards. 

As opposed to the PET process, where a different catalyst is used in each of the two polymerization phases, the PBT process typically uses a single catalyst. In PBT resins, the catalyst is not typically quenched (deactivated) at the end of the polymerization process. An active catalyst in the resin can sometimes lead to further reaction of the PBT in subsequent processing. 

At low temperatures, the activity of acid catalysts in transesterification is normally fairly low and to obtain a sufficient reaction rate it is necessary to increase the reaction temperature to >170 °C. Therefore, sulfonic acid resins can be used in esterification reactions where they perform well at temperatures <120 °C and particularly in the pretreatment of acidic oils. Under these reaction conditions, acidic resins are stable. Poly(styrenesulfonic add), for example, has been used in the esterification of a by-product of a vegetable oil refinery with a 38.1 wt% acidity at 90-120 ° C and 3-6 atm. It was not deactivated after the first batch and maintained a steady catalytic performance in the next seven batches [22]. 

Table 10.2 presents the total coke yields and the nonvaporized hydrocarbons produced over a spent catalyst obtained with different feedstocks. The catalyst used was deactivated for 20 hours, 30 ReDox cycles, and 50% steam. When the 100% vacuum gas oil (VGO) is replaced with a mixture of 5%w DMO-VGO and/or 30%w DMO-VGO an increase of 30% and 120% in the coke yields was observed. While the spent catalyst from VGO cracking does not have adsorbed hydrocarbons, the mixture with DM0 does, becoming almost 1% for the mixture with 30%w DM0. The SARA (saturates, aromatics, resins, and asphaltenes) analysis of these hydrocarbons showed a high concentration of asphaltenes. 

For the SPE of the more polar aromatic sulfonates, IPs with tetralkylammonium are previously formed [85,93,94]. The combination of the formation of IP with cetyltrimethylammonium and SPE is efficacious in the extraction of benzene and naphthalene sulfonates from an aqueous environment. Good recoveries are also obtained with octylammonium acetate as the IP agent, both when it is added to the aqueous sample prior to the extraction and when it saturates the solid phase to produce an anion-exchange column [95,96]. An alternative approach is based on the use of deactivated charcoal (Carbonpack B) [96] or of chemically modified polystyrene-divinylbenzene resins [85]. Often graphitized carbon black (GCB) is used for the clean-up process of the sample [96]. 

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