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English to Thai: METHOD FOR SEPARATION AND PURIFICATION OF ETHANOL General field: Science Detailed field: Chemistry; Chem Sci/Eng
Source text - English TECHNICAL FIELD
The present invention relates to a method for separating and purifying ethanol, and more particularly, to a method for separating and purifying ethanol, which comprises: feeding a portion of ethanol feedstock to a first distillation column to obtain a first ethanol concentrate; feeding the first ethanol concentrate from the first distillation column and the remaining portion of the feedstock to a second distillation column to obtain a second ethanol concentrate; and feeding the second ethanol concentrate from the second distillation column to a membrane module to obtain a third ethanol concentrate.
BACKGROUND ART
In the case in which bioethanol is produced by a pretreatment-saccharification-fermentation process using starchy or lignocellulosic biomass as feedstock, the content of ethanol in a fermentation broth is very low (about 5-7 wt%), because the concentration of water in a fermenter is high. However, because the concentration of ethanol as a final product is required to be as high as 99 wt% or more, technology of effectively separating a small amount of ethanol in high purity from a large amount of water while minimizing energy consumption is required.
Commercial bioethanol processes are broadly divided into a corn ethanol process that uses starchy feedstock such as corn, and a cellulosic ethanol process that uses lignocellulosic biomass as feedstock. In the both processes, the concentration of ethanol in a fermenter is very low (about 5-7 wt%), because ethanol is produced by fermentation.
To separate a small amount of ethanol from a large amount of water, significant amount of energy is generally consumed. For this separation, a distillation method may be currently used, and alternatives to the distillation method are not abundant, if the scale and long-term operability of commercial-scale plants are taken into consideration. In this distillation method, the consumption of steam greatly increases, because lots of water is evaporated together with ethanol.
Water and ethanol form an azeotrope at an ethanol concentration of about 95 wt%. This suggests that it is impossible to produce ethanol with high purity (99 wt% or higher) by the distillation method alone. Thus, an adsorption or membrane technique needs to be additionally applied.
To separate and purify ethanol using an adsorption method in the bioethanol process, a method is generally used which comprises concentrating ethanol to a concentration of about 40-50 wt% using an ethanol stripper, and then concentrating ethanol to a concentration of about 90-95 wt%, which is the azeotropic concentration of ethanol in water, by use of a rectification column, and finally removing remaining water by adsorption with molecular sieve. However, if this method is used, high capital cost is required, because two distillation columns and a large amount of adsorbent are required. In addition, energy efficiency is also low, because a large amount of steam is consumed in the two distillation columns.
In particular, because the rectification column should receive ethanol concentrate as feedstock and produce ethanol with a concentration equal to or higher than 92 wt%, which is the minimum concentration of ethanol that can be treated with molecular sieve, there are problems in that many stages are required and a large amount of steam is consumed. In addition, in the adsorption technique for obtaining high-purity ethanol, a large amount of an adsorbent is generally required, and the adsorption performance thereof is progressively deteriorated over time. Also, a desorption process is necessarily accompanied, and for this reason, two or more adsorbent beds should be installed and operated in a switching mode. Therefore, there is a disadvantage of high initial capital cost for the adsorption technique.
U.S. Patent No. 8328994 discloses a system in which ethanol-containing liquid(Beer) is evaporated using a plurality of flash tanks and fed to a stripper. The invention disclosed in this US Patent has an advantage in that the amount of heat that is used in the stripper can be reduced through use of a plurality of flash tanks, but this method has a disadvantage in that the amount of heat used in the rectification column that uses the largest amount of heat cannot be reduced, because the product from the stripper should be concentrated again to ethanol concentrate in the rectification column.
Korean Patent Publication No. 2008-0089961 discloses an ethanol purification system in which the amount of heat that is used for ethanol concentration is reduced using a low-pressure concentration column and a high-pressure concentration column. The invention disclosed therein has an advantage in that the amount of heat used can be considerably reduced, because the amount of heat used is reduced using the low-pressure concentration column and the high-pressure concentration column and the heat discharged is recovered and recycled, but has a disadvantage of high initial capital cost, because an extraction method is used to remove remaining water from ethanol concentrate obtained from a distillation column.
Meanwhile, a membrane technique has generally been used mainly for solid-liquid separation, but with the recent development of technology, it has also been possible to use the membrane technique for liquid-liquid separation. In addition, the membrane separation technique has an advantage of low initial capital cost, because limitation to the amount of feedstock to be treated is low compared to the adsorption technique and a separate regeneration process is not required. Furthermore, up to date, membranes had a problem in that they are difficult to be used in high-temperature processes, but in recent years, the manufacture of heat-resistant membranes that can resist even a temperature of about 150℃ has become possible, and thus the use of these membranes in combination with high-temperature separation units such as distillation columns has become possible.
Accordingly, the present inventors have made extensive efforts to solve the above-described problems, and as a result, have developed a method for separating and purifying ethanol, which comprises feeding a portion of feedstock to a first distillation column to obtain a first ethanol concentrate, and then feeding the first ethanol concentrate and the remaining portion of the feedstock to a second distillation column to obtain a second ethanol concentrate, and feeding the second ethanol concentrate to a membrane module to obtain a third ethanol concentrate. In addition, the present inventors have performed an experiment on the separation and purification of ethanol using the above method for separating and purifying ethanol, and as a result, have found that the consumption of energy used for ethanol separation was reduced and purification process was also simplified, thereby completing the present invention.
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