Optimal conditions for alkaline detoxification of dilute-acid lignocellulose hydrolysates

Alkaline detoxification strongly improves the fermentability of dilute-acid hydrolysates in the production of bioethanol from lignocellulose with Saccharomyces cerevisiae. New experiments were performed with NH₄OH and NaOH to define optimal conditions for detoxification and make a comparison with Ca(OH)₂ treatment feasible. As too harsh conditions lead to sugar degradation, the detoxification treatments were evaluated through the balanced ethanol yield, which takes both the ethanol production and the loss of fermentable sugars into account. The optimization treatments were performed as factorial experiments with 3-h duration and varying pH and temperature. Optimal conditions were found roughly in an area around pH 9.0/60°C for NH₄OH treatment and in a narrow area stretching from pH 9.0/80°C to pH 12.0/30°C for NaOH treatment. By optimizing treatment with NH₄OH, NaOH, and Ca(OH)₂, it was possible to find conditions that resulted in a fermentability that was equal or better than that of a reference fermentation of a synthetic sugar solution without inhibitors, regardless of the type of alkali used. The considerable difference in the amount of precipitate generated after treatment with different types of alkali appears critical for industrial implementation.     

Viscosity of aqueous NH4Cl and tracer diffusion coefficients of ions,water and non-electrolytes in aqueous NH4Cl,KI, and MgCl2 at 25°C

Viscosities for aqueous NH₄Cl and tracer diffusion coefficients for²²Na⁺,³⁶Cl^–, HTO, and CH₃OH, acetone and dimethylformamide (all¹⁴C-labelled) in NH₄Cl supporting electrolyte are reported for 25°, together with tracer diffusion coefficients for²²Na⁺,³⁶Cl^–, and¹⁴CH₃OH in 1M KI, and for¹⁴CH₃OH in 1M MgCl₂. The diffusion coefficient of HTO in NH₄Cl solutions is slightly larger, for most of the concentration range investigated (0.05 to 4.5 M), than the value for pure water and is almost unaffected by the supporting electrolyte up to about 4M. Similar behavior is shown by CH₃OH, acetone and dimethylformamide in NH₄Cl solutions. Onsager limiting law behavior is approached by Cl^– at NH₄Cl concentrations in the 0.05–0.1M region but at much lower concentrations by Na⁺.     

Limits for alkaline detoxification of dilute-acid lignocellulose hydrolysates

In addition to fermentable sugars, dilute-acid hydrolysates of lignocellulose contain compounds that inhibit fermenting microorganisms, such as Saccharomyces cerevisiae. Previous results show that phenolic compounds and furan aldehydes, and to some extent aliphatic acids, act as inhibitors during fermentation of dilute-acid hydrolysates of spruce. Treatment of lignocellulose hydrolysates with alkali, usually in the form of overliming to pH 10.0, has been frequently employed as a detoxification method to improve fermentability. A spruce dilute-acid hydrolysate was treated with NaOH in a factorial design experiment, in which the pH was varied between 9.0 and 12.0, the temperature between 5 and 80°C, and the time between 1 and 7 h. Already at pH 9.0, >25% of the glucose was lost when the hydrolysate was treated at 80°C for 1 h. Among the monosaccharides, xylose was degraded faster under alkaline conditions than the hexoses (glucose, mannose, and galactose), which, in turn, were degraded faster than arabinose. The results suggest that alkali treatment of hydrolysates can be performed at temperatures below 30°C at any pH between 9.0 and 12.0 without problems with sugar degradation or formation of inhibiting aliphatic acids. Treatment with Ca(OH)₂ instead of NaOH resulted in more substantial degradation of sugars. Under the harsher conditions of the factorial design experiment, the concentrations of furfural and 5-hydroxymethylfurfural decreased while the total phenolic content increased. The latter phenomenon was tentatively attributed to fragmentation of soluble aromatic oligomers in the hydrolysate. Separate phenolic compounds were affected in different ways by the alkaline conditions with some compounds showing an increase in concentration while others decreased. In conclusion, the conditions used for detoxification with alkali should be carefully controlled to optimize the positive effects and minimize the degradation of fermentable sugars.     

Hydrolysis of magnesium hydride in the presence of ammonium salts

The influence of the nature of ammonium salts (NH₄Cl, (NH₄)₂SO₄, (NH₄)HSO₄, [(CH₃)NH₃]Cl) and their concentration in aqueous solutions on the hydrolysis of magnesium hydride has been studied. The highest degree and fastest rate of hydrolysis are observed at an ammonium salt concentration of ～7.5%. The most efficient activator among the ammonium salts under consideration is (NH₄)HSO₄.     

Dosage polarographique de quelques constituants du verre

A method is described for the determination of the following constituents of glass: Na and K together, Ca, Ba, Al, Pb and Zn.The analysis is carried out on a solution from the glass prepared by dissolving it in HF + HClO₄. The alkali metals are determined in the presence of N(CH₃)₄OH + H₃PO₄, and barium in the presence of N(CH₃)₄OH only. Calcium is separated as oxalate, transformed into chloride and determined in the presence of N(CH₃)₄OH. Aluminium is polarographed in a solution of pH3 in the presence of LiCl and dimethyl yellow. Zinc is determined in the presence of NH₄Cl, and lead in the presence of NH₄Cl and methyl red.The relative influence of each constituent element of the glass is discussed and it is shown that there is good agreement between the gravimetric and polarographic methods.     

Integration of Succinic Acid and Ethanol Production With Potential Application in a Corn or Barley Biorefinery

Production of succinic acid from glucose by Escherichia coli strain AFP184 was studied in a batch fermentor. The bases used for pH control included NaOH, KOH, NH₄OH, and Na₂CO₃. The yield of succinic acid without and with carbon dioxide supplied by an adjacent ethanol fermentor using either corn or barley as feedstock was examined. The carbon dioxide gas from the ethanol fermentor was sparged directly into the liquid media in the succinic acid fermentor without any pretreatment. Without the CO₂ supplement, the highest succinic acid yield was observed with Na₂CO₃, followed by NH₄OH, and lowest with the other two bases. When the CO₂ produced in the ethanol fermentation was sparged into the media in the succinic acid fermentor, no improvement of succinic acid yield was observed with Na₂CO₃. However, several-fold increases in succinic acid yield were observed with the other bases, with NH₄OH giving the highest yield increase. The yield of succinic acid with CO₂ supplement from the ethanol fermentor when NH₄OH was used for pH control was equal to that obtained when Na₂CO₃ was used, with or without CO₂ supplementation. The benefit of sparging CO₂ from ethanol fermentation on the yield of succinic acid demonstrated the feasibility of integration of succinic acid fermentation with ethanol fermentation in a biorefinery for production of fuels and industrial chemicals.     

Detoxification of Organosolv-Pretreated Pine Prehydrolysates with Anion Resin and Cysteine for Butanol Fermentation

Bioconversion of lignocellulose to biofuels suffers from the degradation compounds formed during pretreatment and acid hydrolysis. In order to achieve an efficient biomass to biofuel conversion, detoxification is often required before enzymatic hydrolysis and microbial fermentation. Prehydrolysates from ethanol organosolv-pretreated pine wood were used as substrates in butanol fermentation in this study. Six detoxification approaches were studied and compared, including overliming, anion exchange resin, nonionic resin, laccase, activated carbon, and cysteine. It was observed that detoxification by anion exchange resin was the most effective method. The final butanol yield after anion exchange resin treatment was comparable to the control group, but the fermentation was delayed for 72 h. The addition of Ca(OH)₂ was found to alleviate this delay and improve the fermentation efficiency. The combination of Ca(OH)₂ and anion exchange resin resulted in completion of fermentation within 72 h and acetone–butanol–ethanol (ABE) production of 11.11 g/L, corresponding to a yield of 0.21 g/g sugar. The cysteine detoxification also resulted in good detoxification performance, but promoted fermentation towards acid production (8.90 g/L). The effect of salt on ABE fermentation was assessed and the possible role of Ca(OH)₂ was to remove the salts in the prehydrolysates by precipitation.     

Determination of the optimum conditions for the synthesis of praseodymium(III) chloride

In the present work, we have synthesized praseodymium(III) chloride, PrCl₃, from the praseodymium oxide, Pr₆O₁₁, by dry method in the presence of ammonium chloride, NH₄Cl. This study includes the establishment of an assembly synthesis under inert gas. The thermal decomposing process of pure NH₄Cl was investigated by TG–DTG. The results showed that NH₄Cl begins to lose weight at 188 °C, large loss of weight ending at 302 °C when NH₄Cl is heated at the rate of 10 °C/min under N₂ atmosphere. For chlorination, NH₄Cl participates directly in the reaction, and HCl decomposed from NH₄Cl also contributes to the chlorination reaction. The influence of various synthesis parameters (temperature, contact time and chemical composition) on the reaction yield was studied, and the optimum conditions for synthesis were, thus, determined and discussed.     

Komplexone XLVI. EDTA-Komplexe des Pt(II)-Ions mit und ohne einzähnige Fremdliganden

The formation of complexes between Pt(II)EDTA^2? and H⁺, OH^?, Cl^?, Br^?, SCN^?, CN^? and NH₃ was investigated using pH and UV.-spectrophotometric measurements at ionic strength 1.0 and 25°. The existence of the following species could be proved (charges are omitted): H_pPt(EDTA) (0 ≤ p ≤ 3), Pt(EDTA)X (X = OH, NH₃, Cl, Br, I, SCN), H_pPt(EDTA)X (1 ≤ p ≤ 3; X = Cl, Br) and H₄Pt(EDTA)Cl₂. They have been characterised by spectral data as well as with equilibrium constants. The different modes of attachment of EDTA are discussed.     

Determination of237Np in environmental samples using inductively coupled plasma mass spectrometry

Ammonium uranates (AU) obtained by the addition of aqueous NH₄ OH to a solution of UO₂ (NO₃)₂ or the equilibrium reaction of UO₃ · 2H₂ O with the vapour over concentrated NH₄ OH have been studied by X-ray diffraction (XRD) analysis, diffuse reflectance Fourier transform infrared spectrometry (DR-FTIR) and chemical analysis. Ammonia can be present as either NH₃ or NH ₄ ⁺ . For precipitates obtained at a pH of 3.7, ammonia in the form of NH₃ is predominant. For ammonium uranate obtained by reaction over concentrated NH₄OH, most of the ammonia is bonded as NH ₄ ⁺ . The reaction mechanism and structures of the products are also discussed.     

Production of ethanol from sugar cane bagasse hemicellulose hydrolyzate byPichia stipitis

The ability ofPichia stipitis to fermentd-xylose andd-glucose in the acid-hydrolyzed hemicellulose component of sugar cane bagasse depends on the alkali used to neutralize the hydrolyzate to pH 6.5. With NH₄OH and NaOH no fermentation occurred, whereas neutralization with Ca(OH)₂ gave the best results (Q_pmax=0.25 g/L-h; Y_p/s =0.38 g/g sugar). However, the volumetric productivity was still considerably less than observed in a semisynthetic medium with a sugar composition similar to the hydrolyzate. L-arabinose was not fermented but assimilated. Sequential neutralization methods failed to improve the fermentation. Acetic acid and lignin derivatives present in the hydrolyzate were major components that inhibited the fermentation.     

Covalent amination of 3,6-dinitro-1,8-naphthyridines

The preparation of 3,6-dinitro-2-R-1,8-naphthyridines ( 1 , R = OH, NH₂, OC₂H₅, Cl) is described and their addition patterns with liquid ammonia are studied. Compound 1 (R = OH, NH₂) gives with liquid ammonia at - 45° as well as at room temperature formation of the covalent ó-adduct 4-amino-1,4-dihydro-3,6-dinitro-2-R-1,8-naphthyridine ( 2 , R = OH, NH₂). Compound 1 (R = OC₂H₅) yields with ammonia at - 45° two σ-adducts, i.e. the C-4 adduct ( 2 , R = OC₂H₅) and the C-5 adduct 5-amino-5,8-dihydro-3,6-dinitro-2-R-1,8-naphthyridine ( 3 , R = OC₂H₅). The ratio is about 50:50. This ratio depends on the temperature; at room temperature the C-5 adduct is more favoured. After staying overnight the ethoxy group has been exchanged for the amino group, yielding 2 (R = NH₂). With 1 (R = Cl) both adducts 2 (R = CI) and 3 (R = CI) were formed, the C-4 adduct 2 (R = CI) is more favoured at room temperature. Prolonged treatment with liquid ammonia leads to an exchange of the chloro atom by the amino group, yielding 2 (R = NH₂).     

Die Tieftemperatur-Synthese von Oxidhalogeniden,YOX (X = Cl,Br, I), als Quelle der Verunreinigung von Yttriumtrihalogeniden,YX3, bei der Gewinnung nach der Ammoniumhalogenid-Methode. Die Analogie von YOCl und YSCl

Low-Temperature Synthesis of Oxyhalides, YOX (X = Cl, Br, I), as the Source of Impurity in the Preparation of Trihalides, YX₃, via the Ammonium Halide Route. Analogy of YOCl and YSCl Ammonium halides, NH₄X (X = Cl, Br, I), react with Y₂O₃ and Y₂S₃, respectively, at temperatures as low as 230=C (X = Cl), 280=C (Br), and 360=C (I) (molar ratio 12:1) to yield (NH₄)₃YX₆, NH₃, and H₂O (H₂S). The choice of smaller ratios than 12:1 (for example 2:1) results in the formation of oxyhalides, YOX, via the reaction of (NH₄)₃YX₆ with surplus Y₂O₃. This reaction is therefore the actual source of impurity of rare-earth trihalides in their preparation via the ammonium halide routes.     

Kinetics and mechanism of the iodine oxidation of hydroxylamine

Studies of the stoichiometry and kinetics of the reaction between hydroxylamine and iodine, previously studied in media below pH 3, have been extended to pH 5.5. The stoichiometry over the pH range 3.4–5.5 is 2NH₂OH + 2I₂ = N₂O + 4I^? + H₂O + 4H⁺. Since the reaction is first-order in [I₂] + [I₃^?], the specific rate law, k₀, is k₀ = (k₁ + k₂/[H⁺]) {[NH₃OH⁺]₀/(1 + K_p[H⁺])} {1/(1 + K_I[I^?])}, where [NH₃OH⁺]₀ is total initial hydroxylamine concentration, and k₁, k₂, K_p, and K_I are (6.5 ± 0.6) × 10⁵ M^?1 s^?1, (5.0 ± 0.5) s^?1, 1 × 10⁶ M^?1, and 725 M^?1, respectively. A mechanism taking into account unprotonated hydroxylamine (NH₂OH) and molecular iodine (I₂) as reactive species, with intermediates NH₂OI₂^?, HNO, NH₂O, and I₂^?, is proposed.     

Calcium phosphate powders synthesized from solutions with [Ca2+]/[PO 4 3− ]=1 for bioresorbable ceramics

Calcium phosphate powders for manufacturing bioceramics were synthesized via precipitation from stock solutions of (NH₄)₂HPO₄ and Ca(NO₃)₂, or CaCl₂ or Ca(CH₃COO)₂ with [Ca²⁺]/[PO₄³⁻] = 1, without pH regulation. Properties of powdered samples, including density and microstructure of ceramics sintered at 900, 1000, 1100°C, were studied. The following pairs of precursors such as Ca(NO₃)₂/(NH₄)₂HPO₄, CaCl₂/(NH₄)₂HPO₄, Ca(CH₃COO)₂/(NH₄)₂HPO₄ gave both insoluble calcium phosphates and the corresponding by-products of synthesis — NH₄NO₃, NH₄Cl, NH₄CH₃COO. These by-products were released from the calcium phosphate precipitates in the course of heating to the temperature of sintering. Owing to specific buffer properties of the solutions being formed during synthesis, the pH value varied in a wide range during the precipitation process leading to different final values of pH and, thus, to different target phase(s) after annealing at 900–1100°C. After sintering, the samples based on the powders synthesized from Ca(NO₃)₂/(NH₄)₂HPO₄ consisted of β-Ca₂P₂O₇, whereas the samples based on the powders derived from CaCl₂/(NH₄)₂HPO₄ were composed of β-Ca₂P₂O₇ and β-Ca₃(PO₄)₂, and the samples based on the powders synthesized from Ca(CH₃COO)₂/(NH₄)₂HPO₄ contained only β-Ca₃(PO₄)₂. All the powders can be considered as the precursors for fabrication of bioceramics with enhanced resorption.      

Variations in the Electrokinetic Potential of Magnesium Hydrosilicate Fibers upon Treatment with Ammonium Chloride

The effect of the treatment of magnesium hydrosilicate (Mg₃Si₂O₅(OH)₄) fibers with an aqueous 5% ammonium chloride solution at 37?40 and 57?60°C on their electrokinetic potential (ζ potential) is studied. The maximum time of exposure in the NH₄Cl solution was 100 min, while the ζ potential was measured every 20 min. It is shown that the treatment of the initial magnesium hydrosilicate fibers with the NH₄Cl solution leads to a reversal of their surface charge and a rise in the absolute value of the negative charge, which is explained by magnesium leaching out of the surface layer of the fibers. Washing of the treated fibers with distilled water leads again to the sign reversal of the ζ potential. Therewith, the character of the dependences of the fiber ζ potential on the time of the treatment with the 5% NH₄Cl solution at T = 37?40°C is the same before and after washing.     

Chromatographic study of metal ammines

Summary The movement of metal ammines through filter paper strips has been studied. Mixtures of solutions of the metal salts with NH₄Cl and NH₄OH were prepared and spotted on strips. 50% ethanol was used as the solvent. It was noted that excess of NH₄Cl when present, gave better chromatograms. Increase of NH₃ concentration resulted in a change of R_f values. In the case of Cu^II and Ni^II the R_f value decreases, while in the case of Ag^I, Cd^II and Co^II it increases with increasing concentrations of NH₄OH added. With progressive increase in the concentration of NH₄OH the R_f values finally tend to become constant.     

Kinetics and mechanisms of chlorine transfer from chloramine to amines in aqueous medium

The kinetics and the equilibrium constant of the chlorine transfer reaction between monochloramine NH₂Cl and the amines: C₂H₅NH₂, (CH₃)₂CHNH₂, (CH₃)₂NH, and (C₂H₅)₂NH are investigated by spectrophotometry in aqueous medium at 25°C, in the pH range from 8 to 13 and for an ionic strength equal to 1.03 ± 0.05M. For a concentration of total ammonia equal to 1M, the observed rate constant is pH independent below 8 and above 12.8 and reaches a maximum located between the pK_as of NH₄⁺ and RR'NH₂⁺. From these results and those obtained earlier for NH₂Cl and CH₃NH₂, the reaction is shown to involve an interaction between neutral molecules NH₂Cl and RR'NH, subject to general acid catalysis. The ability of an interaction corresponding to a specific catalysis and involving NH₃Cl⁺ and RR'NH rather than NH₂Cl and RR'NH₂⁺ is also discussed. The activation parameters are given for each reaction.     

A Mild and Versatile Method for the Tetrahydropyranylation of Alcohols and Their Detetrahydropyranylation

An efficient and mild method for tetrahydropyranylation of alcohols and their detetrahydropranylation using NH₄Cl is described. This protocol provides a useful alternative tetrahydropyranylation of alcohols and their deprotection at different pH.