Composition Of Reaction Mixture Research Articles

Catalytic decomposition of hydrazine on ruthenium catalysts in nitric acid solutions

The kinetics and stoichiometry of catalytic decomposition of hydrazine on 5% Ru/SiO2 in nitric acid solutions were studied. The major reaction products are N2, N2O, and HN3. Ammonium ion is not formed. HN3 is generated owing to the occurrence of a heterogeneous-catalytic redox cycle on the catalyst surface. The influence exerted on the reaction kinetics by reaction mixture composition and temperature was examined. The process scheme was suggested. The hydrazine decomposition on ruthenium catalysts is a structure-sensitive reaction (positive size effect).

Characterization of cationic dextrin prepared by ultra high pressure (UHP)-assisted cationization reaction

Cationic dextrins were prepared through substitution reaction of dextrin with low and high addition levels of 2,3-epoxypropyltrimethylammonium chloride (ETMAC), respectively. Conventional cationization reactions were carried out for 5h under continued stirring. UHP-assisted cationization reactions were conducted at three pressurization levels of 100, 300 and 500MPa for a pressure holding time of 30min. Degree of substitution (DS) of UHP-assisted cationic dextrins ranged from 0.58 to 1.51, and in general, their DS values were enhanced with increasing pressure levels. FT-IR and 13C NMR spectra indicated the presence of CN bond, which provided clear evidence about incorporation of cationic moieties onto dextrin molecules. In flocculation test, UHP-assisted cationic dextrin revealed higher flocculating activity. Overall results suggested that UHP-assisted cationization reaction could modulate reactivity and flocculating activity of dextrin by controlling pressure levels and reaction mixture compositions, and cationic dextrins likely possessed a higher potential to replace synthetic polymer-based flocculants.

Ternary Interpolyelectrolyte Complexes Insulin-Poly(methylaminophosphazene)-Dextran Sulfate for Oral Delivery of Insulin

Ternary interpolyelectrolyte complexes of insulin with biodegradable synthetic cationic polymer, poly(methylaminophosphazene) hydrochloride (PMAP), and dextran sulfate (DS) were investigated by means of turbidimetry, dynamic light scattering, phase analysis, and high-sensitivity differential scanning calorimetry. Formation of ternary insoluble stoichiometric Insulin-PMAP-DS complexes was detected under conditions imitating the human gastric environment (pH 2, 0.15 M NaCl). A complete immobilization of insulin in the complexes was observed in a wide range of the reaction mixture compositions. The ternary complexes were shown to dissolve and dissociate under conditions imitating the human intestinal environment (pH 8.3, 0.15 M NaCl). The products of the complex dissociation were free insulin and soluble binary Insulin-PMAP complexes. The conformational stability of insulin in the soluble complexes of various compositions was investigated by high-sensitivity differential scanning calorimetry. The dependence of the excess denaturation free energy of insulin in these complexes on the PMAP content was obtained. The binding constants of the folded and unfolded forms of insulin to the PMAP polycation were estimated. Proteolysis of insulin involved in the insoluble ternary complexes by pepsin was investigated under physiological conditions. It was found that the complexes ensure an almost 100% protection of insulin against proteolytic degradation. The obtained results provide a perspective basis for development of oral insulin preparations.

Reaction Chemistry/Nanocrystal Property Relations in the Hot Injection Synthesis, the Role of the Solute Solubility

Various literature studies show that increasing the concentration of free acid in the hot injection synthesis of colloidal nanocrystals raises the diameter of the resulting nanocrystals. We analyze this reaction chemistry/nanocrystal property relation by combining reaction simulations with an experimental study on a particular CdSe nanocrystal synthesis. We find that increasing the free acid concentration has the same effect on a real synthesis as raising the solute solubility in the simulations. Both lead to larger sizes and a deterioration of the size dispersion at constant reaction rate. Since free acids are used to coordinate the cation precursors in these syntheses, this leads to a meaningful link between a parameter in reaction simulations and the composition of an experimental reaction mixture. We thus explain the increase of the nanocrystal size with the acid concentration as resulting from an enhanced consumption of the solute by nanocrystal growth, which reduces the number of nanocrystals formed. This link between a simulation parameter and the composition of the reaction mixture provides a rational basis to further explore and understand reaction chemistry/nanocrystal property relations in the hot injection synthesis.

Steam Gasification of Different Brown Coals Catalysed by the Naturally Occurring Calcium Species

The effects of the constituents of mineral matter in brown coals from different deposits of Kansk-Achinsk, Lenaand from Yallourn Basins on the structural parameters and steam gasification reactivities of respective coal chars at moderate temperature and at low and high pressure were studied in this paper. The data on how the preliminary decationization with diluted hydrochloric, acetic and sulphuric acids affect char gasification reactivities are presented. The importance of surface area and crystallinity of chars and the presence of naturally occurring metals on gasification reactivity is considered. Quantitative correlations between the calcium contents and the extents of gasification are revealed. The gasification results obtained in a flow reactor with steam stream and in an autoclave reactor at high pressure of gaseous products are compared. The catalytic effect of dispersed calcium oxide-carbonate particles produced from the naturally occurring calcium containing carboxylates was shown to be a key factor for char gasification reactivity, the effect in the flow reactor being much larger as compared to that in the autoclave reactor. This was mainly related to different forms of catalytically active calcium species and to the composition of the gaseous reaction mixture.

Micro/Milliflow Processing with Selective Catalyst Microwave Heating in the Cu‐Catalyzed Ullmann Etherification Reaction: A μ2‐Process

A μ(2)-process in the Ullmann-type C-O coupling of potassium phenolate and 4-chloropyridine was successfully performed in a combined microwave (MW) and microflow process. Selective MW absorption in a micro-fixed-bed reactor (μ-FBR) by using a supported Cu nanocatalyst resulted in an increased activity compared to an oil-bath heated process. Yields of up to 80 % were attained by using a multisegmented μ-FBR without significant catalyst deactivation. The μ-FBR was packed with beads coated with Cu/TiO(2) and CuZn/TiO(2) catalysts. Temperature measurements along axial positions of the reactor were performed by using a fiber-optic probe in the catalyst bed. The simultaneous application of MW power and temperature sensors resulted in an isothermal reactor at 20 W. Initially, only solvent was used to adjust the MW field density in the cavity and optimize the power utility. Subsequently, the reaction mixture was added to ensure the maximum MW power transfer by adjusting the waveguide stub tuners to steady-state operations as a result of the changed reaction mixture composition and, therefore, the dielectric properties. Finally, the beneficial influence of the Cu/TiO(2)- and CuZn/TiO(2)-coated glass beads (200 μm) on the MW absorption as a result of the additional absorbing effect of the metallic Cu nanoparticles was optimized in a fine-tuning step. For the catalyst synthesis, various sol-gel, deposition, and impregnation methods provided Cu catalyst loadings of around 1 wt %. The addition of Zn to the Cu nanocatalyst revealed an increased catalyst activity owing to the presence of stable Cu(0). Multilaminar mixing was necessary because of the large difference in fluid viscosities. To the best of our knowledge, this work is the first extended experimental survey of the decisive parameters to combine microprocess and single-mode MW technology following the concepts of "novel process windows" for organic syntheses.

Exploring polysilicon deposition conditions through a laboratory CVD prototype

AbstractCost and energy consumption related to obtaining polysilicon impact significantly on the total photovoltaic module cost and its energy payback time. Process simplifications can be performed, leading to cost reductions. Nowadays, among several approaches currently pursued to produce the so called Solar Grade Silicon, the chemical route, named Siemens process, is the dominant one. At the Instituto de Energía Solar research on this topic is focused on the chemical route, in particular on the polysilicon deposition step by chemical vapor deposition (CVD) from Trichlorosilane through a laboratory prototype. Valuable information about the phenomena involved in the polysilicon deposition process and the operating conditions is obtained from our experiments. A particular feature of our system is the inclusion of a mass spectrometer. The present work comprises spectra characterization of the polysilicon deposition chemical reaction, temperature and inlet gas mixture composition influence on the deposition rate and analysis of polysilicon deposition conditions for the ‘pop‐corn' phenomenon to appear, based on experimental experience (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Formation and properties of nickel catalysts for hydrogenation under the action of lithium Di- and tris(tert-butoxy)hydroaluminates

It was demonstrated that systems based on Ni(II) compounds and the alkoxyhydride derivatives LiAlH(tert-BuO)3 and LiAlH2(tert-BuO)2, in contrast to LiAlH4, exhibit high catalytic activity in the reaction of styrene hydrogenation in the absence of activators. The inhibiting effect of an excess of LiAlH2(tert-BuO)2 was found. The analysis of the composition of reaction mixtures by NMR, EPR, and UV spectroscopy and TEM showed that side reactions of the conversion of aluminum-containing components occurred together with the formation of nickel nanoclusters. The most probable reaction schemes of LiAlH(tert-BuO)3 and LiAlH2(tert-BuO)2 disproportionation were proposed. The nature of the stabilizers of nickel nanoparticles was considered.

Quantitative analysis of enzymatic fractionation of multiple substrate mixtures

The enzymatic conversion of mixtures of multiple substrates was studied quantitatively, based on established methodology used for the enzymatic kinetic resolution of racemic mixtures, involving the use of competitive factors: ratios of specificity constants (k(cat)/K(M)) of substrate pairs. The competitive factors of the substrates were defined in relation to a reference substrate. These competitive factors were used to predict the composition of the reaction mixture as a function of the degree of conversion of the reaction. The methodology was evaluated using three different lipases to hydrolyze a model mixture of four fatty acid methyl esters and for the esterification of a mixture of the same fatty acids in free form with ethanol. In most cases, the competitive factors determined from the initial phase of the reactions predicted the product composition during the rest of the reaction very well. The slowest reacting fatty acid was erucic acid (both in free form and as methyl ester), which was thus enriched in the remaining substrate fraction, while the other fatty acids: lauric acid, palmitic acid and oleic acid were converted faster. Simulations of the compositions of reaction mixtures with different values of the competitive factors were carried out to provide an overview of what could be achieved using enzymatic enrichment. Possible applications include reactions involving homologous substrates and mixtures of multiple isomers. The analysis presented provides guidelines that can be useful in the screening and development of enzymes for enzymatic enrichment applications.

Study on Maillard-reaction driven transformations and increase of antioxidant activity in lysine fortified biscuits

Interaction of amino acids and carbohydrates at elevated temperatures leads to the formation of versatile compounds whose chemical feature has just been partly revealed so far.Major objective of this study was to characterise the composition of reaction mixtures forming as a result of various types of Maillard-reaction. Transformation products were analysed by GC-MS and HPLC-MS techniques. By regarding both the identified specific compounds, and the results of previous studies on Maillard-reaction routes and products, improved, specific, plausible transformation pathways were suggested. Predominant Maillard-reaction products in our analysis were found to be as follows: Schiff-base type compound, Amadori product, pentane-1,5-diamine, propa-dienilimino-etanal, 2-amino-6-{[(1-Z)-2,3,4,5,6-pentahidroxo-hexylydene]amino-hexanoic-acid, 3-hydroxibut-3-en-2-one, 1-[(5-aminopentil)amino]hexane-1,2,3,4,5,6-hexol, 2,6-diaminohex-4-enoic acid. Progress of the Maillard-reaction as well as the increase in antioxidant activity was monitored under versatile conditions. Distinctive types of carbohydrates were involved in the experiments in order to point out the most appropriate one in respect of antioxidant activity and potential health benefits. These results made it possible to develop a new, lysine-fortified, health-beneficial, functional biscuit utilising the generation of antioxidants by Maillard-reaction, whose composition was also examined.

Kinetics and design relation for enzymatic conversion of lactose into galacto-oligosaccharides using commercial grade β-galactosidase

The enzymatic synthesis of galacto-oligosaccharides (GOS) from lactose was studied using commercial grade β-galactosidase (Biolacta FN5) from Bacillus circulans. The reaction was carried out under free enzyme condition varying initial lactose concentration (ILC: 55-525 g/L), enzyme concentration (0.05-1.575 g/L), temperature (30-50°C) and pH (5.0-6.0). Reaction mixture compositions were analyzed utilizing high performance liquid chromatography (HPLC). A maximum GOS formation of 39% (dry basis) was achieved at an ILC of 525 g/L converting 60% of the lactose fed. Tri-saccharides were the major types of GOS formed, accounting approximately 24%; whereas, tetra-saccharides and penta-saccharides account approximately 12% and 3%, respectively. Design correlation was developed in order to observe the quantitative effect of operating parameters on GOS yield. Further, based on Michaelis-Menten model, four-step reaction pathways were considered for simplistic understanding of the kinetics. Apart from predicting the reaction mixture composition, the approach also provided kinetic parameters though simulation using COPASI 4.7®. Excellent agreements were observed between simulated and experimental results.

Considering the polynuclear complexes in the ionic equilibria of the Pb2+-H2O system

Analysis of conditions of the lead hydroxide and sulfide formation in the Pb2+-H2O system was carried out with accounting for the formation of polynuclear hydroxo-complexes. This allows predicting a possibility of the lead hydroxide formation in the solution before the beginning of the synthesis of lead sulfide. The domains of the stable formation of Pb(OH)2 and PbS were calculated for the systems containing lead citrate complexes and hydroxo-complexes. The proposed calculation method can be used for the quantitative determination of the reaction mixture composition and development of the chemical deposition technology of lead chalcogenides in different morphological forms: nanocrystalline powders (hydrophobic sol), quantum dots, heterostructures of the core@shell type or films. The proposed calculation method is applicable to other chalcogenide systems containing metal ions forming mononuclear and polynuclear hydroxo-complexes.

Biodiesel: The influence of dealcoholization on reaction mixture composition after neutralization of catalyst by carbon dioxide

Biodiesel is commonly produced by catalytic transesterification (reversible reaction) of oil/fat with excess alcohol. In the case of the basic catalyst, strong acid is usually used for catalyst neutralization; however acid converts soap to fatty acids (increases the acid number). In this paper, the utilization of carbon dioxide for catalyst neutralization is described. The advantage is that, the carbon dioxide does not transform soaps to fatty acids, but only neutralizes the catalyst (acid number is always less than 0.2mgKOH/g). The neutralization takes place due to by an excess of CO2, which transforms the catalyst to hydrogencarbonate. However during the alcohol removal by distillation from the whole reaction mixture, hydrogencarbonate is transformed to carbonate (catalytic properties). But the alcohol removal is fast enough that the reverse reaction to glycerides does not occur. The catalyst neutralization by CO2 is environmentally friendly (consumed CO2) and it can be used for all types of raw materials, alkali hydroxides and alcohols.

Finding a suitable thermodynamic model and phase equilibria for hydrodeoxygenation reactions of methyl heptanoate

Replacement of fossil fuels with biomass-based components is of increasing public and scientific interest. Unfortunately, most biomass-based compounds contain oxygen and oxygen content must be diminished before use of the compounds as fuel. Removal is usually done catalytically, with hydrogen supplied to convert the oxygen to water. Hydrodeoxygenation (HDO) of biomass-based compounds is often studied with model compounds, and the system investigated here was methyl heptanoate+m-xylene. Modeling of the reaction kinetics requires that behavior of the reaction mixture as a function of reaction time must be described. A suitable thermodynamic model for non-ideal system at high pressure and temperature is needed, and this demands correct modeling of the solubility of hydrogen and the water of reaction. For validation of the thermodynamic models isothermal vapor–liquid equilibrium (VLE) for the methyl heptanoate+m-xylene system was measured at 398.15K and 408.15K with a circulation still. The experimental VLE exhibited slight negative deviation from Raoult’s law. No azeotropic behavior was found. The experimental VLE results were correlated with the Wilson model with temperature-dependent parameters and used in testing of the SRK, original UNIFAC, UNIFAC-Dortmund, and PSRK predictive models. PSRK was preferred for further estimations. All VLE measurements passed the point consistency tests. Simulated reaction conditions for HDO of methyl heptanoate at the initial and final points were calculated to determine the effect of vapor–liquid equilibrium on the composition of reaction mixtures.

Incorporation of vapor permeation process to esterification reaction of propionic acid and isopropanol for performance improvement

A commercial tubular zeolite membrane (NaA) was employed in a vapor permeation system to dehydrate the reaction mixture during the esterification of propionic acid with isopropanol. The reaction was performed in a batch reactor, using Amberlyst 15 as a catalyst with different weight fractions relative to propionic acid. Experiments were conducted to investigate the effect of the alcohol-to-acid molar ratio on the performance of the hybrid process. The integration of the chemical reaction with the vapor permeation process significantly enhanced the conversion of the reversible esterification reaction. It was observed that contrary to the effect of increasing alcohol-to-acid molar ratio from 1: 1 to 1.5: 1, the acid conversion and the permeated water flux decreased when the reactants molar ratio increased from 1.5: 1 to 3: 1. This effect was due to the reducing effect of reaction mixture composition on the boiling point and reaction and evaporation rates during the hybrid process. Also, increasing catalyst loading had noticeable influence on the acid conversion and the permeated water flux.

Transformation of multi-walled carbon nanotubes to amorphous nano-spheres, micron-size rods and flakes by oxidative sulfation reaction

This study unveils a chemical functionalization provoked phase transformation in the naphthalene modified multi-walled carbon nanotubes (MWCNTs) and the associated formation of amorphous carbonaceous particles of various size and morphology. Functionalized nanotubes were prepared by a sulfonation-oxidization and a highly corrosive oxidative sulfation reaction then characterized by means of thermogravimetry/mass spectrometry, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy and Raman spectroscopy. In spite of the small change in the composition of sulfonation and sulfation reaction mixtures, conventional sulfonation with oleum resulted in lower sulfonation and higher oxidative conversion of MWCNTs accompanied with a mediated exohedral amorphization of the nanotubes, induced by the yield of sp 3 hybridization defect introduction. On the other hand, the newly applied oxidative sulfation reaction provided severe oxidative etching, cutting and shortening of MWCNTs with a subsequent high conversion of sulfate derivatisation of oxidized functionalities, which induced complete collapse and phase transformation of the nanotubes. Amorphization and phase transformation of oxidative sulfated MWCNTs have led to the formation of highly dispersed nano- and micron-size amorphous carbon spheres, rods and flake-like structures. Water based colloidal systems of excellent stability were prepared from the oxidative sulfated carbonaceous material. Consequently, the employed highly corrosive sulfation reaction is capable to provide highly functionalized carbonaceous nano and micro-size particles from MWCNTs.

On-line monitoring of the transesterification reaction between triglycerides and ethanol using near infrared spectroscopy combined with gas chromatography

Many analytical procedures have been developed to determine the composition of reaction mixtures during transesterification of vegetable oils with alcohols. However, despite their accuracy, these methods are time consuming and cannot be easily used for on-line monitoring. In this work, a fast analytical method was developed to on-line monitor the transesterification reaction of high oleic sunflower oil with ethanol using Near InfraRed spectroscopy and a multivariate approach. The reactions were monitored through sequential scans of the reaction medium with a probe in a one-liter batch reactor without collecting and preparing samples. To calibrate the NIR analytical method, gas chromatography-flame ionization detection was used as a reference method. The method was validated by studying the kinetics of the EtONa-catalyzed transesterification reaction. Activation energy (51.0 kJ/mol) was also determined by considering a pseudo second order kinetics model.

Etherification of glycerol by isobutylene. Effects of the density of acidic sites in ion-exchange resin on the distribution of products

Etherification of glycerol by isobutylene was performed using ion-exchange resin Amberlyst 15, partially neutralized Amberlyst 15 as heterogeneous catalyst, and p-toluenesulfonic acid as a homogeneous catalyst. Amberlyst 15 exhibited strong internal diffusion limitations for the initial composition of reaction mixture. Diffusion limitations decrease in the course of reaction due to the accumulation of mono-ether having excellent solubilizing properties. Oligomerized isobutylene is a dominant by-product for high isobutylene-to-glycerol ratio and long contact time in the case of Amberlyst 15. Density reduction of acidic protons in Amberlyst 15 by partial ion exchange with sodium ions leads to considerable reduction of isobutylene affinity to Amberlyst 15, and as a result, it reduced losses of isobutylene. This partial neutralization leads to lower space-time yields of target products, but enhances selectivity to higher ethers with maintaining conversion of glycerol over 95%.

Microchip analytic system for multiplex analysis by real-time polymerase chain reaction with reagents immobilized in microreactors

A microarray analytic system that uses a silicon chip with immobilized in microreactor test-system for multiplex analysis of DNA by real-time polymerase chain reaction (RT-PCR) was developed and optimized. We suggested the method of immobilization of PCR-components of a test-system, chose the stabilizer, and conducted the optimization of the composition of reaction mixture to achieve permanent stability of a microarray. We conducted optimization of preparation of samples using magnetic sorbent and indicated that, with 2.6 x 10(4) copies/ml, 60 min are necessary to obtain positive identification including time for preparation of model probes. The abilities of the created system were demonstrated on the example of microarray analysis of samples with different content of DNA, low absolute limits of identification (20 DNA copies in microreactor), and high reproducibility of the analysis.

4A-Molecular Sieve Synthesis by Microwave Heating with Silicon and Aluminum Materials Produced from the Coal Fly Ash

A new method, using sodium silicate and sodium aluminate synthesize 4A-molecular sieve, was developed by using microwave technology. The sodium silicate was a high modulus liquor by-product of nano-silica production from coal fly ash. Meanwhile, the sodium aluminate was a process by-product of alumina extraction from coal fly ash. Reaction mixture composition was defined as follow:SiO2/Al2O3 ratio in 2.0, Na2O/SiO2 ratio in 1.5, and H2O/Na2O ratio in 65. The gelation process was completed in 1 hr. Microwave crystallization power was (800w) 30%. Microwave crystallization period can last 25 mins. The 4A-molecular sieve was obtained by collecting crystals from the reaction mixture through filtration after washing with water to pH 11-12 and drying inside isotherm oven. The calcium exchange capacity and effective pore size of the product were 316mg/g and 0.4nm respectively. Over 90% of surface pore size reached in sizes of less than or equal to 8μm. Purity of 4A-molecular sieve up to 99%. This method significantly reduced the raw material costs for sodium silicate and sodium aluminate. In addition, the adoption of microwave technology also lowered the energy usage and shortened crystallization time. All these contributed final low costs of 4A-molecular sieve product, which made it possible for many practical applications.