Search

The interface area between the bubble and emulsion phases in a fluidized catalyst bed is one of the important parameters used to analyze and design the fluidized bed reactor. We used a fast-scanning X-ray CT system to observe the bubble shape and structure. We then obtained the transient 2-dimensional cross sectional gas-phase distribution in a fluidized catalyst bed. Using image-processing techniques, pseudo 3-dimensional images of the bubbles were reconstructed. The bubble structure was studied based on the 3-dimensional images and the previously obtained results in a 2-dimensional fluidized bed. It was found that the bubble shape was not spherical but complicated, and that the bubbles ascending in a fluidized catalyst bed consisted of some smaller bubbles.

When a fluidizing gas is switched from a low-density gas to a high-density gas, particles in the emulsion phase agglomerate and bubbles disappear. At the same time, channeling occurs and a decrease in the pressure drop over the bed is observed. The disturbance of fluidization is temporary, and normal fluidization is restored after several minutes. The study of mechanisms of the transient phenomena shows that the difference in diffusion rates of the two gases in the emulsion phase caused the agglomeration of particles. Because the mobility of particles was reduced, channels were formed and the fluidizing gas bypassed through them. Effects of the properties of the fluidizing gases and particles on the intensity of the transient phenomena were also studied. The intensity increased with increasing difference in the densities of the two gases. The transient phenomena were considerable for small- and light-particle systems.

A significant defluidization occurs when carrying out reactions involving a decrease in gas volume in a fluidized catalyst bed. The cause of this phenomenon is a decrease in the gas velocity in the emulsion phase below the minimum fluidization velocity. Fluidization quality is improved by a staged gas feed when hydrogenation of CO2 is carried out. To evaluate the experimental results, two parameters are introduced; gas-volume reduction rate and gas-volume ratio. Fluidization quality and defluidization zone are indicated as a map using these parameters. The vertical distributions of these parameters are calculated using a reactor model to obtain operating lines. The calculation shows that fluidization quality can be improved by operating the reactor by avoiding the operating lines of the defluidization zone in the map. For this purpose, it is required to control the gas-volume ratio at a level near unity and maintain the gas-volume reduction rate below 0.01/s. © 2010 American Institute of Chemical Engineers AIChE J, 2010

The surface area and micropore distribution of porous glass prepared from borosilicate glass were controlled by the addition of alumina up to 8 wt%. The surface area increased with increased alumina content in the range from 0 to 3 wt%, but it suddenly decreased when the percent alumina exceeded 4 wt%. The mean pore diameter and micropore volume also decreased with increased alumina content. When nickel ion was supported into the porous glass, the surface area decreased to about one-half that of the original glass. Since the amount of nickel supported on the porous glass increased directly with surface area, the silanol group was considered to be uniformly distributed on the glass. La surface specifique et la distribution de micropores de verre poreux prepare avec du verre de borosilicate. ont ete contro'lees par l'ajout d'alumine jusqu'a 8% en poids. La surface specifique augmente avec la teneur en alumine dans la gamme de 0 a 3% en poids, mais diminue soudainement lorsque ce taux excede 4% en poids. Le diametre moyen des pores et le volume de micropores diminuent egalement lorsque la teneur en alumine augmente. Lorsque du nickel ionique est depose sur du verre poreux, la surface specifique diminue environ de moitie par rapport a la surface originale. Etant donne que la quantite de nickel depose sur du verre poreux augmente directement avec la surface specifique, on considere que le groupe des silanols est distribue uniformement sur le verre.

The hydrogenation of benzene has been carried out over a catalyst prepared from an amorphous Pd-Zr alloy held in an alumina matrix. The catalytic activity was compared with that over the alloy cut into 1 mm fragments. It was found that the fixed alloy in the alumina had not only higher catalytic activity, but also a smaller catalyst fouling rate than the fragments of the alloy. The effect of palladium content in the amorphous alloy on the hydrogenation activity was examined. It was found that the initial activity increased with the fraction of palladium. However, the activity of the catalyst which had the highest palladium content decreased with repeated regeneration and reaction, whereas the activity of the other catalysts reached a stable value. On a effectue l'hydrogenation du benzene a l'aide d'un catalyseur prepare a partir d'un alliage amorphe de Ph-Zr depose sur une matrice d'alumine. L'activite catalytique a ete comparee a celle de l'alliage decoupe en fragments de 1 mm. On a trouve que l'alliage fixe dans l'alumine a non seulement une activite catalytique plus elevee, mais egale-ment une vitesse d'encrassement du catalyseur plus petite que dans le cas des fragments d'aliiage. On a examine l'effet de la teneur en palladium dans l'alliage amorphe sur l'activite d'hydrogenation. On a trouve que l'activite initiale augmente avec la fraction de palladium. Cependant, l'activite du catalyseur qui a la plus haute teneur en palladium diminue a la suite d'une regeneration et d'une reaction repetees, alors que l'activite des autres catalyseurs atteint une valeur stable.

The vapor phase Beckmann rearrangement of cyclohexanone oxime has been carried out over zeolites and boria modified HZSM-5 zeolites to elucidate the effects of acidity and acid strength distribution on the conversion and e-caprolactam selectivity. Although e-caprolactam selectivity was increased with the SiO2Al2O3 ratio in a HZSM-5 zeolite, the highest selectivity in the study was accomplished over a boria modified HZSM-5. The selectivity was dependent on the ratio of weak acid sites to strong acid sites. The boria played an important role in controlling the acid strength distribution of the zeolites. It was found that the production of a polymer over strong acid sites caused a decrease in e-caprolactam selectivity during the reaction. On a effectue la transposition de Beckmann en phase vapeur d'une oxime de cyclohexanone sous l'action de zeolites et de zeolites HZSM-5 modifiees par le bore afin d'elucider les effets de l'acidite et de la distribution de force de l'acide sur la Conversion et la selectivite du e-caprolactam. Bien que la selectivite e-caprolactam soit amelioree avec le rapport SiO2/Al2O3 dans une zeolite HZSM-5, la meilleure selectiavite dans l'etude a ete obtenue avec la HZSM-5 modifiee par le bore. La selectivite depend du rapport des sites acides faibles sur les sites acides forts. Le bore joue un role important dans le controle de la distribution de force de l'acide des zeolites. On a trouve que la production d'un polymere sous l'action de sites acides forts entraǐnait une diminution de la selectivite du e-caprolactam lors de la reaction.

The hydrogenation of benzene and methyl-benzenes was performed over a nickel catalyst supported on the porous glass prepared from borosilicate glass with an alumina content ranging from 3% to 5%. The micropore size of the porous glass decreased with increasing alumina content. Although the overall reaction rates of benzene and toluene did not significantly change with the alumina content in the borosilicate glass, the rate of 1,3,5-trimethylbenzene, which is the bulkiest molecule among the hydrocarbons tested, decreased as the content of the alumina in the support increased. This result indicates that a catalyst support with molecular shape selectivity can be prepared from borosilicate glass containing alumina. On a effectue l'hydrogenation du benzene et de methyle-benzenes sur un catalyseur au nickel depose sur du verre poreux prepare a partir de verre au borosilicate ayant une teneur en alumine comprise entre 3 et 5%. La dimension des micropores du verre poreux diminue quand la teneur en alumine augmente. Bien que les vitesses de reaction globales du benzene et du toluene ne change pas de maniere significative avec la teneur en alumine dans le verre au borosilicate, la vitesse du 1,3,5-trimethylebenzene, la molecule la plus volumineuse parmi les hydrocarbures testes, diminue a mesure que la teneur en alumine du support augmente. Ce resultat montre qu'un support de catalyseur possedant une selectivite de forme moleculaire peut ětre prepare a partir de verre au borosilicate contenant de l'alumine.

The decomposition reaction of p–t-butylcumene and t-butylbromobenzene have been carried out over pyridine poisoned silica-alumina and HY zeolite in order to examine the effect of acid strength on selectivity. Since the catalyst deactivation rate for isomerization over the poisoned silica-alumina was greater than that of de-t-butylation in the reaction of p–t-butylcumene, the selectivity of de-t-butylation gradually improved with process time. In the reaction of t-butylbromobenzene over poisoned HY zeolite, the de-bromination rate was suppressed by the poisoning because the nature of active sites was different between silica-alumina and HY zeolite. The poisoned HY zeolite was found to be favorable for the de-t-butylation of halogenated-t-butylbenzenes. On a realise une reaction de decomposition du p–t-butylcumene et du t-butylbromobenzene sur des catalyseurs a base de silice-alumine et de zeolithe HY empoisonnes par de la pyridine dans le but d'etudier l'effet de la force acide sur la selectivite. La vitesse de desactivation du catalyseur au cours de la reaction du p–t-butylcumene s'etant averee plus grande dans le cas de l'isomeration sur le catalyseur de silice-alumine empoisonne, que dans celui de la de-t-butylation, la selectivite de la de-t-butylation s'est progressivement amelioree avec la duree du procede. Dans la reaction du t-butylbromobenzene sur un catalyseur zeolithique HY empoisonne, la vitesse de de-bromuration a ete diminuee par l'empoisonnement, la nature des sites actifs etant differente entre la silice-alumine et la zeolithe HY. La zeolithe HY empoisonnee s'est averee meilleure pour la de-t-butylation des t-butylbenzenes halogenes.

The kinetics of the methanation of carbon dioxide was investigated using an alumina supported Ni-La2O2 catalyst in a differential and integral reactor. In the differential reactor the molar ratio of H2 to CO2 was varied from 0.6 to 30. In the integral reactor the rates were measured with up to 90% conversion. Both reactor tests were carried out at temperatures between 513 and 593 K. The experimental results were described by a Langmuir-Hinshelwood type equation. The kinetics can be explained by assuming equilibrium of dissociative carbon dioxide and hydrogen adsorption, and assuming hydrogenation of surface carbon as the rate determining step.

De-t-butylation of t-butylbenzenes was carried out over a pyridine poisoned solid acidic catalyst to determine the effect of acid strength distribution on the reaction rate and catalyst fouling rate. The acid sites on the solid acidic catalyst were divided into three groups by their acid strength. Moderate acid sites, which were effective for the de-t-butylation but ineffective for the coke formation, were exclusively left on the catalyst surface by the partial poisoning. It is found that the present modification of the catalyst is useful in preparing an acid catalyst without catalyst fouling by coke deposition. On a effectue la de-t-butylation de t-butylbenzenes sur un catalyseur solide acide empoisonne a la pyridine afin de determiner l'effet de la distribution de la force de l'acide sur la vitesse de reaction et la vitesse d'encrassement du catalyseur. Les sites acides sur le catalyseur solide acide ont ete repartis en trois groupes selon leur force acide. Les sites acides moderes qui se sont averes efficaces pour la de-t-butylation mais inefficaces pour la formation de coke, ont ete exclusivement laisses sur la surface du catalyseur par l'empoisonnement partiel. On a trouve que la modification actuelle du catalyseur est utile a la preparation d'un catalyseur acide qui ne presente pas d'encrassement du catalyseur par depot de coke.

Liquid-solid phase de-t-butylation of p-t-butylphenols was carried out over original and dealuminated zeolites to determine the effect of catalyst pore size and acidity on the reaction rate and catalyst fouling rate. The de-t-butylation rate over the original zeolites was mainly dependent upon their micro pore sizes. Although the dealumination by acid leaching decreased strong acid sites, the de-t-butylation rate over dealuminated HY zeolite was higher than that on the original zeolite. The present dealumination is a useful method to prepare an acid catalyst for de-t-butylation in a liquid-solid system. On a effectue la de-t-butylation en phase liquide-solide des p-t-butylphenols sur des zeolites originales et dealuminees afin de determiner l'effet de la taille des pores du catalyseur et de l'acidite sur la vitesse de reaction et la vitesse d'en-crassement du catalyseur. La vitesse de de-t-butylation sur les zeolites originales depend essentiellement de la taille de leurs micro pores. Bien que la dealumination par lixiviation a l'acide diminue les sites acides forts, la vitesse de de-t-butylation sur la zeolite HY dealuminee est plus elevee que sur la zeolite originale. Cette methode de dealumination est utile pour preparer un catalyseur acide pour la de-t-butylation dans un systeme liquide-solide.

Amorphous Pd-Zr alloys, produced by a rapid solidification technique, were studied to determine their catalytic activity for the hydrogenation of cyclohexene and benzene. The activity of the amorphous alloy without pretreatment by air was lower than that of the corresponding crystalline alloy, but it was gradually increased with the pretreatment. The surface area and the hydrogen adsorption activity of the alloys were simultaneously increased with the pretreatment. It is found from X-ray diffraction pattern and SEM observation that palladium, which is an active species for hydrogenation in the amorphous alloys, is highly dispersed on the granulated ZrO2 surface by the pretreatment. On a etudie des alliages Pd-Zr amorphes, produits par une technique de solidification rapide, dans le but de determiner leur activite catalytique pour l'hydrogenation du cyclohexene et du benzene. L'activite de l'alliage amorphe sans pretraitement a l'air est inferieure a celle de l'alliage cristallin correspondant, mais augmente progressivement avec le pretraitement. La surface et l'activite de l'adsorption d'hydrogene des alliages augmente simultanement avec le pretraitement. On a trouve par l'observation au microscope a balayage (SEM) et par diffraction des rayons X, que le palladium, qui est une espece active pour l'hydrogenation dans des alliages amorphes, est hautement disperse a la surface du ZrO2 granule, par le pretraitement.

Dehydration of 1-phenylethanol has been carried out over a solid acidic catalyst in order to examine the effect of the concentration of effective acid sites on the reaction rate, styrene selectivity and catalyst fouling. The reaction rate increased with the concentration of effective acid sites, while styrene selectivity decreased. The catalyst deactivation depended upon the concentration of the effective acid sites and also the size of the micro pores in the catalyst. Taking into account the reaction rate and selectivity, ALO-4 alumina was the most suitable catalyst for the present reaction. An activation energy for the dehydration over ALO-4 alumina was 83.8 kJ mol−1. The dehydration reaction could be a useful tool for the characterization of the nature of the acid sites.

The fluidization quality significantly decreased when the reaction involving a decrease in the gas volume was carried out in a fluidized catalyst bed. In the present study, we carried out the hydrogenation of carbon dioxide in a transparent column to observe the bed behavior. When the reaction rate was increased, the fluidity of the emulsion phase decreased and channeling occurred. When the fluidity of the emulsion phase decreased even further, the upper part of the bed was defluidized and this part was lifted up through the column. This phenomenon caused the entrainment of a large amount of catalyst particles from the reactor. We studied the effects of the reduction rate of the gas volume and the maximum gas contraction ratio on the fluidization behavior. The criterion for a stable operation, which could be successfully given by the gas-volume reduction rate, is useful for determining the operating conditions needed to establish good fluidization when the reactions involving a decrease in the gas volume are carried out in a fluidized catalyst bed.