Ethanol Flux Research Articles

Ethanol emission from loose corn silage and exposed silage particles

Silage on dairy farms has been identified as a major source of volatile organic compound (VOC) emissions. However, rates of VOC emission from silage are not accurately known. In this work, we measured ethanol (a dominant silage VOC) emission from loose corn silage and exposed corn silage particles using wind tunnel systems. Flux of ethanol was highest immediately after exposing loose silage samples to moving air (as high as 220 g m −2 h −1) and declined by as much as 76-fold over 12 h as ethanol was depleted from samples. Emission rate and cumulative 12 h emission increased with temperature, silage permeability, exposed surface area, and air velocity over silage samples. These responses suggest that VOC emission from silage on farms is sensitive to climate and management practices. Ethanol emission rates from loose silage were generally higher than previous estimates of total VOC emission rates from silage and mixed feed. For 15 cm deep loose samples, mean cumulative emission was as high as 170 g m −2 (80% of initial ethanol mass) after 12 h of exposure to an air velocity of 5 m s −1. Emission rates measured with an emission isolation flux chamber were lower than rates measured in a wind tunnel and in an open setting. Results show that the US EPA emission isolation flux chamber method is not appropriate for estimating VOC emission rates from silage in the field.

Prediction of pervaporation performance of aqueous ethanol solutions by nanopermporometry characterization

This study proposes a new method, nanopermporometry with simultaneous measurement of vapor (NPPV), for prediction of the performance of pervaporation (PV) dehydration of aqueous ethanol solutions. In conventional nanopermporometry (NPP), only the permeate flux of a non-condensable gas such as air is measured as a function of humidity, and the pore size distribution is obtained based on blocking the permeation of a non-condensable gas (air) using a capillary-condensed vapor. With NPPV the permeate flux of both water and air are measured simultaneously. PV measurements of the feed ethanol at a concentration of 94 wt% were carried out at 70 °C after the corresponding NPPV measurement. Both the separation factor and the water flux showed time-dependence before reaching a steady state after several hours. A separation factor of 132 and a water flux of 0.52 kg/(m 2 h) were obtained using sol–gel-derived silica membranes. The NPPV fluxes of water and air at relative humidities of 2, 13 and 60% were used to predict PV performance, i.e., the separation factor and flux. The NPPV air flux at 13% RH (Kelvin diameter: 1 nm) was correlated with PV ethanol flux, and NPPV water flux at 13% RH was correlated with PV water flux. Moreover, the ratio of NPPV water flux to air flux at 13% RH was correlated with the PV separation factor.

Preparation and characterization of vinyltriethoxysilane (VTES) modified silicalite-1/PDMS hybrid pervaporation membrane and its application in ethanol separation from dilute aqueous solution

To improve the affinity between silicalite-1 and polydimethylsiloxane (PDMS), the silicalite-1 particles were modified by a silane coupling agent vinyltriethoxysilane (VTES) and incorporated into polydimethylsiloxane (PDMS) matrix for the preparation of silicalite-1/PDMS hybrid membranes. The modified silicalite-1 particles were examined by XRD, FT-IR and TGA, and the results showed that the silane coupling agent was bonded to the surface of silicalite-1 particles through chemical bonds and the modification did not influence the framework of silicalite-1 crystals. VTES could enhance the interaction of silicalite-1 particles with PDMS through chemical bonds and hence suppressed the formation of microvoids at polymer–silicalite-1 interface, as a result, the thermal stability of the hybrid membrane could be improved. The effect of silicalite-1 loading on the pervaporation performances of the hybrid membranes with dilute ethanol solutions was investigated. As compared with the unmodified hybrid membranes, the VTES modified silicalite-1/PDMS hybrid membranes effectively improved the pervaporation selectivity at different silicalite-1 loadings. With increasing silicalite-1 loading, membrane selectivity increased for both unmodified and VTES modified silicalite-1/PDMS hybrid membranes, and a selectivity of 32 was obtained when VETS modified silicalite-1 loadings was 67%. It was also found that with increasing silicalite-1 loading, the total flux of both unmodified and VTES modified silicalite-1/PDMS hybrid membranes decreased while the ethanol flux of both hybrid membranes increased. With increasing the feed ethanol concentration at a given temperature, the total flux, ethanol flux, and ethanol concentration in permeate increased almost proportionally, while water flux decreased and the separation factor decreased slightly. An increase in temperature increased the permeation fluxes of both ethanol and water, while the separation factor was more or less constant at a given ethanol concentration.

Temperature and air velocity effects on ethanol emission from corn silage with the characteristics of an exposed silo face

Volatile organic compounds (VOCs) from agricultural sources are believed to be an important contributor to tropospheric ozone in some locations. Recent research suggests that silage is a major source of VOCs emitted from agriculture, but only limited data exist on silage emissions. Ethanol is the most abundant VOC emitted from corn silage; therefore, ethanol was used as a representative compound to characterize the pattern of emission over time and to quantify the effect of air velocity and temperature on emission rate. Ethanol emission was measured from corn silage samples removed intact from a bunker silo. Emission rate was monitored over 12 h for a range in air velocity (0.05, 0.5, and 5 m s −1) and temperature (5, 20, and 35 °C) using a wind tunnel system. Ethanol flux ranged from 0.47 to 210 g m −2 h −1 and 12 h cumulative emission ranged from 8.5 to 260 g m −2. Ethanol flux was highly dependent on exposure time, declining rapidly over the first hour and then continuing to decline more slowly over the duration of the 12 h trials. The 12 h cumulative emission increased by a factor of three with a 30 °C increase in temperature and by a factor of nine with a 100-fold increase in air velocity. Effects of air velocity, temperature, and air-filled porosity were generally consistent with a conceptual model of VOC emission from silage. Exposure duration, temperature, and air velocity should be taken into consideration when measuring emission rates of VOCs from silage, so emission rate data obtained from studies that utilize low air flow methods are not likely representative of field conditions.

Influence of acid on the permeation properties of NaA-type zeolite membranes

The acid stability of the NaA-type zeolite membrane was evaluated in this study. For the rapid evaluation of membrane stability, the change in the permeation fluxes of the membrane was monitored in real-time by using a mass spectrometer during pervaporation. When sulfuric acid was added to the feed solution, the permeation flux of water decreased dramatically immediately after the acid addition (step (I)), then decreased slightly (step (II)), and finally increased significantly (step (III)). The permeation flux of ethanol also increased significantly in step (III). As a result, the NaA-type zeolite membrane lost its separation ability for an equimolar mixture of water and ethanol at 313 K in 10 min after the addition of 1.0 mL sulfuric acid. Hydrolysis reaction and dissolution occurred in steps (I)–(III). Furthermore, we also discuss the influence of the amount of added acid and ethanol content of the feed solution on the destruction of the zeolite membrane.

Solvent permeability in commercial ultrafiltration polymeric membranes and evaluation of the structural and chemical stability towards hexane

The membrane technology application in the vegetable oil processing is associated to the hexane recovery from the miscella obtained during the extraction, degumming and subsequent refining stages, where the presence of the hexane results in higher permeate flux. However, the development of this technological alternative depends on membrane chemical stability. The objective of this work was to evaluate six flat-sheet polymeric membranes in relation water affinity, permeability and flux of water, ethanol and hexane, with the purpose of characterizing their hydrophobic and hydrophilic profiles and resistance to hexane. The equipment used was a stirred cell. The following commercial flat membranes were used: 30 kDa and 50 kDa PVDF (polyvinylidene fluoride); 10 kDa PES (polyethersulfone); 0.05 μm PC (polycarbonate); 0.05 μm and 0.025 μm CME (mixed cellulose esters). Membrane permeability with water, ethanol and hexane was evaluated in a laboratory unit at 4 bar, 200 rpm and 40 °C. Regarding flux rates with the tested solvents, the 50 kDa PVDF membrane revealed the highest permeability to water, two of the membranes were characterized as less hydrophilic (PC and PES) and the remaining ones were more hydrophobic. The membrane structural stability towards the hexane was verified by visual observation, filtering area variation (shortening or intumescence) and permeate flux assessments. The permeation with hexane was conducted for 12 h, at 1.5 bar, 200 rpm and 40 °C, with constant flux in all of the membranes during the experiment. Membranes untreated, submersed in hexane for 48 h and submitted to hexane permeation for 12 h were examined by scanning electron microscopy (SEM) in order to verify possible microscopic alterations. All the membranes were hexane-resistant, indicating that they are suitable for use with this solvent.

Pervaporation as a means of recovering ethanol from lignocellulosic bioconversions

Fermentation of AFEX-treated and enzymatically hydrolyzed forages and agricultural residues resulted in weak ethanol concentration in broths (maximum 5 g/L). A porous ethanol-selective membrane was evaluated on a model solution (2 wt/wt% ethanol) using pervaporation process. When used under permeate-side pressure of 20 mmHg, at feed temperature of 30°C and at a feed Re = 2000, a porous polytetrafluoroethylene (PTFE) membrane (0.2 μm pore diameter) produced a maximum ethanol flux of 36 g/m 2 h with selectivity near 1.66. Increasing feed temperature to 60°C resulted in 465 g/m 2 h for the ethanol flux but the selectivity was around 2.25. Decreasing the permeate-side pressure to 10 mmHg at 30°C increased the ethanol flux to 86 g/m 2 h and the selectivity to near 2.85. Two non-porous membranes are presently being investigated. Preliminary results with 10 μm thick polydimethylsiloxane and polyoctylmethylsiloxane membranes showed an increased selectivity to a value near nine. However, the ethanol and total fluxes are greatly reduced, even at a working pressure of 1 mmHg.

Natural rubber/poly(acrylic acid) semi‐interpenetrating polymer network membranes for the pervaporation of water–ethanol mixtures

AbstractPervaporation membranes for the dehydration of water–ethanol mixtures were prepared from a semi‐interpenetrating polymer network (semi‐IPN) of natural rubber (NR) and crosslinked poly(acrylic acid) (PAA). The swelling studies revealed that hydrophilic PAA present in the semi‐IPN membranes caused the membranes to swell greatly in water. The swelling degree of the membranes in water was significantly affected by the amount ratio between the hydrophobic NR and the hydrophilic PAA. The sorption experiments of the NR/PAA membranes in various concentrations of water–ethanol mixtures suggested the preferential sorption to water. However, for the membrane with high PAA content, the water sorption selectivity decreased considerably at high water concentration of water–ethanol mixtures because the membrane was in the highly swollen state. Pervaporation separations of water–ethanol mixtures using NR/PAA membranes were performed and it was found that at low water concentrations of feed mixtures, increasing the PAA content of the membrane can enhance both water permeation flux and selectivity. Additionally, under low feed water concentration, increasing the feed temperature would increase the water flux with the decreasing of the ethanol flux. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Mixed matrix membranes prepared from natural rubber/poly(vinyl alcohol) semi-interpenetrating polymer network (NR/PVA semi-IPN) incorporating with zeolite 4A for the pervaporation dehydration of water–ethanol mixtures

Abstract The pervaporation dehydration of water–ethanol mixtures was investigated using the mixed matrix (MM) membranes prepared from natural rubber (NR) and crosslinked poly(vinyl alcohol) (PVA) semi-IPN embedded with the zeolite 4A. With the presence of NR as well as zeolite, the swelling of MM membranes in water was effectively suppressed. Examined by DSC, the non-freezing bound water in the MM membranes was found decreasing with more zeolite loading because the water–polymer interaction is diminishing. The sorption study of MM membranes revealed a preferential sorption to water with improved water sorption selectivity as increasing the zeolite loading. For pervaporation at 5 vol% water in feed, the reversed trade-off with respect to the zeolite loading was encountered such that the total permeation flux increased along with an enhancement of the water separation factor. For higher feed water concentration, despite the greater total permeation flux, the separation factor was reduced owing to the extensive swelling of the polymer matrix. The temperature dependency of the partial water and ethanol fluxes followed the Arrhenius relationship and the estimated activation energies for water flux were lower than those of the ethanol flux, suggesting that the developed MM membranes are highly water selective.

Impact of TiO 2 nanoparticles on morphology and performance of crosslinked polyimide organic solvent nanofiltration (OSN) membranes

Chemically crosslinked polyimide organic–inorganic composite nanofiltration membranes suitable for application in harsh organic solvents were successfully prepared by phase inversion of dope solutions. TiO 2 nanoparticles were dispersed in these dope solutions, comprising polyimide (PI) in N, N-dimethylformamide/1,4-dioxane. The impact of TiO 2 on the resulting PI membranes was investigated using SEM, TGA, water contact angle, dope viscosity measurements and mechanical strength. The presence of TiO 2 nanoparticles within the membrane matrix was proved by the detection of a peak characteristic of TiO 2 in the WAXS pattern. SEM pictures of the cross-section of the PI/TiO 2 membranes showed dramatically changed morphology compared to reference membranes with no TiO 2 addition. Macrovoids present in reference membranes were suppressed by increasing loading of TiO 2 nanoparticles, and eventually disappeared completely at a TiO 2 loading above 3 wt.%. Decreasing water contact angle and an increase in ethanol flux indicated that hydrophilicity increased as nanoparticle loading increased. The effect of TiO 2 on the functional performance of the membranes was evaluated by measuring flux and rejection using cross-flow filtration. Perhaps surprisingly, the presence of TiO 2 improved the compaction resistance of the membranes, whereas rejection and steady flux were almost unaltered.

Comparison of pressure driven transport of ethanol/ n-hexane mixtures through dense and microporous membranes

The solvent flux was measured in binary mixtures of ethanol and n-hexane for nine solvent-stable polymeric membranes in range of reverse osmosis (RO) to ultrafiltration (UF) (GE AK Osmonics, Dow 102326, GE DK Osmonics, MPF-34, STARMEM™ 122, STARMEM™ 240, NF30, NTR7450, NF-PES-010). GC-analyses of feed and permeate samples showed a separation factor close to 1, which indicates the solvent transport occurs by convection or by coupled diffusion through the membranes. The effect of viscosity, surface tension, di-electric constant and solubility parameter of solvent on permeation rate was studied for four categories of membranes, i.e. RO membranes, dense nanofiltration (NF) membranes, semi-porous NF membranes and micro-porous NF membranes. While viscosity seems to be a main transport parameter (similar composition of feed and permeate), higher fluxes of ethanol compared to n-hexane (with lower viscosity) confirmed that the transport may occur through coupled diffusion. The influences of the solvent–membrane interaction parameters such as surface tension, polarity and solubility parameters of solvent and membranes for dense membranes were investigated. The effect of solvent membrane interaction by means of solubility parameters was more pronounced compared to surface tension since the respective surface tensions of solvents are close to one another ( γ ethanol = 21.9 , γ n ‐ hexane = 17.9 ) . Partial permeabilities were studied as well to evaluate the influence of each component on permeation of the other. Unexpected results were observed for MPF-34, NF30 and NTR7450. Further investigation confirmed that their polymeric structure changed in contact with the solvents. Hydrophobic STARMEM™ membranes, which are expected to have a higher permeability for apolar solvents showed higher fluxes for ethanol compared to n-hexane. The similar solubility parameter of these membranes and ethanol may increase the permeation rate of ethanol molecules through membranes. For porous membranes viscosity was recognized as the key transport parameter, while affinity between membrane and solvent has a lower effect.

Performance and stability of multi-channel MFI zeolite membranes detemplated by calcination and ozonication in ethanol/water pervaporation

Two multi-channel defect-free high-silica MFI membranes have been tested for the removal of ethanol from a 7 mol% and 3 mol% aqueous solution under pervaporation conditions. One membrane is detemplated by calcination at 773 K, and one is ozonicated at 473 K. The flux and ethanol separation factor were determined at 348 K, 360 K, and 373 K. The ethanol separation factors of both membranes were similar and ranged from ∼ 20 at 373 K to ∼ 40 at 348 K. The ethanol and water fluxes through both membranes in this temperature range are proportional to the component fugacity difference over the membranes. The calcined membrane showed an 80% higher flux than the ozonicated membrane, showing the ozonication could not completely remove the template. After the ozonicated membrane was calcined at 723 K, the flux increased to a similar value as the initially calcined membrane, while the separation factor did not change. Both membranes showed an increase in flux by a factor of two after a subsequent calcination at 823 K, also without affecting the separation factor. The high calcination temperature required for complete detemplation indicates the presence of aluminum in the zeolite framework of the membrane. The membrane stability was monitored for 40 h and 177 h of operation for the initially calcined and ozonicated membrane, respectively. At 348 K the membranes showed stable performance, but the stability of the membranes at elevated temperatures is limited, showing a decrease in both flux and selectivity during operation at 373 K. The effect of the exposure to a water/ethanol mixture on the zeolite membrane is investigated by permporometry measurements of the membranes and by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, magic angle spinning nuclear magnetic resonance (MAS NMR), thermogravimetric analysis (TGA), and nitrogen adsorption experiments using several MFI-type zeolite powders. The most plausible mechanism causing the instability of the membrane is ethoxy formation of the ethanol with the silanol groups and Brønsted acid sites in the zeolite framework combined with the formation of hydrophilic extra-framework pathways by hydrolysis.

Pervaporation of water/ethanol mixtures through microporous silica membranes

Several microporous silica membranes prepared by sol–gel processing were studied for separation of water–ethanol mixtures by pervaporation (PV). The permeate flux and separation factor of the prepared silica membranes decreased gradually at the beginning of the pervaporation-based separation of the water–ethanol mixture (ethanol concentration: 94 wt%); after 6–10 h, the PV performance characteristics reached a steady state. The water flux of the silica membranes ranged from 0.3 to 0.8 kg/(m 2 h), while the separation factor ranged from 10 to 500. Repeated PV experiments revealed that water and ethanol flux were high during the initial stages of the experiments and then declined; this pattern was observed more clearly at higher temperatures. A possible explanation for this phenomenon is that gradual physical and physicochemical adsorption subsequently plugged the membrane pores and prevented permeation. The relationship between PV performance and temperature was examined in the context of the adsorption–diffusion model for determination of the appropriate PV temperature.

Experimental study on dealcoholization of wine by osmotic distillation process

The types of stripping solutions and influences of operating parameters including feed and stripping velocities, system temperatures on the ethanol removal of ethanol solution and wine by using osmotic distillation (OD) process were investigated along with the mass transfer study. The experiments were performed by the membrane contactor unit using 0.2 μm pore size diameter microporous PVDF hollow fibers. Three different types of stripping solutions (pure water, 50% (w/w) glycerol, 40% (w/w) CaCl 2) were used to compare the dealcoholization performance of the process. Aroma loss study was also carried out by using ethyl acetate and iso-amyl alcohol solutions to represent the major aroma compounds presenting in the real wine. Long-term tests for ethanol solution and wine were also performed in order to evaluate the dealcoholization performance of OD process. Using water as a stripper presented more promising result compared with the others because it provided higher ethanol flux and lower counter transport of water due to the water activity differences. The results of the study showed that the ethanol flux and ethanol removal performance were enhanced by the increase of feed and stripping solution velocities and system temperatures. Aroma components were significantly lost during the process operation. The ethanol concentration in the wine can be reduced to roughly 34% of the initial concentration for 360 min operation.

Extractive pervaporation to separate ethanol from its dilute aqueous solutions characteristic of ethanol-producing fermentation processes

The addition of a third component to a binary distillation system in extractive distillation leads to a much better separation between the two principal components via modification of the liquid phase activity coefficients and consequently the vapor–liquid equilibria. A small amount of n-butanol added to the solution containing 5–10 wt% ethanol enhances the separation performance in extractive pervaporation using tri- n-octylamine (TOA) as the liquid membrane with coated porous hollow fibers. The selectivity of ethanol increased considerably to as much as 113 at 54 °C for the feed containing ∼10 wt% ethanol when 2.5 wt% n-butanol was added to the feed compared with the selectivity of ethanol without any n-butanol added, namely, 38. The mass flux of ethanol for ∼10 wt% ethanol in feed obtained was 16.2 g/(m 2 h), which is considerably higher (by 73%) than the flux obtained for the experiment without n-butanol added to the feed; further for 2.5 wt% n-butanol in a feed of ∼10 wt% ethanol, the total concentration of solvents in the permeate exceeded 95%. The added n-butanol increases somewhat the solubility of ethanol in the liquid membrane. The solubility measurements of solvents show that the solubility is decreased with increased temperatures. The fluxes of the solvents were increased by a factor of five by reducing the thickness of the TOA layer in the porous substrate wall of the coated fibers. As a result, ethanol flux and selectivity achieved were around 59.8 g/(m 2 h) and 100 respectively for a mixture containing ∼10 and 2 wt% ethanol and n-butanol respectively at 54 °C. The TOA-based LM present throughout the pores of the coated substrate demonstrated excellent stability over many hours and essentially prevented the loss of liquid membrane to the feed solution.

Semi-continuous ethanol production in bioreactor from whey with co-immobilized enzyme and yeast cells followed by pervaporative recovery of product – Kinetic model predictions considering glucose repression

Mathematical models for semi-continuous ethanolic fermentation in a whey medium employing co-immobilized Saccharomyces cerevisiae strain and β- d-galactosidase and for pervaporative product recovery from the resultant broth were developed. Kinetic parameters of biomass growth were estimated using the nonlinear least squares method on the basis of experimental data obtained from culture of suspended yeast cells grown in a mixture of glucose and galactose and during semi-continuous fermentation in a bioreactor in a whey medium with co-immobilized enzyme and yeast cells. Experimentally determined fluxes of ethanol and water from broth were applied for the estimation of kinetic constants of ethanol separation by pervaporation. The degree of sugar utilization and ethanol productivity in bioreactor as well as the time of ethanol separation needed to obtain the desired amount of product can be predicted using this model. The influence of selected operating parameters on the fermentation effectiveness was simulated based on the developed model.

Quantitative Analysis of the High Temperature-induced Glycolytic Flux Increase in Saccharomyces cerevisiae Reveals Dominant Metabolic Regulation

A major challenge in systems biology lies in the integration of processes occurring at different levels, such as transcription, translation, and metabolism, to understand the functioning of a living cell in its environment. We studied the high temperature-induced glycolytic flux increase in Saccharomyces cerevisiae and investigated the regulatory mechanisms underlying this increase. We used glucose-limited chemostat cultures to separate regulatory effects of temperature from effects on growth rate. Growth at increased temperature (38 degrees C versus 30 degrees C) resulted in a strongly increased glycolytic flux, accompanied by a switch from respiration to a partially fermentative metabolism. We observed an increased flux through all enzymes, ranging from 5- to 10-fold. We quantified the contributions of direct temperature effects on enzyme activities, the gene expression cascade and shifts in the metabolic network, to the increased flux through each enzyme. To do this we adapted flux regulation analysis. We show that the direct effect of temperature on enzyme kinetics can be included as a separate term. Together with hierarchical regulation and metabolic regulation, this term explains the total flux change between two steady states. Surprisingly, the effect of the cultivation temperature on enzyme catalytic capacity, both directly through the Arrhenius effect and indirectly through adapted gene expression, is only a moderate contribution to the increased glycolytic flux for most enzymes. The changes in flux are therefore largely caused by changes in the interaction of the enzymes with substrates, products, and effectors.

Alcohol, Volatile Fatty Acid, Phenol, and Methane Emissions from Dairy Cows and Fresh Manure

There are approximately 2.5 million dairy cows in California. Emission inventories list dairy cows and their manure as the major source of regional air pollutants, but data on their actual emissions remain sparse, particularly for smog-forming volatile organic compounds (VOCs) and greenhouse gases (GHGs). We report measurements of alcohols, volatile fatty acids, phenols, and methane (CH4) emitted from nonlactating (dry) and lactating dairy cows and their manure under controlled conditions. The experiment was conducted in an environmental chamber that simulates commercial concrete-floored freestall cow housing conditions. The fluxes of methanol, ethanol, and CH4 were measured from cows and/or their fresh manure. The average estimated methanol and ethanol emissions were 0.33 and 0.51 g cow(-1) h(-1) from dry cows and manure and 0.7 and 1.27 g cow(-1) h(-1) from lactating cows and manure, respectively. Both alcohols increased over time, coinciding with increasing accumulation of manure on the chamber floor. Volatile fatty acids and phenols were emitted at concentrations close to their detection limit. Average estimated CH4 emissions were predominantly associated with enteric fermentation from cows rather than manure and were 12.35 and 18.23 g cow(-1) h(-1) for dry and lactating cows, respectively. Lactating cows produced considerably more gaseous VOCs and GHGs emissions than dry cows (P < 0.001). Dairy cows and fresh manure have the potential to emit considerable amounts of alcohols and CH4 and research is needed to determine effective mitigation.

Separation of ethanol/ethyl acetate mixture by pervaporation at 100–130 °C through NaY zeolite membrane for industrial purpose

Ethanol separation from mixtures of ethanol (EtOH) and ethyl acetate (EtAc) was performed by pervaporation (PV) at feed conditions of 100–130°C and 1, 5, 10 and 30wt.% ethanol content through the NaY zeolite membranes synthesized for industrial purpose. Experimental results showed that higher permeation fluxes up to 2.9kgm−2h−1 at 130°C in a feed mixture of EtOH (30wt.%)/EtAc (70wt.%) was observed. The ethanol permeance (molm−2s−1Pa−1) ranged from 1.6×10−8 to 5.4×10−8 in all feed conditions. Higher temperatures and higher ethanol contents in feed enhanced permeation ethanol flux or ethanol permeance. Higher and moderate separation factors (α) of 27–82 were observed through the results, indicating this membrane performance could be utilized in practical separating process to break up the azeotrope in the ethanol–ethyl acetate mixture. The separating mechanism could be attributed to the affinity difference in two molecules of ethanol and ethyl acetate. This separation could be a typical case for preferential adsorption mechanism that could separate components with smaller molecular sizes than zeolitic pore size.

Specific Ethanol Production Rate in Ethanologenic Escherichia coli Strain KO11 Is Limited by Pyruvate Decarboxylase

Modification of ethanol productivity and yield, using mineral medium supplemented with glucose or xylose as carbon sources, was studied in ethanologenic Escherichia coli KO11 by increasing the activity of five key carbon metabolism enzymes. KO11 efficiently converted glucose or xylose to ethanol with a yield close to 100% of the theoretical maximum when growing in rich medium. However, when KO11 ferments glucose or xylose in mineral medium, the ethanol yields decreased to only 70 and 60%, respectively. An increase in GALP_Ec (permease of galactose-glucose-xylose) or PGK_Ec (phosphoglycerate kinase) activities did not change xylose or glucose and ethanol flux. However, when PDC_Zm (pyruvate decarboxylase from Zymomonas mobilis) activity was increased 7-fold, the yields of ethanol from glucose or xylose were increased to 85 and 75%, respectively, and organic acid formation rates were reduced. Furthermore, as a response to a reduction in acetate and ATP yield, and a limited PDC_Zm activity, an increase in PFK_Ec (phosphofructokinase) or PYK_Bs (pyruvate kinase from Bacillus stearothermophilus) activity drastically reduced glucose or xylose consumption and ethanol formation flux. This experimental metabolic control analysis showed that ethanol flux in KO11 is negatively controlled by phosphofructokinase and pyruvate kinase, and positively influenced by the PDC_Zm activity level.