Continuous fixed-bed reactor

The liquid phase alkoxylation of limonene (3) with C4-C4 alcohols to 1-methyl-4-[a-alkoxy-isopropyl]-l-cyclohexene (5) was carried out both in batch and continuous fixed-bed reactor at 60 °C on various acidic catalysts (Scheme 3.1) [16]. The best yields were obtained in batch (85%) or continuous reactor (81%) using a /1-type zeolite with Si02/Al203 = 25. 

In the following, a model of an anaerobic digestion process carried out in a continuous fixed bed reactor for the treatment of industrial wine distillery vinasses is considered [10] ... 

Abstract The principle of catalytic SILP materials involves surface modification of a porous solid material by an ionic liquid coating. Ionic liquids are salts with melting points below 100 °C, generally characterized by extremely low volatilities. In the examples described in this paper, the ionic liquid coating contains a homogeneously dissolved Rh-complex and constitutes a uniform, thin film, which itself displays the catalytic reactivity in the system. Continuous fixed-bed reactor technology has been applied successfully to demonstrate the feasibility of catalytic SILP materials for propene hydroformylation and methanol carbonylation. 

To verify the homogeneous nature of Rh-3-SILP catalysts, as previously suggested based on IR and NMR spectroscopic studies, [30] kinetic experiments have also been conducted with the catalyst. Here, a continuous fixed-bed reactor setup equipped with online gas-chromatography, described elsewhere in detail, [31] was applied. The general rate law for the hydroformylation of propene was assumed ... 

The disproportionation and isomerization of trimethylbenzene(TrMB) were studied at 200°C using a continuous fixed bed reactor. The reactant TrMB was diluted with nitrogen in a molar ratio of 1 9. The cracking of cumene was carried out at 400 C using a pulse reactor. The catalyst was treated in a stream of nitrogen for 1 h at a desired temperature in the range 400-600°C prior... 

Enzymes, when immobilized in spherical particles or in films made from various polymers and porous materials, are referred to as immobUized enzymes. Enzymes can be immobilized by covalent bonding, electrostatic interaction, crosslinking of the enzymes, and entrapment in a polymer network, among other techniques. In the case of batch reactors, the particles or films of immobilized enzymes can be reused after having been separated from the solution after reaction by physical means, such as sedimentation, centrifugation, and filtration. Immobilized enzymes can also be used in continuous fixed-bed reactors, fluidized reactors, and membrane reactors. 

The partial oxidation of alcohols, to afford carbonyl or carboxylic compounds, is another synthetic route of high industrial interest For this, scC02 was investigated as a reaction medium for the aerobic oxidation of aliphatic, unsaturated, aromatic and benzylic acids with different catalytic systems, mainly based on the use of noble metals, both in batch [58-64] and in continuous fixed-bed reactors [65-70]. In this context, very promising results have been obtained when studying the catalytic activity of supported palladium and gold nanoparticles in the oxidation of benzyl alcohol to benzaldehyde these allowed conversions and selectivities in excess of 90% to be achieved [71-73]. 

Equipment and Procedure. The fixed bed reactor pilot plant is shown schematically in Figure 1. The reactor was operated as a continuous fixed bed reactor, with recycle of the hydrogen. 

Furthermore, in respect to the regioselectivity of the ring opening reaction of oxiranes, electronic as well as steric factors can play a role. These general considerations stimulate the use of zeolites and non zeolitic molecular sieves as heterogeneous catalysts for such rearrangement reactions in the liquid or in the gas phase in a slurry reactor and in a continuous fixed bed reactor, respectively. 

An analysis is made of the factors which pose a limit to representative downscaling of catalyst testing in continuous fixed-bed reactors operated with either gas or gas-liquid flow. Main limiting factors are the axial dispersion and, in the case of gas-liquid operation, also the contacting of the catalyst. The effects of catalyst and reactor geometries are quantified, and boundaries for safe operation are indicated. 

In early studies, carried out batch-wise on Pd-Pt/TS-1, the maximum yield was 11.7%, with 46% selectivity based on propene [156]. By operating in a continuous fixed-bed reactor, Jenzer and others showed that the selectivity could initially be... 

The catalytic hydrogenation of carbon dioxide was performed in a continuous fixed bed reactor. The catalyst was reduced in a flow of hydrogen at 723 K for 20 - 24 hr. After the reduction, the catalyst was brought to the following conditions 573 K, 10 atm, space velocity of 1900 h-i and H2/CO2 = 3. The activity data was taken after 24h of reaction. The products were analyzed by a gas chromatograph (Chrompack CP 9001) equipped with thermal conductivity and flame ionization detectors. Carbon monoxide, carbon dioxide and water were analyzed on a Porapak Q column and the hydrocarbons on a GS Q capillary column. 

A continuous fixed bed reactor coupled on-line with a GC (FID/TCD) was used for the catalytic experiments. The amoimt of catalyst (particle size diameter 0.1 - 0.3 mm) loaded was 0.6 g. The catalytic behaviour of the catalysts was investigated in the total oxidation of methane and chloromethane (1 vol.% in air, feed stream 5 1/h) considering by-product formation. 

Riisager A, Fehrmann R, Haumann M et al (2006) Supported ionic liquid phase (SILP) catalysis an innovative concept for homogeneous catalysis in continuous fixed-bed reactors. Eur... 

The powdered catalysts were evaluated in an integral continuous fixed bed reactor (Ig cat, total gas flow rate 6 1/h), with on line gas analysis by gas chromatogral using both thermal conductivity detector and flame ionization detector. 

The initial alcohol/amine ratio can determine the product distribution. In the synthesis of primary amines a rather high ammonia/alcohol molar ratio (up to 10-25), and usually high pressure, are required to compensate for the low reactivity of ammonia and suppress the formation of secondary amines. Selectivity for primary diamines could be improved in the amination of 1,3-dihydroxy compounds when using supercritical ammonia as solvent and reactant in a continuous fixed-bed reactor [12]. The remarkable changes in selectivity in the near-critical region (100-110 bar) are attributed to the increased concentration of ammonia on the metal surface as a result of elimination of mass-transport limitations in the two-phase system, and to suppression of hydrogenolysis and water elimination reactions which lead to monofunctional by-products. An example is shown in Figure 1. 

Both batch reactors (autoclaves) and continuous fixed-bed reactors are suitable for alcohol amination. High pressure in the range 50-150 bar is necessary only for reactions with ammonia. The usual temperature is ca 200 °C, but achieving good selectivity for unsaturated amines, nitriles, or heteroaromatic compounds requires 300-400 °C. Solvents other than ammonia are rarely applied. 

Amination of phenols with ammonia is a simple route to aromatic amines. Transformation of 2,6-dimethylphenoI in a continuous fixed-bed reactor at 210 °C over Pd/C yielded 90% 2,6-dimethylaniline after only 6 s contact time [17]. 2,6-Dimethylcyclohexanone and 2,6-dimethylcyclohexylamine were identified as key intermediates at low contact times the concentration of the latter reached 25 %. Compared with the performance of other metals, Pd-based catalysts have outstanding activity and selectivity in the amination of phenols [4]. 

There are few reports of successful one-step synthesis of primary diamines, and the examples are limited to amines with a special structure. Amination of 1,4-cy-clohexanediol in supercritical ammonia (135 bar) over a Co-Fe catalyst alforded 67 % 1,4-diaminocyclohexane [21]. Excess ammonia, as both supercritical solvent and reactant, and short contact time in the continuous fixed-bed reactor favored the desired reactions. In the best example the cumulative selectivity for the diamine and the intermediate amino alcohol was 97 % at 76 % conversion. Recycling of the unreacted diol and amino alcohol can provide an alternative to the eurrent process, the hydrogenation of pnra-phenylenediamine. The high seleetivity was because of the rigid structure and the relative positions of OH functionality in the substrate. For comparison, amination of 1,4-butanediol under similar conditions yielded pyiTolidine as the major product 1,4-diaminobutane was barely detectable. When 1,3-cyclohexanediol was aminated with the same catalyst in the continuous system, the yield of 1,3-diaminoeyclohexane dropped below 5%, mainly because elimination of water led to undesired monofunctional products via a,/9-unsaturated alcohol, ketone, and/or amine intermediates [22]. 

Conversion of dihydroxy compounds to diamines requires the repetition of all reaction steps (dehydrogenation, addition, elimination, hydrogenation). Selectivity is much higher when diols are transferred only to amino alcohols or amino alcohols to diamines. This difference is exemplified by the reaction of 1,6-hexanediol with di-methylamine over CU/AI2O3 [25]. Over 90% selectivity for the intermediate N,N-dimethyl-6-amino-l-hexanol was achieved at 180 °C in a continuous fixed-bed reactor. To complete the amination of the second OH group the reactor temperature had to be raised to 230 °C and the highest selectivity for diamine was only 65 %. 

Figure 7 A comparison of the enantiomeric excesses (ee) of (it)-l-hydroxy-l-phenylpropanone in a continuous fixed bed reactor ( ) and in a batch reactor ( ).

Hydrogenation of 1-phenyl-1,2 -propanedione was investigated in batch and continuous fixed bed reactors. The main product in the first hydrogenation step was 1-hydroxy-l-phenylpropanone the ratio between 1-hydroxy-1-phenylpropanone and... 

Figure 2 Suzuki coupling in a semi-continuous, fixed-bed reactor. Four cycles of reaction with 4-bromobenzotrifluoride at 50 °C. 1) fresh catalyst (initial rate, 0.22 mol/h) 2) water-washed catalyst, reagents replenished (initial rate, 0.017mol/h) 3) water-washed catalyst, fresh reaction solution (initial rate, 0.012 mol/h) 4) water-washed catalyst, hydrogen reduction, fresh reaction solution (initial rate, 0.01 mol/h).

For a continuous fixed bed reactor the pseudo-steady state mass balances for the fluid-phase species A and B are solved numerically with respect to the space time (r) at different times. 

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