Optimum Pore Diameter Research Articles

Performance limits of isothermal packed bed and perforated monolithic bed reactors operated under laminar flow conditions. I. General optimization analysis

A global optimization analysis of a general class of perforated monolithic bed reactors is presented for the case of an isothermal first-order reaction and for laminar flow conditions. The resulting design rules indicate how a given amount of catalyst material should best be perforated or distributed in space as a function of the available inlet pressure. It is shown that the influence of the different process variables ( k,Δ P, V cata, C in/ C out, D mol, S reac) on the reactor productivity and on the optimal bed design can be grouped into a single dimensionless number E. This number also allows to discuss the sensitive relation between the total and the volumetric productivity of single bed reactors in a very general, compact manner. Two different perforated monolithic bed designs, a slit pore bed (SPB) and a cylindrical pore bed (CPB) are considered. It is found that, when there is an excess inlet pressure (i.e., for E≪1), the optimal catalyst layer thickness is given by φ=0.3–0.5 and that the optimal pore diameter is in both cases 1.4–1.45 times smaller than the catalyst layer, independently of the internal catalyst diffusivity ( D int) and the other process variables. When the available inlet pressure is limiting ( E>10 −4), and when the absolute reactor productivity is more important than the volumetric productivity, it is found that much more open structures, with much wider pores are needed, i.e., perforated beds show the same behavior as packed beds, where the occurrence of a pressure-drop limitation also induces a shift from the use of full particles to the use of hollow extrudates.

Comparison of different Ni-Mo/alumina catalysts on hydrodemetallization of Maya crude oil

Three Ni-Mo/Al 2O 3 catalysts were used in this work to study the hydrodemetallization reactions on Maya heavy crude oil. Two reactions, HDM and asphaltenes conversion (HDAs), were studied at four different temperatures (653, 673, 693 and 713 K) and four space velocities (0.5, 1.0, 1.5, and 2.0 h −1) at constant pressure and hydrogen-to-oil ratio of 6.86 MPa and 890.47 ml/ml, respectively. Removals of sulfur and nitrogen were also studied at the same conditions. Activities were related to operating conditions and catalyst properties. The activity of the catalysts was different at high and low temperatures. The optimum pore diameter for removal of sulfur and nitrogen compounds was smaller than that required for metals and asphaltene conversions. It was observed that catalyst having high pore volume in the 100–250 Å region showed high HDM activities. Apparent activation energies were also determined for each reaction and each catalyst.

Effect of pore size on bitumen hydrocracking over Al2O3‐AlPO4 supported Ni‐Mo catalysts

AbstractA study of co‐precipitated aluminum oxide‐aluminum phosphate (AAP) materials as supports of Ni‐Mo heavy oil upgrading catalysts has been completed. Results of both short duration (8 h) and longer duration (up to 200 h) experiments at conditions relevant to the commercial H‐Oil process are reported and compared with a commercial NiMo/Al2O3 catalyst.The initial activity of the Ni‐Mo/AAP catalysts correlates with the catalyst average pore diameter which is determined by the P content of the AAP support. An optimum pore diameter of about 20 run exists for HDM whereas for HDS a pore diameter < 10 nm is desirable. After 100 h operation the HDM conversion of the best Ni‐Mo/AAP catalyst was approximately 10 percentage points greater than for the commercial catalyst. The HDS and CCR conversions were comparable over the two catalysts. The difference in performance between the catalysts is attributed primarily to the smaller pore size of the Al2O3 support compared to the AAP support. The amount of coke deposited on the Ni‐Mo/AAP catalyst was less than that on the commercial catalyst, presumably due to differences in pitch conversion levels.

Properties of Aspergillus japonicus ?-fructofuranosidase immobilized on porous silica

β-Fructofuranosidase from Aspergillus japonicus MU-2, which produces fructo-oligosaccharides (1-kestose: O-β-D-fructofuranosyl-(2 → 1)-β-D-fructofuranosyl α-D-glucopyranoside); and nystose: O-β-D-fructofuranosyl-(2 → 1)-β-D-fructofuranosyl-(2 → 1)-β-D-fructofuranosyl α-D-glucopyranoside) from sucrose, was immobilized, covalently with glutaraldehyde onto alkylamine porous silica, at high efficiency (64%). Optimum pore diameter of porous silica for immobilization of the enzyme was 91.7 nm. After immobilization, the enzyme's stabilities to temperature, metal ions and proteolysis were improved, while its optimum pH and temperature were unchanged. The highest efficiency of continuous production of fructo-oligosaccharides (more than 60%), using a column packed with the immobilized enzyme, was obtained at 40% to 50% (w/v) sucrose. The half-life of the column during long-term continuous operation at 55°C was 29 days.

Immobilization ofβ-fructofuranosidase fromAureobasidium sp. ATCC 20524 on porous silica

β-Fructofuranosidase P-1 fromAureobasidium sp. ATCC 20524, which produces a fructo-oligosaccharide (1-kestose) from sucrose, was immobilized covalently onto alkylamine porous silica with glutaraldehyde at high efficiency (44.4%). Optimum pore diameter of porous silica for immobilization of the enzyme was 91.7 nm. The enzymatic profiles of immobilized enzyme were almost identical to the native one except its stabilities to temperature and metal ions were improved. 1-Kestose was produced continuously and selectively from 40% (w/v) sucrose at fast flow rates by a column packed with the immobilized enzyme for up to 26 days, and the effluent concentration of 1-kestose remained in the range 113–135 mg ml−1.

Kinetic study on the hydrotreating of heavy oil. 2. Effect of catalyst pore size

The hydrodemetalation reactions of residual oil were carried out by use of a trickle bed reactor to investigate the relation between catalyst pore diameter and activity. The catalysts used were 3% molybdenum on alumina and silica-alumina. The results showed that the optimum pore diameter was located around 100 -- 150 A at 400/sup 0/C. The optimum pore diameter increases with the elevation of reaction temperature, and the curve showing the change of metals removal with pore diameter becomes broader at higher reaction temperature. The selectivity between two reactions, such as vanadium and nickel removal, passes through a maximum with varying the pore diameter.

Biocatalytic materials having a porous structure

Biocatalytic materials having a porous structure have been prepared by radiation polymerization at low temperatures using hydrophilic 2-hydroxyethyl methacrylate monomer andα-glucosidase. The biocatalytic (enzyme) activity of the materials was examined by enzyme reaction. The enzyme activity was affected by the pore size and surface area, and the optimum pore diameter giving a high enzyme activity was 20 to 40μm. The enzyme activity was also affected by irradiation temperature and addition concentration of crosslinking monomer. The heat and pH stability of the materials were higher than those of the native enzyme.

11] Adsorption and inorganic bridge formations

This chapter describes the adsorption and inorganic bridge formations. Adsorption is the adhesion of an enzyme to the surface of a carrier that has not been specifically functionalized for covalent attachment. Adsorption appears in the author's opinion to be the most economical procedure for immobilizing an enzyme on a carrier (on hydrophobic adsorption of enzymes and on aminoacylase ad sorbed to DEAE-Sephadex.) Although the immobilization procedure may be simple, the reactions involved in adsorption are complex and involve multiple types of bond formations. The stability of an adsorbed enzyme will depend upon the additive strength of those bonds formed under the conditions of immobilization and those bonds maintained under the application conditions that are finally employed for the immobilized enzyme. It is discussed that there are three major points to be considered in the optimization of a carrier for adsorption of enzymes: (1) preconditioning the surface with respect to pH, (2) preconditioning the surface with respect to cofactors, and (3) selection of the optimum pore diameter for immobilizing the enzyme.

Some effects of pore diameter on single pore bony ingression patterns in teflon.

AbstractTeflon implants containing a single cylindrical pore were surgically embedded in the femural bones of rabbits. A total of eight different pore sizes were used for each experimental animal. Their diameters ranged from 274 to 670 μm, with approximately 50 μm intervals between sizes. The amount of bone tissue ingression and its spatial distribution was assessed for each pore diameter at weekly intervals over a sixteen‐week period by bone labeling with Tetracycline injection. From these data an optimum pore diameter of between 400 to 450 μm was observed for maximum bone ingression. The distribution of new bone growth was characterized as an apposition pattern which emanated from the walls and the open end of the pore. No rejection phenomena were observed at the Teflon tissue interfaces.

Das Verhalten von schwerbeladenen trennsäulen in der hochdruck-flüssigchromatographie

The stability and the lifetime of heavily loaded columns are determinied by the pore structure of the support. If linear velocities up to 5–10 cm/sec are wanted the optimum pore diameter should not exceed 500 Å. The retentions are influenced by the support if its specific surface are is larger than 10 m 2/g, especially if the samples are capable of hydrogen bonding. This influence can be reduced by chemical modification of the support. Optimum efficiency is achieved by such supports. Heavily loaded columns are well suited for semi-preparative separations, since the maximum sample size is around 10 mg per gram of a stationary liquid phase. Speedy separations can be achieved by flow programming.