Low Catalyst Concentration Research Articles

Influence of blending methods on the co-gasification reactivity of petroleum coke and lignite

The purpose of this paper is to investigate the influence of blending methods on the co-gasification of petroleum coke and lignite with CO 2 using a thermogravimetric system at 0.1 MPa. The weight loss curves, XRD analysis, SEM images, BET specific surface area, were investigated. It was observed that petroleum coke shows a low reactivity because of the graphitic carbon structure, low catalyst content and small specific surface area. Blending with lignite can get a high reactivity. The co-gasification reactivity was significantly influenced by blending methods. Wet grinding is much effective than dry grinding. Long grinding time made lignite show greater BET specific area. And the sample in long grinding time has more association chances between petroleum coke and AAEM species. The co-gasification reactivity increases linearly with a rise of BET specific area.

Selective aerobic oxidation of para-xylene in sub- and supercritical water. Part 2. The discovery of better catalysts

An extensive and systematic study has been carried out on the catalytic effect of more than 20 elements on the aerobic oxidation of p-xylene to terephthalic acid in super- and subcritical water. Reactions have been performed in a continuous reactor under catalyst unsaturated conditions. Reaction product, by-products and intermediates have been quantified as well as the burn (the amount of CO2 originating from total oxidation of p-xylene). CuBr2 has been found to be a superior catalyst to MnBr2, which has been widely used in the literature for this reaction in water at high temperatures. At catalyst unsaturated conditions (i.e. with low concentrations of catalyst), MnBr2 gives a terephthalic acid yield of 36.1% whereas CuBr2 enhances this value to 55.6%. A strong synergistic effect has been found between CuBr2 and other metals and sources of bromide. Indeed, we show that Cu/Co/Br, Cu/Co/NH4/Br and other mixtures give better results than CuBr2 reaching a terephthalic acid yield of 70.5% for the four component catalyst. The compositions of the catalyst as well as the reactor temperature have been optimized and their effects on the analyzed compounds are discussed. A substantial amount of additional data is included in the electronic supplementary information.

Activity and degradation pathways of pentamethyl-cyclopentadienyl-iridium catalysts for water oxidation

The activity of three [Cp*IrLn] (Cp* = pentamethylcyclopentadienyl) archetypal catalysts ([Cp*Ir (bpy)Cl]Cl (1, bpy = 2,2′-bipyridine), [Cp*Ir(bzpy)(NO3)] (2, bzpy = 2-benzoylpyridine) and [Cp*Ir(H2O)3](NO3)2 (3)) for water oxidation to molecular oxygen was compared using cerium(IV) ammonium nitrate as a sacrificial oxidant. Kinetic studies were carried out by: i) measuring the depletion of Ce4+ through UV-Vis spectroscopy, ii) directly detecting the evolved oxygen through the Clark electrode and iii) measuring the volume of the evolved oxygen. The kinetics of Ce4+ consumption were zero-order in Ce4+ for catalysts 2 and 3, while they were first-order for 1. The order with respect to catalyst was 1 for 1 and 2 while it was 1.5 for 3. As a consequence, 2 (TOFmax = 14.4 min−1) and 3 (TOFmax = 50.4 min−1) were found to be the most active catalysts at low and high catalyst concentration, respectively, while the performance of 1 (TOFmax = 8.6 min−1) increased with increasing the concentration of Ce4+. 1 and 3 were found to be the most robust catalysts at low (3.1 μM, TON = 1240) and high (7.0 μM, TON = 4042) catalyst concentration, respectively. In situNMR studies were performed under exactly the same conditions of the catalytic experiments. It was observed that Cp* underwent an oxidative degradation, ultimately leading to acetic, formic and glycolic acids. Several Ir-containing intermediates of the degradation process were intercepted and fully characterized in solution through 1D- and 2D-NMR experiments. DFT and NMR studies indicated that the degradation proceeds via an initial double oxidative functionalization of both the quanternary carbon and proton of a Cp* C–CH3 moiety.

High activity acetylene polymerisation with a bis(imino)pyridine iron(ii) catalyst

A catalyst system composed of a 2,6-bis(arylimino)pyridineiron(II) dichloride complex and methylaluminoxane is found to be extremely active for acetylene polymerisation. The formation of poly(acetylene) gels and surface films occurs at very low catalyst concentrations, around three orders of magnitude lower than traditional catalyst systems.

Bulk Ring Opening Polymerization of L‐Lactide with Calcium methoxide

AbstractSummary: Bulk ring opening polymerization (ROP) of L‐lactide (LA) initiated by calcium methoxide (Ca(OMe)2) was investigated in LA/Ca molar ratio from 100 to 5000 and reaction times up to 3h at 180 °C. Ca(OMe)2 showed good activity as ROP catalyst, particularly at high catalyst concentration. The polymerization shows a linear relationship between $\overline {{\rm M}} $n and reaction time, typical of a controlled process. The increase of LA/Ca molar ratio decreases the conversion which was maximum (66%) when the polymerization was carried out at 180 °C and LA/Ca = 100. Semicrystalline poly(L‐lactic acid) (PLLA) with moderate $\overline {{\rm M}} $n varying from 8,500 to 19,500 and polydispersities from 1.20 to 1.44 were obtained. The increase of LA/Ca molar ratio decreased $\overline {{\rm M}} $n, increased the degree of crystallinity and decreased racemization processes which can be controlled by the polymerization condition. Racemization could be reduced by using low catalyst concentration.

Room temperature cationic polymerization of β-pinene using modified AlCl3 catalyst: toward sustainable plastics from renewable biomass resources

The polymerization of β-pinene is efficiently prompted by AlCl3 etherates to afford relatively high molecular weight polymers (Mn = 9000–14 000 g mol−1) with good thermal properties (Tg = 82–87 °C) at room temperature and low catalyst content (2.5–5.5 mM).

Fe-TAML/hydrogen peroxide degradation of concentrated solutions of the commercial azo dye tartrazine

Here we describe a catalytic oxidation process for decomposing concentrated dye solutions, as a model for the treatment of concentrated industrial effluent streams. The prototype Fe-TAML/H2O2 oxidizing system rapidly and extensively degrades the recalcitrant azo dye, tartrazine, in water at ambient temperatures and at dye concentrations that are industrially important. Nearly complete dye removal can be obtained with performance-optimized dosing and pH control. At higher, but still remarkably low catalyst and oxidant concentrations, the dye is removed to below detection limits. 3D surface plots reveal that optimum decolorization at high dye concentration (16.5 g L−1, 30.9 mM) requires 50 times less catalyst and 5 times less oxidant per substrate than at low dye concentration (16.5 mg L−1, 30.9 μM), demonstrating a clear process benefit of higher substrate concentrations. The Fe-TAML/H2O2 system generates environmentally benign and/or biodegradable products from tartrazine: small organic acids, 4-phenolsulfonic acid, and a small amount of 4-nitrobenzenesulfonic acid. The acute toxicity of the Fe-TAML/H2O2/tartrazine reaction mixture toward luminescent bacteria is approximately half that of tartrazine as determined by the Microtox® assay. The results suggest a potential utility of the Fe-TAML/H2O2 technology for treating wastewaters containing high substrate concentrations from the dyeing industry in a straightforward manner to ameliorate environmental impacts, and because of the degradation resistance of tartrazine, that this potential utility might extend to other industries.

Atom transfer radical polymerization of functional monomers employing Cu‐based catalysts at low concentration: Polymerization of glycidyl methacrylate

AbstractInitiators for continuous activator regeneration atom transfer radical polymerization (ICAR ATRP) of an epoxide‐containing monomer, glycidyl methacrylate (GMA), was successfully carried out using low concentration of catalyst (ca. 105 ppm) at 60 °C in anisole. The copper complex of tris(2‐pyridylmethyl)amine was used as the catalyst, diethyl 2‐bromo‐2‐methylmalonate as the initiator, and 2,2′‐azobisisobutyronitrile as the reducing agent. When moderate degrees of polymerization were targeted (up to 200), special purification of the monomer, other than removal of the polymerization inhibitor, was not required to achieve good control. To synthesize well‐defined polymers with higher degrees of polymerization (600), it was essential to use very pure monomer, and polymers of molecular weights exceeding 50,000 g mol−1 and Mw/Mn = 1.10 were prepared. The developed procedures were used to chain‐extend bromine‐terminated poly(methyl methacrylate) macroinitiator prepared by activators regenerated by electron transfer (ARGET) ATRP. The SnII‐mediated ARGET ATRP technique was not suitable for the polymerization of GMA and resulted in polymers with multimodal molecular weight distributions. This was due to the occurrence of epoxide ring‐opening reactions, catalyzed by SnII and SnIV. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Rediscovering Silicones: Molecularly Smooth, Low Surface Energy, Unfilled, UV/Vis-Transparent, Extremely Cross-Linked, Thermally Stable, Hard, Elastic PDMS

We demonstrate the preparation of extremely cross-linked poly(dimethylsiloxane) (PDMS)-based materials and report optical, mechanical, and surface properties. Transparent monolithic molded objects are prepared catalytically with no byproducts; parts per million levels of platinum (catalyst) remain in the articles. Essentially the same material was prepared in 1993 and described as a "hard transparent glass." We confirm the thermal stability and chemical structure described in this report. We show that the catalytic reaction used, which was reported in 1999 always to exhibit a "violent exotherm", can be controlled conveniently using a low (parts per million) catalyst concentration. The combination of low surface energy, transparency, hardness, elasticity, and thermal stability makes this an unusual and interesting material. That it can be prepared from commercially available low-viscosity monomers adds to its interest. We comment that the class of materials known as siloxanes or silicones and PDMS in particular is not currently generally well understood (or taught) and review aspects of the structure, properties, and cross-linking chemistry of PDMS.

Controlling Polymer Topology by Atom Transfer Radical Self-Condensing Vinyl Polymerization of p-(2-Bromoisobutyloylmethyl)styrene

A new unsymmetrical AB* inimer, p-(2-bromoisobutyloylmethyl)styrene (BiBMS), was applied to the atom transfer radical polymerization (ATRP) to prepare a family of polymers with the topologies ranging from linear to branched. The catalyst system was Cu/CuBr2 coupled with 2,2′-bipyridine (Bipy) or N,N-bis(2-pyridylmethyl)octylamine (BPMOA) as a ligand in toluene or anisole at different temperatures, which ensured a very low catalyst (CuBr) concentration throughout the polymerization by a slow reduction process. First, BiBMS was polymerized in anisole at 0 °C using Cu/CuBr2/BPMOA as a catalyst system; at this temperature, the initiating activity of the formed A* was frozen and the polymerization was a step-growth polymerization, resulting in the formation of a linear polymer (LP1) whose main chain was linked by ester bonds. Second, BiBMS was polymerized in toluene at 20 °C using Cu/CuBr2/Bipy as a catalyst system. Under this condition, initiation from the B* of BiBMS was slow, followed by a fast radical poly...

Kinetics of the photocatalytic degradation of methylene blue on titanium dioxide

The first step of the photocatalytic degradation of methylene blue (MB) on anatase is photocatalytic reduction with subsequent decomposition of the dye itself and its leucobase. At low catalyst concentrations (≤2 g/L), the dye decomposition rate constant increases with increasing anatase concentration. A plateau appears for anatase concentrations above 2 g/L. Under steady-state conditions, the reaction kinetics is described by the Michaelis-Menten equation if the catalyst concentration is significantly greater than the MB concentration, which permits us to determine the kinetic parameters of the degradation process.

Hybrid atom transfer radical polymerization system for balanced polymerization rate and polymer molecular weight control

A hybrid polymerization system that combines the fast reaction kinetics of conventional free radical polymerization and the control of molecular weight and distribution afforded by ATRP has been developed. High-free radical initiator concentrations in the range of 0.1–0.2 M were used in combination with a low concentration of ATRP catalyst. Conversions higher than 90% were achieved with ATRP catalyst concentrations of less than 20 ppm within 2 h for the hybrid ATRP system as compared with ATRPs where achieving such conversions would take up to 24 h. These reaction conditions lead to living polymerizations where polymer molecular weight increases linearly with monomer conversion. As in living polymerization and despite the fast rates and low ATRP catalyst concentrations, the polydispersity of the produced polymer remained below 1.30. Chain extension experiments from a synthesized macroinitiator were successful, which demonstrate the living characteristics of the hybrid ATRP process. Catalyst concentrations as low as 16 ppm were found to effectively mediate the growth of over 100 polymer chains per catalytic center, whereas at the same time negating the need for post polymerization purification given the low-catalyst concentration. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2294–2301, 2010

Plastic catalytic pyrolysis to fuels as tertiary polymer recycling method: Effect of process conditions

This paper presents results regarding the effect of various process conditions on the performance of a zeolite catalyst in pyrolysis of high density polyethylene. The results show that polymer catalytic degradation can be operated at relatively low catalyst content reducing the cost of a potential industrial process. As the polymer to catalyst mass ratio increases, the system becomes less active, but high temperatures compensate for this activity loss resulting in high conversion values at usual batch times and even higher yields of liquid products due to less overcracking. The results also show that high flow rate of carrier gas causes evaporation of liquid products falsifying results, as it was obvious from liquid yield results at different reaction times as well as the corresponding boiling point distributions. Furthermore, results are presented regarding temperature effects on liquid selectivity. Similar values resulted from different final reactor temperatures, which are attributed to the batch operation of the experimental equipment. Since polymer and catalyst both undergo the same temperature profile, which is the same up to a specific time independent of the final temperature. Obviously, this common temperature step determines the selectivity to specific products. However, selectivity to specific products is affected by the temperature, as shown in the corresponding boiling point distributions, with higher temperatures showing an increased selectivity to middle boiling point components (C8-C9) and lower temperatures increased selectivity to heavy components (C14-C18).

Comparative Modeling Study on the Performance of Solid Foam as a Structured Catalyst Support in Multiphase Reactors

In this paper, the performance of two types of advanced foam packings (viz., Hairy Foam and washcoated Solid Foam) is compared with that of a packed bed of porous spherical particles. The comparison is done for two different types of reactions (viz., the slow hydrogenation of cinnamaldehyde and the fast hydrogenation of 3-methyl-1-pentyn-3-ol) and under two flow conditions (viz., upflow and downflow), in terms of selectivity, conversion, pressure drop, and reactor height. Under similar operating conditions, the simulation results show that, for both reactions, the Hairy Foam and Solid Foam packings reach higher selectivities and conversions than the packed bed of particles. However, in the case of the slow reaction, the pressure drop for the Hairy and Solid Foam packings is significantly larger than that for the bed of particles. This is due to the lower solids holdup, and thus lower catalyst concentration, of the Hairy Foam and Solid Foam packings. Therefore, larger reactors are required for the hairy fo...

Compartmentalization Effects on the Rate of Polymerization and the Degree of Control in ATRP Aqueous Dispersed Phase Polymerization

Compartmentalization in atom transfer radical polymerization (ATRP) in an aqueous dispersed phase system has been investigated theoretically to understand the effects of particle size on the rate of polymerization and the degree of control on the livingness and polydispersity index (PDI) for the system n-butyl methacrylate/CuBr/EHA6TREN. The simulations indicate that there exists a defined range of particle sizes where the rate of polymerization is higher than that of a bulk system and where PDI and frequency of termination remain below that of bulk polymerization. For this highly active catalyst system, the livingness of the chains is a function only of the particle size and is independent of the rate of reaction. Furthermore, simulations conducted with very low catalyst concentrations suggest that the rate of polymerization is dependent on the absolute amount of catalyst in the system rather than the steady-state Cu(I)/Cu(II) ratio that applies for bulk polymerization. At low catalyst concentrations, th...

Study of TATP: Influence of Reaction Conditions on Product Composition

AbstractThe influence of reaction conditions (temperature, catalyst type, catalyst concentration – represented as molar ratio catalyst/acetone nc/na) on the composition of the product formed from the reaction of acetone and hydrogen peroxide (30%) under acid catalysis was studied. 3,3,6,6,9,9‐Hexamethyl‐1,2,4,5,7,8‐hexoxonane (TATP) was found to be the major product when the content of the catalyst in the reaction mixture is low (nc/na ≤ 0.5). A single side product (peak 10.2) in an amount ranging from 1.5 to 8% of the total peak area was present in all the prepared samples. Three other side products were found when catalyzing by hydrochloric and nitric acids. Temperature and catalyst type did not have a significant influence on the composition of the product at low catalyst concentration. Increasing the catalyst concentration led to the formation of 3,3,6,6‐tetramethyl‐1,2,4,5‐tetroxane (DADP) either as a co‐product of TATP or as an exclusive product depending on the concentration of the catalyst.

Peroxidase activity of dimanganese(III) complexes with the [Mn 2(μ-OAc)(μ-OR) 2] 3+ core

Catalytic activity of three dinuclear Mn III complexes of general formula [Mn 2(μ-OAc)(μ-OMe)(L)]BPh 4 (H 3L = 1,5-bis[(2-hydroxy-5-X-benzyl)(2-pyridylmethyl)amino] pentan-3-ol, 1: X = H, 2: X = OMe, 3: X = Br) in the oxidation of phenol, 2,6-dimethoxyphenol and wood pulp by H 2O 2 has been investigated. The role of pH, electronic properties of the ligand and metal coordination environment on the ability of these complexes to activate H 2O 2 has been examined. The three catalysts showed similar activity independently of the aromatic substituent in the ligand and were found to be 2–3 times more active at pH 9.00 than at neutral pH. Bleaching of Kraft pulp by H 2O 2 activated by 1 in alkaline media decreased the kappa number of the pulp by 16%, at room temperature and low catalyst concentration, without damage of cellulose fibers. It was found that the exchange of the methoxo- and acetato-bridges by an oxo-bridge reduces the catalytic activity of these compounds, probably by direct binding of phenolate to a vacant site on the metal center.

Enhanced catalytic hydrogen release of LiBH4 by carbon-supported Pt nanoparticles

Thermally induced dehydrogenation of LiBH4 catalyzed by carbon-supported Pt nanoparticles (Pt/C) shows superior dehydrogenation performance compared to dehydrogenation in the absence of catalyst, even at very low catalyst content. Pt nanoparticles are found to play a crucial role in the catalyzed rehydrogenation/dehydrogenation of LiBH4. For doping with 10 wt.% catalyst of an average Pt particle diameter of ca. 4.7 nm, thermal dehydrogenation of LiBH4 is found to start at ca. 280 °C with total weight loss of 16.3 wt.% for the full temperature range. With increased loading of catalyst within a LiBH4 sample, the dehydrogenation temperature at which the major loss of hydrogen occurs is found to decrease while the hydrogen release amount is found to increase. All the hydrogen, ca. 18.4 wt.%, can be released from LiBH4 below 560 °C at a catalyst doped level of 50 wt.%. Importantly, we observed a reversible hydrogenation/dehydrogenation with a capacity of approximately 6.1 wt.%, which is very close to the theoretical capacity of the mixture of Li5PtH3 and B16H20 that is likely formed during the hydrogenation/dehydrogenation process.

Operations variables in the transesterification process of vegetable oil: a review - chemical catalysis

This article describes the results of a bibliographic review of the effects of operation conditions on process yield in the chemical transesterification of vegetable oil. The parameters studied were: temperature and time reaction, alcohol: oil molar ratio, catalyst and alcohol type, catalyst concentration, mixed intensity and free fatty acid and water concentration. It also reports that this process has been carried out with basic and acid catalysts using homogeneous and heterogeneous catalytic processes for a wide variety of oils. It was found that reaction yield increased when temperature and time reaction increased; however this parameter decreased at low catalyst concentration (<0.5 % w/w) and high free fatty acid (> 1% w/w) and water (> 3% w/w) concentration in oil.

New Iron(II) Complexes for Atom‐Transfer Radical Polymerization: The Ligand Design for Triazacyclononane Results in High Reactivity and Catalyst Performance

AbstractMononuclear cordinatively unsaturated iron(II) complexes having a triazacyclononane ligand were developed as highly efficient and environmentally friendly catalysts for the atom‐transfer radical polymerization (ATRP). These iron catalysts showed high performance in the well‐controlled ATRP of styrene, methacrylates, and acrylates. The high reactivity of these catalysts led to well‐controlled polymerization and block copolymerization even with lower catalyst concentrations.