WO2012036857A2

WO2012036857A2 - Improved milling process with oil recovery

Info

Publication number: WO2012036857A2
Application number: PCT/US2011/049040
Authority: WO
Inventors: Scott H. Harvey
Original assignee: Archer Daniels Midland Company
Priority date: 2010-09-17
Filing date: 2011-08-25
Publication date: 2012-03-22
Also published as: WO2012036857A3

Abstract

A modification is described of a dry grind process for producing ethanol and other co-products from whole grain, for example corn, wherein one or more solid/liquid separators act on a liquefaction discharge or mash, or act on a fermentation medium before the medium is introduced into a still for the production of ethanol, or act on both the liquefaction discharge and the fermentation medium to recover an oil fraction from the grain upstream of the still. The oil product is useful in animal feeds, in the production of biodiesel and in other applications.

Description

IMPROVED MILLING PROCESS WITH OIL RECOVERY

This invention concerns an improved grain milling process, and especially an improved process for the milling of grain, and especially for the milling of corn, for producing ethanol and other value-added products.

Increased demand for ethanol as a fuel additive has in recent years led to a dramatic growth in ethanol production. Currently ethanol is produced from corn by either wet milling or dry grind processing. Wet milling plants are capital intensive and use large amounts of process water, but through fractionation of the corn into its germ, fiber, protein and starch components are able to produce a number of value-added coproducts with ethanol, including high fructose corn syrup, com gluten meal, com gluten feed, germ meal and com oil but also including modified starches, maltodextrins and other materials.

Wet milling ethanol methods conventionally involve five basic processing steps: steeping, germ recovery, fiber recovery, protein recovery and starch washing with subsequent fermentation. In the first step, the grain, typically being corn, is steeped in a solution of weak sulfurous acid to hydrate and soften the kernel for subsequent separation/fractionation and to leach solubles (water-soluble amino acids and proteins) from the germ. After steeping, germ and fiber fractions are removed by differences in density and particle size. Germ, having a lower density than the remaining solid components of the kernel following the steeping step, is removed by a system of hydroclones, then pressed and dried. Where desired, corn oil can be pressed and/or solvent-extracted from the germ and then refined as a further coproduct. The fiber fraction, containing the pericarp of the kernel, is removed by screening, then contacted with the evaporation-concentrated steepwater from the steeping step. This mixture is then dried to yield a corn gluten feed coproduct.

The remaining solids are then separated into a starch fraction and a protein fraction, through a system of centrifuges and hydroclones. The gluten protein fraction is concentrated using a gluten thickener centrifuge and further dewatered by vacuum belt filtration and drying with rotary steam tube or flash dryers. The final dried product, corn gluten meal, has a high protein and low fiber content, and is used primarily in nonruminant and companion animal diets. The starch recovered by the hydroclone is cooked, liquefied and saccharified to yield glucose, which then undergoes fermentation to the desired primary ethanol product. The ethanol is distilled away from the water and residual water-soluble solids. The recovered residual solids can be added to the corn gluten feed, while carbon dioxide produced in the fermentation can be marketed to the beverage industry.

By contrast, dry grind processing methods are much less capital intensive than are wet milling ethanol methods, in that the corn kernel is not fractionated into its primary parts but is handled whole, and do not require large amounts of process water.

Dry grind ethanol methods also have certain disadvantages, however, as compared to wet milling ethanol methods. Processing the entire kernel, including the non-starch portions of the kernel, is less efficient for producing ethanol. As well, dry grind ethanol processes primarily provide one marketable but relatively lower value coproduct, in the form of distillers' dried grains with solubles (DDGS). The non-fermentable portions in a dry grind ethanol process do contain a fairly high oil content, but recovery is difficult.

Briefly, in a typical dry grind ethanol process, whole corn is ground, slurried with water and cooked with the addition of enzymes to yield a liquefied "mash". Yeast and additional enzymes are added to the mash, and the mash undergoes concurrent saccharification and fermentation to yield the desired primary ethanol product in a liquid portion, while the unfermented solids left over are recovered with the yeast as distillers' dried grains.

Carbon dioxide from the fermentation is released from the broth in a vapor liquid separator, and the ethanol is recovered from the liquid portion for use as a fuel additive.

As mentioned, those skilled in the art have for some time appreciated that it would be desirable to be able to recover at least some of the corn oil in the portion of the corn that is not fermented to make ethanol in dry grind processing, if this could be accomplished without the addition of multiple further processing steps and related equipment. This corn oil would then be available for use as a feed for making biodiesel or other products in preference to the aforementioned distillers' dried grains with solubles.

United States Patent No. 7,601 ,858 to Cantrell et al., for example, is representative of a number of related properties which describe post- fermentation approaches to recovering oil from the remaining, unfermented materials exiting an ethanol fermentation still, in the form of "whole stillage". The '858 Cantrell patent relates that "whole stillage" had theretofore largely been treated as waste, being used primarily to supplement animal feed in the form of the aforementioned distillers dried grains with solubles, as made by separating the whole stillage into a solids portion (distillers dried grains) and a liquid, thin stillage portion, then evaporating the thin stillage down to a syrup, recombining the distillers dried grains with the syrup and drying the product to provide a lower moisture content. Cantrell indicates that there had been previous efforts to recover the valuable oil from the whole stillage, and cites an example wherein the centrifugation of the thin stillage prior to the evaporation step had been proposed, but summarizes the previous efforts as "not... successful in terms of efficiency or economy."

Cantrell's solution provided in the '858 patent is to evaporate the thin stillage to form a concentrate, and then recover the oil from the concentrated thin stillage. According to an embodiment described at column 3, line 59 through column 4, line 7, the thin stillage from a press/extruder, a decanter centrifuge or screen centrifuge is evaporated to a moisture content greater than 15% and less than about 90%, especially to a moisture content of between 30% and 90% and ideally about 60 to 85%. The resultant syrup is fed to a centrifuge, for example a self-cleaning bowl type disk stack centrifuge but optionally being a nozzle bowl-type disk stack centrifuge or horizontal centrifugal decanter, at a temperature of between 150 and 212 degrees Fahrenheit, ideally at 180 degrees Fahrenheit, and at a pH of between about 3 and 6, ideally between about 3.5 and 4.5. The solids recovered from the disk stack centrifuge can be dried as an animal feed.

Generally, the present invention provides improved methods for the processing of grain and grain products to obtain greater value therefrom in a dry grind ethanol process, particularly providing alternative, pre-fermentation methods to the post-fermentation approaches described in the '858 patent and its related properties, for example, for recovering an oil product stream. Thus, while the description hereafter will describe such improved methods in the context of preferred embodiments, in processing corn particularly, those skilled in the art will recognize that the methods can be beneficially applied to other grains such as wheat, millet, barley, sorghum, triticale, rice, amaranth, buckwheat, rye, oats and quinoa.

The present invention provides needed improvements through a modification of a typical dry grind process whereby one or more solid/liquid separators are added to recover an oil product from the liquefied mash, or are positioned to recover an oil product from a fermentation medium produced following addition of a further enzyme to the mash, or are employed in both locations in the process.

FIGURE 1 depicts an improved grain milling process of the present invention, in one illustrative embodiment.

FIGURE 2 depicts an improved grain milling process of the present invention, in an alternative embodiment to that shown in Figure 1.

In preferred embodiments of the invention, a typical dry grind process, wherein whole corn is ground, slurried with water, treated with enzymes and cooked to form a liquefied mash, then is treated with additional enzymes, fermented in a still and further processed to yield fuel grade- additive quality ethanol and other products, is modified to incorporate one or more solid/liquid separators after the "mashing" step to recover an oil product from the mash or to incorporate one or more solid/liquid separators after the additional enzymes are included, again to recover an oil product before entry of the fermentation medium into the ethanol still. Conceivably, where process economics permit, solid/liquid separators can be used in both locations within a dry grind process. In general, however, it is expected that conventionally a solid/liquid separator (or combination of such separators) will be employed in one location or the other, as opposed to in both locations.

The present invention is illustrated and understood more fully by reference to Figure 1 , in which a modified dry grind ethanol process 10A is schematically shown wherein one or more solid/liquid separators are used to recover an oil product from the mash prior to the addition of further enzymes. The embodiment 10A is intended to be illustrative only, and those skilled in the art will readily appreciate that numerous modifications and variations to the embodiment 10A may be made as well as that the present invention may be adapted for use with a variety of existing or known dry grind methods, without departing from the proper scope of the invention as defined more particularly by the claims following hereafter.

Returning now to Figure 1 , as shown, whole corn 12 is milled or ground in a milling step 14. Milling may be done by any known method, for example by use of a Fitz mill, Beall degerminator or Satake degerminator. Milling step 14 produces a ground corn stream 16, which is a heterogeneous mixture including germ, endosperm, pericarp and fines. The fines are primarily starch, and the pericarp is primarily fibrous material.

Ground corn stream 16 is slurried with water 18, and is cooked into a mash in mashing step 20 with the addition of an enzyme 22 to aid in the liquefaction of fermentable components of the corn. Typically the ground corn stream 16 is combined with a volume of water 18 having a weight of two to three times the weight of the corn to be mashed, the water 18 usually being supplied in a typical dry grind process in the form of fermentation backset, condensed evaporator water or corn steep liquor.

The corn and water mixture is preferably maintained at a temperature between about 70 degrees and 90 degrees Celsius (and more preferably at a temperature of from about 88 to 90 degrees Celsius) for about 30 minutes, after which a-amylase enzyme is added (indicated by stream 22) and the temperature raised to from 105 to 1 10 degrees Celsius for from 5 to 15 minutes, to aid in the liquefaction of starch and hemicellulose materials from primarily the endosperm and pericarp. The addition of the enzyme combined with heating causes breakdown of the starch to maltooligosaccharides, as in typical dry grind methods.

The mash 24 then proceeds to solid/liquid separations step 26, wherein one or more solid/liquid separators are used to separate an oil product stream 28 which may be further processed using conventionally known methods for making biodiesel fuel, or which may be further processed for other valuable uses appropriate to the composition of the stream 28.

Alternatively, the oil product stream 28 may be supplied in whole or in part (separately from the unfermented solids from the fermentation step described hereafter) for the production of animal feed products.

Any solid/liquid separator device or combination of such devices which are suitable for processing the mash 24 can be contemplated for the separations step 26, and those skilled in the art will be well able to select a device or combination of devices for cost-effectively performing the separations step 26, having regard for the characteristics of the mash 24 produced and the variability of those characteristics in operation of a given mill. Such solid/liquid separator devices may include, for example, those based on filtration or the like (membrane separators, for example), centrifuges such as the self-cleaning bowl type and nozzle bowl type disk stack centrifuges and horizontal centrifuge decanter devices mentioned by the '858 patent, decanters and other devices performing a separation based on settling differences in a medium. United States Patent No. 7,915,458 to Bruckmayer claims an improved horizontal axis centrifuge device that might be used, and unquestionably other devices can be identified for performing the separations step 26. A two stage separation may be especially preferred for producing oil product stream 28 from the mash 24, for example, a decanter or similar device to cost effectively remove solids of higher density, followed by a disk stack centrifuge to efficiently separate the oil from the remainder of the mash 24 and provide the oil product stream 28.

Solvent extraction, filter aids and the like may be employed in addition to facilitate the separation and recovery of the oil in the mash, in the form of oil product stream 28. Along these same lines, several parties have since the '858 patent claimed to have developed improvements for recovering additional oil in a post-fermentative context, which may prove similarly helpful in the different context of the present invention. Ashland Hercules Water Technologies has offered a proprietary, non-polymeric, liquid corn oil extraction aid under the product designation PTV-M5309, for example, while

U.S. Water Ethanol Process Technologies, St. Michael, Minnesota has introduced its COR™ additive for the same purpose. As well, United States Patent Application Publication No. US 201 1/0086149, published April 14, 2011 , describes perfoming a pH adjustment on a "corn fermentation residue" to aid in recovery of a corn oil product from the corn fermentation residue.

The temperature of the deoiled mash stream 30 (after removal of the oil product stream 28) is reduced to between 60 and 75 degrees Celsius, and glucoamylase enzyme (shown as stream 34) is added in step 32 to further produce glucose from the starchy endosperm of the corn kernel, while maintaining a temperature of between 60 and 75 degrees over a period of from about 1 to about 48 hours.

The resultant fermentation medium 36 then is fermented in fermentation step 38 with addition of glucoamylase enzyme and of a fermentative microorganism, which microorganism can be, for example, a yeast (e.g., saccharomyces cerevisiae), bacteria or fungus, such fermentation typically occurring at a temperature of from 30 to 40 degrees Celsius. Typical manufacturer-recommended glucoamylase addition levels may be used, for example, about 0.22 units per gram of starch. Other enzymes may also be added including hemicellulases, proteases, cellulases, and feruloyl esterases.

The fermentation results in the production of a carbon dioxide product stream 40, ethanol and some remaining non-fermentable solids and residues, including yeast, gluten proteins, germ and fiber. After allowing the carbon dioxide to release from the fermentation broth as stream 40, the ethanol and remaining solids are passed (reference number 42) to a distillation step 44, whereby the crude ethanol stream 46 from the fermentation is recovered for further clean-up and purification (not shown) prior to use as a fuel additive.

The remaining water and solids from the fermentation step 38 undergo a second solid/liquid separation as, for example, in a centrifugation step 48, resulting in a solids portion 50 typically containing germ and other solids and a thin stillage portion 52 which is preferably concentrated by evaporation in step 54 for being incorporated in a high protein feed product 56. Any residual oil content in solids portion 50 may be extracted as desired as a crude corn oil coproduct stream 60 for combining with oil product stream 28 and further refining or use, by means of oil recovery step 58.

Oil recovery step 58 can use any conventional technique for extracting the oil value in the solids portion 50, including, for example, chemical extraction, expeller extraction, hydraulic press extraction, carbon dioxide assisted extraction and supercritical fluid extraction. Expeller extraction is preferred. Where supercritical fluid extraction is used, a preferred supercritical fluid is carbon dioxide with or without co-solvents such as propane and/or ethanol. Suitable methods of supercritical fluid extraction are set forth, for example, in U.S. Pat. No. 4,495,207 to Christianson et al., which is incorporated by reference herein.

The remaining high protein solids 62 are then combined as mentioned above with the concentrated stream 64 from evaporation step 54 (and optionally with at least some part of the oil in oil product stream 28 and oil coproduct stream 60) to yield the high protein feed product 56. Those skilled in the art will appreciate as well, that to the extent there remains oil which was not removed via the oil product stream 28 and that would be desirably recovered from the concentrated thin stillage stream 64, then the approach of the '858 Cantrell patent can be followed and additional oil recovered in this fashion.

Turning now to Figure 2, an alternative embodiment 10B of the present invention is illustrated schematically, using the same reference numbers where possible as used in Figure 1 for the same or essentially the same flows or steps.

In embodiment 10B, whole corn 12 is milled in step 14 to again provide a ground corn stream 16. The ground corn is combined with water 18 and cooked into a mash in mashing step 20 with the addition of an enzyme 22 to aid in the liquefaction of fermentable components of the corn.

In a subsequent saccharification step 32b, glucoamylase enzyme is added as indicated by stream 34 to the cooked mash 24, in order to produce glucose from the starchy endosperm of the corn kernel. The resultant fermentation medium 31 is then deoiled of oil product stream 28 by one or more solid/liquid separators 26b. A deoiled fermentation medium 36 is then fermented as described previously, in step 38. The remaining operations and streams are then as previously described in relation to Figure 1 , Thus, the essential difference between the embodiments of Figures 1 and 2 lies in where, in advance of the fermentor, the one or more solid/liquid separators called for by the present invention are deployed to produce the oil product stream 28 - whether after the liquefaction step but prior to the saccharification step as in Figure 1 , or after the saccharification step and the addition of the glucoamylase enzyme as in Figure 2.

Claims

CLAIMS What is claimed is:

1. An improved grain milling process including the production of ethanol by fermentation, comprising: grinding a whole grain; forming a slurry with water of the ground whole grain; adding one or more enzymes to the slurry with heating to liquefy fermentable components of the ground whole grain and produce a mash; separating out an oil product stream from the mash; adding an enzyme to the deoiled mash to form a fermentation medium for producing ethanol; and fermenting the fermentation medium in the presence of yeast and one or more added enzymes.

2. A process as described in Claim 1 , wherein the oil product stream is then incorporated in an animal feed or provided to a process for producing biodiesel.

3. A process as described in Claim 2, wherein the whole grain is com, and the oil product stream consists essentially of corn oil.

4. An improved grain milling process including the production of ethanol by fermentation, comprising: grinding a whole grain; forming a slurry with water of the ground whole grain; adding one or more enzymes to the slurry with heating to liquefy fermentable components of the ground whole grain and produce a mash; adding an enzyme to the mash to form a fermentation medium for producing ethanol; separating out an oil product stream from the fermentation medium; fermenting the deoiled fermentation medium in the presence of yeast and one or more added enzymes.

A process as described in Claim 6, wherein the oil product stream is then incorporated in an animal feed or provided to a process for producing biodiesel.

A process as described in Claim 7, wherein the whole grain is corn, and the oil product stream consists essentially of corn oil.