METHOD OF REFINING OIL RECOVERED FROM ETHANOL PROCESSING BYPRODUCTS

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/813,264, filed June 13, 2006, and U.S. Provisional Patent Application Ser. No. 60/842,398, filed September 5, 2006, the disclosures of which are incorporated herein by reference.

Copyright Statement

A portion of the disclosure of this document contains materia] subject to copyright protection. No objection is made to the facsimile reproduction of the patent document or this disclosure as it appears in the Patent and Trademark Office files or records, but any and all rights in the copyright(s) are otherwise reserved.

Technical Field

The present invention relates generally to refining oil from ethanol processing byproducts and, more particularly, to refining oil recovered from a byproduct of the dry milling process used to obtain ethanol from corn.

Background of the Invention

Over the past thirty years, significant attention has been given to the production of ethy! alcohol, or "ethanol," for use as an alternative fuel. Ethanol not only burns cleaner than fossil fuels, but also can be produced using corn, a renewable resource. At present, an estimated sixty-nine "dry milling" plants in the United States produce over three billion gallons of ethanol per year. Additional plants presentiy under construction are expected to add billions of gallons to this total in an effort to meet the current high demand.

As is well known in the industry, the dry milling process utilizes the starch in the com to produce the ethanoi through fermentation, and creates a waste stream or byproduct termed "whole stillage" (which may be further separated into byproducts commonly referred to as "distillers wet grains" and "thin stillage"). Despite containing valuable oil, these byproducts have for the most part been treated as waste and used primarily to supplement animal feed. This feed is mostly distributed in the form of distillers dried grains with

solubles, which is created by evaporating the thin stillage, recombining the resulting concentrate or syrup with the distillers wet grains, and drying the product to a moisture content of less than about 10% by weight.

Significant attention has recently been given to the use of oil, including corn oil, as an alternative fuel. This fuel oil, frequently termed "biodiesel", is a cleaner fuel than petroleum-based diesel (less emissions), environmentally safe (spills biodegrade quickly), and can be mixed at any concentration to diesel without engine modification. The current value of corn oil as biodiesel is approximately $2.40 per gallon, or $648/toπ, which is essentialiy double the value of the commercial feed that would normally include this oil. Although the market for the biodiesel is growing rapidly and the potential profit is significant, key limiting factors are the cost of obtaining the oil using current techniques and the resulting quality.

Various proposals have been made for recovering oil from thin stillage. A recent proposal involves applying mechanical separation techniques, such as centrifugatioπ, with syrup derived from the thin stillage, such as through evaporation. While such techniques do an excellent job in terms of oil recovery, the recovered oil typically includes undesirable impurities, such as waxes, gums, trace chemicals (e.g., phosphorus, sulfur, etc.) and free fatty acids. These impurities may need to be substantially removed or separated through refining before the recovered oil can be declared food grade or converted to biodiesel. Accordingly, a need exists for more efficient and economical manners of recovering usable oil from byproducts created during the production of ethanol.

Summary of the Invention

In one aspect, the invention comprises a method of processing an oil-bearing byproduct of ethanol production. The method includes the steps of recovering oil from the byproduct, and refining the recovered oil. In one particularly preferred embodiment, the oil- bearing byproduct is concentrated thin stillage, and the recovering step comprises separating the oil from the concentrated thin stiϋage using a centrifuge. Preferably, the centrifuge simuitaneousiy degums the oil.

In one embodiment, the refining step comprises dewaxing the recovered oil. The step of dewaxing produces wax. Accordingly, the method may further include the step of adding the wax to distillers grains, such as those resulting from the ethanol production.

In another embodiment, the refining step comprises degumming the recovered oil. The step fo degumming produces gum. Accordingly, the method may further include the step of adding the gum to distillers grains.

Most preferably, the refining step comprises simultaneously dewaxing and degumming the recovered oil.

Alternatively or in addition, the refining step may comprise altering the color of the recovered oil. Preferably, the altering step comprises bleaching the recovered oil. The bieaching may produce a filtrate. The method may further including the step of adding the filtrate to distillers grains.

Another possible implementation involves processing free fatty acids in the recovered oil as part of the refining. The processing step may comprise using a separation column or other form of mechanical separation to separate the free fatty acids from the recovered oil, neutralization. The refining step may include the step of converting the recovered oil into biodiesel. Preferably, the converting step is accomplished using direct esterification or transesterification or a combination of direct esterification and transesterification. Any free fatty acids resulting from the converting step may be added to distillers grains.

The method may further include the step of refining the biodiesel to remove impurities, such as by example washing the biodiesel (using water or "dry" washing techniques). Furthermore, the biodiesel refining step may comprise degumming the biodiesel, dewaxing the biodiesel, bleaching the biodiesel, and/or cooling and filtering the biodiesel. Any impurities recovered may be added to distillers grains.

In accordance with another aspect of the invention, an ethanol plant for producing ethanoi including means for recovering oil from at least one byproduct is improved. The improvement comprising means for refining the oil. The means for refining the oil may comprise means for dewaxing the recovered oil, means for degumming the recovered oil, means for bleaching the recovered oil, or means for processing free fatty acids in the recovered oil and/or converting the recovered oil into biodiesel.

Another aspect of the inventive method relates to the processing of stϋlage resulting from ethanol production. The method comprises recovering oil from the stillage, refining the recovered oil to remove impurities, producing distillers grains from the stillage, and adding the impurities to distillers grains.

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Brief Description of the Drawing

Figure 1 schematically illustrates one manner of recovering and refining oil according to one aspect of the invention.

io Detailed Description of the Invention

A method of recovering oil from a byproduct resulting from the production of ethanol from corn using a dry milling technique is extensively described in pending PCT Patent Application Ser. No. PCT/US2006/09238, the disclosure of which is incorporated herein by reference. Summarizing that method, at least one byproduct of the dry milling process, is known as "thin stillage," is recovered by separating the distillers wet grain from the "whole stillage" leftover after fermentation is complete. As is known in the art and discussed below in further detail, this mechanical separation may be accomplished using a press/extruder, a decanter centrifuge (also simply known as a "decanter"), or a screen centrifuge. Moisture is then removed from the unfiltered thin stillage to create a concentrate or syrup, such as

20 through evaporation. Usable oil is then easily recovered from this concentrate, such as through mechanical processing.

In one embodiment of this proposed method, oil is recovered from the concentrate by passing it through a centrifuge and, in particular a disk stack centrifuge (and, most preferably, a self-cleaning bowl type). Preferably, the concentrate delivered to the disk

25 stack centrifuge is at a temperature of between about 150 and 212DF (and ideally 205- 210DF), a pH of between about 1 .5 and 6 (ideally between about 3.5 and 4.5) and, as a result of the preceding evaporation step, has a moisture content of less than about 90% (ideally about 60-85%). Under these process conditions, the centrifuge separates the oil from the concentrate in an efficient and effective manner, despite the relatively high level of s o solids present (which may be recovered from the centrifuge in a continuous or intermittent fashion, depending on the particular conditions).

Besides creating oil, the concentrate or syrup recovered from the centrifuge is considered more valuable. This is because the post-evaporation processing to remove the oil improves the efficiency of the drying process used on the combined concentrate syrup and distillers grains leftover. A stable, flowable product for supplementing animal feed results, which thus further complements the vaiue of the oil recovered.

As noted above, the corn oil recovered from ethanol byproducts, such as concentrated thin stillage, washed wet grains, or the like, contains various impurities that may require removal before the oil can be used as food or biodiesel feedstock. Thus, in accordance with one aspect of the invention, the oil recovered from byproducts resulting from the production of ethanol from corn, such as through the popular dry milling process, are refined, preferably at the location where the oil is recovered. One example of a treating step performed as part of the refining is dewaxing the recovered oil. This may be accomplished by cooling the oil, such as to about 45DF, which causes fractionation and crystallization of any waxy compounds present. The fractionated oil is then passed to a separation device, such as filter, settling tank, or a centrifuge, to remove, or at least reduce the amount of, any wax solids present.

Another possible pretreatment step is to degum the recovered oil. This step removes nonhydratable gums present in the oil, and is typically done by adding acid (such as citric acid or phosphoric acid). Filtration (see, e.g., U.S. Patent App. Publication No. 2003/0209493) and/or mechanical separation (e.g., centrifugation, a settling tank, etc.) may then be used to separate the gum and acid from the oil (and thus qualify as a means for degumming).

Instead of using separate steps, as contemplated above, the pretreatment of the recovered oil before use may include a combined dewaxing and degumming step. This technique involves adding an acid to the recovered oil and cooling it at the same time, with a subsequent separation step (e.g., filtration, settling tank, or centrifugation). This process is also effective for removing the phosphorous (generally to less than 30 ppm) and other trace chemicals.

Additionally, pretreatment of the recovered oil may involve a bleaching step. The bleaching step removes color, as well as remaining phosphorous (to generally less than 10 ppm), sulphur, trace metals, and other impurities. Silica, bleaching clay, or the like may be

used as a filter agent, and such filtering is often done using pressure leaf filters. Another treatment option is to remove the free fatty acids from the oϋ. This can be done by way of separation, such as by delivering the oil to a separation column where the free fatty acids (FFA) are removed by sparging. The FFAs, once separated, can be used (such as in soap manufacturing), or alternatively can be converted into biodiesel using an acid esterification step. Still another option is to add the FFAs to the distillers grains leftover from the ethano! production process. The recovered oil without the FFAs can then be used as food or converted into biodiesel using transesterification. Instead of removing the FFAs from the recovered oii, such as using the separation column, neutralization, making soap stock, tank settling, or filtration, it can instead be directly converted to biodiesel using direct acid esterification.

As should be appreciated, it is economically beneficial to avoid the need for transporting the recovered oil away for any of the refining or pretreatment steps described. Thus, in accordance with another aspect of the invention, one or more of these steps can be performed at the ethanol production plant where the oil is recovered. A schematic diagram illustrating one possible arrangement of such a plant is attached as Figure 1 . In this embodiment, whole corn is the genesis for the ethanol and the recovered oil, which upon being refined may be sold as food grade or converted into biodiesel.

The inventive method may further include performing any or all of the above- referenced refining on the oil once it undergoes conversion into biodiesel, such as by way of transesterification. Thus, the biodiesel may be refined to remove impurities, such as through the use of a washing step (such as a wet washing using water, or dry washing, such as by using a magnesium silicate adsorbent treatment (e.g., the MAGNESOL product). Further refining to degum, dewax, or bleach the biodiesel may also be performed. The refining of the biodiesel may further include cooling and filtering the biodiesel to remove impurities, with the resulting filtrate including the impurities being combined with the distillers grains.

A substantial benefit of processing at the site of ethanol production is the ability to dispose of any recovered or separated impurities by combining it with the waste byproducts remaining after the oil is recovered for disposal. For example, this allows for the filter agent used for bleaching to be combined with the waste product (as compared to transporting the

recovered oil off-site for bleaching, in which case any bleaching clay must be separately discarded, a problem recognized in the art; see, e.g., the '493 publication). Likewise, any waxes, gums or other impurities recovered can be incorporated or added to the distillers grains. The foregoing description provides illustration of the inventive concepts. The descriptions are not intended to be exhaustive or to limit the disclosed invention to the precise form disclosed. Modifications or variations are also possible in light of the above teachings. The embodiments described above were chosen to provide the best application to thereby enable one of ordinary skill in the art to utilize the inventions in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention.