Continuous-flow Fixed-bed Reactor System Research Articles

Mesoporous KIT-6 supported Cr and Co-based catalysts for microwave-assisted non-oxidative ethane dehydrogenation

Abstract In the present study, mono and bi-metallic catalysts containing Cr and Co were prepared by impregnating the hydrothermally prepared mesoporous KIT-6 support with 5–10 wt% total metal content. The well-ordered three-dimensional mesoporous structure of the KIT-6 support was confirmed by small angle X-ray diffraction (XRD) patterns. N2 adsorption-desorption analysis results showed that the mesoporous structure of KIT-6 was preserved after metal loading. Structural bonds of KIT-6 support and prepared catalysts were determined by Fourier-transform infrared (FT-IR) spectroscopy. The pyridine adsorbed diffuse reflectance FT-IR (DRIFT) spectroscopy results revealed the presence of Lewis acid sites on the surface of the catalysts. Activity experiments were carried out in a microwave-heated continuous-flow fixed bed reactor system at temperature range of 350–650 °C and feed ratios of Ethane/Argon: 1/2, 1/1, 2/1 with a gas hourly space velocity (GHSV) of 18,000 ml/h.gcat. The 5Cr@KIT-6 catalyst exhibited high ethane conversion (63.5%) while the highest ethylene/hydrogen ratio (0.98) was obtained with the 2.5Cr2.5Co@KIT-6 catalyst at 450 °C. It was concluded that high temperatures (above 450 °C) facilitate the formation of side reactions and the production of aromatic compounds. The high catalytic activities of mesoporous catalysts were thought to be due to hot spots in the microwave reactor system.

Equilibrium, kinetic and thermodynamic studies for dynamic adsorption of benzene in gas phase onto activated carbon produced from elaeagnus angustifolia seeds

Adsorption of pollutants onto activated carbon is very important in air purification systems. In this study, the dynamic adsorption of benzene in gas phase onto activated carbon which was produced from the elaeagnus angustifolia seeds, was investigated using a laboratory-scale continuous flow fixed-bed reactor system, under atmospheric pressure. The effects of the adsorption conditions such as activated carbon particle size (180–500 μm), nitrogen (N2) gas flow rate (0.050–0.120 L min−1) as the benzene in gas phase carrier, amount of activated carbon (0.10–0.75 g), concentration of benzene in gas phase at the inlet (9.95–14.85 ppm) and the adsorption temperature (293–323 K) on both the adsorption capacity and the adsorption efficiency were examined. Adsorption efficiency was achieved up to 100% under various adsorption conditions. Adsorption kinetics data were analyzed by using the Pseudo-First Order and Pseudo-Second Order kinetic models. Langmuir, Freundlich and Dubinin-Radushkevich models were used for the analysis of adsorption isotherms. The results showed that the Langmuir isotherm and Pseudo-Second Order models described the experimental data better when compared to other models. The maximum monolayer adsorption capacity (qmax) of activated carbon was determined to be 99.8 mg g−1 for 303 K. Thermodynamic analyzes indicated that the adsorption process of benzene in gas phase onto activated carbon was spontaneous (ΔG°<0), exothermic (ΔH°<0) and physical (ΔH°<20 kJ mol−1).

Kinetics and Mechanism of Ni/Zeolite-Catalyzed Hydrocracking of Palm Oil into Bio-Fuel

Kinetics and mechanisms of Ni/zeolite-catalyzed cracking reaction of methyl ester palm oil (MEPO) were studied using a continuous flow-fixed bed reactor system at an atmospheric pressure. The catalyst was prepared by wet impregnation method with a solution of nickel nitrate hexahydrate as the precursor and zeolite as carrier. The characteristics of catalyst including active Ni metal content, crystallinity, total acidity, and porosity were evaluated. The reactions were performed with a varied hydrogen flow rate as a carrier gas as well as a reductant and reaction time. Liquid products were analyzed by GC. Analysis by GC-MS was only conducted on a product at hydrogen flow rate with the best conversion. It has been shown that the catalyst has a superior character for hydrocracking reactions of MEPO into green fuel. No considerable effect of hydrogen flow rate on the total conversion was observed. The tests showed that the kinetics of Ni/zeolite-catalyzed cracking reaction followed pseudo-first order kinetics. GC-MS analysis revealed the formation of light hydrocarbon products with C6-C8 of aliphatic and cyclic components without oxygenates. Distribution of the product indicated that the cracking reaction as well as the isomerization of the products of hydrocracking occurred. Thus, Ni/zeolite-catalyzed cracking involved cracking /hydrogenation, isomerization, cyclization, and deoxygenation.

Heterogeneous Enantioselective Hydrogenation in a Continuous-flow Fixed-bed Reactor System: Hydrogenation of Activated Ketones and Their Binary Mixtures on Pt–Alumina–Cinchona Alkaloid Catalysts

Under the experimental conditions of the Orito reaction the individual hydrogenation and the competitive hydrogenations of three binary mixtures of methyl benzoylformate (MBF), pyruvic aldehyde dimethyl acetal (PA) and 2,2-diethoxyacetophenone (DAP) on platinum–alumina catalysts modified by cinchonidine, cinchonine, quinine and quinidine (Pt–CD, Pt–CN, Pt–QN, Pt–QD) were studied for the first time using continuous-flow fixed-bed reactor system. Conversions of chiral (Cc) and racemic (Cr) hydrogenations of all three compounds and enantioselectivities (ee) were determined under the same experimental conditions (under 4 MPa H2 pressure, at room temperature using toluene/AcOH 9/1 as solvent).The order of the rates of the enantioselective hydrogenations of the three substrates studied is MBF > PA > DAP, and the order of their ee values is MBF ~ PA > DAP. The hydrogenation rate and the effect of rate on ee depend on the structure of the cinchona used: hydrogenation of MBF and PA may produce ee values over 90 %, however, the ee values were conspicuously low in the presence of Pt–QN and especially of Pt–QD catalysts. In the chiral hydrogenation of DAP considering racemic hydrogenation rate decrease (Cc/Cr < 1) takes place instead of rate enhancement over all four catalysts. The new experimental data supported the so far known fundamental rules of the Orito reaction based on batch studies.

Catalytic Hydroprocessing of Fast Pyrolysis Bio-oil from Pine Sawdust

Catalytic hydroprocessing has been applied to the fast pyrolysis liquid product (bio-oil) from softwood biomass in a bench-scale continuous-flow fixed-bed reactor system. The intent of the research was to develop process technology to convert the bio-oil into a petroleum refinery feedstock to supplement fossil energy resources and to displace imported feedstock. This paper is focused on the process experimentation and product analysis. A range of operating parameters, including temperature from 170 or 250 to 400 °C in the two-stage reactor and flow rate of 0.19 liquid hourly space velocity, was tested with bio-oil derived from pine wood. Times on stream of up to 90 h were evaluated, and losses of catalyst activity were assessed. Product yields of 0.35–0.45 g of oil product/g of dry bio-oil feed with hydrogen consumptions from 342 to 669 L/L of bio-oil feed were measured. Analyses determined that product oils with densities of 0.82–0.92 g/mL had oxygen contents of 0.2–2.7 wt % and total acid number (TAN) o...

A CuZnAl-Based Hybrid Material for the Direct Synthesis of Dimethyl Ether from Syngas

A CuZnAl-based hybrid material was prepared by co-precipitation impregnation method using the active components of methanol synthesis material and pseudo-boehmite as the precursors. The as-prepared material was evaluated for the direct synthesis of dimethyl ether (DME) from syngas in a pressurized continuous flow fixed-bed reactor system. It was revealed that the hybrid material showed high activity and selectivity after an induced period, i.e. the CO conversion and DME selectivity reached as high as 81% and 67%, respectively. Moreover, it was observed that there was only slight carbon which could be eliminated rather than graphite carbon deposited on the material after run for 150 h, indicating its good stability for the direct synthesis process .

A CuZnAl-Based Hybrid Material for the Direct Synthesis of Dimethyl Ether from Syngas

A CuZnAl-based hybrid material was prepared by co-precipitation impregnation method using the active components of methanol synthesis material and pseudo-boehmite as the precursors. The as-prepared material was evaluated for the direct synthesis of dimethyl ether (DME) from syngas in a pressurized continuous flow fixed-bed reactor system. It was revealed that the hybrid material showed high activity and selectivity after an induced period, i.e. the CO conversion and DME selectivity reached as high as 81% and 67%, respectively. Moreover, it was observed that there was only slight carbon which could be eliminated rather than graphite carbon deposited on the material after run for 150 h, indicating its good stability for the direct synthesis process .

The First Case of Competitive Heterogeneously Catalyzed Hydrogenation using Continuous-Flow Fixed-Bed Reactor System: Hydrogenation of Binary Mixtures of Activated Ketones on Pt-Alumina and on Pt-Alumina-Cinchonidine Catalysts

Under the experimental conditions of the Orito reaction the competitive hydrogenations of four binary mixtures of ethyl pyruvate (EP), methyl benzoylformate (MBF), pyruvic aldehyde dimethyl acetal (PA) and 2,2-diethoxyacetophenone (DAP) on unmodified Pt/Al2O3 (racemic hydrogenation) and catalyst modified by cinchonidine (chiral hydrogenation) were studied using continuous-flow fixed-bed reactor system (CFBR). Conversions of chiral and racemic hydrogenations were determined under 4 MPa H2 pressure, at 293 K using toluene/acetic acid 9/1 as solvent. In the competitive chiral hydrogenation of MBF + EP and DAP + PA binary mixtures (S1 + S2) a new phenomenon was observed: namely the EP and PA are hydrogenated faster than MBF and DAP, whereas in racemic one the MBF and DAP are hydrogenated faster than the former ketones. The phenomenon verified for the first time in CFBR is dependent on the adsorption mode of the surface complexes of various compositions (S1–Pt, S2–Pt, S1–CD–Pt, S2–CD–Pt, CD = cinchonidine). In the chiral hydrogenation of DAP a rate decrease, i.e., “ligand deceleration” was observed instead of rate enhancement.

Reversal of the ee in enantioselective hydrogenation of activated ketones in continuous-flow fixed-bed reactor system

A study on the hydrogenation of ethyl pyruvate, methyl benzoylformate and 2,2,2-trifluoroacetophenone over Pt–cinchona alkaloid chiral catalysts and over the “unmodified” catalysts resulted after a cleaning step at 323 K of the chirally modified surfaces in continuous-flow fixed-bed reactor system is presented. According to these investigations the sense of the residual ee observed in the reactions carried out in the absence of modifiers over the catalysts rinsed after the chiral hydrogenations was influenced by the solvent and the structure of the activated ketone, pointing on the effect of these parameters on the structure of the adsorbed intermediate complexes and implicitly on the chiral induction.

Origin of the rate enhancement and enantiodifferentiation in the heterogeneous enantioselective hydrogenation of 2,2,2-trifluoroacetophenone over Pt/alumina studied in continuous-flow fixed-bed reactor system

A study on the origin of rate enhancement and enantiodifferentiation in the enantioselective hydrogenation of 2,2,2-trifluoroacetophenone (TFAP) over a Pt/alumina catalyst modified by cinchona alkaloids in toluene/acetic acid (AcOH) solvent mixture with and without trifluoroacetic acid (TFA) using continuous-flow fixed-bed reactor system is presented. The experimental data of the racemic – cinchona 1–cinchona 2–cinchona 1 hydrogenation series confirm the intrinsic nature of rate enhancement, namely the so-called “ligand acceleration” phenomenon. Hydrogenation in the presence of 0.1% (v/v) TFA follows the general rule of the Orito reaction, according to which the products formed in excess are ( R)-alcohols on Pt-cinchonidine and Pt-quinine and ( S)-alcohols on Pt-cinchonine and Pt-quinidine chiral catalysts. In toluene/AcOH mixture without TFA, unexpected inversion took place on the Pt-cinchonine and Pt-quinidine catalysts since the ( R)-product formed in excess instead of the ( S)-product. The observed unexpected inversion can be interpreted on the basis of the nucleophilic intermediate complex. Based on these observations we propose that in the hydrogenation of TFAP the reaction route involves the equilibrium of electrophilic and nucleophilic intermediate complexes, which was found to be dependent on the acid strength and concentration.

Novel Evidence on the Role of the Nucleophilic Intermediate Complex in the Orito-Reaction: Unexpected Inversion in the Enantioselective Hydrogenation of 2,2,2-Trifluoroacetophenone on Pt-Cinchona Chiral Catalyst Using Continuous-Flow Fixed-Bed Reactor

The enantioselective hydrogenation of 2,2,2,-trifluoroacetophenone over Pt/Al2O3 catalysts modified by cinchona alkaloids was investigated for the first time using continuous-flow fixed-bed reactor system in toluene/AcOH 9/1 solvent mixture in absence and presence of 0.1 v/v% trifluoroacetic acid (TFA). The enantioselective hydrogenations yielded the (R)-product in excess on Pt–CD, Pt–CN, Pt–QN and Pt–QD catalysts in toluene/AcOH mixture; consequently, unexpected inversion took place on the Pt–CN and Pt–QD catalysts. Hydrogenation in the presence of 0.1% (v/v) TFA follows the general rule of the Orito reaction, according to which the products formed in excess are (R)-alcohols on Pt–CD and Pt–QN and (S)-alcohols on Pt–CN and Pt–QD. Since there is no inversion in the presence of TFA, the observed unexpected inversion can be interpreted on the basis of the nucleophilic intermediate complex.

New data in the enantioselective hydrogenation of ethyl pyruvate on Pt-cinchona chiral catalyst using continuous-flow fixed-bed reactor system: The origin of rate enhancement

The origin of rate enhancement in the enantioselective heterogeneous catalytic hydrogenation of ethyl pyruvate on Pt modified with the parent cinchonas, as compared to the unmodified Pt, was studied in a solvent mixture toluene/AcOH 9/1. Hydrogenation experiments were carried out in a continuous-flow fixed-bed reactor and in several cases for comparison in batch reactors over E4759 catalyst. Our results obtained using a novel procedure, namely racemic hydrogenation followed by three changes of the chiral modifier (on the same catalyst) supported an intrinsic “ligand acceleration” character of the rate enhancement in ethyl pyruvate hydrogenation.

New data to the origin of rate enhancement on the Pt-cinchona catalyzed enantioselective hydrogenation of activated ketones using continuous-flow fixed-bed reactor system

A study on the origin of rate enhancement (RE) in the enantioselective heterogeneous catalytic hydrogenation of methyl benzoylformate (MBF), ketopantolactone (KPL) and pyruvic aldehyde dimethyl acetal (PA) under the Orito reaction conditions over Pt catalyst modified with parent cinchona alkaloids, as compared to the unmodified catalyst is presented. The hydrogenations were carried out in continuous-flow fixed-bed reactor system over 20–100 mg Pt/Al 2O 3 catalyst in 1 mL min −1 flow of toluene/acetic acid 9/1 solvent mixture under 40–80 bar H 2 pressure, at 283 or 293 K using 0.044–2 mM modifier concentration and 45 mM substrate concentration. Our results obtained using racemic hydrogenations followed by three changes of the chiral modifier (on the same catalyst) supported the so-called “ligand acceleration” phenomenon in the enantioselective hydrogenation of activated ketones such as MBF, KPL and PA. In our opinion, RE produced by the first modifier added after racemic hydrogenation can also be explained by the purifying effect of the cinchona. REs observed following further exchanges of modifiers are indicative of the intrinsic character of the phenomenon. This research suggested that the origin of enantiodifferentiation and rate enhancement is the same, namely, both may be traced back—probably in different ways—to the role of the intermediate complexes of the hydrogenation, to its formation and transformation, which in turn depends on numerous factors.

The olefin metathesis reaction: An experiment in heterogeneous catalysis

Illustrates the incorporation of heterogeneous catalysts in a continuous flow fixed-bed reactor system, providing the student with the bonus of exposure to some of the common tools of industrial re...