Minimum Reaction Temperature Research Articles

Atom-Modified gDNA Enhances Cleavage Activity of TtAgo Enabling Ultra-Sensitive Nucleic Acid Testing.

The DNA-guided (gDNA) Argonaute from Thermus thermophilus (TtAgo) has little potential for nucleic acid detection and gene editing due to its poor dsDNA cleavage activity at relatively low temperature. Herein, the dsDNA cleavage activity of TtAgo is enhanced by using 2'-fluorine (2'F)-modified gDNA and developes a novel nucleic acid testing strategy. This study finds that the gDNA with 2'F-nucleotides at the 3'-end (2'F-gDNA) can promote the assembly of the TtAgo-guide-target ternary complex significantly by increasing its intermolecular force to target DNA and TtAgo, thereby providing ≈40-fold activity enhancement and decreasing minimum reaction temperature from 65 to 60°C. Based on this outstanding advance, a novel nucleic acid testing strategy is proposed, termed FAST, which is performed by using the 2'F-gDNA/TtAgo for target recognition and combining it with Bst DNA polymerase for nucleic acid amplification. By integrating G-quadruplex and Thioflavin T, the FAST assay achieves one-pot real-time fluorescence analysis with ultra-sensitivity, providing a limit of detection up to 5 copies (20µL reaction mixture) for miR-21 detection. In summary, an atom-modification-based strategy has been developed for enhancing the cleavage activity of TtAgo efficiently, thereby improving its practicability and establishing a TtAgo-based nucleic acid testing technology with ultra-sensitivity and high-specificity.

Optimization of reaction temperature and Ni–W–Mo catalyst soaking time in oil upgrading: application to kinetic modeling of in-situ upgrading

Decreasing the conventional sources of oil reservoirs attracts researchers’ attention to the tertiary recovery of oil reservoirs, such as in-situ catalytic upgrading. In this contribution, the response surface methodology (RSM) approach and multi-objective optimization were utilized to investigate the effect of reaction temperature and catalysts soaking time on the concentration distribution of upgraded oil samples. To this end, 22 sets of experimental oil upgrading over Ni–W–Mo catalyst were utilized for the statistical modeling. Then, optimization based on the minimum reaction temperature, catalysts soaking time, gas, and residue wt.% was performed. Also, correlations for the prediction of concentration of different fractions (residue, vacuum gas oil (VGO), distillate, naphtha, and gases) as a function of independent factors were developed. Statistical results revealed that RSM model is in good agreement with experimental data and high coefficients of determination (R2 = 0.96, 0.945, 0.97, 0.996, 0.89) are the witness for this claim. Finally, based on multi-objective optimization, 378.81 °C and 17.31 h were obtained as the optimum upgrading condition. In this condition, the composition of residue, VGO, distillate, naphtha, and gases are 6.798%, 39.23%, 32.93%, 16.865%, and 2.896%, respectively, and the optimum condition is worthwhile for the pilot and industrial application of catalyst injection during in-situ oil upgrading.

Effect of preheat temperature, pressure, and residence time on methanation performance

The present work studies the effect of reagent preheat temperature on methanation while maintaining the initial temperature of the catalytic bed constant. An adiabatic packed bed reactor was used with 193 g of commercial 10% Ni/Al2O3 catalyst. The tested preheat temperatures were 25 °C, 100 °C, 180 °C, and 280 °C, while the initial catalytic bed temperature was 280 °C. Two tests were performed in which the effect of preheat temperature was evaluated: the first comparing gas hourly space velocities (GHSVs) of 935 h−1 and 1559 h−1, and the second comparing gauge pressures of 0 bar, 1 bar, and 4 bar. Similar behavior was observed for the temperature inside the reactor and final CO2 conversion for preheating temperatures of 100 °C, 180 °C, and 280 °C at a gauge pressure of 0 bar. However, at this pressure, conversion was considerably reduced for the preheat temperature of 25 °C, due to a large part of the catalytic bed serving to preheat the reactants to the minimum reaction temperature. This effect can be partially attenuated by decreasing the GHSV, due to the increased residence time. Finally, increased pressure significantly improved the final CO2 conversion for all preheating temperatures (Tin), and attenuates the effect of Tin. These results show that certain operating conditions do not require as high a reactant preheat temperature for methanation, which offers energy savings in certain processes such as power-to-gas (P2G), where the hydrogen is produced from electrolysis and can leave the process at a lower temperature than that required for methanation.

H+−H− Pairs in Partially Oxidized MAX Phases for Bifunctional Catalytic Conversion of Furfurals into Linear Ketones

AbstractCurrently, less favorable C=O hydrogenation and weak concerted acid catalysis cause unsatisfactory catalytic performance in the upgrading of biomass‐derived furfurals (i.e., furfural, 5‐methyl furfural, and 5‐hydroxymethyl furfural) to ketones (i.e., cyclopentanone, 2,5‐hexanedione, and 1‐hydroxyl‐2,5‐hexanedione). A series of partially oxidized MAX phase (i.e., Ti3AlC2, Ti2AlC, Ti3SiC2) supporting Pd catalysts were fabricated, which showed high catalytic activity; Pd/Ti3AlC2 in particular displayed high performance for conversion of furfurals into targeted ketones. Detailed studies of the catalytic mechanism confirm that in situ hydrogen spillover generates Frustrated Lewis H+−H− pairs, which not only act as the hydrogenation sites for selective C=O hydrogenation but also provide acid sites for ring opening. The close intimate hydrogenation and acid sites promote bifunctional catalytic reactions, substantially reducing the reported minimum reaction temperature of various furfurals by at least 30–60 °C.

H+ -H- Pairs in Partially Oxidized MAX Phases for Bifunctional Catalytic Conversion of Furfurals into Linear Ketones.

Currently, less favorable C=O hydrogenation and weak concerted acid catalysis cause unsatisfactory catalytic performance in the upgrading of biomass-derived furfurals (i.e., furfural, 5-methyl furfural, and 5-hydroxymethyl furfural) to ketones (i.e., cyclopentanone, 2,5-hexanedione, and 1-hydroxyl-2,5-hexanedione). A series of partially oxidized MAX phase (i.e., Ti3 AlC2 , Ti2 AlC, Ti3 SiC2 ) supporting Pd catalysts were fabricated, which showed high catalytic activity; Pd/Ti3 AlC2 in particular displayed high performance for conversion of furfurals into targeted ketones. Detailed studies of the catalytic mechanism confirm that in situ hydrogen spillover generates Frustrated Lewis H+ -H- pairs, which not only act as the hydrogenation sites for selective C=O hydrogenation but also provide acid sites for ring opening. The close intimate hydrogenation and acid sites promote bifunctional catalytic reactions, substantially reducing the reported minimum reaction temperature of various furfurals by at least 30-60 °C.

The ortho effect in directed C-H activation.

The success of transition metal-catalysed ortho-directed C–H activation is often plagued by the effects of undesirable interactions between the directing group (DG) and other groups introduced into the aromatic core of the substrate. In particular, when these groups are in neighbouring positions, their interactions can affect profoundly the efficacy of the C–H activation by transition metals. In this work we introduce a simple substrate-only-based model to interpret the influence of steric hindrance of a group in ortho position to the DG in directed ortho-C–H bond activation reactions, and coined the term Ortho Effect (OE) for such situations. We consider simple descriptors such as torsion angle and torsional energy to predict and explain the reactivity of a given substrate in directed C–H activation reactions. More than 250 examples have been invoked for the model, and the nature of the ortho effect was demonstrated on a wide variety of structures. In order to guide organic chemists, we set structural and energetic criteria to evaluate a priori the efficiency of the metalation step which is usually the rate-determining event in C–H activations, i.e. we provide a simple and general protocol to estimate the reactivity of a potential substrate in C–H activation. For borderline cases these criteria help set the minimum reaction temperature to obtain reasonable reaction rates. As an example for the practical applicability of the model, we performed synthetic validations via palladium-catalysed 2,2,2-trifluoroethylation reactions in our lab. Furthermore, we give predictions for the necessary reaction conditions for several selected DGs.

Facile High Throughput Wet-Chemical Synthesis Approach Using a Microfluidic-Based Composition and Temperature Controlling Platform.

The wet-chemical technique has been widely applied in material synthesis. In recent years, high throughput (HT) technique has shown its potential in parallel synthesis and the investigation of synthesis parameters. However, traditional ways of HT parallel synthesis require costly equipment and complex operating procedures, restricting their further applications. In this paper, we prepared a cost-effective and timesaving microfluidic-based composition and temperature controlling platform to carry out HT wet-chemical synthesis in a facile and automated workflow. The platform uses a microfluidic chip to generate 20–level concentration gradients of the two reagents and uses 100–channel reactor arrays for wet-chemical synthesis with 5–level temperature gradients. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were applied to characterize Co–Ni bimetallic powder materials synthesized under 100 different reaction conditions. X-ray photoelectron spectroscopy (XPS) was conducted to confirm the oxidation state of the products. This platform not only enables one-step determination of the minimum reaction temperature required for a wet-chemical system but also provides a significant increase in efficiency compared with the traditional wet-chemical approach. The microfluidic-based composition and temperature controlling platform shows promise in facile, efficient, and low-cost HT wet-chemical synthesis of materials.

Synthesis of Biodiesel from Waste Cooking Oil and Emission Characteristics of Its blends

In converting different vegetable oils for the respective esters, at a minimum reaction temperature and faster rate of the fatty acids, the catalyst plays a very important role which can be changed into fatty acid esters (FAME), also known as biodiesel by transesterification reaction with methanol. Homogenous and heterogeneous catalysts have been identified as catalysts and among these catalysts. Homogeneous catalysts were chosen because it was possible to generate more biodiesel at a comparatively faster rate. As a feedstock, soybean waste cooking oil (SWCO) was used in this research work. With the help of a conventional mechanical stirrer reactor, SWCO with methanol was heated at various temperatures. As a catalyst, sodium hydroxide (NaOH) and potassium hydroxide (KOH) is used. It evaluated the effect of various parameters such as reaction temperature (60°C, 70°C, and 80°C), the reaction time of 2 hours, and loading of the catalyst (0.5 wt. %, 0.7 wt. %, and 1 wt. % KOH and NaOH). Results show that biodiesel produced from soybean waste cooking oil was within the recommended standards of biodiesel fuel. The transesterification reaction using KOH catalyst was more effective than the NaOH catalyst. The yield and conversion of biodiesel produced from SWCO by using 0.5 wt. % KOH catalysts at 60°C are 93.2 % and 96.16 % respectively while; the yield and conversion of biodiesel produced from SWCO by using 0.5 wt. % NaOH catalysts at 60°C are 91.35 % and 94.5 % respectively. Blends of 10, 20, 30, 50 and 100% by volume of biodiesel derived from soybean waste cooking oil and diesel fuel were prepared as B10, B20, B30, B50 and B100. Biodiesel blends have ASTM standards that are similar to diesel fuel, and the ORSAT apparatus has used to exhaust gas.

Kinetic modeling and development of optimal trajectories for biodiesel production using multi-objective optimization

A kinetic model has been developed based on the experimental data in the open literature for the simultaneous esterification of myristic acid and transesterification of rapeseed oil with methanol by using sulphated zirconia catalyst at three different temperatures (120 °C, 150 °C, 170 °C) and methanol to oil ratio (20:1). The developed kinetic model has been utilized for the cross-validation of methanol to oil ratio of 10:1 and 4:1 and at a temperature of 170 °C, which is in accordance with the experimental data. Furthermore, the validated kinetic model has been extended to find the optimal process conditions for the desired conflicting objectives. Trade-off solutions for this process are obtained by utilizing the non-dominated sorting genetic algorithm (NSGA-II). The objective is to obtain maximum FAME (fatty acid methyl ester) in minimum methanol to oil ratio and minimum reaction temperature. Addition of oil, methanol, myristic acid and temperature are considered as decision variables with relevant process constraints. A wide range of choices have been obtained for the present optimization setup. The yield of FAME is strongly depends on the reaction temperature, reaction time and methanol to oil ratio. The optimal methanol to oil ratio of 10–15 is sufficient to enhance the FAME yield. • Kinetic modeling of simultaneous Transesterification and esterification. • Kinetic parameter estimation using RCGA. • Formulation of Multi-objective optimization. • Pareto optimal set obtained for the desired conflicting objectives.

Evaluation of the performance of an engineered β-fructofuranosidase from Aspergillus fijiensis to produce short-chain fructooligosaccharides from industrial sugar streams

Abstract An engineered β-fructofuranosidase, GAPfopA_V1, was compared to the native enzyme, GAPfopA, to produce short-chain fructooligosaccharides (scFOS) from white and brown sugar (commercial table sugar), and refinery and A-molasses (refinery mill and sugar mill, respectively). The minimum reaction temperature and enzyme dosage required to produce scFOS with a composition similar to that of a commercial prebiotic product, consisting of oligomers with 2–4 fructose moieties, were determined using response surface methodology. At 62 °C and 10 U/g sucrose, the GAPfopA_V1 resulted in a 28% and 25% decrease in reaction time required to reach the target scFOS composition, in comparison to the native enzyme, using white and brown sugar as substrate, respectively. Whereas the target scFOS composition could not be reached using refinery molasses, this composition was reached with A-molasses using both enzymes, where GAPfopA had a 6% shorter reaction time than GAPfopA_V1.

In-situ reforming of biomass primary tars via reactive flash volatilization

Tar formation during biomass gasification has remained a major challenge. Using acetol and guaiacol as model tar compounds from cellulose and lignin, respectively, in-situ tar conversion into synthesis gas (H2 and CO) was studied using a Rh–Ni/Al2O3 catalyst under reactive flash volatilization conditions. The influence of operating conditions, including temperature, steam-to-carbon molar ratio (S/C), carbon-to-oxygen molar ratio (C/O), gas hourly space velocity (GHSV), and catalyst weight, on the H2/CO molar ratio in the product gas were experimentally examined. The contribution of non-catalytic thermal oxidation on overall conversion was also measured by varying the distance between the catalyst bed and the feeding point position. In the case of acetol reforming at 650 °C, more than 60% of the carbon in the feed was converted via thermal oxidation into permanent gases before reaching the catalytic bed. Moreover, a minimum reaction temperature of 500 °C was necessary to avoid coke formation and the optimal operating conditions for reforming of acetol were 650 °C, C/O = 1.7, S/C = 1.2, and atmospheric pressure. Likewise, for guaiacol, the minimum operating temperature of 600 °C was required. By using two pure components, this study has provided insight into how reactive flash volatilization generates tar-free synthesis gas.

Thermal study of polyester networks based on renewable monomers citric acid and gluconolactone

A detailed thermal study is presented of the melt polycondensation between the renewable monomers citric acid and d-glucono-δ-lactone. It was found that the polyester networks formed have glass transition temperature ranges that increase with increasing reaction temperature and time, corresponding to an increase in molecular weight. The minimum reaction temperature was investigated and found to be 130 °C for a 1/1 system. Moreover, the monomers show eutectic melt behaviour, with a eutectic melting temperature of 125 °C. A range of additional co-monomers were evaluated, revealing that aliphatic and aromatic bifunctional co-monomers result in lower glass transition temperatures. When polyfunctional co-monomers were employed it was found that the chain flexibility influenced the resulting thermal properties. Moreover, it is shown that the ring structure of d-glucono-δ-lactone plays a key role in the thermal properties of the resulting polyesters. © 2016 Society of Chemical Industry

Types of Failure in Cellular Concrete Blocks (Thermostone)

Cellular or aerated autoclaved concrete blocks ( called Thermostone in Iraq ) may undergoes several problems during and after manufacturing ,these problems cost both time and money. The present work aims to determine the main types and causes of failure occurred in cellular concrete blocks (Thermostone) during and after production process. Physical and mechanical tests, chemical analysis, as well as X-ray diffraction technique were conducted to investigate the main causes of failures and to suggest solutions. The results showed that the complete reaction (Hydrogen bubbles formation) between lime (CaO) , water ,and Aluminum powder always occurs when the minimum reaction temperature is 43 oC or more, No observed reaction took place when the hydration temperature was less than 40 oC . Aluminum powder diameter of (50-100) µm was found to be suitable for best product properties. X- Ray diffraction results showed a presence of detrimental components causing moisture spots and excessive expansion in both green and autoclaved products. Controlling raw materials, increasing autoclaving period from 10 to 14 hours or adding up to 5% limestone aggregate are essential to get a product fulfills the specifications requirements

Influence of Ce/Cu ratio on the performance of ordered mesoporous CeCu composite oxide catalysts

Abstract CeCu composite oxide catalysts were prepared by a hard-template method using different mole ratios of Ce/Cu (being designated as CeCu-HTx, where x is the Ce/Cu molar ratio). The prepared catalysts were characterized by XRD, TEM, AAS, XPS, and H2-TPR. The catalytic properties of the prepared CeCu composite oxide catalysts were also investigated by phenyl VOCs (benzene, toluene, xylene, and ethylbenzene) catalytic combustion in air. XRD results showed that the CuO species can fully dissolve into the CeO2 lattice to form CeCu solid solutions having the fluorite structure of crystal-phase CeO2. TEM and low-angle XRD results indicated that CeCu-HT3 had a well-ordered and developed mesoporous structure with uniform pore size, which is better than the CeCu-HT2 and CeCu-HT4. XPS and H2-TPR results showed that CeCu-HT3 had abundant active oxygen species and superior reducibility. CeCu-HT3 had higher toluene catalytic combustion activity than CeCu-HT2 and CeCu-HT4 in air. The minimum reaction temperature at which toluene conversion exceeded 90% on CeCu-HT3 was 225 °C. Toluene catalytic combustion conversion on CeCu-HT3 at 240 °C exceeded 99.3% with decreased toluene concentration in air to below 70 ppm. The phenyl VOCs catalytic combustion activity on the CeCu-HT3 catalyst follows the order ethylbenzene > toluene > xylene > benzene. The CeCu-HT3 catalyst shows high stability and efficiency for toluene catalytic combustion in air. And the CeCu-HT3 catalyst can be applied in purification treatments for air containing a wide range of toluene concentrations.

Effects of the structure of CeCu catalysts on the catalytic combustion of toluene in air

Abstract CeCu composite oxide catalysts were prepared by a hard-template method (CeCu-HT) and a complex method (CeCu-CA). The prepared CeCu composite oxide catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET) analyses. The catalytic properties of the prepared CeCu composite oxide catalysts were also investigated by the catalytic combustion of toluene in air. XRD results showed that the synthesized CeCu composite oxide catalysts had different phase components and crystallinities but similar CeO 2 CuO solid solution phases. Low-angle XRD, TEM, and BET results indicated that the prepared CeCu-HT catalyst had a developed ordered mesoporous structure and a large specific surface area of 206.1 m 2 g −1 . Toluene catalytic combustion results indicated that the CeCu-HT catalyst had higher toluene catalytic combustion activity in air than the CeCu-CA catalyst. The minimum reaction temperature at which toluene conversion exceeded 90% for toluene catalytic combustion on the CeCu-HT catalyst was 225 °C. The toluene catalytic combustion conversion on the CeCu-HT catalyst at 240 °C exceeded 99.3% with decreased toluene concentration in air to below 70 ppm. On the other hand, the toluene catalytic combustion conversion on the CeCu-CA catalyst was only 92% even when the reaction temperature reached 280 °C. The differences between the toluene catalytic combustion performances of the CeCu composite oxide catalysts prepared by different methods can be attributed to their discrepant compositions and structures.

Low temperature oxidation of toluene by ozone over MnOx/γ-alumina and MnOx/MCM-41 catalysts

Ozonation of toluene catalyzed by manganese oxides supported on γ-alumina and siliceous MCM-41 was studied at temperatures from 22 to 100°C. Nitrate and acetate precursors of manganese were used to compare structure and activity of dispersed manganese oxides on γ-alumina and MCM-41. Catalysts were characterized by X-ray diffraction, Raman spectroscopy, BET and ICP-MS. Catalysts became deactivated at room temperature due to accumulation of carbon species. A minimum reaction temperature of 65°C was required to achieve steady state oxidation of toluene with ozone. Alumina supported catalysts prepared from the nitrate and acetate precursors had comparable activity. MCM-41 supported catalyst resulted in lower toluene and ozone conversion in comparison to γ-alumina catalysts above 40°C. CO and CO2 were the main reaction products while oxalic acid, acetic acid, benzene and maleic anhydride were also detected as the minor reaction byproducts.

Dual-bed catalyst system for improving product purity and catalytic stability in alkylbenzene transalkylation

A versatile catalyst system for the transalkylation of alkylbenzenes was developed, comprising Pt/ZSM-12 as the top bed catalyst and H-Beta as the bottom bed catalyst. The dual-bed catalyst system could improve the purity of the benzene product as well as the catalyst stability. The minimum ratio of H-Beta/ZSM-12 can achieve the industrial specification by interplaying the reaction temperatures, feed compositions, and the relative activities for the hydrogenation over Pt/ZSM-12 and the selective naphthene-cracking reaction rate over H-Beta. With increasing the trimethylbenzene (TMB) content of the feed mixture, the product yields of the dual-bed catalyst systems approached thermodynamic compositions due to the enhancement of the TMB reactivity; and the required amount of H-Beta and the minimum reaction temperature to meet benzene product specification became lower. Performance curves in terms of feed compositions, catalyst bed ratios, and reaction temperatures were constructed to aid the design of optimum dual-bed catalyst systems.

Highly conformal film growth by chemical vapor deposition. I. A conformal zone diagram based on kinetics

The authors present a unified description of conformal film growth in recessed features by low pressure chemical vapor deposition. Experimental data on step coverage and growth rate are interpreted in terms of a kinetic model for the elementary surface processes. This model is combined with the continuity equation for gas transport and consumption to predict the values of the precursor pressure and substrate temperature (p,T) that are necessary for conformal coverage to occur for a given precursor. They introduce a conformal zone diagram that considers the gas phase limitations (maximum precursor pressure and onset of secondary reactions), the surface limitations (minimum reaction temperature, precursor adsorption and desorption rates, and film growth rate), and the aspect ratio of the feature to be coated; the allowed intersection between the resulting boundaries defines the (p,T) zone for conformal growth. Sufficient precursor pressure is identified as a major requirement for conformal film growth, one that is not met by many commercially available molecules. Finally, they derive an approximate analytical solution to the inverse problem: what are the experimental conditions necessary to afford a desired degree of step coverage on a given aspect ratio feature at a desired growth rate. The solution depends on a set of rate constants in the kinetic model that can be extracted from measurements of the film growth rate as a function of precursor pressure and substrate temperature on trench or planar substrates.

Effect of O 2 on NO removal by ammonia radical injection using one-cycle sinusoidal power source

NO reduction experiment was performed by injecting ammonia radicals, which were externally generated by flowing the NH 3 gas diluted with Ar gas through a dielectric barrier discharge with a one-cycle sinusoidal-wave power source. The discharge was intermittently formed between coaxial cylindrical electrodes with a space of 1.5 mm at an applied peak-to-peak voltage of 3–25 kV. The generated radicals were injected into simulation gas (NO/O 2/N 2). The simulation gas contained 0–5.6% O 2, and the effect of O 2 on NO x removal was discussed. The minimum reaction temperature for NO reduction was low when simulation gas contained O 2. High O 2 concentration (O 2=5.6%) in simulation gas, high repetition rate to NH 3, and high applied power to NH 3 decreased NO removal efficiency.

Measurement of the pressure-composition isotherms of high-temperature and low-temperature metal hydrides

Many interesting applications are based on the knowledge of the thermodynamic equilibrium of the metal–metal hydride–hydrogen system. Practical applications for this system include hydrogen storage for stationary and vehicular purposes, hydrogen compression, heat pumps, cooling apparatus as well as heat stores. One of the most advantageous metal hydrides for high-temperature heat stores is nickel-doped magnesium, a material with excellent kinetic properties, high hydrogen concentration, low density and high heat of reaction. A disadvantage of magnesium is the minimum reaction temperature of about 423 K. The objective of this research work is to find low-temperature metal hydrides whose reaction enthalpy ΔrH is able to heat up the magnesium, starting from ambient temperature. In this study the results of an isochoric measurement method for determining pressure–composition isotherms (PCI), reaction enthalpies and reaction entropies are presented on the basis of already investigated as well as hitherto unsurveyed metal hydrides. The measuring method considers the real gas behavior in addition to a test reactor, which employs an improved sealing system. Presented in this study are the results of five metal–metal hydride–hydrogen systems in thermodynamic equilibrium. The measuring method has proved to be reliable because of the test reactor's sealing system.