Thermochemistry of the hydrates of k2CoCl4

A study of the dissociation pressure of crystalline K₂CoCl₄·2H₂O. The reactions can be summed up as K₂CoCl₄·nH₂O(c) = K₂CoCl₄·mH₂O(c)+(nm)H₂O (v). Below 50°C, n = 2 and 1, m = 1 and 0, above 50°C, n = 2 and m = 0. Below 50°C, the dihydrate is octahedral, the monohydrate and anhydrous compounds are tetrahedral. ΔH° and ΔS° are respectively 7.0 kcal and 14.2 e.u. for the loss of the first mole of water and 12.7 kcal and 32.0 e.u. for the loss of the last mole of water. Above 50°C, ΔH° and ΔS° are respectively 29.8 kcal and 77.6 e.u. for the loss of both waters. The changes in structure are discussed using the spectral and magnetic properties as indications for structural changes.     

Chiral 1,1′-Binaphthyl Molecular Clefts for the Complexation of Excitatory Amino-Acid Derivatives

The complexation of N-benzyloxycarbonyl (Cbz) derivatives of the excitatory amino acids L -aspartic acid (Asp; 1 ), L -glutamic acid (Glu; 3 ), and, for the first time, L -kainic acid ((2S,3S,3S)-2-carboxy-4-(1-methylethenyl)pyrrolidine-3-acetic acid; Kai; 5 ) was studied in CDCl₃ with a diversity of chiral receptors consisting of a 1,1′-binaphthyl spacer with (carboxamido)pyridine (CONH(py)) functionality attached to the 6,6′-positions in the major groove. Receptors of type A possess two N-(pyridin-2-yl)carboxamide H-bonding sites (e.g. 7 ), whereas type B-receptors have two N-(pyridine-6,2-diyl)acetamide residues attached (e.g. 8 and 9 ). Complexes of excitatory amino-acid derivatives and other, achiral α,β-dicarboxylic acids with these receptors are primarily stabilized by two sets of C?O···H? N and O? H ··· N H-bonds. Optically active type-A receptors such as (R)- and (S)- 7 showed a preference for the larger Glu derivative, whereas type- B receptors such as (R)- and (S)- 8 and (R)- and (S)- 9 formed more stable complexes with the smaller Cbz-Asp. To improve the poor enantioselectivity shown by 7–9 , additional functionality was introduced at the 7,7′-positions of the 1,1′-binaphthyl spacer, and the nature of the H-bonding sites in the 6,6′-positions was varied. Screening the diversity of new racemic receptors for binding affinity, which had been shown in many examples by Cram to correlate with enantioselectivity, demonstrated that (+)- 10 and (+)- 11 formed the most stable complexes with dicarboxylic acids, and these receptors were synthesized in enantiomerically pure form. Both are type- B binders and contain additional PhCH₂O ( 10 ) and MeO ( 11 ) groups in the 7,7′-positions. By ¹H-NMR binding titrations, the complexation of (R)- and (S)- 10 and (R)- and (S)- 11 with the excitatory amino-acid derivatives was studied in CDCl₃, and association constants K_a between 10³ and 2 · 10⁵ l mol^?1 were measured for the 1:1 host-guest complexes formed. Whereas both 10 and 11 formed stable complexes, enantioselective binding was limited to the PhCH₂O-substituted receptor 10 , with the (R)-enantiomer complexing Cbz-Asp by 0.7 kcal mol^?1 more tightly than the (S)-enantiomer. The structures of the diastereoisomeric complexes were analyzed in detail by experimental methods (complexation-induced changes in ¹H-NMR chemical shifts, ¹H{¹H} nuclear Overhauser effect (NOE) difference spectroscopy) and computer modeling. These studies established that an unusual variety of interesting aromatic interactions and secondary electrostatic interactions are responsible for both the high binding affinity (? ΔG° up to 7.2 kcal mol^?1) and the enantioselection observed with (R)- and (S)- 10 . In an approach to enhance the enantioselectivity by reducing the conformational flexibility of the 1,1′-binaphthyl spacer, an additional crown-ether binding site was attached to the 2,2′-positions in the minor groove of the type- B receptors (R)- and (S)- 48 . Both the binding affinity and the enantioselectivity (Δ(ΔG°) up to 0.7 kcal mol^?1) in the complexation of the excitatory amino-acid derivatives by (R)- and (S)- 48 were not altered upon complexation of Hg(CN)₂ at the crown-ether binding site, demonstrating lack of cooperativity between the minor- and major-groove recognition sites.     

Cellulose and hemicellulose hydrolysis models for application to current and novel pretreatment processes

Acids catalyze the hydrolysis of cellulose and hemicellulose to produce sugars that organisms can ferment to ethanol and other products. However, advanced low- and no-acid technologies are critical if we are to reduce bioethanol costs to be competitive as a pure fuel. We believe carbohy drate oligomers play a key role in explaining the performance of such hydrolysis processes and that kinetic models would help us understand their role. Various investigations have developed reaction rate expressions based on an Arrhenius temperature dependence that is first order in substrate concentration and close to first order in acid concentration. In this article, we evaluate these existing hydrolysis models with the goal of providing a foundation for a unified model that can predict performance of both current and novel pretreatment process configurations.     

中国纤维素乙醇技术的研究进展

中国面临着严重的能源短缺和环境污染问题,中国政府正在局部几个省份内政策性鼓励燃料乙醇生产和使用。尽管当前主要是用玉米和谷物作为生产乙醇的原料,然而中国具有大量潜在的低成本的纤维素生物质原料,可以极大地扩大乙醇的产量,降低原料成本。近20年来,由于技术的革命性进步,已使得纤维素乙醇的生产成本从4美元/加仑以上,降低至约1.2—1.5美元/加仑。其中,每吨生物质约44美元。因此,目前乙醇掺汽油具有十分强的市场竞争力。已有几个公司正在建造首批商业纤维素乙醇工厂,虽然这些刚起步的小型设施在合理利用和管理上风险较小,但规模经济需要较大型工厂。尽管配送生物质原料的成本会随需求的增加而增加,但在乙醇生产基础上的生物精炼技术的发展,尤其是化工产品和动力的协同生产,将会使全过程的经济可行性大大提高。进一步深入的基础研究,将解决低成本下实现纤维素的完全利用,以确保在无政策性补贴的前提下,真正使纤维素乙醇成为具有市场竞争力的低成本纯液体燃料。     

Heat transfer considerations in design of a batch tube reactor for biomass hydrolysis

Biologic conversion of inexpensive and abundant sources of cellulosic biomass offers a low-cost route to production of fuels and commodity chemicals that can provide unparalleled environmental, economic, and strategic benefits. However, low-cost, high-yiel technologies are needed to recover sugars from the hemicellulose fraction of biomass and to prepare the remaining cellulose fraction for subsequent hydrolysis. Uncatalyzed hemicellulose hydrolysis in flow-through systems offers a number of important advantages for removal of hemicellulose sugars, and it is believed that oligomers could play an important role in explaining why the performance of flow-through systems differs from uncatalyzed steam explosion approaches. Thus, an effort is under way to study oligomer formation kinetics, and a small batch reactor is being applied to capture these important intermediates in a closed system that facilitates material balance closure for varying reaction conditions. In this article, heat transfer for batch tubes is analyzed to derive temperature profiles for different tube diameters and assess the impact on xylan conversion. It was found that the tube diameter must be <0.5 in, for xylan hydrolysis to follow the kinetics expected for a uniform temperature system at typical operating conditions.     

Twenty years of trials,tribulations, and research progress in bioethanol technology

The projected cost of ethanol production, from cellulosic biomass has been reduced by almost a factor of four over the last 20 yr. Thus, it is now competitive for blending with gasoline, and several companies are working to build the first plants. However, technology development faced challenges at all levels. Because the benefits of bioethanol were not well understood, it was imperative to clarify and differentiate its attributes. Process engineering was invaluable in focusing on promising opportunities for improvements, particularly in light of budget reductions, and in tracking progress toward a competitive goal. Now it is vital for one or more commercial projects to besuccessful, and improving our understanding of process fundamentals will reduce the time and costs for commercialization. Additionally, the cost of bioethanol, must be cut further to be competitive as a pure fuel in the open market, and aggressive technology advances are required to meet this target.     

Cellulase production on bagasse pretreated with hot water

Because pretreatment of biomass with hot water only in differential flow systems offers very digestible cellulose and potentially less inhibition by liquid hydrolysate, solids and liquid hydrolysate from bagasse pretreated with hot water were fed to a batch cellulase production system using the Rut C30 strain of Trichoderma reesei to determine the suitability of these substrates for cellulase production. The organism was found to be sensitive to inhibitors in the liquid hydrolysate but could be adapted to improve its tolerance. In addition, filtering of the material reduced inhibitory effects. The organism was also sensitive to some component in the solids, and they had to be washed heavily to achieve good growth and cellulase production rates. Even then, a lag was found before enzyme production would commence on pretreated solids whereas no such lag was experienced with Solka Floc. However, once enzyme production began, as high and even somewhat greater cellulase productivities were realized with washed pretreated solids. Adding lignin to Solka Floc delayed enzyme production, suggesting that lignin or other materials in the lignin solids could cause the lag observed for pretreated bagasse, but more studies are needed to resolve the actual reason for this delay.     

Likely features and costs of mature biomass ethanol technology

Applied Biochemistry and Biotechnology - Analysis is undertaken motivated by the question: “What are the likely features and cost of a facility producing ethanol from cellulosic biomass at a...     

Encapsulation of charge-diffuse peralkylated onium cations in the cavity of cucurbit[7]uril

Cucurbit[7]uril binds, with considerable size selectivity, NR(4)(+), PR(4)(+), and SR(3)(+) cations (R=Me, Et, (n)Pr, (n)Bu), with the smaller guests inside its cavity, rather than at the carbonyl-lined portals.     

Cucurbit[7]uril host-guest complexes with small polar organic guests in aqueous solution

The host-guest stability constants for the inclusion of a series of small neutral polar organic guests in cucurbit[7]uril (CB[7]) have been determined in aqueous solution by (1)H NMR titrations. The dependence of the stability constant on the nature of the guests indicates that hydrophobic and dipole-quadrupole interactions are responsible for the binding. The complexation-induced chemical shift changes in the guest proton resonances, coupled with energy-minimization calculations, suggest that the guests are located such that their dipole moment is aligned perpendicular with the quadrupole moment of the CB[7] host. The stability constants for acetone and acetophenone decrease in the presence of Na(+) or K(+) cations as a result of cation capping of the CB[7] portals.