Search

The pyrolysis of Eucalyptus globulus(EG) with different blends of high density polyethylene (HDPE) and low density polyethylene (LDPE) by thermogravimetry has been studied. ASTM-E1641-16 standard method has been used to evaluate the kinetics during the pyrolysis of the studied blends. For all feedstocks (EG, HDPE and LDPE) and blends studied, the relative content (%) of the volatile organic compound has been determined by GC–MS analysis. Different synergistic effects on the activation energy of EG blends with HDPE and LDPE have been found. EG-HDPE blends showed a minimum activation energy (Ea) (125 kJ mol−1) at the 80% EG–20% HDPE ratio, while the minimum Ea value for EG-LDPE blends was found at the 60% EG–40% LDPE ratio (135 kJ mol−1) has been identified. To test which components exert a greater synergistic effect, mixtures of HDPE and LDPE with the main components of eucalyptus (cellulose, hemicellulose and lignin) have also been studied. However, no synergistic effects on the pyrolysis of cellulose have been detected. Moreover, in hemicellulose and lignin with both types of polyethylene mixtures, a significant decrease in Ea has been appreciated. The lowest Ea values for 60% cellulose–40% HDPE (167 kJ mol−1) and 60% lignin–40% HDPE (140 kJ mol−1) has been calculated. On the other hand, minimum values for 40% cellulose–60% LDPE (166 kJ mol−1) mixture and for 40% lignin–60% LDPE (168 kJ mol−1) mixture have been detected. Thus, the decrease in both Ea and the Arrhenius pre-exponential factor on the eucalyptus-polyethylene blends to the presence of hemicellulose and lignin can be attributed. Moreover, during the co-pyrolysis of HDPE-EG mixtures, n-paraffins, ketones, phenols and sugars are the main VOCs identified. In contrast, in LDPE-EG mixtures, only n-paraffins (55%) and olefins (44%) have been identified.

Ensuring environmental and social-economic sustainability in the use of materials from lignocellulosic biomass requires their fractionation and valorization of their main components. In this work, we used Eucalyptus urograndiswood to obtain chemicals and energy. The raw material was characterized in chemical terms and then subjected to autohydrolysis under variable operating conditions to optimize the extraction of hemicellulose derivatives relative to cellulose. The kinetics of the pyrolysis process was modeled in terms of activation energy and hydrogen production. Using temperatures in the range of 180–190 °C and treatment times in the range of 15–30 min allowed more than 74.5% of all hemicellulosic components in the raw material to be selectively extracted into the liquid post-hydrolysis phase, more than 90% of all glucan to remain in the solid phase and up to 27.8% of lignin to be removed. The thermal behavior of solid fraction was examined by thermogravimetric analysis, using variable heating rates under a nitrogen atmosphere, and the activation energy can be estimated by using the Flynn-Wall-Ozawa method. Based on the results, the pyrolysis of E. urograndiscan be modeled as a first-order reaction. The activation energy (Ea) at a fractional conversion αbetween 0.3 and 0.7 was 183 to 199 KJ mol−1for the raw material, whereas that for the solid residue from autohydrolysis ranged from 179 to 186 kJ mol−1at same fractional conversion when operational temperature in autohydrolysis was upper 185 °C. Based on the results, using temperatures above 180 °C and times of 15 min or longer [i.e., operating at the (0,0) experimental point for the autohydrolysis process] in combination with degrees of conversion from 0.3 to 0.8 reduced the activation energy of the pyrolysis process in relation to the raw material by up to 12% and removed hemicellulose by more 74.5% from it. In parallel, the comparative analysis of the Eavalues and the composition of the pyrolysis gas obtained showed a negative relationship between Eaand the amount of hydrogen produced.

Stevia rebaudianaresidues composting is studied and optimized using a central composite experimental design The influence of controllable composting variables [moisture (40–70%), aeration (0.05–0.30 Lairmin−1kg−1), and time (0–50 days)] on the temperature history and the properties of the compost (pH, organic matter) produced to determine suitable composting conditions. Mass balance and emitted gases of all the composting reactors have been done. Compost with high degradation entails operating at 50 days of composting under high moisture content (70%) and aeration level with values close to 0.05 Lairmin−1kg−1. Moreover, the composting process kinetic for Stevia rebaudianaresidues has been studied. The magnitude of the kinetic parameters on the studied conditions varies among 1/42 and 1/46 for 1/K1and 0.15 and 1.6 for K2. Where 1/K1is a value that measures the affinity between microorganisms and substrate and K2depends on the composting variable optimization. Both moisture and aeration affects positively and negatively the composting process. Moreover, low effect of aeration has been found. The values of 1/K1and K2obtained showed higher values (higher degradation kinetic) under 55% moisture content and 0.30 Lairmin−1kg−1.

This paper presents polarographic and voltammetric studies on the electroreduction of 2,6‐dimethoxy‐4‐chloro‐1,3,5‐triazine on mercury electrodes in aqueous solutions and in the acidity range 2 M H2SO4to pH 7. Above pH 6.5 no signals were obtained. In both DC and DP polarography and voltammetry, one or two partially overlapped reduction waves were observed, depending on the pH of the medium. The overall process corresponded to a four‐electron irreversible reduction. In strongly acidic media (pH<4.5) the protonated reactant was reduced through a two‐electron process to give a dechlorinated molecule that is subsequentely reduced at the potentials of the second wave. It was concluded that the reduction of the chlorinated s‐triazine rings seems to occur through the reductive cleavage of the chlorine irrespective of the nature of the groups bonded to the ring in positions 2, 6.

The electrooxidation of the bactericide and fungicide agent 2‐mercaptopyridine‐N‐oxide (PySH), or pyrithione, was investigated by using mercury (Hg), glassy carbon (GCE), plastic formed carbon (PFCE) and paste (CPE) electrodes. From controlled‐potential electrolyses or chronoamperometric measurements, the number of electrons involved in the oxidation processes was found to be close to unity in all cases. Voltammetric measurements showed that the irreversibility of the electron transfer must be related to the roughness and ordering in the surface of the electrode material: as the amorphous character of the carbon electrode was increased, the transfer appeared faster. Other effects as the O/C ratio or the removal of impurities can also influence the reversibility of the transfer. The rate constants of the electron transfers at zero potential were obtained. In addition, the extension of the adsorptive oxidation decreased when the amorphous character of the electrode was increased, but the Gibbs free enthalpy of this process did not vary from one electrode to another nor for the Hg electrode.

The polarographic (direct current, dc, and differential pulse, DP) and voltammetric oxidation of hydrogen peroxide on mercury electrodes has been examined. The electrooxidation of H2O2involves hydroperoxide radical and superoxide anion radical able to interact with radical scavengers (antioxidants), namely 3-hydroxycoumarin, carvacrol, vanillin and gallic acid. For such interaction, theoretical equations are derived using the convective diffusion approximation and the steady-state conditions, as well as solving the differential equations of the Nernst diffusion-layer approximation by the method of dimensionless variables. The experimental results agree with the theoretical predictions and a kinetic parameter is proposed to evaluate the scavenging activity of antioxidants.

This paper presents polarographic (dc and differential pulse) and voltammetric (linear-sweep cyclic voltammetric) studies of the electroreduction of 2-chloroisonicotinic acid (2-chloro-4-pyridinecarboxylic acid), 2-CISO, at mercury electrodes. The dissociation constants of 2-CISO were obtained from the UV-visible absorption spectra (pKof 0.5±0.03corresponding to the –COOHgroup) and by potentiometric titration (pKof 3.46 corresponding to the protonation–dissociation of the heterocyclic nitrogen). The electrochemical studies were performed in the acidity range 2.7 M H2SO4to pH 7. Above the last pH value no signals were observed. The overall reduction process involves the uptake of four electrons. Kinetics parameters such as Tafel slopes and electrochemical reaction orders have been determined at potentials corresponding to the foot of the waves. From the results a reaction mechanism can be proposed, consisting of an electrochemical–chemical process having two reversible electron transfers preceding a chemical step. At the scan rates used in cyclic voltammetry, the rate-determining step is the second irreversible electron transfer. At pH0.5the recombination of the carboxylate anion with the H+ion takes place prior to the reduction process.