Dilute Aqueous Alkali Research Articles

Pure Hydrolyzable Cellulose from Rice Straw, Wheat Straw and Sugarcane Bagasse by a Simple Scalable Two-Step Treatment

Utilization of amply available lignocellulosic biomass for a cost-effective conversion to renewable chemicals has proven more difficult than anticipated. Sustainable and viable fractionation of any biomass to its individual monomeric components for their further conversion to products at commercial scale therefore remains elusive. A rapid and scalable multi-step pretreatment strategy for fractionation of rice straw using a combination of dilute aqueous acid and aqueous alkali treatment steps under subcritical conditions was investigated. The process steps and parameters were optimized for yield and purity of the resulting biomass components. Effects of acid and alkali concentrations on the fractionation efficiency were studied in the range of 0.2% to 12% w/v at temperatures ranging from 110°C to 200°C for time spanning from 15 to 30 min. The simple optimum sequence of operations and conditions was found to be a diluteacid hydrolysis step at 130°C for 15 min with 2% HNO3 followed by the second treatment step at 130°C for 15 min with 2% NaOH. This combination gave 90% pure cellulose in more than 80% overall yield. Formation of furfurals in the hydrolysate was prevented significantly, and the cellulose obtained showed good amenability for enzymatic hydrolysis to sugars. The same process was applied to wheat straw and sugarcane bagasse, and the obtained results were found to be similar to those obtained for rice straw. The process was successfully scaled up to 50 L batch process with negligible deviations from smaller scale run results.

Preparation and characterization of cross‐linked polymeric nanoparticles for enhanced oil recovery applications

AbstractChemically cross‐linked nanoparticles from dilute aqueous alkali solutions of hydroxyethylcellulose (HEC) in the presence of a cross‐linker agent (divinyl sulfone, DVS) were prepared from a reaction mixture, which was exposed to different stirring speeds during the cross‐linking process. At various stages during the cross‐linking procedure, the reaction was terminated and the species were characterized by means of turbidimetry, asymmetric flow field‐flow fractionation (AFFFF), dynamic light scattering (DLS), and rheo‐small‐angle light scattering (rheo‐SALS) methods. During the cross‐linking of a dilute polymer solution, the competition between intrapolymer and interpolymer is a prominent feature. The DLS results show that at early times in the cross‐linking process, intrachain cross‐linking with contraction of the complexes is promoted by high stirring speeds; at later times the growth of aggregates is inhibited by high stirring speeds. The results from the rheo‐SALS measurements disclosed that at early times during the cross‐linker reaction, the complexes are fragile against shear forces if the reaction mixture had been subjected to low stirring speeds. At a later state of cross‐linking, more cross‐links lead to better stability of the species, even for solutions that have been exposed to low stirring speeds during the cross‐linking process. This study shows that the sizes of the particles can be tuned by exposing the solutions to different stirring speeds during the cross‐linker reaction and to terminate the reaction at desired reaction times. The strategy discussed in this work for the preparation of particles of various sizes is of special interest in connection with enhanced oil recovery applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Intramolecular and Intermolecular Association during Chemical Cross-Linking of Dilute Solutions of Different Polysaccharides under the Influence of Shear Flow

Effects of shear flow on intramolecular and intermolecular associations of dilute aqueous alkali solutions of dextran, hydroxyethylcellulose (HEC), and a hydrophobically modified analogue (HM-HEC) in the presence of a chemical cross-linker agent were characterized with the aid of viscometry and rheo-small-angle light scattering (rheo-SALS) methods. The picture that emerges at short times in the course of cross-linking of the polymer solutions under the influence of a constant shear rate is that HEC coils contract because of intramolecular cross-linking, whereas the HM-HEC species show an incipient association and the dextran molecules are unaffected. At longer times, interchain cross-linking of the polymers promoted the growth of large flocs, which were disrupted by shear forces when they were sufficiently large. These findings are novel, and both the building up of aggregates and disaggregation are well substantiated by the SALS results.

Physical, thermal, dielectric and chemical properties of a hyperbranched polyether and its linear analog

The hyperbranched and the linear polyethers were prepared by one-pot nucleophilic displacement polymerization technique using cyanuric chloride and aromatic diol as reported earlier. The physical, thermal, dielectric and chemical properties of the hyperbranched polyether and its linear analog have been studied. The amorphous character of both the polyethers was observed in XRD study. The solubility studies showed that the hyperbranched polyether has relatively higher solubility in different solvents compared to its linear analog. The thermal properties of both polymers have been studied by thermogravimetric (TG) and differential scanning calorimetric (DSC) analyses. The chemical resistance tests indicated that both polyethers are very good chemical resistances except in dilute aqueous alkali solution. The dielectric properties such as dielectric constant and loss factor for both polyethers have also been studied with respect to changes of frequency (50–500 kHz) and temperature (303–343 K).

Effect of Shear on Intramolecular and Intermolecular Association during Cross-Linking of Hydroxyethylcellulose in Dilute Aqueous Solutions

Intramolecular and intermolecular associations of dilute aqueous alkali solutions of hydroxyethylcellulose (HEC) in the presence of a chemical cross-linker agent (divinyl sulfone, DVS) are studied with the aid of dynamic light scattering (DLS) and rheological methods. At quiescent state, DLS detected only interchain aggregation of HEC during the cross-linker reaction, and the magnitude and start of this effect depend on the cross-linker concentration. The growth of clusters has been investigated at various stages in the course of the cross-linking process by quenching the reaction mixture to a lower pH. After quenching, no further association of the species occurred. When the dilute reaction mixtures are subjected to shear, intrapolymer cross-linking with contraction of the molecules is observed, and at moderate shear rates this effect is followed by interpolymer cross-linking and the formation of aggregates at longer times. The rate of the growth of the multichain aggregates decreases with increasing shear rate, and at sufficiently high shear rates no cross-linking effect is observed. Depending on the shear rate, the aggregates continue to grow until they reach a certain size where an incipient breakup of interaggregate chains can be observed. The delicate interplay between intramolecular and intermolecular association effects is governed by factors such as the magnitude of the shear rate, polymer concentration, and cross-linker density.

Regioselectivity of alkylation of cyclomaltoheptaose (β-cyclodextrin) and synthesis of its mono-2- O-methyl, -ethyl, -allyl, and -propyl derivatives

Mono-2- O-methyl-, -2- O-ethyl-, and -2- O-allyl-cyclomaltoheptaose were prepared by alkylations of cyclomaltoheptaose in dilute aqueous alkali, and mono-2- O-propylcyclomaltoheptaose was obtained by hydrogenation of the allyl derivative. All the 2- O-alkyl derivatives were less soluble in water than was cyclomaltoheptaose. All formed inclusion complexes with toluene in aqueous solution, but only the methyl ether was less soluble in the water-toluene system than in water. The solubilities of the other ethers in water were enhanced by the addition of toluene. Partial methylation of cyclomaltoheptaose with 13C-enriched dimethyl sulfate in dilute aqueous alkali yielded mixtures of products. The substitution patterns were analyzed by GLC-MS of the alditol acetates, prepared by hydrolysis, reduction, and acetylation, and by 13C NMR after complete permethylation with nonenriched reagent. The results showed that methylation at O-2 is a predominant but not an exclusive reaction; as expected, the regioselectivity decreases with increasing degree of methylation.

Tandem Microscopic-Electrochemical Examination of A Charge-Induced Surface Phase Sequence: Ordered Au(110) in Aqueous Iodide Electrolytes As Probed by Potentiodynamic Scanning Tunneling Microscopy

Abstract : Atomic-level structural and dynamical aspects of the electrode potential-induced sequence of surface phases on ordered Au(110) in dilute aqueous alkali iodide electrolytes have been explored by scanning tunneling microscopy (STM) coupled with cyclic voltammetry. This system exhibits a potentially rich series of electro-induced phase transitions triggered primarily by increasing iodide adsorption towards more positive potentials, together with alkali cation coadsorption. Exploration of the real-space phase-transition dynamics, in particular, is facilitated by means of 'potentiodynamic' STM image sequences obtained during potential steps or especially voltammetric sweeps, thereby providing a direct link to conventional (macroscopic) electrochemical phenomena. At the most negative potentials, beyond ca -0.7 V vs SCE, Au(110) forms a largely uniform (1 x 3) phase. The microscopic steps associated with the formation and iodide adsorbate-induced removal of this reconstruction were examined by potentiodynamic STM. In cesium iodide electrolyte, 'one-missing-row' (1 x 3) and (1 x 2) regions are seen to be formed by periodic row displacement en route to the final 'three-missing-row' (1 x 3) phase.

Sensitivity of Electrochemical Adlayer Structure to the Metal Crystallographic Orientation: Potential-Dependent Iodide Adsorption on Au(100) in Comparison with Other Low-Index Surfaces

Abstract : The potential-dependent ordered atomic structures formed for iodide adsorption on Au(100) from dilute aqueous alkali iodide electrolytes as discerned by means of in-situ scanning tunneling microscopy (STM) are reported and compared to the corresponding behavior of the other two low-index faces, Au(111) and (110) . As in related studies, emphasis is placed on linking the microscopic structural information to the voltammetric and other macroscopic electrochemical response, including the use of 'potentiodynamic' STM tactics where real-space images are acquired during appropriate electrode potential steps or sweeps. While relatively low iodide coverages, theta sub I approx. 0.1, are sufficient to lift the hexagonal Au(100) reconstruction, yielding large ordered (1 x 1) domains by ca-0.6 V vs SCE, ordered iodide adlayers are formed only above -0.2 V. A compressible incommensurate (2 sq rt 2 x p sq rt 2) phase (theta sub I, approx. 0.46 - 0.49) is observed between ca -0.2 and 0 V, which reverts to a distinct (2 sq rt of 2 x sq rt of 2)R45 deg structure (theta sub I approx. 0. 5) featuring uniform binding in twofold bridging sites. Interestingly, while the latter structure is retained locally at higher potentials, it is interspersed with narrow (3-4 atom wide) strips having a rotated hexagonal pattern. The latter becomes increasingly dense, and eventually dominant, towards higher potentials. This microscopically nonuniform (or spatially modulated ) phase is noteworthy as well as unusual; the corresponding iodine phases on Au(111) and (110) display, as is common, structural uniformity at a given potential.

Some Characteristic Features of Dilute Aqueous Alkali Solutions of Specific Alkali Concentration (2.5 mol l−1) Which Possess Maximum Solubility Power against Cellulose

Some Characteristic Features of Dilute Aqueous Alkali Solutions of Specific Alkali Concentration (2.5 mol l −1 ) Which Possess Maximum Solubility Power against Cellulose

Thermal diffusion of alkali bromides

The molar entropies (or heats) of transport of dilute aqueous alkali bromide solutions have been measured by the potentiometric method using the silver, silver bromide thermocell at a mean temperature of 25°C and over a concentration range of 5×10−4 to 0.1M. Experimental results were extrapolated to infinite dilution to obtain the standard molar entropies of transport. The limiting behavior observed is compared with theory based on the electrostatic model.

Interaction of proteins with sorghum tannin: Mechanism, specificity and significance

AbstractThe grain of some varieties of sorghum contains 2% or more condensed tannin; many other varieties contain no tannin at all. Agronomic advantages, e.g., resistance to bird depredation, are associated with high‐tannin sorghums, which have relatively low nutritional value for nonruminants. The biological effects of tannin are a result of its propensity for binding proteins; both hydrogen bonding and hydrophobic interactions are involved. Sorghum tannins can bind dietary proteins and reduce their digestibility. Purified digestive enzymes are inhibited by tannin, but significant inhibition in vivo is unlikely. Proteins differ greatly in their affinity for tannin. Those with highest affinity are large, have an open structure, contain no bound carbohydrate and are rich in proline. Sorghum proteins of the alcohol‐soluble prolamine fraction associate strongly with tannin, are difficult to remove during tannin purification and are found combined with tannin in the indigestible residue after in vitro digestion with pepsin. On germination, the seed may sacrifice a portion of these proteins to bind the tannin that might otherwise interfere with metabolism by inhibiting seed enzymes. During seed development, tannin molecules are relatively short and do not effectively precipitate proteins; as the seed dries, tannins undergo polymerization to an average of ca. 6 flavan‐3‐ol units/molecule. The antinutritional effects of sorghum tannins can be eliminated by soaking the grain in dilute aqueous alkali, but not by cooking. When rats are put on high‐tannin sorghum diets, their parotid glands undergo hypertrophy and produce a group of unique salivary proteins with extremely high affinity for tannin. These proteins contain over 40% proline and are devoid of sulfur‐containing and aromatic amino acids. This metabolic adaption may protect rats against tannin by binding and inactivating it immediately when it enters the digestive tract.

The Effect Of Oxygen Functions On The Properties Of Bitumen Fractions

Abstract Various in-situ methods of recovery have been proposed for the Athabasca bitumen which rely on the reaction of the bitumen with an oxygen-containing gas, but the properties of the products are usually ill-defined or, at best; largely speculative. Therefore, methods of introducing oxygen functions into the bitumen have been investigated. Comparisons of the product properties with those of the untreated bitumen are described in order to study the effects of these functions and to evaluate their performance during in-situ recovery. Introduction Current methods of bitumen recovery from the Athabasca oil sands are centred around a mining process whereby mined oil sand is conveyed to the plant and bitumen is recovered by hot-water washing, with the bitumen thermally upgraded to a "synthetic" crude oil(1). The mining method is, of course, subject to the limitation of easy access to the deposit through the overburden and as only about 10 per cent of the deposit lies within the economical limit of 150 feet from the surface(1), it is conceivable that, in the foreseeable future, bitumen recovery by in-situ techniques will become a reality. Thus, it is not surprising that a variety of methods have been proposed, and investigated, for the in-situ recovery of the Bitumen(2). Recognition that the bitumen in the oil sands is too -viscous to flow at reservoir conditions(1) has resulted/in the development of methods that are not usually employed as conventional secondary oil recovery techniques for example, the bitumen is quite mobile at temperatures above 30 °C (formation temperature – 4 °C) and successful application of a combination of forward combustion followed by water flooding (COFCAW) to bitumen recovery has been recorded(3). Other methods involve flooding the formation with aqueous solutions(3) and one method in particular, which involves fracturing the formation between two spaced wells add flushing the bitumen out of the formation using steam and dilute aqueous alkali, was recognized as having the disadvantage that recovered materials periodically plug the formation adjacent to the production well(4). Following from this, an in-situ method has been proposed which requires: initial contact of the bitumen in the formation with an oxidizing gas and subsequent treatment with alkaline solutions of sulphites and/or bisulphites(2). The resulting water-soluble bituminous derivatives were successfully applied to the removal of part of the bitumen from packed columns of oil sand(2). The course of the reaction of the bitumen with an oxygen-containing gas is extremely complex(5,8), but there are indications(9,10) that, in addition to the formation of higher-molecular-weight material by condensation esters, other oxygen functions, such as carbonyl, carboxylic and hydroxyl groups, are formed in the bitumen. The major introduction of oxygen functions occurs in the higher molecular-weight fractions(9–11) and it therefore seemed worthwhile to study the effects of these particular oxygen functions on the properties of the asphaltenes. Methods of introducing oxygen functions into bitumens, without severe oxidative degradation, are limited and subject to uncertainty and speculation(12,13). However, coals and humic acids react with diazonium salt(14,15), although, in contrast, asphaltenes have been reported to be inert towards diazonium salts(14,15) .

Kinetics and mechanism of di-n-butylphosphoric acid transfer between toluene and aqueous phases

The rate of inter-phase distribution of di-n-butylphosphoric acid (HDBP) between toluene and dilute aqueous acid or alkali has been studied, using a quiescent interface, stirred mass-transfer cell. The initial rate of organic to aqueous (o → a) partition is first order with respect to total initial organic phase HDBP concentration; the order with respect to initial aqueous phase hydrogen ion activity ({H+}a, i) changes from zero at low {H+}a, i to –1.0 at high {H+}a, i. A mechanism is proposed in which the rate controlling process is diffusion of the singly ionized HDBP dimer (HD–2) from the interface into the aqueous phase; consistency with initial rate laws is demonstrated and information is obtained on the state of interfacially adsorbed HDBP species. In the absence of mineral acid the initial aqueous to organic (a → o) transfer rate is third order with respect to total initial aqueous phase HDBP concentration (Ca, i). Variation of {H+}a, i at constant Ca i showed the order with respect to {H+}a, i to be 1.0. A mechanism, consistent with experiment, is proposed in which the interfacial formation of (HD–2) is the rate-controlling process.Initial rate data are used for the first time in liquid-liquid extraction to predict successfully equilibrium distribution ratios. The correlation shows that transfer mechanisms remain the same under equilibrium and non-equilibrium conditions. A treatment was developed for derivation of “absolute” extraction rates and it is shown that under certain conditions during net o → a transfer, the mechanism of a → o transfer changes from the observed for initial rates.

Asymmetric degradation of DL-leucine with longitudinally polarised electrons.

FOLLOWING Wu's experimental demonstration1 of Lee and Yang's predicted violation of the parity principle during β decay2 and following Goldhaber's demonstration3 of the circular polarisation of the bremsstrahlung produced by β-decay electrons, Vester and coworkers (ref. 4 and F. Vester, unpublished) proposed the following unique mechanism for the abiotic origin of optically active organic molecules Attempts to demonstrate this mechanism experimentally4,5 were unsuccessful, however, until Garay's report in 1968 that D-tyrosine in dilute aqueous alkali was more decomposed (as evidenced by greater eradication of its ultraviolet absorption bands) than was L-tyrosine after 18 months exposure to 0.36 mCi of 90SrCl2 in solution6. One of us has attempted7 to repeat Garay's experiment using DL-tyrosine in alkaline solution, looking for optical rotation after exposing the sample to a dose of 4.1 × 108 rad of β-ray bremsstrahlung in a 61,7000-Ci 90Sr–90Y source at Oak Ridge National Laboratory for 1.34 yr. No optical activity was noted, using optical rotary dispersion (ORD) measurements in the region 250–630 nm. At the same time7 Garay's experiments were extended to include other racemic amino acids, both in the solid state and in neutral, acidic or alkaline solution. In no case, after the same 1.34-yr exposure, did we notice the development of optical activity either by ORD measurements or (in the case of DL-leucine) by the gas-chromatographic determination of the enantiomeric composition of the irradiated samples. Our explanation7 for these negative results has been that most of the bremsstrahlung causing radiolysis of the samples was of low energy8 and therefore of very slight circular polarisation3,9. In the hope of overcoming this difficulty, we have now undertaken similar experiments using longitudinally polarised electrons (and their bremsstrahlung) from a linear accelerator.

The polarographic reduction of perbromate and its use as a probe of double layer structure

o 1. The reduction of perbromate has been studied in dilute (1, 10 and 100 m M ) aqueous alkali halide solutions, in which they exhibit a polarographic minimum and an associated negative faradaic admittance. 2. In electrolytes which exhibit only weak specific ion adsorption ( e.g. , 0.1 M NaF), the perbromate reduction is characterized by a low and apparently potential-dependent transfer coefficient. 3. The marked effects of the adsorbable ions Cl − , Br − and I − can be accounted for quantitatively by the Frumkin correction, using classical double layer theory and assuming that the intrinsic perbromate reduction rate is not affected by specific halide adsorption. 4. The 1 m M electrolyte solutions, the charge density due to specifically adsorbed Cl − and F − almost equals the electronic charge density, but the double layer potentials do not vanish. 5. Specific advantages of the use of anions as quantitative probes of double layer structure have been outlined.

Determination of Ammonia In Dilute Aqueous Alkali and In a Nitrogen-Ethylene Environment By Gas Chromatography

The methods described in this paper were developed to allow fast and accurate analysis of ammonia in aqueous solution and also the co-determination of ethylene and ammonia in a nitrogen atmosphere. Resuits are presented to compare the accuracy of these methods with that of the classical Kjeldahl distillation technique.

Synthesis of long chaina,B‐alkynoic anda,B‐alkynoic acids viaB‐keto esters

AbstractA general method for the synthesis of long chain α,β‐alkynoic acids from β‐keto esters is described. The synthesis involves conversion of the β‐keto ester to the corresponding pyrazolone, then halogenation and treatment of the resultant 4,4‐dihalo product with dilute aqueous alkali to form the α,β‐alkynoic acids. Specifically, 2‐octynoic, 2‐nonynoic and 2‐decadecynoic acids were prepared as representative examples. If the β‐keto ester has an alkyl group at the α‐position, the final product is a mixture ofcis andtrans α‐substituted‐α,β‐unsaturated alkenoic acids, which may be separated by gas‐liquid chromatography. Pertinent IR and proton magnetic resonance data are used in characterizing the stereochemistry of products and a possible mechanism for the product forming reactions is presented.

The glucan components of the cell wall of baker's yeast (Saccharomyces cerevisiae) considered in relation to its ultrastructure.

1. Commercial pressed baker's yeast, and cell walls prepared from it, were extracted in various ways and the products examined by a number of techniques, including infrared spectroscopy and electron microscopy. 2. The glucan components of the walls cannot be extracted from intact yeast cells by 3% (w/v) sodium hydroxide at 75 degrees , but at least one-third of the glucan of cell wall preparations is dissolved under these conditions, and more will dissolve after ultrasonic treatment. 3. If intact cells are given a preliminary treatment with acid the wall glucans dissolve in dilute aqueous alkali. 4. Acid conditions as mild as sodium acetate buffer, pH5.0, for 3hr. at 75 degrees are sufficient for this preliminary treatment; the glucan then dissolves in 3% sodium hydroxide at 75 degrees leaving a very small residue, which contains chitin and about 1% of the initial glucan of the wall. Dissolution is hindered by exclusion of air, or by a preliminary reduction with sodium borohydride, suggesting that some degradation of the glucan by alkali is taking place. 5. After treatment with 0.5m-acetic acid for 24hr. at 90 degrees the glucan dissolves slowly at room temperature in 3% sodium hydroxide, or in dimethyl sulphoxide. The extraction with acetic acid removes glycogen and a predominantly beta-(1-->6)-linked glucan (not hitherto recognized as a component of baker's yeast), but none of the beta-(1-->3)-glucan, which remains water-insoluble. 6. Without treatment with acid, the glucan is not significantly soluble in dimethyl sulphoxide, but can be induced to dissolve by ultrasonic treatment. 7. These results are interpreted by postulating the presence of an enclosing membrane, composed of chitin and glucan, that when intact acts as a semipermeable membrane preventing the escape of the alkali- and dimethyl sulphoxide-soluble fraction of the glucan. Mild acid treatments damage this membrane, and ultrasonic and ballistic disintegration disrupt it. 8. Some support for this hypothesis is given by the effects of certain enzyme preparations, which have been found to render a substantial part of the glucan extractable by dimethyl sulphoxide.

Reactions of nitro sugars. VII. A study on acetylation and some chemical properties of acetates

The 2,4,6-tri-O-acetates of methyl 3-deoxy-3-nitro-β-D-glucopyranoside, -galactopyranoside, and-mannopyranoside, the 2-O-acetates of the 4,6-O-benzylidene derivatives of the two first-mentioned glycosides, and the tetra-O-acetate of 1,4-dideoxy-1,4-dinitro-neo-inositol are prepared by boron trifluoride–catalyzed acetylation. The advantages of the procedure over acetylation in pyridine are pointed out. The gluco triacetate, when produced in the presence of pyridine, is accompanied by crystalline by-products of a novel nature. It suffers undetermined changes by the action of activated alumina, and in dilute aqueous alkali it is instantly converted into an unsaturated nitronate.

Chemical modification of cotton with chloroacetamide

AbstractChemically modified cellulosic textile materials have been prepared by treatment of cotton with chloroacetamide in the presence of strong alkali by a variety of techniques. Ether groups bearing carboxyl and amide functions were attached to the cellulose. The effects of process variables on the chemical and physical properties of the products are discussed. These variables include time and temperature of reaction, concentration of reactants, choice of solvent, and method of application. Nucleophilic reaction of cellulose with chloroacetamide introduces carbamoylmethyl ether groups along the polymer chain. In the alkaline reaction media employed the hydrolysis of these substituents proceeds with loss of ammonia, yielding carboxymethyl ether groups. The amount and ratio of the carboxymethyl and carbamoylmethyl substituents introduced can be altered by varying the reaction conditions. In general, low temperature and a high ratio of chloroacetamide to alkali in the reaction medium favor carbamoylmethylation, whereas at higher temperatures the overall reaction kinetics favor amide hydrolysis, and carboxymethylation predominates. Chloroacetamide is an excellent carboxymethylating agent for cellulose; in some instances greater carboxymethyl substitution was achieved with this agent than with chloroacetic acid. Degrees of substitution can be attained that render the cotton soluble in dilute aqueous alkali. However, the original fibrous nature of the cotton was retained even in products with relatively high degrees of substitution.