The preparation of lignocellulosic aerogels from ionic liquid solutions

Nanofibrillar aerogels were prepared from cellulose, spruce wood and from mixtures of cellulose, lignin and xylan. The lignocellulosic polymers were first dissolved in an ionic liquid and coagulated from solution by adding aqueous ethanol. The obtained gel was washed with ethanol and liquid carbon dioxide and finally dried by releasing the carbon dioxide from the porous structure at supercritical temperature to obtain the aerogel. The bulk densities of the biopolymer aerogels ranged from 25 to 114 g/l and the internal surface areas (BET) from 108 to 539 m²/g depending on the biopolymer mix and on the polymer concentration in the ionic liquid solution. All aerogels were compressible and consisted of nanofibrillar biomaterial network with open-pore structure.     

Lipase Catalysed Esterification at High Pressure

From the comparation of esterification between oleic acid and oleyl alcohol, catalyzed by the Mucor miehei immobilized lipase in a batch stirred tank reactor, in a solvent free system and system where the solvent was supercritical carbon dioxide it is obvious that reaction rates are higher at supercritical conditions than in the solvent free system. To obtain the data on the solubility of substrates and product (oleyl oleate) in supercritical carbon dioxide, fluid phase equilibria measurements in the static equilibrium cell have been done. The results showed that the temperature change between 30 d`C and 50 d`C doesn't affect the solubility of the substances in SC CO₂ very much, but with higher pressure (between 100 and 300 bar) the solubilities of oleic acid, oleyl alcohol and oleyl oleate slightly increase. From the data it is obvious that oleic acid and oleyl alcohol have better solubility in supercritical CO₂ than oleyl oleate and therefore the separation of both substrates from oleyl oleate with supercritical CO₂ is possible-Key words: esterification, supercritical fluids, lipase.     

Supercritical fluid extraction of naringin from the peel of Citrus paradisi

The highest yield (14.4 g/kg) of naringin, the major flavonoid from the peel of Citrus paradisi L., that could be achieved by supercritical fluid extraction was obtained using supercritical carbon dioxide modified with 15% ethanol and fresh (rather than dried) peels at 95 bar and 58.6 degrees C. This yield is higher than that attained by the conventional technique of maceration, and close to those obtained by reflux and Soxhlet methods. Furthermore, supercritical fluid extraction consumes less solvent and provides a shorter extraction time than conventional extraction methods.     

Calcium exchanges in Anodonta cygnea: barriers and driving gradients

Electrical potential differences between the haemolymph and the extrapallial fluid, and between the haemolymph and the mantle cavity fluid, and ionic concentrations of calcium in the haemolymph and in extrapallial fluid were measured in vivo in Anodonta cygnea. The electrochemical potential of ionic calcium in the haemolymph is clearly above the electrochemical potential of ionic calcium in the environment and is very nearly in equilibrium with that of the extrapallial fluid. Simultaneous measurements of carbon dioxide partial pressure and pH in the extrapallial fluid showed that in this compartment ionic calcium is clearly above saturation. It is proposed that calcium deposition is regulated through the secretion of the organic matrix and by controlling the pH and the carbon dioxide partial pressure of the extrapallial fluid. An estimation of the minimum positive balance of calcium required to sustain shell growth together with the electrophysiological characterization of the mantle cavity epithelium showed that this tissue is not the route of entry of calcium into the animal.Abbreviations BW body weight - DW dry weight - E_EPF-S chemical potential difference - EPF extrapallial fluid - G_tot total conductance - I_sc short-circuit current - K_sp solubility product - MCE mantle cavity epithelium - MCF mantle cavity fluid - OME outer mantle epithelium - PCO₂ partial pressure of carbon dioxide - PVC Poly(vinyl chloride) - S shell - SEM standard error of mean - V _ic intracellular electrical potential - V _oc open-circuit voltage     

Performance of tapered column packed-bed bioreactor for ethanol production

A tapered column type of bioreactor system packed with immobilized Saccharomyces cerevisiae was used to study the bioreactor performance as a function of design and operating variables. The performance of tapered column bioreactor system was found to be better than that of the conventional cylindrical column reactor system for the ethanol fermentation. The new bioreactor design alleviated problems associated with carbon dioxide evolution and provided a significantly better flow pattern for both liquid and gas phases in the bioreactor without local channelling. A mathematical simulation model, which takes into account of the axial convection and dispersion, interphase mass transfer, and apparent kinetic design parameters, was developed. The effect of radial concentration gradients on the bioreactor performance was found to be insignificant. For the reactor system studied, the maximum ethanol productivity obtained was 60 g ethanol/L gel/h, and the maximum glucose assimilation rate was 140 g glucose/L gel/h. One of the most important findings from this study was that the apparent kinetic parameters change at the glucose concentration of 2 g/L This change was found to be due to the changes in yeast physiology and metabolism. The values of V(m) (') and V(m) (') decreased from 0.8 to 0.39 g ethanol/g cell/h and from 97mM to 11mM, respectively. The substrate inhibition constant was estimated as 0.76M and the product inhibition constant was determined as 113 g ethanol/L The degree of product inhibition showed practically a linear relationship with an increasing ethanol concentration. Based on the hydro-dynamic analysis of the bioreactor system, it was found that the Peclet number, N(Pe) was not a strong function of the flow velocity at low flow rates through the bioreactor system, but its value decreased somewhat at an interstitial velocity greater than 0.03 cm/s. The tapered column bioreactor system showed a much better flow pattern of gas and liquid phases within the reactor, thereby providing a more homogeneous distribution of gas-liquid-solid phases in the reactor without any phase separation.     

Extraction of monocrotaline from Crotalaria spectabilis using supercritical carbon dioxide and carbon dioxide-ethanol mixtures

Monocrotaline, a pyrrolizidine alkaloid of chemotherapeutic interest, was successfully extracted from the crushed seeds of Crotalaria spectabilis using supercritical carbon dioxide and ethanol mixtures. Overall solubilities of the plant material in the supercritical fluid phase were as high as 1.1 mass percent, and monocrotaline solubilities were as high as 0.07 mass percent. The solubility of monocrotaline in the presence of other plant material was smaller by 50 to 98% compared with the solubility of pure monocrotaline in the supercritical fluid. Also, it was found that the extraction of the complex plant material was time-dependent after approximately one percent of the original mass of the material had been extracted.     

水/乙醇溶剂中阿奇霉素的热力学及多晶型研究

在278.2~308.2 K温度范围内,测定阿奇霉素在水/乙醇混合溶剂中的溶解度,根据固液平衡理论建立了该体系的溶解度修正模型。采用X线粉末衍射法和差示扫描量热法,对阿奇霉素在不同温度、不同体积比的水/乙醇混合溶剂中得到的晶体进行鉴别。同时利用溶解度数据估算了阿奇霉素在水/乙醇体系中的溶解热(-25.26~-16.11 k J/mol)、混合热(-9.94~-3.25 k J/mol)。通过溶液化学理论推导了阿奇霉素溶剂化平衡常数K与活度系数γ2的方程:γ2=1/(1+K),建立了溶剂化焓与温度、水/乙醇两者体积比(φ)之间的关系式,为ΔH=RTln(17.86exp(3.4φ)-1)。采用溶析结晶方法得到的6种阿奇霉素晶体,均属单斜晶系,但具有不同的晶胞参数且其密度和熔点也不同。同时发现温度越高,水/乙醇体积比越大,得到的晶体稳定性越差(晶体的熔点和密度降低)。在水/乙醇混合溶剂的溶析结晶体系中,产生阿齐霉素多晶型的现象与溶剂化作用的强弱有关。     

A Mathematical model for ethanol production by extractive fermentation in a continuous stirred tank fermentor

Extractive fermentation is a technique that can be used to reduce the effect of end product inhibition through the use of a water-immiscible phase that removes fermentation products in situ. This has the beneficial effect of not only removing inhibitory products as they are formed (thus keeping reaction rates high) but also has the potential for reducing product recovery costs. We have chosen to examine the ethanol fermentation as a model system for end product inhibition and extractive fermentation and have developed a computer model predicting the productivity enhancement possible with this technique together with other key parameters such as extraction efficiency and residual glucose concentration. The model accommodates variable liquid flowrates entering and leaving the system, since it was found that the aqueous outlet flowrate could be up to 35% lower than the inlet flowrate during extractive fermentation of concentrated glucose feeds due to the continuous removal of ethanol from the fermentation broth by solvent extraction. The model predicts a total ethanol productivity of 82.6 g/L h if a glucose feed of 750 g/L is fermented with a solvent having a distribution coefficient of 0.5 at a solvent dilution rate of 5.0 h(-1). This is more than 10 times higher than for a conventional chemostat fermentation of a 250 g/L glucose feed. The model has furthermore illustrated the possible trade-offs that exist between obtaining a high extraction efficiency and a low residual glucose concentration.     

超临界流体萃取——高效液相色谱法测定百合中秋水仙碱

分别用超临界二氧化碳流体和有机溶剂萃取百合中的秋水仙碱,然后用高效液相色谱法直接测定萃取物中秋水仙碱的含量,从而测得百合中秋水仙碱的含量。超临界流体萃取的条件是：用乙醇作提携剂,萃取压力为18MPa,萃取温度为40℃,高效液相色谱测定条件为：ODS柱,甲醇：磷酸二氢钾溶液作流动相,检测波长为220nm,此法快速,简便,准确,可应用于秋水仙碱原料,制剂及其它植物中秋水仙碱含量的测定。     

Determination of food constituents based on SFE: applications to vitamins A and E in meat and milk

A method has been developed for the determination of vitamins A and E in food using supercritical fluid extraction (SFE), applying liquid or solid trapping, with an accuracy equal to conventional solvent extraction methods. Under optimal conditions, using methanol modified carbon dioxide as a supercritical fluid, Hydromatrix as a water adsorbent, and with a small amount of ascorbic acid and methanol added to the sample, the extraction time is reduced to 80 min. This time is considerably shorter than in conventional methods. Other advantages are the reduction of manual manipulations leading to lower labour costs and reduced consumption of organic solvents in the sample preparation step.     

Biocatalytic synthesis of acrylates in organic solvents and supercritical fluids: I. optimization of enzyme environment

Biocatalytic transesterification of methylmethacrylate is possible in many different solvents. The reaction rate is readily controlled by variation in solvent physical properties. The reaction proceeds better in hydrophobic solvents, and activity can be restored in hydrophilic solvents by the addition of water. We have now demonstrated that supercritical carbon dioxide is not a good solvent for the reaction between 2-ethlhexanol and methylmethacrylate. It apperars that the supercritical carbon dioxide may either alter the pH of the microaqueous environment associated with the protein or reversibly form covalent complexes with free amine groups on the surface of the enzyme. Although supercritical carbon dioxide is a poor solvent for acrylate transesterification, many other supercritical fluids (ethane, ethylene, sulfur hexafluoride, and fluoroform) are better than most conventional solvents. In supercritical ethane it is possible to control the activity of the enzyme by changing pressure, and the enzyme appears to follow Michaelis-Menten Kinetics. We find that sulfur hexafluoride, the first anhydrous inorganic solvent in which biocatalytic activity has been reported, is a better solvent than any conventional or supercritical organic fluid tested.     

Extraction of astaxanthin from Haematococcus pluvialis by supercritical carbon dioxide fluid with ethanol modifier

Conventional solvent extraction methods cannot attain high‐quality antioxidant extracts from microalgae and also require solvent recovery and posttreatment. In this study, we utilized environmental friendly supercritical carbon dioxide fluid extraction (SFE‐CO₂) techniques to obtain pigment (i.e. astaxanthin) from Haematococcus pluvialis. The effects of key operating parameters on the extraction efficiency of astaxanthin were investigated, giving an optimal condition of H. pluvialis weight, 6.5 g; CO₂‐flow rate, 6.0 NL/min; extraction time, 20 min; extraction pressure, 4500 psi; volume of ethanol modifier added, 9.23 mL/g; extraction temperature, 50°C; modifier composition, 99.5%. Under these optimum conditions, the astaxanthin yield was 73.9% (10.92 mg/g dry H. pluvialis powder) after eight cycle of extraction cycles. The saponification index (C_S/C₀, representing the ratio of astaxanthin concentration after and before the saponification procedures) of the extract could be increased from 1 to 12.78 by saponification with 3.5 M NaOH.     

A New Potential Model for Carbon Dioxide from AB Initio Calculations

Abstract

Ab initio quantum chemical calculations have been carried out for carbon dioxide dimer and the results have been used to establish potential functions usable in molecular simulations. Since the intermolecular interaction in carbon dioxide is fairly weak, careful treatment is required: this study uses 6–31G* basis set and takes electron correlations by the 2nd order Møller-Plesset theory into account. The potential energy surface is elucidated using the four representative relative configurations of the dimer. A new potential function model has been proposed on the basis of these ab initio data. In the super-critical region, this model is used to calculate the PVT relation of carbon dioxide fluid by the Monte Carlo simulations and confirmed to reproduce reasonably well the experimental isotherms.     

Critical Point Drying Method Using Dry Ice

A critical point drying method using dry ice (solid carbon dioxide) instead of liquid carbon dioxide is reported. After the specimens are placed in the chamber of the medical point drying apparatus, dry ice cut to the shape of the chamber is inserted. The chamber is closed and warmed to change the dry ice into liquid carbon dioxide. This method needs no gas cylinder and even minute or fragile specimens do not blow away because there is no flow of gas. This method can be used with any kind of critical point drying apparatus.     

A kinetic model for simultaneous saccharification and fermentation of Avicel with Saccharomyces cerevisiae

This work describes a numerical model for predicting simultaneous saccharification and fermentation of Avicel, an insoluble crystalline cellulose polymer. Separate anoxic cultivations of 40 g/L glucose and 100 g/L Avicel were conducted to verify model predictions and obtain parameters to describe the reaction kinetics. Saccharification of Avicel was achieved with Trichoderma reesei cellulases from the enzyme preparation Spezyme CP with an enzyme loading of 10 FPU/g cellulose. Cultivations were supplemented with 50 IU/g cellulose of β‐glucosidase from Novozym 188 to prevent product inhibition by cellobiose. Saccharomyces cerevisiae MH‐1000 is a robust industrial strain and was used to ferment glucose to ethanol, glycerol, and carbon dioxide. The numerical model presented in this paper differs from previous models by separating the endoglucanase and exoglucanase enzyme kinetics and allowing for inhibitive site competition. Assuming all enzymes remain active and that each enzyme complex has a corresponding constant specific activity, the model is capable of predicting adsorbed enzyme concentrations with reasonable accuracy. Comparison of predicted values to experimental measurements indicated that the numerical model was capable of capturing the significant elements involved with cellulose conversion to ethanol. Biotechnol. Bioeng. 2011; 108:924–933. © 2010 Wiley Periodicals, Inc.     

HPLC comparison of supercritical fluid extraction and solvent extraction of coumarins from the peel of Citrus maxima fruit

The efficiency of carbon dioxide supercritical fluid extraction (SFE) of the biologically active compounds imperatorin, meranzin and meranzin hydrate from the fruit peel of Citrus maxima Merr. has been compared with that of solvent extraction with acetone. Under the best SFE conditions tested for the three coumarins, which involved extraction at 50 degrees C and 27.6 MPa, the extractive efficiencies were 84, 76 and 18% for imperatorin, meranzin and meranzin hydrate, respectively. The presence of modifiers significantly affected the extraction efficiency: the highest extraction efficiency of the three coumarins was obtained with ethanol as modifier.     

Modelling alterations in the partition coefficient in in vitro biological systems using headspace gas chromatography

Headspace gas chromatography was used to determine the physiological media–air partition coefficient (K) of four volatile organic solvents of industrial importance. The experimental conditions were those likely to be used in in vitro metabolic and toxicological studies on volatile compounds. The addition of solvent to the liquid phase from a stock solution in ethanol, or the presence of organic material at concentrations normally seen in in vitro studies, did not significantly alter the K value. Binary solvent addition resulted in a dose-dependent decrease in K for each solvent that was also influenced by the solvent solubility and the constituents of the liquid matrix. The aromatic solvents exerted the greatest effect and showed the greatest change in K value.     

Synergistic effects of climate change and local stressors: CO2 and nutrient-driven change in subtidal rocky habitats

Climate-driven change represents the cumulative effect of global through local-scale conditions, and understanding their manifestation at local scales can empower local management. Change in the dominance of habitats is often the product of local nutrient pollution that occurs at relatively local scales (i.e. catchment scale), a critical scale of management at which global impacts will manifest. We tested whether forecasted global-scale change [elevated carbon dioxide (CO₂) and subsequent ocean acidification] and local stressors (elevated nutrients) can combine to accelerate the expansion of filamentous turfs at the expense of calcifying algae (kelp understorey). Our results not only support this model of future change, but also highlight the synergistic effects of future CO₂ and nutrient concentrations on the abundance of turfs. These results suggest that global and local stressors need to be assessed in meaningful combinations so that the anticipated effects of climate change do not create the false impression that, however complex, climate change will produce smaller effects than reality. These findings empower local managers because they show that policies of reducing local stressors (e.g. nutrient pollution) can reduce the effects of global stressors not under their governance (e.g. ocean acidification). The connection between research and government policy provides an example whereby knowledge (and decision making) across local through global scales provides solutions to some of the most vexing challenges for attaining social goals of sustainability, biological conservation and economic development.     

Measurement of ethanol concentration using solvent extraction and dichromate oxidation and its application to bioethanol production process

A method for measuring the ethanol concentration in a yeast culture broth was developed using both microtubes and a 96-deepwell microplate. The strategy involved first the solvent extraction of ethanol from the yeast culture broth and measurements of the ethanol concentration using the dichromate oxidation method. Particular focus was made on selecting the extraction solvent as well as determining the measurable range of ethanol concentrations using this solvent extraction-dichromate oxidation method. This method was developed as an assay format in 2.0-ml microtubes and 1.2-ml 96-deepwell microplates, and the ethanol concentration in the batch cultures and fed-batch fermentations was measured. Tri-n-butyl phosphate [non-alcoholic solvent, density = 0.9727, solubility in water = 0.028% (w/v)] was used for solvent extraction when measuring the ethanol concentration from the yeast culture broth. The maximum detectable ethanol concentration was 8% (v/v) when 10 g potassium dichromate in 100 ml of 5 M sulfuric acid was used. The concentrations determined from the solvent extraction-dichromate oxidation methods were remarkably similar to those of gas chromatography in which samples were prepared from seven experiments, such as four batch cultures and three fed-batch fermentations.     

The combination of transformed and constrained Gibbs energies

Gibbs free energy is the thermodynamic potential representing the fundamental equation at constant temperature, pressure, and molar amounts. Transformed Gibbs energies are important for biochemical systems because the local concentrations within cell compartments cannot yet be determined accurately. The method of Constrained Gibbs Energies adds kinetic reaction extent limitations to the internal constraints of the system thus extending the range of applicability of equilibrium thermodynamics from predefined constraints to dynamic constraints, e.g., adding time-dependent constraints of irreversible chemical change. In this article, the implementation and use of Transformed Gibbs Energies in the Gibbs energy minimization framework is demonstrated with educational examples. The combined method has the advantage of being able to calculate transient thermodynamic properties during dynamic simulation.