Zeolite batch reactions

Trapped by a suitable compound, a transient intermediate can be converted into a more stable species for unequivocal identification. Stepanov and Luzgin (82) investigated the reaction of acetonitrile with 1-octene or tert-butyl alcohol on acidic zeolite HZSM-5 ( 2si/ Ai = 49) at 296 K by in situ MAS NMR spectroscopy under batch reaction conditions. Upon coadsorption of acetonitrile and 1-octene, a C MAS NMR signal at 108 ppm was observed, indicative of TV-alkylnitrilium ions 2 in Scheme 3. As depicted in Scheme 3a, the formation of these cations was explained by trapping the chemically unstable alkylcarbenium ions (formed from the adsorbed... 

The first in situ MAS NMR investigation of the synthesis of MTBE on acidic zeolites was performed by Mildner et al. (228) under batch reaction conditions. In this investigation, the temperature-jump MAS NMR technique (stop-and-go experiment, see Section III.A) was applied to characterize the reaction dynamics under non-equilibrium conditions on a boron-modified pentasil zeolite ( si/... 

Various NMR spectroscopic techniques have been applied to investigate the conversion of methanol on acidic zeolites in the low-temperature (r<523K) formation of DME and the high-temperature (T>523 K) formation of alkenes and gasoline. Techniques successfully applied were the stop-and-go method under batch reaction conditions 258,259), the pulse-quench method 113), and various flow techniques 46,49,74.207,260 263). This section is a summary of the recent progress in investigations of the mechanism of the MTO process by NMR techniques. 

Among the early investigations of methanol adsorption and conversion on acidic zeolites, most of the H and C MAS NMR experiments were performed under batch reaction conditions with glass inserts in which the catalyst samples were fused. Zeolites HZSM-5 76a,204,206,264-272), HY 71,72), H-EMT 273), HZSM-12 274), HZSM-23 275), H-erionite 275), H-mordenite 271,272), and H-offretite 275,276), silicoaluminophosphates H-SAPO-5 271,274), H-SAPO-11 274), and H-SAPO-34 76,277,278), as well as montemorillonite 279) and saponite 279) were investigated as catalysts. 

Prochatska et al. screened (in liquid-phase batch reactions, with cyclohexane under reflux as solvent) fourteen different zeolites with five different unsymmetri-cal ketones, both in one-pot reactions and with isolated hydrazones as substrates... 

The rearrangement of styrene oxide can also be performed in liquid-phase reactions with the well known catalyst TS-1 [11,25]. The framework-titanium gives the MFI-type zeolite Lewis acidic properties and 100 % conversion and 98 % phenylacetaldehyde selectivity was achieved after 1-2 h at 70 °C in a batch reaction with acetone (100 mL) as solvent, epoxide (50 g), and catalyst (3 g) as feed. 

The use of mesoporous H-US-Y zeolites as catalysts in this reaction is an environmentally benign alternative to conventional homogeneous catalysts. Because demand for this product is rather low and results from gas-phase reaction are only moderate, the liquid-phase batch reaction is a reasonable choice although it must be performed at 0 °C. 

Good synthetic results can be achieved by performing the same reaction in the presence of a dealuminated Y(36) zeolite. Thus, 3,4-dimethoxy-acetophenone is obtained in 97% yield by performing the batch reaction at 90°C for 6 h. ... 

Isomerization of 1-acetyl-2-methoxynaphthalene was investigated over HFAU, HBEA and HMFI zeolites (batch reactor, T=120°C). Due to its pore size, HMFI was inactive for isomerization while HFAU is about 3 times more active than HBEA. This can be attributed to the easier desorption of the isomers from the HFAU pores. However, the selectivity of 2-acetyl-6-methoxynaphthalene (the desired isomer) is favoured over HBEA. Analysis of the compounds retained in the zeolite pores show that the reaction occurs inside the micropores of the zeolites. Indeed, the desired isomer was found to be retained in the pores of HMFI showing that even for this zeolite, isomerization occurs in its micropores and that the desorption of the reaction products appears to be the limiting step. 

Zeolite X was also examined for the decomposition of polyethylene in a series of articles by Ayame and co-workers.Using both a batch reactor and a fixed bed tubular flow reactor, the rate of conversion of polyethylene was enhanced in the presence of CaX and NaX. Deactivation was observed in the flow studies, as the rate of formation of gaseous products decreased by a factor of three after 2.5 hours time on stream when the reaction was carried out at 750 K with 4.0 g of catalyst and a polyethylene flow rate of 7.23 x 10 g min . When a CaX catalyst was used, C4 species were observed in the highest yield. In the batch reaction, the yield of iso-C4 species was increased dramatically compared with thermal degradation, as thermal degradation afforded no iso-C4. 

The first in situ MAS NMR investigation of the synthesis of MTBE on acidic zeolites was performed by Mildner et al. (228) under batch reaction conditions. In this investigation, the temperature-jump MAS NMR technique (stop-and-go experiment, see Section III.A) was applied to characterize the reaction dynamics under non-equilibrium conditions on a boron-modified pentasil zeolite ( si/ Mg = 80). The catalyst was calcined in a glass insert, which was sealed after the loading with MTBE. H MAS NMR spectra were recorded during the heating period of 100 s. Then the laser power was switched off and the temperature of the samples fell back to room temperature within about 60s. During the stop period of 1 h, when the reaction state was frozen, a C MAS NMR spectrum was recorded. By repetition of the stop-and-go periods for several times, the complete reaction could be measured by both H and MAS NMR spectroscopy. 

For the non-oxidative activation of light alkanes, the direct alkylation of toluene with ethane was chosen as an industrially relevant model reaction. The catalytic performance of ZSM-5 zeolites, which are good catalysts for this model reaction, was compared to the one of zeolite MCM-22, which is used in industry for the alkylation of aromatics with alkenes in the liquid phase. The catalytic experiments were carried out in a fixed-bed reactor and in a batch reactor. The results show that the shape-selective properties of zeolite ZSM-5 are more appropriate to favor the dehydroalkylation reaction, whereas on zeolite MCM-22 with its large cavities in the pore system and half-cavities on the external surface the thermodynamically favored side reaction with its large transition state, the disproportionation of toluene, prevails. 

Nickel containing MCM-36 zeolite was used as new catalyst in the ethylene oligomerization reaction performed in slurry semi-batch mode. This catalyst, with micro-mesoporous structure, mild acidity and well balanced Ni2+/acid sites ratio, showed good activity (46 g of oligomers/gcataLh) and selectivity (100% olefins with even number of carbon atoms). The NiMCM-36 behaviour was compared to those obtained with NiMCM-22, NiY, NiMCM-41 and NiMCM-48 catalysts. 

Under the same conditions (batch or GL-PTC) discussed for CHg-acidic compounds, primary aromatic amines also react with DMC. In this case, although the reaction yields selectively the mono-A-methylated amines with no dimethylated by-products, sizable amounts of methyl carbamates (ArNHCOgMe) are formed. ° Much better results can be gathered in the presence of zeolites, particularly alkali metal exchanged Y and X faujasites. These aluminosilicates posses pseudospheri-cal cavities (supercavities) of 11-8 A in diameter, which can be accessed through channels whose size is 7.4 kP ... 

The acetylation over protonic zeolites of aromatic substrates with acetic anhydride was widely investigated. Essentially HFAU, HBEA, and HMFI were used as catalysts, most of the reactions being carried out in batch reactors, often in the presence of solvent. Owing to the deactivation effect of the acetyl group, acetylation is limited to monoacetylated products. As could be expected in electrophilic substitution, the reactivity of the aromatic substrates is strongly influenced by the substituents, for example, anisole > m-xylene > toluene > fluorobenzene. Moreover, with the poorly activated substrates (m-xylene, toluene, and fluoroben-zene) there is a quasi-immediate inhibition of the reaction. It is not the case with activated substrates such as anisole and more generally aromatic ethers. It is why we have chosen the acetylation of anisole and 2-methoxynaphtalene as an example. 

Peterson and Scarrah 165) reported the transesterification of rapeseed oil by methanol in the presence of alkaline earth metal oxides and alkali metal carbonates at 333-336 K. They found that although MgO was not active for the transesterification reaction, CaO showed activity, which was enhanced by the addition of MgO. In contrast, Leclercq et al. 166) showed that the methanolysis of rapeseed oil could be carried out with MgO, although its activity depends strongly on the pretreatment temperature of this oxide. Thus, with MgO pre-treated at 823 K and a methanol to oil molar ratio of 75 at methanol reflux, a conversion of 37% with 97% selectivity to methyl esters was achieved after 1 h in a batch reactor. The authors 166) showed that the order of activity was Ba(OH)2 > MgO > NaCsX zeolite >MgAl mixed oxide. With the most active catalyst (Ba(OH)2), 81% oil conversion, with 97% selectivity to methyl esters after 1 h in a batch reactor was achieved. Gryglewicz 167) also showed that the transesterification of rapeseed oil with methanol could be catalyzed effectively by basic alkaline earth metal compounds such as calcium oxide, calcium methoxide, and barium hydroxide. Barium hydroxide was the most active catalyst, giving conversions of 75% after 30 min in a batch reactor. Calcium methoxide showed an intermediate activity, and CaO was the least active catalyst nevertheless, 95% conversion could be achieved after 2.5 h in a batch reactor. MgO and Ca(OH)2 showed no catalytic activity for rapeseed oil methanolysis. However, the transesterification reaction rate could be enhanced by the use of ultrasound as well as by introduction of an appropriate co-solvent such as THF to increase methanol solubility in the phase containing the rapeseed oil. 

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