Hydroconversion kinetics of Marlim vacuum residue

A kinetic model was obtained for the Marlim crude vacuum residue (VR) hydroconversion. Marlim VR mixed with FCC decant oil in an 80%/20% weight basis was put in contact with a commercial NiMo on γ-alumina catalyst in a stirred batch reactor. Several temperatures and oil/catalyst ratios were used over different times (0–240 min), at a 110 bar pressure and constant hydrogen flow. The analysis of the collected product showed residua conversions of up to 70%. Hydroconversion kinetics involving thermal and catalytic cracking contributions was proposed to represent the obtained data. The resulting system of differential equations of the kinetic model was solved within reaction time, taking into account the experimental temperature profile. The chi-square objective function was minimized to adjust model parameters. A proposed effective hybrid minimization method was used, by applying a Newton-type method between certain simulated annealing minimization steps. The proposed kinetic model allowed the representation of thermal and catalytic cracking effects, in order to take into account different catalyst concentrations. Therefore it is possible to consider distinct reactor hydrodynamics, such as expanded or bubble column reactors.     

Selectivity of large pore zeolites in the alkylation of naphthalene with tert-butyl alcohol: analysis of experimental results by computational modelling

Liquid phase alkylation of naphthalene with tert-butanol has been studied using HY and H-beta zeolites with varying silicon to aluminium ratios. Both series of zeolites underwent efficient activities and high selectivities for the mono- and di-(tert-butyl) derivatives. In all cases, 2-(tert-butyl)naphthalene (2-TBN) was the only monoalkylated product (100%,β-selectivity). Over H-beta zeolites, 2-TBN was obtained as the main product with relatively small amounts of dialkylated compounds. Over HY samples, a 2,6-di(tert-butyl)naphthalene (2,6-DTBN) selectivity up to 84% was obtained, with a 2,6-DTBN/2,7-DTBN ratio of 5.6–5.9 and β,β′-selectivity (2,6-+2,7-) of 98–99%. This constitutes the first published observation of such high β,β′ selectivity and 2,6-/2,7- ratio in the liquid phase alkylation of naphthalene. In order to understand such a differentiation in the formation of the two di-(tert-butyl)naphthalenes over the HY zeolites, computational analysis of both energies and molecular dimensions of these derivatives and of the monoalkylated counterparts has been performed, using quantum mechanics (AM1 and PM3) and molecular mechanics (MM⁺) methods. The energy calculations are in agreement with the experimental results regarding the selective formation of the β and β,β′ isomers. The determination of the kinetic diameters shows that, in their most stable conformation, 2,6-DTBN has a smaller kinetic diameter (7.1 Å) than 2,7-DTBN (7.5 Å), which may explain the selective formation of the 2,6-isomer against the 2,7- within the faujasite framework.     

Kinetic model for the hydrolysis of sterilized palm press fibre

In this study, a kinetic model for enzymatic hydrolysis of oil palm residues considering the effect of sterilization was proposed and validated. Experiments were performed in batch reactor using palm oil mill effluent (POME) supplemented with sterilized and non-sterilized pressed pericarp fibers (PPF) as substrates. Kinetic parameters were estimated by fitting the experimental data to the models. It was found that the sterilization process as well as the variety in substrate particle size exerted an effect on the apparent rate constant (k), but no effect on the apparent Michaelis constant (K_M) and apparent competitive inhibition constant (K_I). When compared with the experimental data, the kinetic model provided good prediction to the oil palm residues hydrolysis with mean square error less than 10%.     

Effect of β-Cyclodextrin Complexation on Solubility and Enzymatic Conversion of Naringin

In the present paper, the effect of β-cyclodextrin (β-CD) inclusion complexation on the solubility and enzymatic hydrolysis of naringin was investigated. The inclusion complex of naringin/β-CD at the molar ratio of 1:1 was obtained by the dropping method and was characterized by differential scanning calorimetry. The solubility of naringin complexes in water at 37 ± 0.1 °C was 15 times greater than that of free naringin. Snailase-involved hydrolysis conditions were tested for the bioconversion of naringin into naringenin using the univariate experimental design. Naringin can be transformed into naringenin by snailase-involved hydrolysis. The optimum conditions for enzymatic hydrolysis were determined as follows: pH 5.0, temperature 37 °C, ratio of snailase/substrate 0.8, substrate concentration 20 mg·mL⁻¹, and reaction time 12 h. Under the optimum conditions, the transforming rate of naringenin from naringin for inclusion complexes and free naringin was 98.7% and 56.2% respectively, suggesting that β-CD complexation can improve the aqueous solubility and consequently the enzymatic hydrolysis rate of naringin.     

Study of hydrogen evolution reaction in acid medium on Pt microelectrodes

This work describes the utilization of a Pt UME in the study of the hydrogen evolution reaction in 0.5 M H₂SO₄. A non-linear fitting procedure was employed in order to analyze polarization curves obtained at several temperatures (25–75 °C). The results revealed that the traditionally accepted model described by a Volmer–Tafel route fails to fit the obtained experimental data. In this sense, a new model was proposed involving the Volmer–Heyrovsky mechanism, being the Heyrovsky reaction rate determining step. To achieve the best fit between experimental and calculated data, the kinetic equations had to be proposed with a small value of the transfer coefficient (β<0.2). This unusual value was associated with an activationless process, which can also justify the limiting kinetic current (not diffusional) observed. Trying to get further insight into this possibility, the polarization studies were also performed on a surface modified by underpotentially deposited copper. With a degree of coverage as high as 0.8, the only observed effect on the polarization curves was a shift towards minor current values. This shift can be completely justified by the blocking of surface area. A change in mechanism was not observed albeit the Cu UPD eliminated the pairs of neighbor active sites necessary to the Volmer–Tafel pathway.     

Enzymatic hydrolysis of rawhide using papain and neutrase

Rawhide split was hydrolysed separately by two proteolytic enzymes, papain and neutrase. The effects of enzymatic conditions of the hydrolysis reaction were investigated. During the first 10 min of the enzymatic hydrolysis, the yield of the hydrolysed protein increased sharply, then it slowly increased or became essentially constant due to the limited availability of the substrate. The optimum hydrolysis conditions of papain and neutrase for highest protein yield are at 70 °C, pH 6–7 and 40–50 °C, pH 6–7, respectively. The product from papain hydrolysis is a gelatin with low gel strength and viscosity, while that from neutrase hydrolysis is collagen hydrolysate with viscosity as low as water. This is considered to indicate that longer fragments of protein are obtained from papain hydrolysis than that from neutrase implying different mechanisms of papain and neutrase hydrolysis.     

Effects of sulfur on coal treatment in aqueous sodium hydroxide

The dissolution of Wyodak subbituminous and North Dakota lignite coals in 50% aqueous sodium hydroxide was enhanced by the addition of sulfur. The added sulfur was not incorporated into the undissolved coal residues. The effects of temperature (140–200°C), time (5–90 min), and added elemental sulfur (1–25% by weight) on dissolution were examined. Temperature affected the dissolution of subbituminous and lignite coal, while time affected the dissolution of subbituminous coal.     

Characterization of the extracts and residues from CS2-N-methyl-2-pyrrolidinone mixed solvent extraction

The extracts and residues obtained by extraction of five bituminous coals with CS₂-N-methyl-2-pyrrolidinone mixed solvent (1:1 by volume) were characterized at room temperature. The extraction yields were 31.1–63.0% (daf) and the extracts were fractionated into acetone soluble (AS), acetone insoluble-pyridine soluble (PS) and pyridine insoluble-mixed solvent soluble (MS) fractions. The MS fraction, which was the heaviest fraction examined, had higher values of % oxygen, f_a, molecular weight and spin concentration than the corresponding AS and PS fractions, but a similar degree of aromatic condensation. The quantities of volatile matter (daf) in the residues were similar or slightly less than those in the extracts.     

Vacuum pyrolysis of Prince Mine coal, Nova Scotia, Canada

Preliminary results are given on thermal decomposition characteristics of a high volatile A bituminous coal from Eastern Canada using vacuum pyrolysis experiments (pressure 2–200 mm Hg) over the temperature range 322–1000 °C. The objectives of the study were to determine the optimum temperature range for the formation of coal tar and to study the influence of reaction temperature on the nature of the solid residues. Significant decomposition reactions start at 300–400 °C and the optimum temperature range for the production of coal tar was 450–600 °C. The major gaseous products H₂S, CO₂ and CH₄ are formed up to 600 °C. Above 600 °C the coal decomposes mainly into CO and H₂. The solid residues are characterized by volatile matter content, calorific values and elemental analysis. The volatile matter content decreases rapidly from 322 °C and stabilizes at reaction temperatures > 750 °C. The 15% VM level, a minimum requirement in coal combustion processes, was reached at 500 °C. The changes in calorific values do not show any significant trend up to 600 °C, but decrease markedly above 600 °C. From the preliminary results vacuum pyrolysis is regarded as an effective process in which valuable coal tar by-products can be obtained from coal prior to its combustion.     

Free electron charging of ultrafine aerosol particles

Experiments of free electron charging of aerosol particles in the free molecule regime are reported. Monodisperse ultrafine silver particles of 5–30 nm were exposed to known concentrations of low energy electrons produced by ionization by -particles in a unipolar aerosol charger. The kinetic energy of the electrons was varied by changing the electric field intensity in the charger (i.e. between 93 and 279 V cm⁻¹). The range of Knudsen number for aerosol charging (i.e. the ratio of the electron mean free path to the particle radius) was from 30 to 261. The charged fraction was measured as a function of particle size in high-purity helium and nitrogen under different charging conditions. The experimental results for the combination coefficient between neutral particles and electrons suggested a free-molecule diffusion charging mechanism which was dependent on the electron mobility, transverse diffusion coefficient, mean free path, and mean kinetic energy (i.e. electron temperature). The functional dependence was similar to that given by the ionic charging theories of Natanson (1960, Sov. Phys. 5, 538–551), and Fuchs (1963, Geofis. Pura Appl. 56, 185–193) when the appropriate electron properties were used. The electron charging models of O'Hara et al. (1989, J. Aerosol Sci. 20, 313–330), and Zagnit'ko et al. (1989, Russ. J. Phys. Chem. 63, 883–888) did not fit the experimental results because they were not derived for the free-molecule regime. A modified Fuchs charging theory that uses an empirical accommodation coefficient for the electrons at the surface of the particle was used to fit the experimental results. Good agreement was found by using an accommodation coefficient of 0.4 for both helium and nitrogen.     

Study of the pyrolysis of Maoming oil shale lumps

Pyrolysis experiments on Maoming oil shale lumps (10–60 mm in diameter) were carried out with the aid of large-particle thermogravimetric analysis apparatus at constant heating rates of 1, 2 and 5 °C min⁻¹. A pyrolysis kinetic model was developed which took into account both the pyrolysis reaction and intraparticle heat transfer. Oil shale pyrolysis kinetic parameters were then determined on the basis of experimental data concerning weight loss, shale oil production, gas evolution and intraparticle temperature distribution versus time, by using the developed model. Furthermore, the effects of variables (e.g. temperature, lump size, heating rate) on oil shale pyrolysis were assessed during experimentation. It is found that model predictions agree reasonably well with experimental data.     

Kinetics and mechanism of ethyl tert-butyl ether liquid-phase synthesis

This paper presents the results of an experimental investigation on ethyl tert-butyl ether (ETBE) liquid-phase synthesis from isobutene (IB) and ethanol (EtOH), catalyzed by an acidic macroreticular ion exchange resin, Amberlyst 15 (A15). The experiments were carried out batchwise in a Parr reactor in the range 323–363 K at 2 MPa for different initial EtOH/IB mole ratios and amounts of catalyst. Data collected at equilibrium gave thermodynamic information which was compared with theoretical calculations using the UNIFAC method. The kinetic results were used to develop a reaction mechanism and a kinetic model. The resin's affinity for polar substances and the strong nonideality of the liquid phase lead to a complex kinetic expression, which is valid both in the presence of high and low alcohol concentrations. Simulations performed with this kinetic model agree satisfactorily with the experimental results.     

Catalytic oxidation of phenol in aqueous solutions

The objective of this work is to investigate catalyst systems for the oxidation of phenol in water in a batch autoclave. The main experimental variables are the type and the composition of the catalyst, the catalyst loading, temperature, oxygen partial pressure, initial phenol concentration and the stirrer speed. Commercial catalysts were used. Experimental work was conducted in two different laboratories. In one laboratory, the catalysts tested were 35% CuO+65% ZnO; 5–15% CuO+85–95% Al₂O₃; 26% CuO+74% Cu Chromite. In the other laboratory, the catalysts tested included 35% CuO+65% ZnO; 5–10% Ba₂CO₃+<5% C+30–40% CuO+60–70% ZnO; and 8–15% Al₂O₃+1–5% C+35–45% CuO+40–50% ZnO. With some of these catalysts depending on the operating conditions, complete phenol conversion could be obtained within 90 min. Under certain experimental conditions, the reaction underwent an induction period after which there was a transition to a much higher activity regime. The induction period may be due to an autocatalytic reaction system or to a very slow rate of formation of hydroquinone and catechol which then readily oxidize to o- and p-benzoquinone. An increase in the temperature and the oxygen partial pressure decreased the induction period, which increased as the catalyst to phenol ratio increased. 26% CuO+74% Cu Chromite and 8–15% Al₂O₃+1–5% C+35–45% CuO+40–50% ZnO were found to be the most active catalysts.     

Analyzing molecular weight distribution of whey protein hydrolysates

Process parameters on enzymatic hydrolysis and molecular weight (MW) distribution of whey protein hydrolysates were investigated. Whey protein hydrolysates were first gained by the alkaline protease alcalase for 7 h at temperature (50 °C), pH (8.0) and E/S (3%). The diversification of the hydrolysis degree and dissociative amino acid content was investigated during the whey hydrolysis. The dissociative amino acid content was 56.09 μmol/mL with the hydrolysis degree of 20.04%. The results of Sephadex G25 washing and high performance liquid chromatography–electrospray ionization–mass spectrometry (HPLC–ESI–MS) indicated the molecular weight distribution of whey protein hydrolysates ranged from 300 to 1400 Da, and most of whey peptide was under 1000 Da.     

Studies of the effects of synthetic procedure on base catalysis using hydroxide-intercalated layer double hydroxides

Layer double hydroxides (LDHs) based on the hydrotalcite structure (Mg₆Al₂(OH)₁₆CO₃·4H₂O) have been synthesized by coprecipitation, sol–gel and urea hydrolysis methods and with Mg:Al ratios of 2:1 and 5:1. Scanning electron microscopy shows the coprecipitated phases present the smallest individual crystallite sizes (ca. 150 nm) with the largest crystallites (2–4 μm) for urea hydrolysis. Sol–gel samples show crystallites (150–450 nm) fused together into much larger particles. The samples have been calcined at 723 K in flowing air to produce metal oxide phases which have then been rehydrated in the presence of hydroxide ions to produce meixnerite-like LDH phases (Mg₆Al₂(OH)₂₀·4H₂O). The base catalytic activity of these rehydrated samples has been measured by GC for the aldol self-condensation of acetone. Activity data has been correlated with sample characteristics to gain insight into the active sites and mode of action of these catalysts.     

Acid hydrolysis of olive tree biomass

Olive tree cultivation generates a great amount of biomass residues which have no industrial application. Pruning residues are usually grindered or burnt on fields, causing economical costs and environmental concerns. An alternative issue for these renewable sugar-containing feedstocks may be the conversion into fuel ethanol by hydrolysis and fermentation.As a first step in the bioconversion process, the acid hydrolysis of olive tree pruning is studied and a mathematical model predicting both fiber content and sugar release as a function of operation variables is proposed. Sulphuric acid concentration in the range 0–32% (w/w), process temperature between 60 and 90 °C and hydrolysis time from 0 to 240 min were used as hydrolysis conditions. The process was modelled by first-order reaction kinetics. The apparent kinetic constant relating acid concentration to fiber hydrolysis and sugar release shows a potential dependence; on the other hand, an Arrhenius-type equation has enabled the evaluation of activation energy values of 26.4 and 25.9 kJ/mol for fiber hydrolysis and sugar generation, respectively.     

Kinetics of Soybean Oil Hydrolysis on Niobium Catalysts

The catalytic hydrolysis of soybean oil was used as an alternative for the production of monoglycerides (MG) and diglycerides (DG). The reactions were conducted in a stainless-steel tubular reactor in the temperature range of 240–290 °C, on niobium phosphate (NBP) and niobium oxide (NBO) as catalysts. In the hydrolysis reactions at 270 °C, the maximum selectivities of the products of interest were obtained at 22 % MG and 48 % DG for the reaction with NBP, and 7 % MG and 33 % DG with NBO, for 59 % and 36 % of triglyceride conversion in 10 min, respectively. The proposed kinetic model presented a good fit of the theoretical model with the experimental data, showing that the previous hypotheses considered for the mechanism development are suitable for describing the kinetics of soybean oil hydrolysis.     

Kinetics of the selective catalytic reduction of NO by NH3 on a Cu-faujasite catalyst

The kinetics of the selective catalytic reduction (SCR) of NO by NH₃ in the presence of O₂ has been studied on a 5.5% Cu-faujasite (Cu-FAU) catalyst. Cu-FAU was composed of cationic and oxocationic Cu species. The SCR was studied in a gas phase-flowing reactor operating at atmospheric pressure. The reaction conditions explored were: 458<T_R<513 K, 2503 (ppm) < 4000, 12 (%) < 4. The kinetic orders were 0.8–1 with respect to NO, 0.5–1 with respect to O₂, and essentially 0 with respect to NH₃. Based on these kinetic partial orders of reactions and elementary chemistry, a wide variety of mechanisms were explored, and different rate laws were derived. The best fit between the measured and calculated rates for the SCR of NO by NH₃ was obtained with a rate law derived from a redox Mars and van Krevelen mechanism. The catalytic cycle is described by a sequence of three reactions: (i) Cu^I is oxidized by O₂ to “Cu^II-oxo”, (ii) “Cu^II-oxo” reacts with NO to yield “Cu^II-N_xO_y”, and (iii) finally “Cu^II-N_xO_y” is reduced by NH₃ to give N₂, H₂O, and the regeneration of Cu^I (closing of the catalytic cycle). The rate constants of the three steps have been determined at 458, 483, and 513 K. It is shown that Cu^I or “Cu^II-oxo” species constitute the rate-determining active center.     

Treatment of potato chips manufacturing wastewater by electrocoagulation

Treatment of wastewater from potato chips manufacturing by electrocoagulation (EC) was investigated. Experiments were conducted to determine the optimum operating conditions such as electrode type, pH, current density and retention time. Aluminium and iron electrodes were used, and aluminium electrodes were found to be more suitable since it had a higher removal rate of COD, turbidity and suspended solids than the iron electrode. The removal efficiencies of COD and turbidity were high, being 60% and 98%, respectively, with retention time < 40 min. 0.05–1.75 kg (per kg COD removed) of dried sludge was removed. COD removal kinetics during EC process was described by a macro-kinetics model. Results from the kinetic studies showed that the kinetic data fit the second-order kinetic model well. The operating costs investigated in the present study were the energy cost of EC and the material cost due to the consumption of aluminium electrode. Operating costs were varied in the range of 0.48 to 5.42 $/m³ and 0.62 to 6.32 $/m³ wastewater treated at 20–300 A/m² and 5–40 min, respectively. The energy consumption was 4 kWh/m³ for wastewater treated less than 8 min under typical operating conditions.     

Development of a kinetic model for the oxidation of methane over Pd/Al2O3 at dry and wet conditions

The kinetics of the oxidation of methane over a commercial 0.5% Pd on γ-Al₂O₃ catalyst has been studied in a lab-scale fixed-bed reactor, the effect of temperature, and methane, oxygen and water partial pressures being investigated, in a range of interest for environmental applications. Different Eley–Rideal, Langmuir–Hinshelwood and Mars–van Krevelen models were fitted to the experimental results, the best fitting being obtained for a Mars–van Krevelen model that considers slow desorption of the reaction products. The model parameters obtained both from differential and integral treatment of the experimental data are in good agreement with each other. A modification of the proposed model, taking into account that water is adsorbed over oxidised sites, is also able to model the inhibition produced by steam.