Abstract
The present disclosure provides systems and methods for purifying ethanol.
Claims
1. A method of integrating the production of high grade ethanol into a fuel grade ethanol facility comprising: processing beer containing ethanol from a fermentation process in a first distillation system, comprising: feeding the ethanol to a first stripper, the ethanol containing a first quantity of impurities; feeding an overhead vapor stream from the first stripper to a first rectifier; feeding a bottom stream from the first rectifier to a second stripper; feeding steam to the bottom of the second stripper at a rate that leaves 5% to 100% of the ethanol entering the side stripper in the side stripper bottoms; feeding the second stripper bottoms to a second distillation system; and withdrawing ethanol from the second distillation system having a second quantity of impurities, the second quantity of impurities being less than the first quantity of impurities.
2. The method of claim 1 wherein the first quantity of impurities comprises one or more impurities selected from the group consisting of acetaldehyde, methanol, isopropanol, 1-propanol, ethyl acetate, 2-butanol, isobutanol, amyl alcohol, and isoamyl alcohol.
3. The method of claim 1 wherein the second stripper has a decreasing ethanol concentration from the top to the bottom.
4. The method of claim 1 further controlling the ethanol concentration in the bottom stream from the rectifier feeding the second stripper in conjunction with the rate of steam fed to the second stripper to produce a desired amount of ethanol in the second stripper bottoms.
5. The method of claim 1 wherein the amount of ethanol in the second stripper bottoms is greater than 10% of the ethanol entering the second stripper.
6. The method of claim 1 wherein the amount of ethanol in the second stripper bottoms is greater than 30% of the ethanol entering the second stripper.
7. The method of claim 1 wherein the amount of ethanol in the second stripper bottoms is greater than 50% of the ethanol entering the second stripper.
8. The method of claim 1 wherein the amount of ethanol in the second stripper bottoms is greater than 75% of the ethanol entering the second stripper.
9. The method of claim 1 wherein the amount of ethanol in the second stripper bottoms is greater than 90% of the ethanol entering the second stripper.
10. The method of claim 1 wherein the second distillation system comprises a second rectifier including a column, the ethanol entering the second rectifier having a concentration from 5% to 50%, and the method further comprising withdrawing ethanol from the second rectifier column having a concentration of greater than 80%.
11. The method of claim 10 further comprising withdrawing the ethanol from the second rectifier column above a fusel purge port and below a heads purge port.
12. The method of claim 1 wherein the second distillation system comprises a third stripper and a second rectifier.
13. The method of claim 1 wherein the second distillation system comprises a third stripper, a second rectifier, and a fourth stripper.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a process flow diagram illustrating a general overview of a dry mill ethanol production process;
[0016] FIG. 2 is a process flow diagram illustrating a typical dry mill ethanol distillation process;
[0017] FIG. 3 is a process flow diagram illustrating a typical dry mill ethanol distillation process with traditional ethanol purification including methanol removal;
[0018] FIG. 4 is a process flow diagram illustrating a typical dry mill ethanol distillation process with traditional ethanol purification without methanol removal;
[0019] FIG. 5 is a process flow diagram illustrating an embodiment according to the present disclosure of a dry mill ethanol distillation process with integrated ethanol purification including methanol removal;
[0020] FIG. 6 is a process flow diagram illustrating another embodiment according to the present disclosure of a dry mill ethanol distillation process with integrated ethanol purification without methanol removal;
[0021] FIG. 7 is a process flow diagram illustrating another embodiment according to the present disclosure of a dry mill ethanol distillation process with integrated ethanol purification using repurposed equipment;
[0022] FIG. 8 is a process flow diagram illustrating another embodiment according to the present disclosure of a dry mill ethanol distillation process with simplified integrated ethanol purification using repurposed equipment; and
[0023] FIG. 9 is a process flow diagram illustrating another embodiment according to the present disclosure of a dry mill ethanol distillation process with simplified integrated ethanol purification using repurposed equipment without heads purge.
DETAILED DESCRIPTION
[0024] One novel method for integrating the production of USP grade ethanol into a dry mill facility already producing ASTM fuel grade ethanol is shown in FIG. 5. In this process, the side stripper from the traditional dry mill ethanol production process is operated to remove impurities by passing volatile impurities out the top of the side stripper while producing a significant amount of ethanol in the bottoms of the side stripper. This is counter to how a side stripper is normally operated. Normally, a side stripper is operated to minimize the amount of ethanol in the bottoms and is typically in the range of 1% or less of the ethanol entering the side stripper. In the present invention, the side stripper is operated to remove impurities while passing 5% to 100% of the ethanol entering the side stripper to the side stripper bottoms; in an embodiment greater than 10%; in an embodiment greater than 30%; in an embodiment greater than 50%; in an embodiment greater than 75%; in an embodiment greater than 90%. The resulting side stripper bottoms stream may contain 5% to 50%, even 8% to 40%, even 8% to 15% ethanol concentration. This is different from an extractive distillation step in a traditional ethanol purification process. The primary differences between these two methods is that the traditional extractive distillation column includes a zone of relatively constant ethanol concentration above the feed tray due to the introduction of water to the column at a location above the feed tray. By contrast, the column in the proposed system configuration and method has a decreasing ethanol concentration from the top to the bottom of the column. The ethanol concentration feeding the side stripper (rectifier column bottoms) and/or the steaming rate to the side stripper are adjusted in order to remove volatile contaminants while passing ethanol through the bottoms. At a minimum, the steam rate to the bottom of the side stripper is significantly reduced compared to its normal operation in order to leave a significant portion of ethanol in its bottoms stream that is then further purified. For example, acetaldehyde, methanol, sulfides and other volatile contaminants may be removed via the top stream of the side stripper. In the illustrative example of FIG. 5, the bottoms stream from the side stripper is processed through rectification and demethylization steps. A heads purge from the rectifier may be used to remove e.g. acetaldehyde, methanol, sulfides and other volatile contaminants. Alternatively, if the demethylization step is not required, there may only be the single rectification step in addition to the typical dry mill ethanol distillation process equipment as shown in FIG. 6.
[0025] The novel ethanol purification method described above may be particularly suitable to implement at dry mill ethanol production facilities that have been expanded by adding an additional set (or train) of distillation columns. Rather than using the second distillation train to process additional beer it may be utilized to further refine the ethanol produced from the first train as shown in FIG. 7. In this configuration the bottoms of the side stripper from the first train is sent to the beer stripper of the second train. The beer stripper, rectifier, and side stripper from the second train operate similarly to how they would in a normal configuration to produce near azeotropic ethanol from the top of the rectifier and ethanol-free water from the bottoms of both of the stripper columns. The energy for both of the stripper columns may be supplied by either direct-inject boiler steam, process steam from an evaporator, or from a reboiler. A purge stream of fusel oils is removed from the rectifier and sent back to the first distillation train for reprocessing into fuel grade ethanol. The purified ethanol product is withdrawn from a tray near the top of the rectifier, and the overhead product, which may contain higher levels of volatile impurities such as acetaldehyde or methanol, is sent back to the first distillation train for reprocessing. Alternatively, if a sufficient quantity of volatile impurities have been removed in the side stripper from the first train, the overhead stream of the rectifier from the second train may be used as the purified ethanol product.
[0026] In addition to the novel ethanol purification method described above, the system may be further simplified by sending the bottoms of the train two rectifier back to the train two beer stripper rather than the side stripper as shown in FIG. 8. The normal reason to separate the rectifier bottoms into a separate column from the beer stripper is to minimize the amount of water in the whole stillage that will eventually be removed through either centrifugation or evaporation. In the ethanol purification mode, the present inventors recognized that neither of the bottoms streams from either the beer stripper or side stripper contain any solids, so there is no need to keep them separate. Also, depending on the degree of purification required and the quantity of volatile impurities removed in the side stripper from the first train, the overhead stream of the rectifier from the second train may be used as the purified ethanol product (as shown in FIG. 9) rather than removing it from a side draw.
Example 1
[0027] A pilot scale distillation system was configured as shown in FIG. 9 and operated at steady state for 50 hours. Beer from a fermentation system at an average ethanol concentration of 18.8% v/v was fed to the beer stripper at an average flowrate 80.0 gallons per minute (gpm). Prior to and during the steady state run the 190 proof ethanol produced from the rectifier on average contained 555 μL/L of acetaldehyde+acetal, 128 μL/L of methanol, and 362 μL/L of total other impurities. During the steady state run the rectifier bottoms from the first train at an average ethanol concentration of 21.3% v/v was fed to the side stripper at an average flow of 16.6 gpm. The energy input into the side stripper was reduced such that the average ethanol concentration of the bottoms stream was 13.7% v/v. The side stripper bottoms stream, measured at 15.3 gpm, was continuously fed into the beer stripper of the second distillation train. The second distillation system was operated at a reflux ratio of 3.0 and with a sufficient amount of direct-inject boiler steam to ensure a negligible concentration of ethanol in the beer stripper bottoms stream. A fusel draw stream of on average 0.54 gpm was removed from different draw ports on the rectifier and returned to the first distillation train for reprocessing. Condensed overhead product from the second rectifier was removed as the purified 190 proof ethanol product with no additional heads purge stream. The average concentration of the purified ethanol was 4.9 μL/L acetaldehyde+acetal, 125 μL/L methanol, and 15.5 μL/L total other impurities.
REFERENCES
[0028] ASTM D4806-12, Standard Specification for Denatured Fuel Ethanol for Blending with Gasolines for Use as Automotive Spark-Ignition Engine Fuel [0029] The United States Pharmacopeial Convention, Alcohol [0030] The Alcohol Textbook 3.sup.rd Edition. Chapter 13—Production of neutral spirits and preparation of gin and vodka, J. E. Murtagh [0031] The Alcohol Textbook 5.sup.th Edition, W. M. Ingledew, D. R. Kelsall, G. D. Austin, and C. Kluhspies. Chapter 30—Beverage Alcohol Distillation, R. Piggot [0032] U.S. Pat. No. 2,647,078. Alcohol distillation process, J. M. Chambers
