Ethanol Feed Research Articles

Preparation and optimization of nanocomposite membranes for ethanol dehydration via pervaporation by using response surface methodology

BackgroundAlcohol dehydration using pervaporation, as a fast-developing process, requires more facilitation by improving their membrane performance. MethodsGraphene oxide nanosheets (GONs) were incorporated into blend matrixes of chitosan (CS) and polyvinyl-alcohol (PVA) to prepare nanocomposite membranes (NCMs) for ethanol dehydration. The membranes' structure was evaluated using SEM and FTIR analysis and their dehydration performance was studied against membrane composition (GONs loading and the CS/PVA blending ratio) and operational variables (feed temperature and ethanol concentration) using response surface methodology. Significant FindingsSEM images revealed GONs uniform dispersion within the membrane matrix and the FTIR results revealed the hydrogen bonds formation and minor changes after GONs incorporation. The optimum NCM was selected as 50 wt. % CS/PVA blended polymer matrix loaded by 4 wt. % GONs with permeation flux (PF) and separation factor (SF) were improved by 50 % and 5-fold, to 299 g/m2h and 1142. Its PF and SF reached 418 g/m2h (45 % increment) and 652 (30 % decrement) as its temperature elevated from 50 to 70 °C. These values were measured as 311 g/m2h (25 % decline) and 1106 (66 % improvement) by increasing the feed's ethanol content from 80 to 90 wt. %.

Carbon quantum dots (CQDs) incorporated dual-layer hollow fibers for pervaporative dehydration of ethanol

Pervaporative ethanol dehydration is a promising approach to concentrate ethanol from biofuel stocks. In this study, we have fabricated high performance dual-layer cellulose triacetate (CTA)/Ultem hollow fiber membranes incorporated with a small amount of superhydrophilic carbon quantum dots (CQDs) via the immiscibility induced phase separation (I2PS) method. The flow rates of the inner- and outer-layer dopes were firstly optimized. Subsequently, various small amounts of CQDs were added into the inner- and outer-layer dope solutions to explore their impacts on membrane structure and separation performance. It was found that the incorporation of a reasonably small amount of CQDs, whether to the inner or outer layer of I2PS membranes, could significantly enhance the mechanical properties and pervaporation performance by altering their structures. The most effective membrane containing 0.2 wt% CQD in the outer layer (0.2CQD_OL) demonstrated exceptional pervaporation performance. Using an 85 wt% ethanol feed solution, this membrane achieved a total flux of 4306 ± 130 g m−2h−1 (equivalent to a water permeance of 33.28 mol m−2h−1 kPa−1) and a water content of approximately 95 wt% (equivalent to a mole-based selectivity of 153) in the permeate over a 172 hr long-term test. A comparison with literature underscores the superior performance of this newly developed I2PS membrane, particularly in terms of water permeance. In summary, the CQD-embedded CTA/Ultem HF membranes demonstrate substantial potential for industrial applications in the pervaporative ethanol dehydration.

High-performance double-separation-layer pervaporation membranes for ethanol dehydration

Pervaporation membranes are used to dehydrate ethanol, but standalone sodium alginate (SA) and polyvinyl alcohol (PVA) membranes pose challenges owing to their inherent issues, such as low stability and limited separation performance. Despite employing various complex and costly membrane preparation methods to address these shortcomings, the improvement in separation performance, especially in permeate flux, remains limited. In addition, the complexity and costliness of these methods hinder their industrial applications. Herein, we developed a simple and cost-effective method to prepare high-performance pervaporation membranes. First, a SA solution was cast on the polyacrylonitrile (PAN) bottom membrane to form a SA separation layer, and subsequently a PVA separation layer was applied atop of the SA separation layer, yielding double-separation-layer PVA/SA/PAN membranes. The smooth, compact and hydrophilic SA intermediate layer apparently decreased the defects in the PVA separation layer and the presence of the PVA separation layer isolated the SA layer from the liquid feed on the outer side and inhibited the swelling of SA separation layer, leading to high selectivities and stabilities. Under operating conditions of 69°C and a feed ethanol concentration of 90 wt%, the permeate flux and separation factor of the PVA4/SA/PAN membrane are 1201 g m−2 h−1 and 5164, respectively. Notably, the pervaporation separation index (PSI) of this membrane is 79 times that of the PVA4/PAN membrane. Moreover, the membrane performance remained stable over a continuous 10-day operation at 69°C, affirming its reliability and durability. We successfully prepared a high-performance two-separation-layer pervaporation membrane for ethanol dehydration.

Influence of Anode Diffusion Layer on the Performance of a Passive Direct Ethanol Fuel Cell

One of the main challenges with passive direct ethanol fuel cells (DEFCs) is ethanol transport management since the liquid ethanol is supplied to the anode compartment by natural processes including convection and diffusion with a low cell operating condition. The significant layer in the cell is the diffusion layer (DL), which facilitates reactants to reach the anode catalyst layer (CL). In this study, the impact of various DLs fabricated of readily accessible commercial materials on cell performance in passive DEFCs with different ethanol feed concentrations was examined with various in-situ characterization methods. The results demonstrate that the cell with a DL coated by the hydrophobic microporous layer (MPL) yielded the best performance of 0.887 mW·cm-2 at the optimal ethanol feed concentration of 5 M. In conclusion, the benefits of enhancing ethanol mass transfer to the anode CL would outweigh the drawbacks of preventing ethanol crossover to the cathode. HIGHLIGHTS The effect of the anode diffusion layer (DL) on passive direct ethanol fuel cell (DEFC) performance was determined Five different anode DLs fabricated of readily accessible commercial materials were employed Various characterizations enabled the assessment of each loss affecting the passive DEFC performance The cell with an anode DL modified with a hydrophobic microporous layer (MPL) exhibited the best cell performance The optimal ethanol feed concentration of the best cell was found to be 5 M GRAPHICAL ABSTRACT

Surface hydrophobicity and catalytic performance of cerium incorporated HZSM-5 zeolite for conversion of bio-ethanol

Cerium incorporated HZSM-5 (CeHZSM-5) catalyst prepared by impregnation method was tested for aqueous ethanol conversion at 200–400 °C. The CeHZSM-5 catalyst was found to be very active (21.02 %Conversion), compared to the parent HZSM-5 catalyst (9.39 %Conversion), especially at low reaction temperatures (200 °C) and when fed with high water content (80 wt% ethanol). FTIR, FT-Raman, DR-UV, NH3-TPD, IPA-TPD, DSC and contact angle techniques reveal that the incorporation of cerium species into zeolites results in the acidity and hydrophilic/hydrophobic nature. Cerium species are thought to tend to migrate into ZSM-5 channels and associate with the zeolite framework. As a result, the net electrostatic charge decreases due to the presence of tetrahedral cerium atoms. Therefore, the CeHZSM-5 exhibits a hydrophobic character, compared to the parent one. The decrease in competitive adsorption of water versus ethanol feed at the Brønsted acid site may lead to an increase in CeHZSM-5 catalyst activity.

Electric-field-assisted arrangement of carbon nanotube inside PDMS membrane matrix for efficient bio-ethanol recovery via pervaporation

Pervaporation is recognized as an efficient technology for solvent recovery and biorefinery from aqueous solutions. However, due to the low permeability and slow mass transfer of traditional polymeric membranes, pervaporation process is still restricted for practical application. Herein, we prepared electric-field arranged K-MWCNTs/PDMS MMMs to utilize the fast mass transfer property of CNTs surface to achieve high-efficient ethanol recovery via pervaporation. Before served as fillers, MWCNTs-NH2 were first functionalized with silane coupling agent to improve the surface affinity between K-MWCNTs and PDMS matrix. The correlation between electric field property, K-MWCNTs arrangement behavior and ethanol separation performance was thoroughly investigated. Results indicated that electric-field arranged K-MWCNTs/PDMS MMMs presented superior hydrophobicity (contact angle reached 130.5° at 6 wt% K-MWCNTs loading) and lower water swelling degree compared with pure PDMS membranes. By introducing electric field, K-MWCNTs achieved ordered morphology in casting solutions and the final MMMs, which is supposed to generate more mass transfer pathways for small molecules and thus help boost the mass transfer of membranes. When the electric-field parameters were set as10kHz, 1500 V/cm and exposure time maintained around 5 min, the electric-field arranged K-MWCNTs/PDMS MMMs (2 wt% loading, 50 ℃, 6 wt% feed ethanol concentration) could achieve superior and stable ethanol recovery performance with separation factor reaching 11 and total flux increased by ∼ 40 % from 982 g·m−2·h−1 to 1348 g·m−2·h−1 compared with MMMs prepared without electric field. In view of this, we here fabricated a novel electric-field arranged K-MWCNTs/PDMS MMM and provide a facile method in achieving better dispersion of K-MWCNTs in MMMs for high-efficient ethanol recovery.

Effect of butanol, ethanol and acetone feed composition through activated carbon-containing polydimethylsiloxane pervaporation membrane

The ABE route, whose products are acetone, butanol and ethanol, is an industrial process that has been investigated by the possibility of incorporating renewable resources as inputs of chemical compounds and fuels. In view of the toxicity of 1-butanol to the cells of the fermentation broth, pervaporation by means of a polydimethylsiloxane mixed matrix membrane containing 1 wt% activated carbon was used as an alternative to recover this alcohol simultaneously to its production. Synthetic aqueous solution of acetone, 1-butanol and ethanol was investigated with total organic content varied from 1.5 to 2.7 wt%. Permeate flux and selectivity (separation and enrichment factors) were reported. Regarding the organics transport through the membrane, there was not a linear relation of their content in feed stream and flux. Besides, the permeation sequence did not follow a single transport mechanism. High separation and enrichment factors for acetone and butanol were observed.

NiMo/CZ internal reforming layer for ethanol-fueled metal-supported solid oxide fuel cell

A metal-supported solid oxide fuel cell (MS-SOFC) consisting of infiltrated NiMo/CZ internal reforming catalysts is operated under a direct ethanol feed condition at 700 °C with a steam-to-carbon (S/C) ratio of 2. The additional catalyst functional layer is required to internally reform the ethanol fuel into syngas while preventing the cell's rapid deactivation due to unwanted carbon deposits or coking. Our experimental results show that the cell with NiMo/CZ catalyst shows a higher maximum current density of 0.355 A cm−2 compared to 0.052 A cm−2 for the cell without catalyst at 0.4 V. The constant current stability performance was also improved. The cell with NiMo/CZ can operate for 90 h and shows less carbon deposition than the cell without a catalyst. Adding NiMo/CZ reforming catalyst into the MS-SOFC is a promising solution to enhance the operating lifetime and coke resistance in the ethanol steam reforming fed MS-SOFC system.

Advanced downstream processing of bioethanol from syngas fermentation

Syngas fermentation is used industrially to produce diluted bioethanol (about 1–6 wt%). This research study proposes a novel downstream process that recovers bioethanol in an energy-efficient and cost-effective manner, improves fermentation yield by recycling all fermentation broth components (microbes, acetate and water), and is designed for full-scale industrial-level application. Therefore, vacuum distillation at fermentation temperature was conceptually studied as an initial ethanol recovery step, leading to a bottom stream that may be recycled. Advanced separation and purification techniques were designed to recover 99.5% of initially present ethanol as high-purity product (99.8 wt%). Mechanical vapor recompression and heat integration methods were used to maximize sustainability and eco-efficiency of the proposed recovery process. Implementation of these techniques on a process using 6 wt% ethanol feed stream decreased the total annual costs by 54.2% (from 0.175 to 0.080 $/kgEtOH), reduced the primary energy requirement by 66.1% (from 2.82 to 0.96 kWthh/kgEtOH), lowered the CO2 emission by up to 82.6% (from 0.414 to 0.072 kgCO2/kgEtOH), and reduced the fresh water usage by 62.6% (from 0.242 to 0.091 m3W/kgEtOH). Sensitivity analysis for ethanol concentrations ranging from 6 to 1 wt% showed that the recovery costs and energy use increased to 0.336 $/kgEtOH and 1.78 kWthh/kgEtOH respectively. Since ethanol recovery performs better but fermentation will perform worse at higher ethanol concentration in fermentation broth, there is a trade-off concentration for the overall process. The current analysis is an important step toward determining this trade-off.

Better Performance in C2-Conversion to Aromatics by Optimized Feed and Catalysts

We identify favorable parameters for the formation of aromatics from ethanol-based feeds over ZSM-5. An ethanol partial pressure of 0.3 bar, a reaction temperature of ∼700 K, a low weight hourly space velocity (WHSV), and a high Brønsted acid site density increase the content of aromatics, in the latter case, on the expense of lifetime. The aromatic fraction composition changes with the WHSV and nSi/nAl ratio. Water cofeed increases the content of aromatics in the C2:H2O stoichiometry of 1:0.5 (equals diethyl ether as feed) but decreases it if this is exceeded. Diethyl ether and ethylene lead to more aromatics than ethanol feed. The lifetime until deactivation increases in the order ethanol < diethyl ether < ethylene. This points at different reaction and/or deactivation mechanisms in converting the three feeds. Thus, a water-poor feed effectively improves the catalyst lifetime and productivity in the ethanol conversion to aromatics.

Fabrication and Characterization of Carbon Nanotube Filled PDMS Hybrid Membranes for Enhanced Ethanol Recovery.

Ethanol separation via the pervaporation process has shown growing application potential in solvent recovery and the bioethanol industry. In the continuous pervaporation process, polymeric membranes such as hydrophobic polydimethylsiloxane (PDMS) have been developed to enrich/separate ethanol from dilute aqueous solutions. However, its practical application remains largely limited due to the relatively low separation efficiency, especially in selectivity. In view of this, hydrophobic carbon nanotube (CNT) filled PDMS mixed matrix membranes (MMMs) aimed at high-efficiency ethanol recovery were fabricated in this work. The filler K-MWCNTs was prepared by functionalizing MWCNT-NH2 with epoxy-containing silane coupling agent (KH560) to improve the affinity between fillers and PDMS matrix. With K-MWCNT loading increased from 1 wt % to 10 wt %, membranes showed higher surface roughness and water contact angle was improved from 115° to 130°. The swelling degree of K-MWCNT/PDMS MMMs (2 wt %) in water were also reduced from 10 wt % to 2.5 wt %. Pervaporation performance for K-MWCNT/PDMS MMMs under varied feed concentrations and temperatures were evaluated. The results supported that the K-MWCNT/PDMS MMMs at 2 wt % K-MWCNT loading showed the optimum separation performance (compared with pure PDMS membranes), with the separation factor improved from 9.1 to 10.4, and the permeate flux increased by 50% (40-60 °C, at 6 wt % feed ethanol concentration). This work provides a promising method for preparing a PDMS composite with both high permeate flux and selectivity, which showed great potential for bioethanol production and alcohol separation in industry.

Hydrogen production by decomposition of ethanol in the afterglow of atmospheric-pressure nitrogen microwave plasma torch

The atmospheric-pressure microwave plasma torch (MPT) is employed to produce hydrogen via the decomposition of ethanol (C2H5OH). The ethanol aerosol is injected directly into the early afterglow of a nitrogen plasma and the products are analyzed with Fourier transformation infrared spectrometery and gas chromatography. Meanwhile, optical emission spectroscopy is used to diagnose the plasma. The influencing factors for the hydrogen production are investigated with respect to the location of the ethanol injection, the ethanol feed rate, the ethanol microdroplet size, the absorbed microwave power, the total flow rate of carrier gas, and the Ar–N2 mixture ratio, respectively. It is found that the excited species and high temperature play important roles in ethanol decomposition. In addition, the effect of the gas flow pattern in the reaction chamber on hydrogen production is analyzed with the aid of computational fluid dynamics and the mechanism of ethanol decomposition by MPT is discussed. Hydrogen production in our experiment was successful, with a production rate of up to 1309 l h−1, an energy yield of up to 468 l kWh−1, and a hydrogen yield of up to 95%, respectively.

Simulation, optimization and intensification of the process for co-production of ethyl acetate and amyl acetate by reactive distillation

A new energy-saving process is proposed here for the co-production of ethyl acetate (EtAC) and amyl acetate (AmAC) by reactive distillation(RD). The thermodynamic feasibility of the ethyl acetate/amyl acetate system was determined based on its physical properties. As amyl acetate has a higher water-carrying capacity than ethyl acetate, water can be removed from the reaction system in the form of azeotrope to improve the conversion rate, and amyl acetate can be easily separated from the water. The reactive distillation process of ethyl acetate-amal acetate co-production with different alcohol feed ratios was studied in this paper. When the amyl alcohol to ethanol feed mole ratio was set at 2, the process performed better in terms of economy and energy consumption; it also had a less environmental impact at the same time. The reactive distillation process with intermediate condenser and intermediate reboiler (RD-IC-IR) process and the reactive dividing-wall column (RDWC) process are established based on process optimization. Compared with the RD process, the TAC and CO2 emissions for the RD-IC-IR process reduced by 21.92 % and 28.27 %, respectively, and the thermodynamic efficiency improved 38.86 %; the TAC and CO2 emissions for the RDWC process reduced by 36.11 % and 42.49 %, respectively, and the thermodynamic efficiency improved 74.45 %.

Catalytic Properties Study of Mixed MFI-MORD Type Zeolite in Bioethanol Transformation

The decrease in stocks of traditional fossil fuels contributes to the widespread growth of interest in renewable sources of raw materials and energy. Bioethanol can become a serious alternative to traditional types of fossil raw materials and fuels due to the possibility of its widespread production from agricultural waste and wood processing. Bioethanol can be used directly as a fuel, or after transformation into hydrocarbons. The transformation of bioethanol into hydrocarbons is carried out using zeolites and zeotypes of various types, while the main problem encountered for these systems is deactivation during the catalytic transformation. In this case, one of the possible solutions to this problem is the regulation of the acidic and diffusion properties of the catalytic surface of zeolites. Changing the acidic properties can contribute to a significant increase in the stability and activity of zeolites. In this case, the variation of acidic properties is possible by combining different types of zeolites. The article presents the results of a study of a mixed zeolite of the MFI type and mordenite in the reaction of the transformation of ethanol into hydrocarbons. Zeolite synthesis was carried out by a sequential method using zeolite seed grains for the synthesis of MFI structures and n-butylamine for the synthesis of a mordenite layer. The synthesized sample was tested on a flow-type setup with a tubular reactor. The effect of temperature, specific ethanol feed rate, and total pressure in the system was investigated. An increase in the reaction temperature from 350℃ to 370℃ contributed to an increase in the rate of accumulation of liquid hydrocarbons from 0.52 to 0.64 g(HC)/(g(Cat)*h), while a further increase in temperature to 430℃ contributed to a decrease in the rate of formation of liquid hydrocarbons to 0.32 g(HC)/(g(Cat)*h). An increase in the specific feed rate of ethanol from 0.5 to 2 g(EtOH)/(g(Cat)*h) contributes to a decrease in the yield of liquid hydrocarbons. An increase in the total pressure in the system from 1 atm to 15 atm promotes an increase in the rate of accumulation of liquid hydrocarbons from 0.34 to 0.83 g(HC)/(g(Cat)*h).

Bioethanol Conversion into Propylene over Various Zeolite Catalysts: Reaction Optimization and Catalyst Deactivation.

Catalytic conversions of bioethanol to propylene were investigated over different zeolite catalysts. H-ZSM-5 (SiO2/Al2O3 = 80) was found to be the most effective for propylene production. Furthermore, H-ZSM-5 (SiO2/Al2O3 = 80) was investigated under different variables of catalytic reaction (calcination temperature, feed composition, reaction temperature, and time on stream) for the conversion of ethanol to propylene. The H-ZSM-5(80) catalysts calcined at 600 °C showed the highest propylene yield. The moderate acidic site on ZSM-5 is required for the production of propylene. The activity on ZSM-5 is independent of the ethanol feed composition. H-ZSM-5 catalyst deactivation was observed, owing to dealumination. The highest propylene yield was 23.4% obtained over HZSM-5(80). Propylene, butene, and ≥C5 olefins were formed by parallel reaction from ethylene. Olefins were converted to each paraffin by sequential hydrogenation reaction. HZSM-5(80) catalyst is a promising catalyst not only for ethanol but also for the conversion of bioethanol to light olefins.

Inovasi pembuatan Cassava Crackers berbahan Ubi Kayu pada kelompok home industri kue di desa Toaya Vunta Kecamatan Sindue

Many carbohydrates are produced from the Cassava plant (Manihot esculenta Crantz) and have an essential role for humans. Cassava is used not only as a food source but also as industrial raw material, ethanol, and animal feed. To avoid the rapid deterioration of post-harvest Cassava products, Casava is very potential to be developed into various processed products and industrial raw materials. The development of the snack or snack industry has proliferated, both in type, taste, and packaging. The results of interviews conducted by a service team with the home industry Cake group in Toaya Vunta village showed that many cassava plants still have not been used optimally. This service aims to provide training and mentoring workshops on making Cassava crackers (Cassava crackers) of various flavors to mothers of the home cake industry group in Toaya Vunta village. Through the community service program, the Toaya Vunta village home industry group can be assisted in training and workshops to manufacture more modern Cassava chips with different flavors to improve their knowledge and skills. The method in this activity is to use the method of lectures, demonstrations, discussions, practices, and observations, which are the results of the activities. This activity has three stages: material presentation, direct practical assistance in making cassava chips, and the packaging process. The results of this service can improve the knowledge and skills of the home industry group of mothers in making cassava chips with various flavors. Based on these results, it is hoped that it can improve the family economy as well as support the development of creative economy businesses and community empowerment in Toaya Vunta village

Metal-supported solid oxide fuel cell system with infiltrated reforming catalyst layer for direct ethanol feed operation

In this work, we introduce a Rhodium-Ceria-Zirconia (Rh/CZ) internal reforming catalyst layer to a high-performance metal-supported solid oxide fuel cell (MS-SOFC). The catalyst is applied by infiltrating Rh, CeO2, and ZrO2 precursors into the stainless steel (SS 430) support. The cell is tested by directly feeding an ethanol solution (45 vol%) into the anode at 600 °C. Our experimental results show that the button cell with the infiltrated 5 wt% Rh/CZ demonstrates an improved performance over the button cell without the catalyst layer by enhancing the internal reforming activity of ethanol toward the production of synthesis gas. The maximum current density improved from 0.3 A cm−2 to 0.4 A cm−2 while the long-term stability was also greatly improved. Post mortem cell analysis reveals that the infiltrated catalyst layer can prevent severe coke deposition from the cell's anode functional layer. The proposed integrated reforming catalyst and MS-SOFC system is a promising pathway to enable bioethanol fed-SOFC technology for future electric vehicles.

Preparation and pervaporation performance of PVA membrane with biomimetic modified silica nanoparticles as coating

Polyvinyl alcohol (PVA) has been widely used in pervaporation dehydration due to its low price and good stability. However, the inherent “trade-off” effect of polymer membrane makes the pervaporation performance relatively limited. In this work, the rough and super-hydrophilic surface were constructed by biomimetic modification of silica (SiO2) coating on the PVA membrane, which achieved simultaneous growth of total flux and separation factor compared with the control, and overcame the “trade-off” effect. The morphology, structure and hydrophilicity of membranes were characterized. Results demonstrated that PVA/polydopamine (PDA)/SiO2 composite membranes had strong hydrophilicity and high surface roughness. In addition, the effects of SiO2 loading amount, operating temperature, feed ethanol concentration and long-term stability on the ethanol dehydration performance were investigated. For the PVA/PDA/SiO2-6 composite membrane, total flux was 1388 g m−2 h−1, and the separation factor was 150(69 °C,90 wt% ethanol concentration), which was 1.8 times and 1.4 times that of the pristine PVA membrane, respectively.

Robust and high selective chitosan asymmetric Membranes: Relation between microporous structure and pervaporative efficiency in ethanol dehydration

• Asymmetric membranes are prepared in the presence of ethanol in chitosan solution. • Fabricated membrane is used for ethanol dehydration via pervaporation. • Changes of membrane structure during pervaporation process are extensively analyzed. • Analysis of transport parameters for transient and quasi-stationary state is provided. To improve the process of ethanol dehydration, asymmetric chitosan membranes were prepared and applied in the pervaporation process. A porous structure was obtained by adding absolute ethanol into chitosan solution. Fabricated membranes were comprehensively characterized by means of contact angle measurements, degree of swelling analysis, scanning electron microscopy, positron annihilation lifetime spectroscopy and wide angle X-rays scattering, to provide an extensive analysis of their physicochemical properties. The results showed a strong correlation between structure, amount and size of pores, and separation effectiveness of investigated membranes. Additionally, an interesting phenomenon of changing in membrane structure during pervaporation process was observed and was found to cause a nonlinear time dependence of transport and separation parameters. Consequently, the best performance of PV separation of 96 vol% ethanol (feed) was obtained for a membrane prepared from casting solution containing 0.1 ml of absolute ethanol, for which the values of separation factor and permeate flux reached 599.7 and 3.534 kg∙m −2 ∙h −1 , respectively.

Novel Propagation Strategy of Saccharomyces cerevisiae for Enhanced Xylose Metabolism during Fermentation on Softwood Hydrolysate

An economically viable production of second-generation bioethanol by recombinant xylose-fermenting Saccharomyces cerevisiae requires higher xylose fermentation rates and improved glucose–xylose co-consumption. Moreover, xylose-fermenting S. cerevisiae recognises xylose as a non-fermentable rather than a fermentable carbon source, which might partly explain why xylose is not fermented into ethanol as efficiently as glucose. This study proposes propagating S. cerevisiae on non-fermentable carbon sources to enhance xylose metabolism during fermentation. When compared to yeast grown on sucrose, cells propagated on a mix of ethanol and glycerol in shake flasks showed up to 50% higher xylose utilisation rate (in a defined xylose medium) and a double maximum fermentation rate, together with an improved C5/C6 co-consumption (on an industrial softwood hydrolysate). Based on these results, an automated propagation protocol was developed, using a fed-batch approach and the respiratory quotient to guide the ethanol and glycerol-containing feed. This successfully produced 71.29 ± 0.91 g/L yeast with an average productivity of 1.03 ± 0.05 g/L/h. These empirical findings provide the basis for the design of a simple, yet effective yeast production strategy to be used in the second-generation bioethanol industry for increased fermentation efficiency.