Comparative heterogeneous contacting efficiency in fixed bed reactors: Opportunities for new microstructured systems

Novel microstructured heterogeneous contacting systems called microfibrous entrapped catalysts (MFEC) were prepared by entrapping small particles of γ-alumina (150–180 μm) in sinter-locked network of metal (SS-304) microfibers (8 and 12 μm). These materials are in the form of thin flexible sheets (0.5–2.0 mm) and have uniform structures of high and variable voidages. Head-to-head theoretical comparisons of the performance efficiencies of flow-through pleated MFEC structures of various pleat factors (PF = face area of MFEC/cross-sectional area of the reactor) were made with packed bed reactors of various particle sizes (0.16–2.0 mm) and monolith reactors of various cpsi (100–900 cells per square inch). These comparisons showed that while packed beds produced high pressure drops, monoliths resulted in low fluid-solid mass transfer rates. On the other hand, MFEC structures with high PF (≥4) showed remarkable improvements in terms of conversion along with significant reduction in pressure drops and catalyst requirements compared to monoliths and packed beds. While small particles used in MFEC improved interphase and intraparticle mass transport rates, high voidages and ease of pleating helped lower the pressure drops in MFEC. To further ascertain these results, pleated structures of MFEC containing Pd/γ-alumina were tested for application in catalytic aircraft cabin air purification (ozone decomposition). Pressure drop and ozone conversion efficiency of pleated MFEC designs were measured at various flow rates and temperatures, and compared with those of a commercial monolith based ozone catalytic converter. The experimental results substantiated the mathematical findings.     

Oxalic acid destruction at high concentrations by combined heterogeneous photocatalysis and photo-Fenton processes

Heterogeneous photocatalysis (HP) using UV/TiO₂, photo-Fenton (PF) reaction using UV/Fe/H₂O₂ and the combination UV/TiO₂/Fe/H₂O₂ (HP–PF) were tested as processes to degrade oxalic acid (Ox) at relatively high concentrations (0.032 M). PF reactions were generally more efficient than HP including the reaction in the absence of H₂O₂. Oppositely to previous results (e.g., with EDTA), HP–PF combinations did not result, in the case of oxalate, better techniques for degradation than systems in the absence of TiO₂. The kinetic behavior was not unique and two parameters were taken to evaluate the efficiency of each system: initial rates (R₀) and time to 95% of total mineralization (TOC₉₅). Addition of hydrogen peroxide improves the initial HP reaction rate and reduces TOC₉₅. Addition of Fe³⁺ also affects the reaction parameters but the effect of H₂O₂ seems to be higher, at least under the present conditions. When both H₂O₂ and iron were added simultaneously, the efficiency was higher. The optimal H₂O₂:Ox:Fe molar ratio was established and the results indicated that, at a fixed iron concentration, H₂O₂ increased R₀ until a limit beyond which it did not cause any effect. No intermediates were formed in the reaction, oxalate being degraded directly to CO₂. Analogies and differences with the EDTA system are presented.     

A novel gas-liquid contacting route for the synthesis of layered double hydroxides by decomposition of ammonium carbonate

Layered double hydroxides (LDHs) carbonate with the M²⁺/Al³⁺ (M=Mg or Zn) molar ratio of 2/1 has been synthesized by a gas-liquid contacting route with the decomposition of ammonium carbonate. The key feature of this method is a pH gradient germinated by the diffusion of NH₃ and CO₂ vapors in the metal salts solutions from solid (NH₄)₂CO₃ in a closed environment. The physicochemical properties of these two particles were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, simultaneous thermogravimetric and differential thermal analysis (TG-DTA), scanning electron micrograph (SEM) or transmission electron micrograph (TEM), laser particle size analysis and low-temperature N₂ adsorption-desorption analysis. The results manifested that these two particles obtained by the method present well-crystalline, uniform crystallite size and relatively high surface area. The particle sizes of MgAl-LDH and ZnAl-LDH are around 0.55 and , respectively. Both the BET surface areas of them are about .     

Kalsilite based heterogeneous catalyst for biodiesel production

Kalsilite (KAlSiO₄) was used as a heterogeneous catalyst for transesterification of soybean oil with methanol to biodiesel. Kalsilite showed relatively low catalytic activity for transesterification reaction. The catalytic activity of this catalyst was significantly enhanced by introducing a small amount of lithium nitrate by the impregnation method. A biodiesel yield of 100% and a kinematic viscosity of 3.84 cSt were achieved at a mild temperature of only 120 °C over this lithium modified kalsilite catalyst (2.3 wt.% Li).     

With different structure ligands heterogeneous Ziegler-Natta catalysts for the preparation of copolymer of ethylene and 1-octene with high comonomer incorporation

Comparison with the conventional Ziegler-Natta catalyst TiCl₄/MgCl₂ (I), the modified supported Ziegler-Natta catalysts (iso-PentylO)TiCl₃/MgCl₂ (II) and (BzO)TiCl₃/MgCl₂ (III) were prepared as efficient catalysts for copolymerization of ethylene with 1-octene. The complexes (II) and (III) were desirable for the production of random ethylene/1-octene copolymers coupled with higher molecular weight, higher comonomer incorporation within copolymer chain and good yield even at high temperature 80 ^°C and fairly low Al/Ti molar ratio of 100. The effects of catalysts ligands, Al/Ti molar ratio, polymerization temperature, as well as concentration of 1-octene on the catalytic activity, molecular weight and microstructure of the copolymer were investigated in detail. The structure and properties of the copolymers were characterized with ¹³C NMR, GPC, DSC and WAXD. The kinetic results also indicate that these catalysts (II) and (III) show higher catalytic activity and the produced polymers feature higher molecular weight, because of lower ratio of K_trm/K_p and K_tra/K_p, and higher ratio of K_tra/K_trm which indicates that chain transfer to cocatalyst is predominant.     

The Fermi-Dirac concept for isotherms of adsorbents with heterogeneous surfaces

The integral equation for isotherms is reviewed in order to select simple, practical, high-performance energy distributions from among the numerous existing models. Adsorption equilibria can be derived from occupation indices of suitable distributed energy levels. For mono sites, the occupation index is a Fermi-Dirac function. Whether a surface is energetically heterogeneous or homogeneous depends on the ratio of the breadth of the energy level distribution σ to the thermal fluctuation kT. Although, there are only a few energy distributions for which analytic isotherm equations are known, the numerical evaluation shows general properties: the symmetry point , the temperature domain for real or ideal behaviour and isotherm shapes without extrema. As an example, experimental equilibria of CO at molecular sieve 5A are fitted to a hyperbolic energy distribution using four physical parameters: the reference loading, a reference fluid phase pressure , the mean value and the standard deviation of the adsorption energy level distribution.     

Platanus orientalis leaves based hierarchical porous carbon microspheres as high efficiency adsorbents for organic dyes removal

Water contamination caused by hazardous organic dyes has drawn considerable attention, among all of the techniques released, adsorption has been widely used, which however to a large degree is dependent on the development of high efficiency adsorbents. Waste biomass based porous carbon is becoming the new star class of adsorbents, and thus contribute more to the sustainable development of the society. In this work, for the first time to the best of our knowledge, abundant waste fallen Platanus orientalis leaves are employed as the raw material for hierarchical activated porous carbon(APC) microspheres via a mild hydrothermal carbonization(210 °C,12.0 h) followed by one-step calcination(750 °C, 1.0 h). The APC microspheres exhibit a specific surface area of1355.53 m~2·g~(-1) and abundant functional groups such as O—H and C=O. Furthermore, the APC microspheres are used as the adsorbents for removal of Rh B and MO, with the maximum adsorption capabilities of 557.06 mg·g~(-1) and 327.49 mg·g~(-1), respectively, higher than those of the most porous carbon originated from biomass. The adsorption rates rapidly approach to 98.2%(Rh B) and 95.4%(MO) within 10 min. The adsorption data can be well fitted by Langmuir isotherm model and the pseudo-second-order kinetic model, meanwhile the intra-particle diffusion and Boyd models simultaneously indicate that the diffusion within the pores is the main rate-limiting step. Besides, the APC microspheres also demonstrate good recyclability, and may also be applied to other areas such as heterogeneous catalysis and energy storage.     

Control of particle size distribution for the synthesis of small particle size high solids content latexes

A polymerization process to synthesize bimodal latexes with maximum particle diameters below 350 nm and solids content above 65 wt% has been developed.The process is based on an iterative strategy to determine the optimal particle size distribution that gives the maximum packing factor for a given range of particle sizes and at a given solids content. The calculated optimal bimodal PSD was experimentally obtained in a seeded semi-continuous emulsion polymerization reaction as follows: in the first step, a polymer seed latex was loaded in the reactor and grown, under monomer starved conditions, until a given particle size. At this point a fraction of the same seed was added to the reactor and the feed was continued until the desired particle size distribution and solids content were achieved. The point at which the seed was added again to the reactor and the amount of seed required were determined by the iterative strategy and depended on the competitive growth rate ratio of large and small particles that is an input for the iterative strategy.Implementation of the solution obtained from the iterative strategy, and for the first time in the open literature, led to the production of a coagulum free and stable bimodal latex with 70 wt% of solids content and particle sizes below 350 nm.     

Comparison of wash‐coated monoliths vs. microfibrous entrapped catalyst structures for catalytic VOC removal

Head‐to‐head experimental performance comparisons for flow through pleated microfibrous structures (flat‐, V‐, and W‐shaped) were made with wash‐coated monolith of different cells per square inch (230 and 400). Microfibrous entrapped catalyst (MFEC) was prepared by entrapping support particles (γ‐Al₂O₃, 150–250 μm diameter) into nickel microfibers. Pleated structures of MFECs and wash‐coated monoliths containing Pd‐Mn/γ‐Al₂O₃ were investigated systematically for volatile organic compound (e.g., ethanol) removal at various face velocities (ca. 3–30 m/s) and at low temperatures (≤473 K). The experimental studies showed that pleated MFEC (W‐shaped) had shown significantly improved performance in VOC removal in terms of conversion and pressure drop than tested monolith for high face velocity system. The flexibility of pleating lowered the effective velocity inside the media that resulted lower pressure drop and higher conversion. Furthermore, a reaction kinetic model was developed for pleated MFEC considering the Peffer's model to substantiate the experimental results. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3814–3823, 2014     

Advances on the development of novel heterogeneous catalysts for transesterification of triglycerides in biodiesel

This paper describes experimental work done towards the search for more profitable and sustainable alternatives regarding biodiesel production, using heterogeneous catalysts instead of the conventional homogenous alkaline catalysts, such as NaOH, KOH or sodium methoxide, for the methanolysis reaction. This experimental work is a first stage on the development and optimization of new solid catalysts, able to produce biodiesel from vegetable oils. The heterogeneous catalytic process has many differences from the currently used in industry homogeneous process. The main advantage is that, it requires lower investment costs, since no need for separation steps of methanol/catalyst, biodiesel/catalyst and glycerine/catalyst. This work resulted in the selection of CaO and CaO modified with Li catalysts, which showed very good catalytic performances with high activity and stability. In fact FAME yields higher than 92% were observed in two consecutive reaction batches without expensive intermediate reactivation procedures. Therefore, those catalysts appear to be suitable for biodiesel production.     

乙醇羰化非均相催化剂的研究进展

介绍了乙醇羰化制丙酸及丙酸乙酯的非均相催化过程,综述了非均相催化反应过程中的活性组分、催化助剂、载体的选择及其对催化过程的影响。介绍了活性组分分类(络合物、金属氯化物、贵金属和非贵金属),同时介绍了助剂的使用情况和活性炭载体的应用。论述了以往研究的成果和不足,提出了今后的发展方向。     

Environmentally friendly, heterogeneous acid and base catalysis for the methylation of catechol: Chances for the control of chemo-selectivity

The properties of catalysts with (i) Brønsted-type acidity (H-mordenite and Al/P mixed oxide), (ii) Lewis-type acidity (Al trifluoride) or (iii) basic characteristics (Mg/Fe mixed oxide) were investigated in the gas-phase methylation of catechol. When methanol was used as the methylating agent, H-mordenite and AlF₃ gave high selectivities to guaiacol (the product of O-methylation) under mild reaction conditions, that is at very low catechol conversions. An increase in temperature led to the transformation of guaiacol to phenol and cresols, and to considerable catalyst deactivation. The basic catalyst Mg/Fe/O also favored an extensive degradation of guaiacol to phenol. On the mildly acidic catalyst Al/P mixed oxide a stable catalytic performance and a high selectivity to guaiacol at 40% catechol conversion were obtained. When methylformate, a more reactive methylating agent, was used with AlF₃ and Mg/Fe mixed oxide as catalysts, higher catechol conversions and slower deactivation rates could be achieved under mild reaction conditions, with a low extent of guaiacol degradation. However, methylformate rapidly decomposed when temperatures above 350 °C were used. Finally, tests were made by reacting catechol and diethoxymethane with acid catalysts, with the aim of synthesizing methylenedioxybenzene. The latter product was obtained with high selectivity, but with very low yield, due to both catalyst deactivation and decomposition of diethoxymethane.     

Dolomite as a heterogeneous catalyst for transesterification of canola oil

In this study, the catalytic activity of dolomite was evaluated for the transesterification of canola oil with methanol to biodiesel in a heterogeneous system. The influence of the calcination temperature of the catalyst and the reaction variables such as the temperature, catalyst amount, methanol/canola oil molar ratio, and time in biodiesel production were investigated. The maximum activity was obtained with the catalyst calcined at 850 °C. When the reaction was carried out at reflux of methanol, with a 6:1 molar ratio of methanol to canola oil and a catalyst amount of 3 wt.% the highest FAME yield of 91.78% was obtained after 3 h of reaction time.     

Development of porous ultra high molecular weight polyethylene scaffolds for the fabrication of orbital implant

Porous implants having interconnecting channels allow ingrowth of host connective tissue. Complete implant vascularization reduces the risk of infection, extrusion, and other complications associated with nonintegrated implants. Attempts were made to develop 60% and 70% porous ultra high molecular weight polyethylene (UHMWPE) scaffolds and blocks using sodium chloride as channeling agent, which when dissolved in boiling water leaves behind the interconnecting channels. The average diameter of the pores of 60% and 70% porous scaffolds was found to be approx. 170 μm and 210 μm, respectively. Mechanical characterizations of the scaffolds indicated sufficient strength to be used for orbital implant fabracation. Surface roughness of the scaffolds indicated increase in surface roughness with the increase in porosity. The scaffolds developed were found to be hemocompatible with the human blood. Subsequently, the 70% porous scaffold was dip coated with a solution mixture of sodium carboxy methyl cellulose (SCMC)/polyvinyl alcohol (PVA)/hydroxyapatite (HA) which also showed hemocompatibility. Ciprofloxacin release pattern from the membrane was determined. Finally an orbital implant was fabricated from the 70% porous scaffold.     

Permeability of sintered microfibrous composites for heterogeneous catalysis and other chemical processing opportunities

Microstructured materials have potential for enhanced mass and heat transfer compared to typical catalyst particulates used in industrial processes. The pressure drop through catalyst-containing materials is a very important reactor design consideration. A model equation to predict porous media permeability (PMP) over the entire range of possible bed voidages is extended to predict properties of sintered metal meshes. A correlation of data for sintered meshes of nickel fibers is presented in the form of a Kozeny constant form drag plot. Comparison of predictions by the PMP equation with data taken on a sintered composite fiber/particle mesh is presented. Use of the PMP equation as a design tool for optimization of media for adsorbents, catalysts, and filters is discussed.     

Generalised method for the determination of heterogeneous batch distillation regions

A new, general method for the calculation of residue curves and for the determination of batch distillation regions of heteroazeotropic distillation is suggested. The method proposed, which means the extension of the method of Pham and Doherty, takes into consideration the possibility of the withdrawal of any fraction of either liquid phase from the decanter as distillate. The simplified and rigorous simulation calculations were carried out for the mixtures dichloromethane-acetone (low α) + water (heavy, selective, heterogeneous entrainer), water-ethylenediamine (maximum azeotrope) + benzene (light, selective, heterogeneous entrainer) and isopropanol-water (minimum azeotrope) + benzene (light, non-selective, heterogeneous entrainer). The new method gives the right sequence of the cuts for all operation modes and strategies of heterogeneous batch distillation.     

A semicontinuous approach for heterogeneous azeotropic distillation processes

The separation of azeotropes has substantial energy and investment costs, and the available methods require high capital costs for reconstruction of process plants. As an alternative, a semicontinuous configuration that utilizes an existing plant with minor modifications has been explored. In this paper, a semicontinuous, heterogeneous azeotropic distillation process is proposed and acetic acid dehydration process is used as a case study. To carry out the simulation work, Aspen HYSYS^® simulation software is used along with MATLAB^® and an interface program to handle the mode-transition of the semicontinuous process. Sensitivity analyses on operating parameters are performed to identify the process limits. Comparisons are made to conventional heterogeneous azeotropic distillation, and dividing-wall distillation column on the annual cost. The results proved that the semicontinuous system is the best setup in terms of total annual costs and energy requirements.     

Zirconium phosphonate immobilized chiral amino alcohol for heterogeneous enantioselective addition of diethylzinc to benzaldehyde

The chiral (1R,2S)-(−)-2-amino-1,2-diphenylethanol and (1S,2R)-(+)-2-amino-1,2-diphenylethanol had been immobilized on the layered frame of zirconium phosphate to obtain zirconium phosphonates (1R,2S)-(−)-4a and (1S,2R)-(+)-4b. The enantioselective addition of Et₂Zn to benzaldehyde using zirconium phosphonates (1R,2S)-(−)-4a and (1S,2R)-(+)-4b as heterogeneous catalysts yielded secondary alcohol in 80.1% yield and e.e. values of up to 54.3%, which was only 7.6% e.e. lower than that using the corresponding ligands (1R,2S)-(−)-2a and (1S,2R)-(+)-2b as homogeneous catalysts. The zirconium phosphonates (1R,2S)-(−)-4a and (1S,2R)-(+)-4b were characterized by IR, SEM, XRD and TG analysis. SEM and XRD data showed that the catalysts (1S,2R)-(+)-4b and (1R,2S)-(−)-4a were in aggregate and mesopore structure with the same interlayer spacing 2.48 nm and pore diameter 5.6 nm.     

Novel mesoporous polyoxometalate hybrid catalysts for heterogeneous oxidation of thioethers

K₆P₂W₁₈O₆₂ and K₁₄[NaP₅W₃₀O₁₁₀] polyoxometalate salts are synthesized and immobilized within MCM-48, SBA-3, SBA-15 and NH₃⁺ functionalized mesoporous silicas. The newly designed hybrid materials are studied as catalysts for oxidation of thioethers. Preyssler complex is found to be a more active catalyst compared to its Dawson analog. Texture and chemical composition of the silica framework is shown to have indispensable effect on oxidation efficiency, stability, and reusability of catalysts. Catalysts with larger pores are proved to be more proper for the oxidation of relatively large thioethers and functionalization improves catalyst's properties.     

Iron species incorporated over different silica supports for the heterogeneous photo-Fenton oxidation of phenol

Iron-containing catalysts have been prepared following different synthesis routes and silica supports (amorphous, zeolitic and mesostructured materials). Activity and stability of these materials were assessed on the photo-Fenton degradation of phenolic aqueous solutions using near UV irradiation (higher than 313 nm) at room temperature and initial neutral pH. Their catalytic performance was monitored in terms of phenol and total organic carbon (TOC) conversions. Aromatic compounds and carboxylic acids as by-products coming from incomplete mineralization of phenol as well as the efficiency of each catalytic system in the use of the oxidant were also studied. Stability of the materials throughout the photo-Fenton reaction was evaluated in terms of metal leachibility. Activity and stability depend on the environment of iron species and features of silica support. The evolution of pH with the reaction time and their relationship with TOC degradation and leaching degree has been discussed. A nanocomposite material of crystalline iron oxides supported over mesostructured SBA-15 material is shown the most successful catalyst for degradation of phenolic aqueous solutions by photo-Fenton processes, achieving an outstanding overall catalytic performance accompanied with a noteworthy stability.