Recovery of ethanol

Some experiments (Table 1, Experiments No. 97 and 108) were carried out in one leg of an H-shaped reactor. After the killing of the reaction, all volatiles were distilled into the other leg of the reactor which was then scaled off, and its contents were analysed by GLC for ethanol. We hoped to measure in this way the ethanol formed from the sec-oxonium ions by reaction (v), but as the results show, the recovery of ethanol was rather incomplete, presumably because much of it remained trapped in the polymer. In some experiments a phial containing a measured amount of water was broken before the initiator phial (Table 1, Experiments No. 115, 111 B, 114). 

While sulfite pulping is less popular than Kraft pulping, it is more prevalent in the production of dissolving pulps. Further, sulfite pulping permits recovery of ethanol from the spent pulping liquor before incineration, as is... 

The first distillation column has 32 trays, with the feed on tray 12, being operated at a reflux rate of 50 000 kg/h. The column has a partial condenser and delivers 1000 kg/h vapor distillate (sent to the absorption column) and 32 000 kg/h liquid distillate. The liquid distillate contains mainly ethanol (77% weight) and water (20% weight), with furfural the main impurity. The recovery of ethanol is almost 100%. The bottoms stream (2.9 x 10s kg/h) consists mainly of water, the concentration of dissolved organic compounds being around 7% (weight). 

Changing the recovery of ethanol from 99-99.99%m produces only minor increases in the heat loads. A summary of the column material balance for one mole of feed is shown in Table V when the solvent-feed ratio is 3.5 mole basis. This calculation was made for a recovery of 99.99% ra ethanol using 46 equilibrium trays with the solvent on 43 and the feed on 22. The reflux-feed ratio was 1.5537 mole basis. The corresponding data for temperature, composition, and volatility profiles are summarized in Table VI. 

The remaining liquid is sent to a distillation column known as a beer column, which concentrates the alcohol to about 40mol% ethanol and 60mol% water in the distillate. The recovery of ethanol in the beer column is 99.9%. The bottoms stream from the beer column contains the remaining components of the fermentation broth and can be processed for use as animal feed. 

In an ethanol plant, the mixture of water and ethanol from the beer column distillate contains about 40% ethanol (molar basis) in water, together with the fusel oils described in the previous problem. This mixture is distilled to give an azeotropic mixture of ethanol and water (89% ethanol) overhead, with 99.9% recovery of ethanol. The fusel oil can cause blending problems if it is allowed to accumulate in the distillate. Fusel oil is a mixture of higher alcohols and ethers that can be approximated as a mixture of n-butanol and diethyl ether. This mixture is usually removed as a side stream from the column. When the side stream is contacted with additional water, a two-phase mixture can be formed and the oil phase can be decanted to leave an ethanol-water phase that is returned to the column. 

The lower phase from the separator is redistilled in column C, to recover the ternary azeotrope as the overhead product and water-rich ethanol as the bottom product. The ternary azeotrope from column B joins that from column A. A third distilling column, column D, completes the recovery of ethanol as the ethanol/water azeotrope top product of this column, from the water-rich ethanol stream of the second column. The bottom product of the third column is the water originally present in the ethanol/water azeotrope feed to column A, now entirely freed of solvents. 

There have been many simple modifications to airlift bioreactors for specific applications. For example, a novel airlift loop fermenter (schematic unavailable in the literature) utilizes a side arm. The external loop in this integrated system overcomes the problem of ethanol inhibition by continuously stripping ethanol from the fermentation broth and recovering it by condensation. This is suitable for the simultaneous production and recovery of ethanol. ... 

Vast amounts of renewable biomass are available for conversion to liquid fuel, ethanol. In order to convert biomass to ethanol, the efficient utilization of both cellulose-derived and hemicellulose-derived carbohydrates is essential. Six-carbon sugars are readily utilized for this purpose. Pentoses, on the other hand, are more difficult to convert. Several metabolic factors limit the efficient utilization of pentoses (xylose and arabinose). Recent developments in the improvement of microbial cultures provide the versatility of conversion of both hexoses and pentoses to ethanol more efficiently. In addition, novel bioprocess technologies offer a promising prospective for the efficient conversion of biomass and recovery of ethanol. 

Attach the condenser to the dual manifold using a gas-inlet adapter, and place the system under a nitrogen atmosphere, Heat the reaction mixture on an oil-bath, with stirring at 140°C for 2-3 h under nitrogen until quantitative recovery of ethanol (32 mL theoretical) is obtained. Replace the nitrogen line with an aspirator vacuum ( 25 mmHg) to remove the residual ethanol. 

Let us assume that the concentration of the feed ethanol is 10 wt%, a level readily produced by fermentation processes. For simplicity, let us assume furthermore that the recycled CO2 contains no ethanol and that the desired recovery of alcohol is 95% of the amount in the feed. Figure 8.12 reproduces the equilibrium line shown previously in figure 8.11. In this case, the minimum solvent-to-feed (S/F) ratio is shown in figure 8.12 by the so-called operating line, the dashed line drawn between the abscissa at 0.5 wt% ethanol in water (we specified that the recovery of ethanol from the feed is 95%) and the equilibrium line at 10 wt% ethanol (the feed concentration). The minimum S/F ratio is 10.5 for this case. This S/F ratio is the equivalent of 105 lb C02/lb ethanol in the feed stream this is a rather high solvent requirement. Since the operating line touches the equilibrium line, an infinitely tall column is required. 

The low distribution coefficients, the attendant requirement of recycling CO2 containing very little ethanol in order to achieve a high recovery of ethanol from the feed stream, and the inability to achieve the separation of ethanol from the extract stream by pressure letdown required the development of this SCF extraction-distillation process. The diagram shown in figure 8.14 pictorially summarizes that an old distillation technique can be combined with new supercritical CO2 extraction to solve the separation problem supercritical CO2 can extract the ethanol from the feed stream, distillation can separate and regenerate the solvent for recycle, and vapor compression can achieve energy efficiency. 

A flow chart of the process is shown in the figure. The stream from fermenter 1 containing 5.6 wt % ethanol is heated to 75 C and pumped via 2 to column 3 where it is contacted with CO2 at 80 atm and 75 °C. The raffinate leaving the column contains 2.2% ethanol and is returned to the fermenter through valve 4. (Note that with recycle of the raffinate to the fermenter, it is not necessary to achieve a high recovery of ethanol.) The C02-ethanol stream, which also contains some dissolved water, leaving the top of the extractor is conveyed to vessel 5 which is filled with activated carbon. The ethanol is adsorbed by the activated carbon, and the CO2 is recycled by compressor 6 to the extractor. 

A batch distillation column with six theoretical stages (the first stage is the still pot) is charged with 100 kmol of a 20 mol% ethanol in water mixture at atmospheric pressure. The boilup ratio is constant at 10 kmol/h. If the distillate composition is to be maintained constant at 80 mol% ethanol by varying the reflux ratio, calculate the distillation time required to reduce the still residue composition to 5 mol% ethanol. Calculate the fractional recovery of ethanol in the distillate. The equilibrium distribution curve at column pressure is given in Table 6.2. 

EXAMPLE 9.3 Recovery of ethanol by heterogeneous azeotropic distillation... 

Pangarkar VG. 2002. Separation of ethanol by pervaporation (In-situ recovery of ethanol from fermentation broth). Technical proposal for funding by Department of Biotechnology, Government of India, New Delhi, India. 

Dl. A distillation column with a total condenser and a partial reboiler is fed a mixture of alcohols. The feed is 19 wt % methanol, 31 wt % ethanol, 27 wt % n-propanol, and 23 wt % n-butanol. (Methanol is most volatile and n-butanol is least volatile.) The feed rate is 12,000 k h. We desire a 97.8% recovery of ethanol in the distillate and a 99.4% recovery of n-propanol in the bottoms. 

In Figure 8-13 the A product will be the ethanol product and the B product (distillate from column 2) will be water. We want the A product to be 0.9975 mole frac ethanol (this exceeds requirements for ethanol used in gasoline). Use an external reflux ratio in column 1 L7D = 1.0. (Normally these would be optimized, but to save time leave it constant.) The reflux is returned as a saturated liquid. This set of conditions should remove sufficient ethylene ycol from the distillate to produce an ethanol of suitable purity (check to make sure that this happens). The bottoms product from column 1 should have less than 0.00009 mole frac ethanol. This number is low to increase the recovery of ethanol. 

Wasewar K L and Pangarkar V G (2006), Intensification of recovery of ethanol from fermentation broth nsing pervaporation economical evalnation , Chem Biochem Eng <2,20,135-145. 

Apart from separating the toxic byproducts or recovering the valuable chemicals, the removal of furfural and other compounds originating from the raw materials is also important because they can cause significant membrane fouling during subsequent recovery of ethanol (Gaykawad et al., 2013). 

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