Adsorbent deactivation procedures

The products of the reaction are the following /-butyl-phenyl-ether (TBPE), p-/-butyl-phenol (p-TBP), o-/-butyl-phenol (o-TBP) and 2,4-di-/-butyl-phenol (2,4-DTBP). Compounds adsorbed on the external surface were recovered in methylene chloride (CH2C12) by a soxhlet treatment for 24 hours of the deactivated zeolite sample. The content of the compounds inside the zeolite (coke) was determined after dissolution, in 40 % HF at room temperature, of the catalyst recoved after 5 min, 45 min, 5h and 7.5 h extraction by CH2C12 then followed. The composition of soluble coke was investigated by analysis GC-MS. The procedure is reported in detail elsewhere [10]. 

The fact that soil always contains water, or more precisely an aqueous solution, is extremely important to keep in mind when carrying out an analytical procedure because water can adversely affect analytical procedures and instrumentation. This can result in an over- or under-determination of the concentrations of components of interest. Deactivation of chromatographic adsorbents and columns and the destruction of sampling tools such as salt windows used in infrared spectroscopy are examples of the potential deleterious effects of water. This can also result in absorbance or overlap of essential analytical bands in various regions of the spectrum. 

However the catalyst can be easily reactivated in flow of o2/Ar at 350°C (compare runs 2 and 2.1, Table 1) using the procedure reported in the previous section. Catalytic activity can be restored also by a thermal treatment in flow of He (350°C, 15 h), and this suggests that strongly adsorbed produts could be responsible for catalyst deactivation. The amount of 4-hexen-3-one converted depends on the nature of the catalyst precursor and on its thermal pretreatment. Thus, over a non activated commercial Mgo (obtained by thermal decomposition of MgC03, surface area 17 m2/g), 0.5 moles of 4-hexen-3-one/mole Mgo are converted, while when the same Mgo was activated at 350°C (surface area 34 m2/g), 2 moles of 4-hexen-3-one/mole MgO are converted. Over a high surface area Mgo (prepared by thermal decomposition of Mg(OH)2r surface area 281 m2/g) up to 5 moles of 4-hexen-3-one/mole Mgo can be converted. Conversion of 4-hexen-3-one depends also on reaction temperature 250°C is found to be the best one, since both at higher and lower temperatures side reaction are favoured (runs 2.2 and 2.3, Table 1). Since different oxides were employed, the product distributions reported in Table 1 were measured in stationary conditions after 1 hour of reaction. 

To diminish any eventual residual adsorptive activity of the support that may still be present after deactivation by acid and alkaline washing, and by chemical procedures, Bohemen et al. introduced a precoating with 0.1 % PEG 400. The PEG molecules are thought to be adsorbed tightly to the residual active sites of the support. This precoating procedure was also used by Brochmann-Hanssen and Baerheim Svendsen in their gas chromatographic studies on... 

Perot et al. [7] in collaboration with Rhodia have studied the deactivation of industrial catalysts HBEA and HY during the acylation of veratrole and anisole. After reaction, the spent catalysts were extracted with methylene chloride. This Soxhlet extraction makes possible the elimination of compounds that were not strongly adsorbed on the zeolites. The composition of the residue obtained after evaporation of methylene chloride was practically the same as that of the reaction mixture at the end of the experiment. By this extraction procedure, approximately 80% of the compounds remaining on the catalysts after reaction were recovered. After Soxhlet extraction, the catalyst samples were recovered and dissolved with hydrofluoric acid. The organic compounds released by the catalysts were extracted again by methylene chloride and, after evaporation of solvent, the residues contained di- and triketones as well as cyclization compounds, the structures of which are presented in Scheme 14.1. 

The acylation of benzofuran by acetic anhydride was carried out in the presence of Y zeolites in the liquid phase (60°C, atmospheric pressure). It is shown that the reaction procedure has a significant influence on the activity of the catalyst. Deactivation takes place but the zeolite can be completely regenerated by reactivation in air. A reaction mechanism is proposed in which the acylium ion adsorbed on the zeolite reacts with non activated benzofuran. 

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