Abstract:BACKGROUND: The energy demand of distillation-based systems for ethanol recovery and dehydration can be significant, particularly for dilute solutions. An alternative separation process integrating vapor stripping with a vapor compression step and a vapor permeation membrane separation step, termed membrane assisted vapor stripping (MAVS), has been proposed. The hydrophilic membrane separates the ethanol-water vapor into water-rich permeate and ethanol-enriched retentate vapor streams from which latent and sen… Show more
“…A promising method has been described recently [24]; -When feeding the fermentation with "real world" producer gas derived from pyrolysis of biomass, toxic contaminants that inhibit syngas fermentation [7,25] have to be removed by a gas cleaning process; -The relatively high costs for media ingredients required to support growth of the biocatalyst [26,27] suggest that the operational costs of syngas fermentation will remain in an uneconomical range, unless cheaper sources of growth medium are found for this process.…”
Abstract:We have established a two-stage continuous fermentation process for production of ethanol from synthesis gas (syngas) with Clostridium ljungdahlii. The system consists of a 1-L continuously stirred tank reactor as a growth stage and a 4-L bubble column equipped with a cell recycle module as an ethanol production stage. Operating conditions in both stages were optimized for the respective purpose (growth in stage one and alcohol formation in stage two). The system was fed with an artificial syngas mixture, mimicking the composition of syngas derived from lignocellulosic biomass (60% CO, 35% H 2 , and 5% CO 2 ). Gas recycling was used to increase the contact area and retention time of gas in the liquid phase, improving mass transfer and metabolic rates. In stage two, the biocatalyst was maintained at high cell densities of up to 10 g DW/L. Ethanol was continuously produced at concentrations of up to 450 mM (2.1%) and ethanol production rates of up to 0.37 g/(L·h). Foam control was essential to maintain reactor stability. A stoichiometric evaluation of the optimized process revealed that the recovery of carbon and hydrogen from the provided carbon monoxide and hydrogen in the produced ethanol was 28% and 74%, respectively.
“…A promising method has been described recently [24]; -When feeding the fermentation with "real world" producer gas derived from pyrolysis of biomass, toxic contaminants that inhibit syngas fermentation [7,25] have to be removed by a gas cleaning process; -The relatively high costs for media ingredients required to support growth of the biocatalyst [26,27] suggest that the operational costs of syngas fermentation will remain in an uneconomical range, unless cheaper sources of growth medium are found for this process.…”
Abstract:We have established a two-stage continuous fermentation process for production of ethanol from synthesis gas (syngas) with Clostridium ljungdahlii. The system consists of a 1-L continuously stirred tank reactor as a growth stage and a 4-L bubble column equipped with a cell recycle module as an ethanol production stage. Operating conditions in both stages were optimized for the respective purpose (growth in stage one and alcohol formation in stage two). The system was fed with an artificial syngas mixture, mimicking the composition of syngas derived from lignocellulosic biomass (60% CO, 35% H 2 , and 5% CO 2 ). Gas recycling was used to increase the contact area and retention time of gas in the liquid phase, improving mass transfer and metabolic rates. In stage two, the biocatalyst was maintained at high cell densities of up to 10 g DW/L. Ethanol was continuously produced at concentrations of up to 450 mM (2.1%) and ethanol production rates of up to 0.37 g/(L·h). Foam control was essential to maintain reactor stability. A stoichiometric evaluation of the optimized process revealed that the recovery of carbon and hydrogen from the provided carbon monoxide and hydrogen in the produced ethanol was 28% and 74%, respectively.
“…This leaves room for newer, more energyefficient systems to be developed, especially based on membrane-separation techniques. In a study on a hybrid distillation-vapor permeation [10] using a hydrophilic membrane to separate the ethanol-water vapor from the stripper into a water-rich permeate and ethanol-enriched retentate vapor, the energy demand was reduced significantly. For a feed with a concentration of 5 wt% ethanol the energy demand for a stripper was 6 MJ kg −1 ethanol to reach a vapor of 40 wt% while it was reduced to 2.2 MJ kg −1 ethanol to reach an ethanol concentration of about 80 wt%.…”
“…The typical separation process involves distillation near to the azeotropic point, followed by zeolite 3A adsorption or a steam membrane process using organic or zeolite 4A membranes. [8][9][10] However, this process is generally operated under high temperature and consumes a lot of heat energy. Alternatively, pervaporation process is a very promising technology as it can be operated under moderate working conditions.…”
Ethanediamine-modified zeolitic imidazolate framework (ZIF)-8 particles ) is synthesized and incorporated in the poly(vinyl alcohol) (PVA) matrix to fabricate novel PVA/ZIF-8-NH 2 mixed matrix membranes (MMMs) for pervaporation dehydration of ethanol. The PVA/ZIF-8-NH 2 MMMs exhibit enhanced membrane homogeneity and separation performance because of the higher hydrophilicity and restricted agglomeration of the particles, as compared to corresponding MMMs loaded with unmodified particles. The effect of ZIF-8-NH 2 loading in the MMMs is studied and the MMM with a 7.5 wt % ZIF-8-NH 2 loading shows the best pervaporation performance for ethanol dehydration at 408C. Various characterization techniques (Fourier transform infrared, scanning electron microscope, contact angle, sorption test, etc.) are used to investigate the MMMs loaded with ZIF-8 and ZIF-8-NH 2 particles. The impact of operation conditions on pervaporation performance is also performed. The performance benchmarking shows that the MMMs have superior separation factors and comparable flux to most other PVA hybrid membranes.
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