Hydrolysis of pentosans in bagasse pith

Work has been conducted on the hydrolysis of pentosans in bagasse pith as the first part of a study of the chemistry of bagasse processing aimed at establishing an integrated industry. Bagasse pith is the fine part screened out and discarded as waste during the preparation of raw material for bagasse pulping plant. By using dilute sulphuric acid at a concentration less than 2% by weight and at a temperature lower than 165°C, pith is hydrolysed to pentoses in a yield of 80–90% based on potential pentoses in pith. Hydrolysis of pentosans in pith, within the scope of experiment, seems to be a first order reaction. However, the semi-logarithmic time plot for the hydrolysis of potential pentoses in the residue consists of two straight lines of different slope. This may be explained on the assumption that bagasse pith contains two major fractions of pentosans that are hydrolysed at different rates. Saeman's equation for hydrolysis of wood with sulphuric acid may be adapted to represent dependence of rate constant K on acid concentration C and reaction temperature T in hydrolysis of the two major parts of pentosans in bagasse pith.      

Evaluation of acids and cellulase enzyme for the effective hydrolysis of agricultural lignocellulosic residues

This paper reports the results of experimentation carried out to compare the ability of mineral acids (HCl and H₂SO₄) and cellulase enzyme (from Trichoderma reesei QM 9414) in the saccharification of corn-cob, groundnut shell, sugarcane bagasse and wheat straw. With the exception of corn-cobs, acids proved to be better saccharifying agents than the cellulase complex, but the former gave a poor substrate for alcoholic fermentation since the saccharified mashes contained large amounts of pentoses which are not metabolized by most strains of yeast. In addition, both acids and enzymes have been found to be substrate specific. Maximal saccharification of groundnut shell, sugarcane bagasse and wheat straw were obtained with sulphuric acid at 15.0, 5.0 and 5.0% (v/v) under 15, 15 and 15 psi pressure for 15, 30 and 30 min, respectively; whereas hydrochloric acid at 7.5% (v/v) with. autoclaving for 30 min at 10 psi resulted in maximum saccharification of corn-cob. However, the order of susceptibility of substrates to enzymatic attack was corn-cob > wheat straw > sugarcane bagasse > groundnut shell. Increase in enzyme concentration (1–4 IU ml^?1) and treatment duration (12–72 h) improved saccharification, but increases in substrate concentration (>5.0%, w/v) had an inhibitory effect on the hydrolytic ability of the cellulase enzyme complex. Of the various substrate-acid ratios tested, a ratio of 1:8 was found to be optimal for the eflcient hydrolysis of the substrates under study.     

Synthesis and studies of egyptian bagasse pith phenol formaldehyde cationic exchangers

The article is concerned with a simple method for preparing cationic resins from polycondensation of Egyptian bagasse pith (as a source of cheap and renewable material) with phenol and paraformaldehyde as a cross-linking agent. Optimum principal reaction conditions of the preparation and properties are determined and compared with resin without bagasse pith content. The Synthesized resins are stable in water, organic solvents, thermal treatment, and mineral acids (1M). The sample having a cation exchange capacity up to 3.92 meq g^?1 of dry resins are being introduced as new cationic exchangers. The synthesized resins are used in the study of the possible separation of univalent cations. The rational thermodynamic equilibrium constants (In K) are calculated for Li⁺ ?Na⁺ exchanges on the resins having a various amount of bagasse pith. The thermodynamic parameters are computed and suitable explanations are described. © 1994 John Wiley & Sons, Inc.     

Hydrogen Atom Attack on Fluorotoluenes: Rates of Fluorine Displacement

Rates of hydrogen atom attack on o-fluorotoluene (o-FTOL) and m-fluorotoluene (m-FTOL) at temperatures of 988–1144 K and pressures of 2–2.5 bar have been determined in a single-pulse shock tube study. Hydrogen atoms, generated from the decomposition of hexamethylethane, were allowed to react with the substrates and the characteristic products observed. Rate constants for two reaction channels, displacement of fluorine or methyl, were determined relative to displacement of methyl from 1, 3,5-trimethylbenzene (135TMB). Evidence is presented that abstraction of F is unimportant over the studied temperature range. With k(H + 135TMB → m-xylene + CH₃) = 6.7 × 10¹³ exp(–3255/T) cm³ mol⁻¹s⁻¹, the following rate expressions have been derived: k(H + o-FTOL → C₆H₅CH₃ + F) = 8.38 × 10¹³ exp(–6041/T) cm³ mol⁻¹s⁻¹; (1012–1142 K) k(H + o-FTOL → C₆H₅F + CH₃) = 2.37 × 10¹³ exp(–2938/T) cm³ mol⁻¹s⁻¹; (988–1142 K) k(H + m-FTOL → C₆H₅CH₃ + F) = 1.33 × 10¹⁴ exp(–6810/T) cm³ mol⁻¹s⁻¹; (1046–1144 K) k(H + m-FTOL → C₆H₅F + CH3) = 2.04 × 10¹³ exp(–3104/T) cm³ mol⁻¹s⁻¹; (1008–1144 K) Uncertainties in the relative rate constants are estimated to be factors of about 1.1, while the above absolute values have estimated expanded uncertainties of about a factor of 1.4 in rate, 10 kJ mol⁻¹ in the activation energy, and a factor of 3 in the A-factor. The present data are compared with relevant literature data. From our data and the thermochemistry, a model of the elementary steps comprising displacement of F is developed. On the basis of the model fit to our data, rate constants for the addition of atomic fluorine to toluene at 1100 K are derived. Rate expressions for fluorination reactions of toluene are also determined. The significance of the present results is discussed in the context of the formation of fluorinated byproducts in high-temperature systems.     

Acid and enzymatic saccharification of agricultural mixed polymers for alcohol production

The paper reports the evaluation of potentials of acid (HCl and H₂SO₄) and enzymatically (cellulase) saccharified corncob, groundnut shell, sugarcane bagasse and wheat straw biopolymers for ethanol production. Of the three yeast isolates tested, Saccharomyces cerevisiae var. ellipsoideus was found to be most efficient, closely followed by Kluyveromyces marxianus NCYC 179 in its ability to ferment enzymatically hydrolysed mash of all the substrates tested to ethanol. However, S. cerevisiae NCYC 240 and acid hydrolysed agricultural polymers were found to be a poor organism and poor substrates, respectively, for ethanol fermentation. The order of ethanol production on substrate basis was corncob > wheat straw > sugarcane bagasse > groundnut shell biomass biopolymer. An incubation period of 24 h was found optimum for the optimal production of ethanol by S. cerevisiae var. ellipsoideus in both acid and enzymatically hydrolysed agricultural residues.     

Some properties of β-D-Glucosidase from Trichoderma harzianum C1R1

β-D-Glucosidase from Trichoderma harzianum C₁R₁ consists of several isocomponents having isoelectric points in the pH range of 4.85-7.50. All the components exhibit both cellobiase and 4-nitrophenyl β-D-glucosidase (4NPGase) activity. The enzyme affinity for cellobiose (K_m = 3.92 mmol dm^?3) is 14.5 times weaker than for 4NPG (K_m = 0.27 mmol dm^?3). The hydrolysis of both substrates is competitively inhibited by glucose, the inhibition of 4NPG hydrolysis (K₁ = 2.00 mmol dm^?3) being about 4.2 times stronger compared to the hydrolysis of cellobiose (K₁ = 8.43 mmol dm^?3). The 4NPG hydrolysis is also competitively inhibited by the presence of cellobiose and D-glucono-1,5-lactone (K_i(cellobiose) = 5.00 mmol dm^?3; K_{i(D-glucono-1,5-lactone}) = 22 μmol dm^?3). The optimal hydrolysis conditions are the same for both substrates (pH 4.5,55° C). The half-lives of thermal inactivation at 61° C are 27 and 10min for cellobiase and 4NPGase, respectively.     

Shock Tube Study of High-Temperature Reactions of Cyclopentadiene

The thermal decomposition of cyclopentadiene has been studied in the temperature range 1260–1530 K behind reflected shocks. The total pressure ranged from 1.5 to 2.3 bar. Resonance absorption was used to record the temporal concentration profiles of H atoms. This sensitive technique allowed the study of the reaction systems under favorable conditions by applying very low initial concentrations (0.5–8 ppm). For cyclopentadiene decomposition R1, C₅H₆ → C₅H₃-c + H, a rate expression of k₁ = 1.1 × 10¹⁵ exp(–38760/T) s⁻¹ was deduced. In a separate series of experiments the consumption by cyclopentadiene of H atoms, which had been generated by the thermal decay of ethyl iodide, was investigated. A preliminary value of k₂ = 1.4 × 10¹⁴ exp(–2739/T) cm³ mol⁻¹ s⁻¹ was deduced for the total rate of H-atom consumption by cyclopentadiene R2, C₅H₆ + H → products.     

Study of Aromatic Compounds Derived from Sugarcane Bagasse. Part I: Effect of pH

This work aims at increasing the knowledge about the recovery of aromatic compounds from the lignin fraction of sugarcane bagasse, as well as exploring the possibility to recover these fine chemicals of great concern for many industrial sectors. The major natural products contained in the lignin fraction of such a straw material were extracted in previous work by alkaline hydrolysis using different concentrations of NaOH and amounts of bagasse, and HPLC analyses revealed that the extracts mainly contained p‐coumaric acid, ferulic acid, syringic acid, and vanillin, the first three containing and the last lacking a carboxyl group. All these aromatic compounds have well‐known antioxidant power and are very important in pharmacology. For these reasons, they have been investigated in this study by UV spectrophotometry, with special concern to the pH effect on their spectra and determination of their pK_a values.     

Solvent extraction of hydrofluosilicic acid with alamine 336

Extraction constants for the solvent extraction of hydrofluosilicic acid with Alamine 336 have been determined. Two species were identified, (R₃NH⁺ )₂ SiF₆^2- and R₃NH⁺ HSiF₆, whose respective extraction constants were determined to be log K₂₁ = 7.42 and log K₁₁ = 2.60. For the dissociation of hydrofluosilicic acid the activity coefficient model presented by Bromley was adapted to sulphuric acid and the values used for hydrofluosilicic acid. The effect of the diluent was experimentally investigated.     

Why C1 = 16–17 in the WLF equation is physical-and the fragility of polymers

From the well-recognized equivalence of the Williams-Landel-Ferry (WLF) equation and the Vogel-Tammann-Fulcher (VTF) equation, τ = τ_o exp (B/[T - T_o]), we shall show that the parameter C₁ in the former is just the number of orders of magnitude between the relaxation time at the chosen reference temperature and the pre-exponent of the VTF equation. Thus C₁^g = log(τ_g/τ_o) (a relation which is not found in the present polymer literature), measures the gap between the two characteristic time scales of the polymer liquid, microscopic and α-relaxation, at the glass transition temperature. For systems which obey these two equations over wide temperature ranges, τ_o is consistent with a quasilattice vibration period in accord with theoretical derivations of the VTF equation and also with the microscopic process of mode coupling theory. Thus for such systems, C₁^g is obliged to have the value 16–17 (depending on how T_g is defined), while C₂^g scaled by T_g will reflect the non-Arrhenius character, i.e. fragility, of the system. In fact when C₁^g has the physical value of 16–17, then (1 − C₂^g/T_g), which varies between 0 and unity, conveniently gives the ‘fragility’ of the polymer within the ‘strong/fragile’ classification scheme. This is useful because it permits prediction from the WLF parameters of other properties such as physical ageing behaviour through the now-established correlation of fragility with other canonical characteristics of glassforming behaviour. Where the best fit C₁^g is not 17 ± 2, the corresponding best fit τ_o must be unphysical, and then the range of relaxation times for which the VTF or WLF equations are valid with a single parameter set will be limited, and the predictions of other properties based on that parameter set will be unreliable. © 1997 Elsevier Science Ltd.     

Fatty Acid Specificity of Candida cylindracea Lipase

Candida cylindracea lipase (SIGMA) was tested against triglycerides (TG) and wax esters (WE) of marine origin as substrates. Under the same conditions, wax esters were hydrolysed at a lower rate than the triglycerides. The C₁₄ to C₁₈ saturated and monounsaturated fatty acids were preferentially hydrolysed whereas the longer chain monoenes (20:1 and 22:1) and particularly the polyunsaturated fatty acids (18:4,20:5 and 22:6) were resistant to the hydrolysis in triglycerides as well as in wax esters. No specificity was demonstrated for the fatty alcohols in the wax esters.     

Some dynamic regression simulated equations for electrochemical doping processes of polypyrrole

Polypyrrole films in the oxidized state are positively charged, so the anions of sulphuric acid and p-toluensulphonic acid with a certain electrochemical activity were selected as dopants for the polypyrrole film. When the anions were electrochemically incorporated in commercial polypyrrole films at constant temperature (20° C) and constant voltage (3.0 V), the conductivities increased from 67 to 165 and 94 Scm^–1, respectively. Dynamic regression simulation of the electrochemistry of the doping process was performed. A new parameter, r, was introduced, and the dynamic equation dS _A/dC _t = f(S _A) for the electrochemical doping of the polypyrrole films with sulphuric acid and p-toluensulphonic acid was obtained.Author to whom correspondence should be addressed.     

Modelling the temperature dependence of kinematic viscosity for refined canola oil

Viscosities of refined, bleached, deodorized (RBD) and refined, bleached, winterized (RBW) canola oils were measured at temperatures from 4 to 100°C. The viscosities of these refined canola oils were exponentially related to the oil temperature. Viscosity of the RBW oil was slightly greater than that of the RBD oil when the temperature was below 15°C. Compared to refined soybean oil, the canola oils were substantially more viscous. The viscosity of canola oil was modelled asv = exp(C₀ + C₁T + C₂T²). The maximum predicted error was less than 1.6% over the tested temperature range.     

Study on Volumetric Oxygen Transfer Coefficient of the Simulated Plant Cell Two‐Phase Culture System

The effects of the volumetric percentage of simulated plant cells, organic solvents, agitation speeds and aeration rates on the volumetric oxygen transfer coefficient, K_La, were studied in the simulated plant cell two‐phase culture system. The experimental results showed that K_La increased as the volumetric percentage of organic solvents, H, increased, but this effect became less significant at high values of H. When the volumetric percentage of simulated plant cells, E, was higher than 30%, the effects of H on K_La became less appreciable. In comparison with a one‐phase culture system, K_La was higher in the two‐phase culture system and can be regulated more easily to suit the cell growth and the production of secondary metabolites. Combining with the rheological properties of the system, it was found that the effects of E on K_La were very similar to that of E on the flow behavior index, n, in the system. An experiential correlation of K_La of the system (with oleic acid as organic solvent) was obtained as K_La = 0.21N^0.91Q^0.90exp(4.1H–4.3E) (herein N is the stirring speed and Q, the aeration rate), which may be useful for the design of the two‐phase culture system.     

Rheological study of the isothermal reticulation of an epoxy resin

The complex modulus of shearing G* = G' + jG″ was measured during the isothermal hardening of several epoxy resins. The gelation induces a slowing down of the rate of growth of viscous modulus ν″ = d(log G″)/dt between two zones where this rate is constant. This slowing down of growth rate varies with the temperature and is null for T = T_{C gel}: ν″₂ ?ν″₁ = K(1/T_{C gel} ?1/T). We have shown that the two phenomena of gelation and vitrification stay perfectly distinct at all temperatures and in particular at T_{C gel}. So the decrease of the rate ν″ associated with gelation disappears at this temperature without the vitrification being responsible.     

Salt‐Induced Modulation of the Krafft Temperature and Critical Micelle Concentration of Benzyldimethylhexadecylammonium Chloride

In this work, the effect of some sodium salts on the Krafft temperature (T_K) and critical micelle concentration (CMC) of benzyldimethylhexadecylammonium chloride (C16Cl) in aqueous solution has been studied. It was observed that the T_K can be modulated to lower and higher values and the CMC can be depressed significantly upon the addition of the electrolytes. More chaotropic Br^? and I^? raise the T_K with an increase of the concentration of the ions. On the other hand, less chaotropic NO₃^? initially lowers and then raises the T_K. Kosmotropic F^?, SO₄^2? and CO₃^2? gradually lower the T_K with increasing concentration of the electrolytes. The more chaotropic ions form contact ion pairs with the surfactant and decrease the solubility with a consequent increase in the T_K. On the other hand, kosmotropic ions, being extensively hydrated in the bulk, remain separated from the surfactant by hydrated layers of water molecules. As a result, a significant electrostatic repulsion exists between the charged headgroups of the surfactant, resulting in a decrease in the T_K. The CMC of the surfactant decreases significantly in the presence of these ions. The surface tension at the CMC (γ_CMC) also decreases in the presence of all the salts except for F^?. The electrostatic repulsion between the charged headgroups is significantly reduced because of screening of the surface charge of both micelles and adsorbed monolayers by the associated counterions, resulting in a decrease in both the CMC and γ_CMC.     

Studies on viscosity build‐up properties of sodium alcohol ether sulphates

Narrow and broad range distributed ethoxylates of linear C₁₂–C₁₄ alcohols were synthesised using a calcium‐based unconventional catalyst and NaOH, respectively. Their composition was determined by gas chromatography. Sulphates were synthesised in the traditional way by reaction of ethoxylates with sulphur trioxide in a film reactor and neutralised with sodium hydroxide. Products were characterized by the ethoxylate homologue distributions and acid value of the intermediate sulphuric acid derivatives. Viscosity build‐up properties of the narrow and broad range distributed ethoxylates‐based sodium alcohol ether sulphates were studied. Effects of ethoxylate homologue distribution were compared with those of average ethoxylation grade and sulphation degree. It was shown that the acid number of the obtained sulphates, ethoxylate homologue distribution, average polyaddition degree and sodium chloride content influenced remarkably the thickening ability of ethoxylates. Furthermore, it was found that the limited content of the longer ethoxylate chains in narrow range distributed alcohol ethoxylates is responsible for enhanced viscosity build‐up properties of their sodium sulphate derivatives. The following empirical relationship was obtained: log η = (2.99 ± 1.25) + (3.78 ± 0.86) × 10⁻²V − (1.48± 0.15)N_av − (2.69 ± 0.7) × 10⁻²A_N + (0303 ± 0.058) × C_surf + (0.832 ± 0.041) × C_NaCl where η is the viscosity in cP, V is the distribution coefficient, N_av is the average oxyethylation degree, A_N is the acid number of alcohol ether sulphuric acid and C_surf and C_NaCl are concentrations (wt%) of the studied surfactants and sodium chloride, respectively. © 1999 Society of Chemical Industry     

A Shock Tube Study of the Reactions of H Atoms with COS,CS2, and H2S

Reactions of H atoms with COS, CS₂, and H₂S were studied behind reflected shock waves at temperatures between 1170 K and 1830 K and pressures around 1.0 bar by applying atomic resonance absorption spectroscopy (ARAS) for time-resolved measurements of H atoms at L_α. The thermal decomposition of a few ppm ethyl iodide (C₂H₅I) was used as a H-atom source. In the presence of a large excess of the molecular reactant COS, CS₂, or H₂S, a consumption of H was observed which follows a pseudo first-order rate law. Rate coefficients for the reactions: were determined to be: k₁ = 2.4 × 10¹⁴exp(–3415 K/T) cm³mol⁻¹s⁻¹ k₂ = 1.4 × 10¹⁵exp(–9250 K/T) cm³mol⁻¹s⁻¹ k₃ = 2.5 × 10¹⁴exp(–2890 K/T) cm³mol⁻¹s⁻¹     

Fiber spinnability of glass melts

Fiber spinnability is the ability of a glass-forming melt to be steadily stretched and spun into defect-free fiber filaments. However, its quantification has not been well established owing to many controlling factors such as melt fragility, melt strength, surface tension, liquidus temperature, liquidus viscosity, and crystallization. To understand and quantify the fiber spinnability of a glass melt, we consider two key aspects: fiberizing viscosity window and melt stability. The fiberizing viscosity window is defined by the upper and lower viscosity limits. Fibers rupture above the upper viscosity limit, whereas a stable melt stream cannot form below the lower limit (η_low). We introduce a simple parameter to quantify fiber spinnability, namely, K_fib=η_L/η_low, where η_L is the viscosity at liquidus temperature (T_L). A fiber can only form if K_fib>1. To quantify melt stability we propose the parameter of S=(T_L-T_C)/(T_L-T_g), where T_L and T_C are the liquidus temperature, and the onset temperature of melt crystallization during cooling, respectively. Both parameters (K_fib and S) are important for a rational design of glass fiber compositions, and fiberizing process. We use two basalt melts as examples of this study to demonstrate the high sensitivity of fiber spinnability to a minor variation in chemical composition of melts.     

The anodic dissolution of lead in oxygenated and deoxygenated sulphuric acid solutions

Steady-state and impedance measurements were carried out in oxygenated and deoxygenated sulphuric acid solutions to investigate the effects of dissolved oxygen. Impedance measurements in deoxygenated sulphuric acid were used to determine values ofC _o.