Ethanol, extractive fermentation

Because ethanol fermentation is inhibited by product, the selective extraction of ethanol during fermentation is also important to improve process performance. Silva et al. (3) have reported that the scheme that combines a fermentor with a vacuum flash vessel presents many positive features and good performance when compared to a conventional process (4). 

A 300 g portion of fermented material was placed in 500 ml of deionized water and slurried. The slurry was then heated for about 15 minutes at 75°C, 300 g of filter aid were then added and the material was filtered. The solid filtered material containing the anabolic substance was then air dried, and 333 g of the dried cake were then extracted with 500 ml of ethanol. This procedure was repeated three more times. The ethanol extract was then dried under vacuum to give 6.84 g of solid material. This solid material was then dissolved in 20 ml of chloroform and extracted with 30 ml of an aqueous solution containing 5% by weight of sodium carbonate having an adjusted pH of about 11.2. The extraction process was repeated seven more times. The pH of the sodium carbonate extract was then adjusted to 6.2 with hydrochloric acid, to yield an anabolic substance containing precipitate. The precipitate and the aqueous sodium carbonate extract were then each in turn extracted with... 

Extraction of Ethanol from Fermentation Broth Using Supercritical CO2... 

In all of the previous studies, ethanol extraction utilizing CO2 was investigated using synthetic ethanol solutions, the concentrations of which were higher than those in the fermentation broth. The extraction conditions were not also optimized. 

In this study, ethanol extraction using SC CO2 was achieved from 15 to 75 %(v/v) synthetic ethanol solutions and also from fermentation broth. Effects of temperature, pressure, extraction time and initial ethanol concentration on extraction yield were investigated in the ranges of 313 to 333 K and 80 to 160 atmospheres. Optimum conditions for the batch extraction of 15%(v/v) ethanol solution were found using the Box-Wilson optimization method in a linear form. In addition, the effect of consecutive solvent feeding on extraction yield were investigated both with 15 %(v/v) ethanol solution and with fermentation broth. 

One can envisage the future production of liquid fuels and commodity chemicals in a biorefinery Biomass is first subjected to extraction to remove waxes and essential oils. Various options are possible for conversion of the remaining biofeedstock, which consists primarily of lignocellulose. It can be converted to synthesis gas (CO + H2) by gasification, for example, and subsequently to methanol. Alternatively, it can be subjected to hydrothermal upgrading (HTU), affording liquid biofuels from which known transport fuels and bulk chemicals can be produced. An appealing option is bioconversion to ethanol by fermentation. The ethanol can be used directly as a liquid fuel and/or converted to ethylene as a base chemical. Such a hiorefinery is depicted in Fig. 8.1. 

Nomura M, Bin T, and Nakao S. Selective ethanol extraction from fermentation broth using a silicalite membrane. Sep Purif Technol 2002 27 59-66. 

The cyciomaitodextrins (a-CD, -CD, and y-CD) can be selectively obtained from a fermentation culture or an enzyme digest of cyclomaltodextrin glucanotransferase reaction with solubilized starch. The majority of the cyclomaltohexaose (a-CD) can be separated from cycloma-Itoheptaose (/3-CD) and y-CD by their selective precipitation with p-cymene from the culture supernatant or from an enzyme digest [168]. The a-CD can then be precipitated from the supernatant with cyclohexene, which is extracted with acetone to remove the cyclohexene and the a-CD can be crystallized from water or a propanol-1/water solution [169]. The p-cymene precipitates of /3-CD and y-CD are put into a water solution and /3-CD selectively precipitated from y-CD with fluorobenzene. The y-CD is then precipitated with anthracene saturated in diethyl ether. After the removal of the fluorobenzene from /3-CD with acetone or ethanol extraction, /3-CD can be crystallized from water, and after the removal of anthracene with acetone or ethanol extraction from y-CD, it can also be crystallized from water [170,171]. The selective precipitations of the cyciomaitodextrins with various organic molecules is based on the selective formation of complexes of the organic molecules with the specific sizes of the cyciomaitodextrins and the relatively hydrophobic interior cavities of the cyciomaitodextrins [166,167,168]. 

There are many different approaches for in situ ethanol removal during fermentation. These approaches include vacuum distillation, solvent extraction, membrane reactors, and gas stripping (see 114] for review). Gas stripping of ethanol during fermentation offers advantages in terms of its effectiveness and ease of operation [15]. Ethanol can be recovered from the carrier gas stream by adsorbing onto activated carbon [16] or by condensation of the recycled gas stream under low temperatures [17]. 

The effect of pressure on biphasic fermentations has been reported for extremely thermophilic organisms (34), supercritical and compressed solvent extractions (35-37), biomethanation of synthesis gases (38), biohydrogenations (39), and bacteria for enhanced oil recovery (40). Fermentation in the presence of compressed and SCF CO2 has been conducted with a goal of using pressurized CO2 as an in situ extraction solvent. Extractive fermentation using compressed solvents could prevent toxicity due to the buildup of a fermentation product—in particular, ethanol—and greatly enhance the yield... 

Although CO2 is inhibitory to microbes, compressed hydrocarbon solvents may be appropriate for extractive bioconversions and extractions in biphasic (aqueous-compressed solvent) systems. Our laboratory investigated the metabolic activity of the anaerobic, thermophilic bacteria Clostridium ther-mocellum as a model system (45). Thermophilic bacteria have a distinct advantage over conventional yeasts for ethanol production in their ability to use a variety of inexpensive biomass feedstocks. Extractive fermentation using compressed solvents is an approach to address the end-product toxicity of these bacteria to ethanol and improve the economic viability of biofuel production by thermophilic organisms. 

Christen, P., Minier, M., Renon, H. (1990). Ethanol extraction by supported hquid membrane during fermentation. Biotechnol. Bioeng., 36, 116-23. 

Production of bulk chemicals. The production of solvents is normally characterized by a general inhibition phenomenon which has been mainly attributed to the changes in membrane permeability, or to the toxic effects on the metabolic pathway. Aqueous two-phase systems have been shown to be effective as media for the extractive fermentation of a number of solvents which include ethanol, acetone-butanol and acetic acid (3). Improved productivity has been achieved in most of the cases as compared to the conventional fermentations, which is significantly due to the elimination of product inhibition. However, there is an indication that changes in the microenvironment of the microbial cells due to the presence of non-metabolizable polymers could also contribute, in the initial phases, to the increased production. The addition of PEG and dextran to a growth medium, for instance, was shown to give increased initial ethanol yields, as a result of decrease in the chemical potential of water (8). 

Most of the substances found in the culture broth to be separated are polar components. Besides, the very low concentration of many other components (apart from ethanol and water), called congeners, lead to difficulties to correlate and predict the concentration of the distilled product in the continuous extractive fermentation. Some of these substances (acetic acid, flufural, and methanol) are considered as a source of valuable co products [3], so that further downstream separation is justifiable. 

The extractive fermentation process for bioethanol production proposed by Silva et al. [1] is shown in Fig. 1. TTie process is composed of four interlinked units feimentor (ethanol... 

Ethanol permselective membrane system has been used for the extraction of ethanol from fermentation broth. However, both membrane distillation and polymeric silicon rubber membranes showed low separation factors of ethanol and were invalid in this case. M. Nomura et al. [26] investigated the continuous extraction of ethanol from ethanol fermentation broth through a silicalite-1 membrane. From 4.73wt.% ethanol concentration of broth, the permeate ethanol concentration was 81.0wt.%. In our group, we have also investigated the potentiality of silicalite-1 membrane for alcohol extraction from aqueous solution [27]. 

The same as F-T produced mixed-alcohols, low purity bio-ethanol extracted from fermentation broth must be refined into high purity fuel grade ethanol. The pervapo-ration dehydration pilot plant based on NaA zeolite membrane was set up by Mitsui Engineering Shipbuilding Co., Ltd. (MES) in 1999. Recently, a pilot-scale NaA zeolite membrane based vapor permeation dewatering installation has been setup in our group with a handling capacity of 250 L/D. This installation can continuously produce 225 L 99.7wt.% ethanol per day. Meanwhile the permeate is nearly pure water. 

In the case of ethanol, extraction with water is undesirable due to the dilution of the ethanol, whereas direct pressing gives poor yields [184]. Direct distillation from the fermented solids performs relatively poorly, although distillation is economically feasible if combined with animal feed production from the solid wastes [217,218]. As an alternative, forced gas circulation can be used to strip ethanol from the substrate. This has been shown for a gas-solid fluidized bed and for a stirred bed [90, 219, 220]. A further advantage is that continuous stripping during the fermentation, rather than simply recovering the ethanol at the end of the fermentation, avoids the product inhibition... 

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