Subcritical Water Reaction Behavior of D‐Glucose as a Model Compound for Biomass Using Two Different Continuous‐Flow Reactor Configurations

Recently, cellulosic materials have been considered as a useful resource for the recovery of valuable chemicals and liquid fuels, etc. Cellulose is a homopolymer of D ‐glucose, which is often used as a model compound for biomass. Reactions of D ‐glucose in subcritical water as the reaction solvent were conducted using a single‐flow‐type reactor ( S1 ) and an admixture‐type reactor with feed and preheated‐water flow ( S2 ) at temperatures from 200 to 240 °C, pressures from 15 to 20 MPa, residence times from 40 to 120 s, and initial feed concentrations of 1.5–10 wt %. D ‐Glucose was converted into aldehydes, organic acids and furans, with mainly organic acids obtained at 240 °C. D ‐Glucose decomposition using reactors S1 and S2 revealed that the conversion rate of D ‐glucose was promoted more using S2 than by S1 . The yield of furans with S1 was higher than with S2 , while the yield of organic acids from S1 was lower than that from S2 .     

Thermal degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)

The degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate), a member of the Nodax family of polymers, were investigated using transient constant shear rate and dynamic time sweep rheological tests. The rate of chain scission at several times and temperatures was correlated with viscosity data and verified using molecular weight determination of the degraded samples. The experimental results show that the molecular weight and the viscosity of Nodax decrease with time over the range of temperatures that were studied (155–175°C). The degradation kinetics, which exhibited first‐order behavior, were determined as a function of the flow history and thermal history. An apparent activation energy of 189 ± 5 kJ/mol for thermal degradation was found by modeling variations in the rate with temperature using an Arrhenius law model. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 66–74, 2005     

Kinetics and chemical reactions of acetaldehyde stripping and 2‐methyl‐1,3‐dioxolane generation in poly(ethylene terephthalate)

Poly(ethylene terephthalate) (PET) resins were air stripped at temperatures from 160 to 190°C to monitor changes that occur during reduction of residual acetaldehyde (AA) concentrations. During this process diffusion and generation of AA, 2‐methyl‐1,3‐dioxolane (2MD), ethylene glycol (EG), and water occurred as the molecular weight and crystallinity increased through complex chemical reactions involving polymerization, formation of by‐products, and some degradation at higher temperatures. This process was characterized in terms of time and temperature of stripping, with determination of residual concentrations of AA and other less volatile compounds such as 2MD and EG. Residual AA concentrations continually decreased from their initial values, while concentrations of 2MD decreased initially, then increased, and later decreased with time. Empirical rate constants for resin solid‐state polymerization were determined at the air‐stripping temperatures, and free EG concentrations as well as intrinsic viscosity, density, crystallinity, and color were monitored to aid in studying the kinetics of AA removal. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Reaction mechanisms and kinetics of xylo‐oligosaccharide hydrolysis by dicarboxylic acids

Hydrothermal pretreatment of lignocellulosic materials generates a liquid stream rich in pentose sugar oligomers. Cost‐effective hydrolysis and utilization of these soluble sugar oligomers is an integral process of biofuel production. We report integrated rate equations for hydrolysis of xylo‐oligomers derived from pretreated hardwood by dicarboxylic maleic and oxalic acids. The highest xylose yield observed with dicarboxylic acids was 96%, and compared to sulfuric acid, was 5–15% higher with less xylose degradation. Dicarboxylic acids showed an inverse correlation between xylose degradation rates and acid loadings unlike sulfuric acid for which less acid results in less xylose degradation to aldehydes and humic substances. A combination of high acid and low‐temperature leads to xylose yield improvement. Hydrolysis time course data at three different acid concentrations and three temperatures between 140 and 180°C were used to develop a reaction model for the hydrolysis of xylo‐oligosaccharides to xylose by dicarboxylic acids. © 2012 American Institute of Chemical Engineers AIChE J, 59: 188–199, 2013     

Treatment of dyehouse waste‐water by supercritical water oxidation: a case study

BACKGROUND: Supercritical water oxidation (SCWO) of dyehouse waste‐water containing several organic pollutants has been studied. The removal of these organic components with unknown proportions is considered in terms of total organic carbon concentration (TOC), with an initial value of 856.9 mg L^?1. Oxidation reactions were performed using diluted hydrogen peroxide. The reaction conditions ranged between temperatures of 400–600 °C and residence times of 8–16 s under 25 MPa of pressure. RESULTS: TOC removal efficiencies using SCWO and hydrothermal decomposition were between 92.0 and 100% and 6.6 and 93.8%, respectively. An overall reaction rate, which consists of hydrothermal decomposition and the oxidation reaction, was determined for the hydrothermal decomposition of the waste‐water with an activation energy of 104.12 ( ± 2.6) kJ mol^?1 and a pre‐exponential factor of 1.59( ± 0.5) × 10⁵ s^?1. The oxidation reaction rate orders for the TOC and the oxidant were 1.169 ( ± 0.3) and 0.075 ( ± 0.04) with activation energies of 18.194 ( ± 1.09) kJ mol^?1, and pre‐exponential factor of 5.181 ( ± 1.3) L^0.244 mmol^?0.244 s^?1 at the 95% confidence level. CONCLUSION: Results demonstrate that the SCWO process decreased TOC content by up to 100% in residence times between 8 and 16 s under various reaction conditions. The treatment efficiency increased remarkably with increasing temperature and the presence of excess oxygen in the reaction medium. Color of the waste‐water was removed completely at temperatures of 450 °C and above. Copyright © 2010 Society of Chemical Industry     

Supercritical water oxidation treatment of humic acid as a model organic compound of landfill leachate

Landfill leachate is a complex and variable effluent, rich in organic and inorganic matters resistant to decomposition, and is an extreme pollutant. Humic acids (HA) are some of the most refractive substances in the leachates, which is the reason why they have been used as an organic model. The degradation of an HA solution through supercritical water oxidation (ScWO) was evaluated under a constant pressure of 22.5 MPa, temperatures from 400°C to 600°C, and reaction times from 15 to 60 seconds. The results showed that the most influential factor was temperature and it guided the operational conditions of the ScWO for the landfill leachate (22.5 MPa, 600°C, and 60 seconds). The landfill leachate treatment promoted high removal rates of true colour (87%), total dissolved solids (94%), nitrate (70%), and total phosphorus (96%). In addition, it removed 57% of the COD, which was similar to the HA removal rate (61%) under the same operational conditions. This indicates that HA are an adequate organic model for landfill leachates. The results suggest that ScWO is a clean and promising treatment technology that can be applied to landfills and can have even better results if used in combination with oxidizers and catalysts, or with the use of higher temperatures.     

Formation of fluorescent substances from degradation products of methyl linoleate hydroperoxides with amino compound

The degradation products formed from methyl linoleate hydroperoxides by reaction with heme were fractionated by Sephadex LH-20 column chromatography and by reverse-phase high performance liquid chromatography, and the ability of each compound to form fluorescent substances through reaction with amino compound was compared. Maximum formation of fluorescent substances was obtained from monomeric degradation products with amino compound, but low molecular weight aldehydes such as hexanal, 2-hexenal and 2,4-decadienal, formed only a small amount of fluorescent substances. However, the major monomeric degradation products described previously, the hydroxy-, keto- and epoxy-derivatives, do not significantly contribute to the formation of fluorescent substances through reaction with amino compound. It was suggested that formation of fluorescent substances from lipid peroxides with amino compound may originate from a precursor present in monomeric degradation products formed from hydroperoxide of methyl linoleate during lipid peroxidation, and that low molecular weight aliphatic aldehydes are not involved in fluorescent substance formation. Moreover, the majority of TBA-reactive substances in secondary oxidation products prepared from autoxidized methyl linoleate are also unrelated to the formation of fluorescent substances through reaction with amino compound.     

Tetrachloroethylene and hexachloroethane degradation in Fe(III) and Fe(III)–citrate catalyzed Fenton systems

BACKGROUND: Tetrachloroethylene (PCE) and hexachloroethane (HCA) degradation, individually and in mixture, is investigated by Fe(III) or Fe(III)‐citrate initiated Fenton reaction under a range of hydrogen peroxide (H₂O₂) concentrations to illustrate the applicability and constraints of Fenton chemistry in degrading contaminants in polluted groundwater. RESULTS: In individual solutions Fe(III) rapidly degraded PCE for all H₂O₂ concentrations, but HCA at ≥ 0.2 mol L^?1 H₂O₂; the apparent PCE degradation rate initially increased but then decreased with increasing H₂O₂, while the HCA degradation rate was either unaffected or increased. With Fe(III)‐citrate PCE degradation was lower and no HCA degradation occurred. PCE degradation was lower in PCE‐HCA mixture, but the trend with H₂O₂ concentration was similar to the individual chemical; for HCA the residual was smaller for higher H₂O₂ concentration, but the apparent degradation rate constant was unaffected. CONCLUSION: Fe(III) catalyzed reactions can potentially degrade chemicals through reductive as well as oxidative transformations. Degradation of chemicals in mixtures occurs at a slower rate due to competition for radical moieties. The Fe(III)‐citrate complex further slowed chemical transformation. This study expands on the use of different forms of iron to catalyze the Fenton reaction to degrade chemicals. Copyright © 2012 Society of Chemical Industry     

High‐temperature esterification of fatty acids with methanol at ambient pressure

The article presents the results of the kinetic study of the acid‐catalyzed esterification of free fatty acids (FFA) with methanol (MeOH) at elevated temperatures above the boiling point of MeOH, at ambient pressure, and at continual flow of liquid MeOH into the reaction mixture. Under these conditions, the reaction follows the rate equation valid for reactions of the first order. Beside temperature, the pseudo rate constant depends also on the flow rate of MeOH and on the concentration of a catalyst. At temperatures 50–60 °C higher than the boiling point of MeOH, the reaction rate is two to three times higher than at the temperatures close to the boiling point of MeOH. Apart from the temperature, the increase of the rate is facilitated also by a high local molar excess of MeOH in the input site with respect to FFA and by effective removal of water from the reaction mixture. The composition of the reaction mixture is then farther from the equilibrium composition. High conversion of FFA to methyl esters (above 99%) with low residual acidity of the product (acid value around 2–3 mg KOH/g) is achieved at short times of several tens of minutes and at a low total molar ratio of MeOH/FFA of around 3–4.     

Synthesis and characterization of poly(glycidyl methacrylate)/Na‐montmorillonite nanocomposites

Poly(glycidyl methacrylate)/Na–montmorillonite nanocomposites were synthesized by free‐radical polymerization of glycidyl methacrylate containing dispersed montmorillonite. By changing the concentration of glycidyl methacrylate several polymer–clay nanocomposites were prepared and the resulting nanocomposites were characterized by X‐ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. The results indicated that the properties of the composite were significantly improved. The thermogravimetric analysis results revealed that the degradation temperatures of nanocomposites were higher than that of pure polymer and the thermal degradation rates decreased. Examination of these materials by scanning electron microscopy showed that the clay layers are dispersed homogenously in the polymer matrix and the formation of intercalation nanostructure. Furthermore, adsorptive, moisture regain, and water uptake properties of nanocomposites were also investigated. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1532–1538, 2004     

Chain extension reaction in solid‐state polymerization of recycled PET: The influence of 2,2′‐bis‐2‐oxazoline and pyromellitic anhydride

Conventional and chain extended‐modified solid‐state polymerization (SSP) of postconsumer poly(ethylene terephthalate) (PET) from beverage bottles was investigated. SSP was carried out at several temperatures, reaction times, and 2,2′‐bis‐2‐oxazoline (OXZ) or pyromellitic anhydride (ANP) concentrations. The OXZ was added by impregnation with chloroform or acetone solution. Higher molecular weights were reached when the reaction was carried out with OXZ, resulting in bimodal distribution. The molecular weights of the flakes reacted at 230°C for 4 h were 85,000, 95,000, and 100,000 for samples impregnated with 0, 0.5, and 1.25 wt % OXZ solution, respectively. In the case of reactions with ANP, branched chains were obtained. The thermal and thermal‐mechanical‐dynamic properties of these high‐molecular‐weight recycled PET were determined. For OXZ‐reacted samples, the reduction of crystallinity was observed as the reaction time was increased, becoming evident the destruction of the crystalline phase. The chain extended samples did not show changes in thermal relaxations or thermal degradation behavior. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Ageing of polyamide 11 used in the manufacture of flexible piping

The influence of temperature and pH on the ageing of piping made from polyamide 11 (PA‐11) was studied using water from an oilfield (pH = 5.5) and deionized water (pH = 7.0) with monitoring by corrected inherent viscosity (CIV) measurements. The hydrolytic degradation was more extensive at high temperatures in oilfield water. When the system reaches equilibrium, the pH affects mainly the CIV plateau values. Thermogravimetry, energy‐dispersive X‐ray spectroscopy, differential scanning calorimetry, X‐ray diffraction, and scanning electron microscopy measurements were also used to investigate aspects involved in the ageing PA‐11. The hydrolytic degradation of PA‐11 leads to formation of low molar mass compounds, such as oligomers dispersed in the polymeric matrix. This is a process that occurs preferentially in the amorphous domain of PA‐11, which leads to an increase in the degree of crystallinity and the formation of a new γ‐phase. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Surface modification of PHBV films with different functional groups: Thermal properties and in vitro degradation

Polyacrylamide was photografted on solution‐cast poly(3‐hydroxybutyric acid‐co‐3‐hydroxyvaleric acid) (PHBV) films (amide‐PHBV), on which amide groups were transformed into amine groups through Hofmann degradation reaction (amine‐PHBV), followed by collagen coupling reaction to prepare collagen‐modified PHBV (collagen‐PHBV). Amide‐, amine‐, and collagen‐PHBV had higher water absorption and d‐spacing values than PHBV, and melting temperatures and enthalpies decreased in the order of collagen‐PHBV < amine‐PHBV < amide‐PHBV < PHBV. Thermal decomposition kinetics of PHBV component in the films has been investigated by means of nonisothermal thermogravimetric and derivative thermogravimetric studies. Applying the Avrami‐Erofeev equation with index of 2/5 as the probable kinetic function, the suitable activation energy was calculated by the Friedman method through linear fitting (correlation coefficient > 0.98). The activation energy of PHBV was lower than that of amide‐PHBV but higher than that of amine‐ and collagen‐PHBV. Being incubated in phosphate‐buffered saline at 37°C, the modified PHBV films showed more weight loss than PHBV during 360 days; however, pH of degradation fluids was nearly neutral as the initial pH was recorded at 7.2. The modified PHBV films with different functional groups may provide an improved biodegradation rate for various cytocompatible biomaterials constructs. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Flame retardancy and nondripping properties of ammonium polyphosphate/poly(butylene succinate) composites enhanced by water crosslinking

Ammonium polyphosphate (APP)/poly(butylene succinate) (PBS) composites were prepared with a unique water‐crosslinking technique to improve the flame retardancy and nondripping properties of the composites and to maintain the main structure of the composites during flame tests. The composites were treated with a coupling agent (tetraethoxysilane) and then were compounded in a twin‐screw extruder. The compound was moisture‐crosslinked. Fourier transform infrared spectra were used to monitor the water‐crosslinking reaction. The composites via the water‐crosslinking treatment exhibited improved mechanical properties because of the interfacial bonding between the APP and PBS matrix. Scanning electron microscopy of the fractured surfaces of the water‐crosslinked composites showed that the void size increased with increasing water‐crosslinking time. Composites with 15 wt % APP were classified as UL‐94 V‐2; however, the ones with only a 0.5‐h water‐crosslinking reaction were classified as UL‐94 V‐0. Thermal analyses of the water‐crosslinked composites indicated that the thermal degradation temperature of the composites increased with increasing water‐crosslinking time. Differential scanning calorimetry results revealed that the water‐crosslinking reaction could limit the crystallization rate of PBS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2935–2945, 2006     

Oxidation of Chemically-Vapor-Deposited Silicon Nitride and Slnglem-Crystal Silicon

Oxidation of {111} single-crystal silicon and dense, chemically-vapor-deposited silicon nitride was done in clean silica tubes at temperatures of 1000° to woo°C. The oxidation rates of silicon nitride under various atmospheres (dry O₂, wet O₂, wet inert gas, and steam) were several orders of magnitude slower than those of silicon under the identical conditions. The activation energy for the oxidation of silicon nitride decreased from 330 to 259 kJ/mol in going from dry O₂ to steam while that for Si decreased from 120 to 94 kJ/mol. The parabolic rate constant for Si increased linearly as the water vapor pressure increased. However, the parabolic rate constant for silicon nitride showed nonlinear dependency on the water vapor pressure in the presence of oxygen. The oxidation kinetics of silicon nitride is explained by the formation of nitrogen compounds (NO and NH₃) at the reaction interface and the counterpermeation of these reaction products.     

Continuous distribution kinetics for the thermal degradation of LDPE in solution

Polymer degradation in solution has several advantages over melt pyrolysis. The degradation of low‐density polyethylene (LDPE) occurs at much lower temperatures in solution (280–360°C) than in conventional melt pyrolysis (400–450°C). The thermal degradation kinetics of LDPE in solution was investigated in this work. LDPE was dissolved in liquid paraffin and degraded for 3 h at various temperatures (280–360°C). Samples were taken at specific times and analyzed with high‐pressure liquid chromatography/gel permeation chromatography for the molecular weight distribution (MWD). The time evolution of the MWD was modeled with continuous distribution kinetics. Data indicated that LDPE followed random‐chain‐scission degradation. The rapid initial drop in molecular weight, observed up to 45 min, was attributed to the presence of weak links in the polymer. The rate coefficients for the breakage of weak and strong links were determined, and the corresponding average activation energies were calculated to be 88 and 24 kJ/mol, respectively. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 681–690, 2002; DOI 10.1002/app.2344     

Multifunctional coupling agents. II. Chain extension and terminal group modification of polyamides

New bifunctional coupling agents possessing one 2‐oxazoline group and one 2‐oxazinone group were converted in a Haake melt mixer or extruder with PA6 and PA12. It was shown by means of NMR spectroscopic investigations that the 2‐oxazoline group reacted mainly with carboxylic groups whereas the oxazinone group reacted preferably with the amino groups. Both reactions proceeded with high selectivity and independent from each other. In the case of carboxy/amino group terminated polyamides, the conversions resulted in increased molecular weights since both reactive terminal groups of the polyamides were addressed simultaneously by the coupling agent. In the case of amino group terminated polyamides, the conversion with the bifunctional coupling agent resulted in oxazoline terminated polymer chains. Unlike PA6, it was possible to convert PA12 in two steps. At lower temperatures (210°C) and short reaction times (2 min), the reaction of the oxazinone group with the amino groups was predominant, whereas the reaction of the oxazoline group with the carboxylic groups proceeded to a sufficient extent only after longer reaction times or at higher temperatures. In the case of PA6, processing temperatures of about 250°C were necessary. Here, a side reaction was observed that resulted in the formation of cyclic quinoxaline structures under evolution of water. This side reaction did not disturb the chain extension significantly. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2170–2177, 2004     

Synthesis and characterization of hydroxyethyl methacrylate/acrylamide responsive hydrogels

Hydrogels based on an aqueous solution of hydroxyethyl methacrylate (HEMA) and acrylamide (AM) in the presence of trithioglycolic acid (TTGA) were prepared under the effect of gamma irradiation. These hydrogels were characterized by IR spectroscopy and thermogravimetric analysis and investigated for temperature‐ and pH‐responsive materials. It was found that TTGA is essential for the formation of HEMA/AM hydrogels at different compositions, in which the gel fraction depends on composition. A binary mixture of HEMA and AM at equal ratios was the critical composition that forms hydrogels, even in the presence of TTGA. The IR spectroscopic analysis showed that the formation of hydrogels depends on hydrogen bonding and crosslinking. The TGA investigations with respect to mass loss and the temperatures of the maximum value of the rate of reaction showed that HEMA/AM hydrogels possess higher thermal stability than that of pure HEMA and this stability increases with increasing ratio of the AM component. Also, it was observed that the temperature of the maximum value of the rate of thermal decomposition reaction depends on hydrogel composition. However, calculations of the activation energy showed that the hydrogel composed of 90% HEMA and 10% AM exhibits the highest thermal stability during the increasing or decreasing rate of reaction. Kinetic studies of swelling in water showed that HEMA/AM hydrogels displayed a temperature‐responsive character within the temperature range 25–30°C, and showed a stepwise swelling behavior in the pH range 2–10, depending on composition. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1105–1115, 2005     

Electrochemical mediators for total oxidation of chlorinated hydrocarbons: formation kinetics of Ag(II), Co(III), and Ce(IV)

Mediated electrochemical oxidation (MEO) with Ag(n) and Co(iii) in 7 m HNO₃ and 3.5 M H₂SO₄ has been studied. High degradation rates were found for superchlorinated organic substances such as pentachlorophenol (PCP), Lindane and polychlorinated biphenyls (PCBs) using Ag(ii) in HNO₃ as mediator. An investigation on the formation kinetics of Ag(ii), Co(iii), and Ce(iv) by means of a rotating disc electrode (RDE) led to a quantitative determination of limiting currents at various mediator concentrations. Reaction rate constants of water oxidation by Ag(ii) were determined at various temperatures and compared to reaction rates of Co(iii).