Patent Application
20110136194
The invention relates to a process for producing ethanol, and more particularly, a process for increasing ethanol yield using controlled cavitation and enhanced enzyme activity.
Alcohols are a renewable and clean fuel source. A grain alcohol commonly used as a fuel source is ethanol, which can be produced, in large part, from corn by the fermentation of starch. Generally, ethanol production is accomplished through a fermentation and distillation process wherein starches are released and converted to sugars, then the sugars are converted to alcohol by the addition of yeast. At an industrial level, yeast fermentation processes only convert about one-third of the corn into ethanol.
Ethanol production facilities often begin the production process with a dry or wet milling process. In dry milling, corn, or another suitable grain, is ground up by a hammer or roller mill into a manageable mixture of coarse particles. The dry mixture of particles is combined with water and enzymes to break up the starch from the corn into smaller fragments and then subject the fragments to a saccharification phase wherein the starch is converted to sugar. After the saccharification phase, the resulting sugars are fermented with yeast to facilitate their conversion to ethanol.
Ethanol yield is dependent upon the initial starch content of the corn as well as the availability of the starch to the enzymes that are used in the saccharification process. In conventional processes, the availability of starch is governed, in part, by the success of the milling or similar step in which the corn is broken up into smaller particles. The production processes currently used in commercial ethanol plants are not able to achieve maximum theoretical ethanol yield, thus more corn than theoretically needed must be used to produce a certain amount of ethanol.
In an attempt to increase ethanol yield, the use of cavitation has been included, however it has been limited to reducing the particle size of the feed material for the purposes of, for instance, enhancing subsequent treatment and providing more surface area for enzymatic breakdown of the starches to take place. Additionally, to achieve good particle size reduction, the cavitational forces apply aggressive shear stresses to the grain particles. If the cavitational forces apply too aggressive a shear force in terms of intensity, energy and/or duration, it is possible to cause damage to the components being treated. For example, a significant decrease in the particle size could have an adverse affect on downstream processing steps.
Also, aggressive cavitational forces can degrade desirable proteins and inactivate the enzymes. The collapse of hydrodynamic cavitation bubbles formed by under specific conditions can generate extremely high local pressures and temperatures, which can promote enzyme denaturation. Cavitation can also promote chemical reactions involving H. and OH. free radicals formed by the decomposition of water inside the collapsing bubbles. These free radicals could be scavenged by some amino acid residues of the enzymes participating in structure stability, substrate binding, or catalytic functions.
Accordingly, there is still a need for a process that can obtain a closer to theoretical maximum yield. The method preferably uses a controlled cavitation device to increase enzyme activity and subsequently increase ethanol yield. Ultimately, an enhanced enzymatic bio-conversion process of starches to ethanol could increase domestically produced bio-fuels and decrease importation of foreign oil.
The present invention is a process for producing alcohol, more specifically ethanol, from grain wherein the use of cavitation energy to enhance enzyme activity substantially increases the ethanol yield, comprising mixing a grain-based material with water and enzyme to form mashed pre-gelatinized grain-based liquid medium; and subjecting the said grain-based liquid medium to cavitation activation energy not less than 0.44 kJ and not more than 1.56 kJ per kilogram of said grain-based liquid medium at a temperature in the range of 130 F to 190 F.
Herein, when a range such as 5-25 (or 5 to 25) is given, this means preferably at least 5 and, separately and independently, preferably not more than 25. In an example, such a range defines independently not less than 5, and separately and independently, not more than 25.
The controlled use of cavitational energy to enhance enzyme activity in an ethanol production process can substantially increases the yield of ethanol from corn. Although the exact mechanism by which such cavitational energy enhances enzyme activity, and thus increasing ethanol yield, is not known, there are several possible explanations. For example, the forces obtained from cavitation are used to disaggregate, disassociate, shake off and/or strip away starch granules from protein, and fiber, as well as disassociate tightly packed granules and tightly packed amyloplasts containing starch granules to make them more accessible to an enzyme for subsequent enzymatic treatment. This increase in accessibility may increase enzyme action. Cavitation energy may also enhance the transport of enzyme macromolecules toward the surface of the grain substrate. In another example, absorption of cavitation energy by a protein may produce a transient conformational shift (modifying the 3-dimensional structure) and alter the protein's functional activity. In yet another example, the collapse of cavitation bubbles, which can enhance the removal of hydrolysis reaction products from the reaction zone, may contribute to an overall increase in the reaction rate.
Referring now to the Figures,
Next, the grain-based material is mixed with water and enzyme in a slurry mixer to form a pre-gelatinized grain-based liquid medium, which can be in the form of a slurry. The time in which the grain-based material, water, and enzyme are mixed together is preferably in the range of 15 to 60 minutes, for example at least 15, 20, 30, 40, 50 or 60 minutes. The temperature at which the mixing will take place is preferably in the range of 130 to 190° F., for example at least 130, 137, 140, 150, 160, 170, 180, 185 or 190° F. The enzyme added to the pre-gelatinized grain-based liquid medium can be, but is not limited to, alpha-amylase, glucanase, beta-glucosidases, pectinases, xylanase, amylases, lignainases, proteases, beta-mannosidase, and similar enzymes, or a mixture thereof. Enzyme or a mixture of enzymes can be added at a concentration of 0.015 to 0.5 weight percent by weight of grain, such as corn, in the pre-gelatinized grain-based liquid medium, for example enzyme can be added at a concentration of at least 0.015, 0.016, 0.2, 0.28, 0.3, 0.4 or 0.5. For instance, as shown in the Example below, the enzyme can be alpha-amylase and can be present in the grain-based liquid medium in the range of 0.16 to 0.40 weight percent by weight of corn grain in the pre-gelatinized grain-based liquid medium. The grain-based material in the pre-gelatinized grain-based liquid medium can be present at a concentration of 20 to 50 weight percent by weight of the pre-gelatinized grain-based liquid medium, for example, less than 50, 45, 40, 35, 30 or 25 weight percent. Preferably, the grain-based material is present at less than 35 weight percent.
Next, the pre-gelatinized grain-based liquid medium is sent through a cavitation device or apparatus that is used to apply a specified cavitation activation energy to the liquid medium sufficient to activate the enzymes and enhance their activity within the pre-gelatinized grain-based liquid medium. In the processes described herein, enzyme can be added to form the pre-gelantinized grain-based liquid medium without the need for additional enzyme, such as enzyme addition upstream of the process prior to formation of the pre-gelatinized grain-based medium. A one-time addition of enzyme to a grain-based material prior to applying cavitation activation energy, such as through a cavitation device, reduces the need for multiple enzyme additions upstream of liquefaction and increases processing efficiency. For example, enzyme is slurried and mixed with water and grain-based material for less than one hour prior to cavitation. Multiple processing steps prior to cavitation may not be needed, such as long periods of steeping with enzymes, grinding steps, etc. The process therefore can consist of forming mixing a grain-based material, preferably finely ground, with water and enzyme for a period of less than one hour to form a pre-gelatinized grain-based liquid medium prior to application of cavitation activation energy as discussed below.
The cavitation activation energy should be applied at least at a level of about 0.4 kJ per kilogram of grain-based or pre-gelantinized grain-based liquid medium. Preferably, the cavitation activation energy is 0.4 to 1.6 kJ per kilogram of grain-based or pre-gelantinized grain-based liquid medium, for example at least 0.6, 0.8, 1, 1.2 or 1.4 kJ per kilogram. The temperature of the stream of grain-based liquid medium entering the cavitation device can be in the range of 130 to 190° F., for example at least 140, 150, 160, 170 or 180° F. The product exiting the cavitation device can be passed through the cavitation device only one time, or optionally recirculated back through the same cavitation device as many times as desired.
After the pre-gelatinized liquid medium stream passes through the cavitation device it will then move on to the liquidation and cooling phase, as shown in
Adding a cavitation step to the ethanol production process to enhance enzyme activity, wherein parameters such as pressure and temperature can be controlled, can increase ethanol yield. In general, cavitation can be described as the generation, subsequent growth and collapse of cavitation bubbles and cavities. During the collapse of the cavitation bubbles, high-localized pressures and temperatures are achieved, The bubbles contain mostly steam, although the level of steam fluctuates depending on the temperature at which the bubbles are formed. For instance, cavitation bubbles formed at lower temperatures contain less steam. Cavitation bubbles containing less steam collapse more energetically and generate higher local temperatures and pressures. These high temperatures and pressures can stimulate the progress of various chemical reactions which may not be possible under ordinary conditions, such as standard temperature and pressure (STP). However, temperatures and pressures that are too high can have a deleterious effect on a reaction and promote enzyme denaturation. The processing and reaction conditions described below prevent undesirable reactions and minimize enzyme denaturation such that ethanol yield can be increased.
In one embodiment,
As shown in
As shown, the first chamber 4 has a pressure P1 and the second chamber 5 has a pressure P2. Flow into the apparatus 10 can be provided with the aid of fluid pumping devices as known in the art, such as a pump, centrifugal pump, positive-displacement pump or diaphragm pump. An auxiliary pump can provide flow under a static pressure P1 to the first chamber 4. As discussed herein, pressure P1 is defined as the processing pressure for the controlled flow cavitation apparatus 10. The processing pressure is preferably at least 30, 40, 50, 60, 70, 80, 90, 100, 120, 140, 150, 170, 200, 300, 400, 500, 600, 700, 800, 850, 900, or 1000, psi. The processing pressure is reduced as the grain-based liquid medium or pre-gelantinized grain-based liquid medium passes through the flow-through channel 1 and orifice 3. Maintaining a pressure differential across the orifice 3 allows control of the cavitation intensity in the flow through channel 1. The pressure differential across the orifice 3 is preferably at least 30, 40, 50, 60, 70, 80, 90, 100, 120, 140, 150, 170, 200, 300, 400, 500, 600, 700, 800, 850, 900, or 1000, psi. The velocity of the grain-based liquid medium or pre-gelantinized grain-based liquid medium through the orifice 3 in the controlled flow cavitation apparatus is preferably at least 1, 5, 10, 15, 20, 25, 30, 40, 50, 60 or 70 meters per second (m/s).
In the Example below, the controlled flow cavitation apparatus 10 described herein can be used as a single-pass process for enhancing the activity of the enzyme in the pre-gelantinized grain-based liquid medium. Hydrodynamic cavitation arises in the fluid jets flowing from the orifice 3 in the form of intermingling cavitation bubbles and separate cavitation cavities. That is, the orifice 3 creates a hydrodynamic cavitation zone that promotes a high density of cavitation power dissipation locally inside the flow-through channel 1, and more preferably in the orifice 3 chamber and downstream of the orifice 3 in the second chamber 5. The high energy dissipation in the hydrodynamic cavitation zone causes a cavitation activation energy for promoting the activity of the enzymes in the pre-gelatinized grain-based liquid medium for increasing ethanol yield.
The given dynamic pressure and residence time of the bubble or steam bubble in the localized flow constriction 2 allows production of cavitation bubbles and cavities in the liquid flow. The cavity sizes are dependent on the magnitude of the dynamic pressure jet as well as the sizes of orifice 3 in the localized flow constriction 2. Increase of the dynamic pressure jet as well as size of orifice 3 leads to the increase in the sizes of cavitation bubbles. Increase of the dynamic pressure of the cavitation fluid jet also promotes increase of the concentration of cavitation bubbles. Therefore, given the dynamic pressure of the cavitation fluid jet, its shape, and the number of fluid jets, it is possible to produce a cavitation field or zone of cavitation bubbles in the downstream second chamber 5. Cavitation bubbles and cavities together with the liquid jets enter into the second chamber 5, where they collapse under the influence of static pressure P2. The energy emitted during collapse of cavitation bubbles is directly proportional to the magnitude of the static pressure in the surrounding liquid bubbles. Therefore, the greater the magnitude of P2 the greater the energy emitted during collapse of cavitation bubbles and the better the dispersion and/or size reduction effect. In other words, the level of energy dissipation in the grain-based fluid medium increases as the magnitude of P2 increases and thus the severity or hardness of collapse of each cavitation bubble separately increases, as well as the level of energy dissipation due to the decrease of the volume in which these bubbles collapse.
As shown in the Example below, it has been found that cavitation generates a specific cavitation activation energy for promoting the activity of the enzymes. The specified range of cavitation activation energies preferably create hydrodynamic steam cavitation bubbles that collapse less energetically to avoid enzyme denaturation and deleterious effect on a reactions in the alcohol production process. Because cavitation bubbles containing less steam collapse more energetically and generate higher local temperatures and pressures, which can be undesirable, the specified cavitation activation energy, processing temperature and pre-gelatinized grain-based liquid medium make up are believed to create steam-filled hydrodynamic cavitation bubbles that avoid these disadvantages.
The length (l) in orifice 3 in localized flow constriction 2 is selected in such a manner in order that the residence time of the cavitation bubble, for example a hydrodynamic steam cavitation bubble, in the orifice 3 and/or the second chamber 5 is less than 10 seconds, preferably less than 1 second or preferably less than 0.1 second. The time in the hydrodynamic cavitation zone that is needed to enhance and promote the enzyme activity is much smaller than know methods, such as ultrasonic or acoustic, and thus the controlled flow cavitation apparatus can reduce processing time and costs associated with an alcohol production process. Because processing time directly relates to the amount of alcohol that can be produced, the use of a controlled flow cavitation apparatus can increase the yield of alcohol and reduce the amount of processing time required to produce the alcohol. Hydrodynamic cavitation is more efficient than acoustic cavitation and much more efficient than conventional agitation and/or heating methods. Further, the scale-up of hydrodynamic cavitation apparatuses is relatively easy compared to other methods, which makes it well suited to the processing of dispersions and slurries, such as those present in an alcohol production process.
In another embodiment,
In operation of the device 20 shown in
The cavitation activation energy through any of the cavitation devices of
wherein ε (kJ/kg) is cavitational energy, P1 (Pa) is the static pressure in the first chamber, P2 (Pa) is the static pressure in the second cavitation chamber, Q (m3/sec) is the flow rate of the liquid medium through the cavitation apparatus, t (sec) is the residence time in the hydrodynamic cavitation zone, Vc (m3) is the volume of the downstream cavitation zone, and ρ (kg/m3) is the density of the pre-gelantinized grain-based liquid medium.
In addition to the pressure differential created by the localized flow restriction 2 in
Examples of static cavitational energy sources that can be used to apply cavitational energy to the pre-gelatinized grain-based liquid medium include, but are not limited to, static mixers, orifice plates, perforated plates, nozzles, venturis, jet mixers, eductors, cyclonettes (e.g., Fluid-Quip, Inc.), and control flow cavitation devices (e.g., Arisdyne systems, Inc), such as those described in U.S. Pat. Nos. 5,810,052; 5,931,771; 5,937,906; 5,971,601; 6,012,492; 6,502,979; 6,802,639; 6,857,774 and 7,667,082. Additionally, the dynamic cavitational energy sources that can be used include, but are not limited to, rotary milling devices (e.g., EdeniQ Cellunator™), rotary mixers (e.g., HydroDynamics SPR, Magellan™), rotor-rotor (e.g., Eco-Fusion Canada Inc.) and rotor-stator devices (e.g., IKA® Works, Inc., Charles Ross & Son Company, Silverson Machines, Inc., Kinematica Inc.), such as those described in U.S. Pat. Nos. 6,857,774; 7,178,975; 5,183,513; 5,184,576; 5,239,948; 5,385,298; 5,957,122; and 5,188,090.
Achieving increased alcohol yield within a particular type of cavitation process however, is dependent on many factors, including the location of the process at which the cavitation is applied, intensity of the cavitation, duration of time spent in hydrodynamic cavitation zone, pressure maintained in cavitation chamber, temperature, amount of enzyme, and others process variables.
In order to promote a further understanding of the invention, the following Example is provided. This Example is shown by way of illustration and not limitation.
Corn flour was fed into a slurry mixer where it was mixed with hot process water. Total dry solids concentration was of 30.9% (w/w). Residence times in the slurry mixer were 30 minutes. A dose of α-amylase was included in the mixture that was supplied to the slurry mixer (0.016% w/w enzyme based on the weight of corn flour in the slurry) such that a pre-gelatinized grain-based liquid medium was formed. The temperature, level and pH of the slurry were continuously measured using online instrumentation. Next, the pre-gelatinized grain-based liquid medium was passed from the slurry mixer to a cavitation device as illustrated in
The resulting liquid mixture that was produced after traveling through the cavitation device was discharged to a portable collection tank. Samples of the mixture were collected from this tank in 1-liter bottles and immediately taken to the fermentation laboratory. Once in the fermentation laboratory, an overhead agitator was used to continuously stir the samples to ensure that the corn solids stayed in suspension. While still stirring the samples with the agitator, 160 grams of the mixture was pumped from each of the sample bottles into tarred, sterile, 250-ml Erlenmeyer flasks using a peristaltic pump. Prior to filling, the flasks were weighed to determine their total mass.
Once the mixture was transferred to the flasks, the flasks were left to incubate for 1 hour at 180° F. Subsequently, the flasks were transferred to an incubator shaker to facilitate the cooling of the samples, wherein the temperature was held to 68° F. and the flasks were shaken at 150 rpm. After all of the samples were liquefied and cooled, glucoamylase, urea, and yeast nutrients were added to the flasks. The samples were then left to ferment for at least 60 hours.
After completion of this process, the total mass of each fermentation flask, including beer, was measured and compared to the initial mass of each fermentation flask. The concentration of ethanol was then measured by HPLC. Results are shown in Table 1 below.
The experimental data demonstrated that introduction of specified cavitation activation energy from at least 0.44 to 1.56 kJ per kilogram of grain-based or pre-gelantinized grain-based liquid medium into the pre-gelatinized grain-based liquid medium containing enzymes can improve the effectiveness of the enzymes so that the ethanol yield from grains is increased. As can be seen, the lower temperature is less effective with respect to enzyme activation, for example the processing temperature of 137° F. generally yielded a lower increase in ethanol as compared to the results at the processing temperature of 170° F. This result is mostly likely due to the fact that the bubbles were formed at lower temperatures, thus containing less steam in the bubbles which caused them to collapse more energetically and generate higher local pressures and temperatures. This sequence of events can promote the formation of free-radicals, which can have a negative effect on the catalytic function of the enzymes, thus explaining the lower relative yields.
It should now be apparent that there has been provided, in accordance with the present invention, a novel process for enhancing enzyme activity in grain-based liquid medium that satisfies the benefits and advantages set forth above. Moreover, it will be apparent to those skilled in the art that many modifications, variations, substitutions and equivalents for the features described above may be effected without departing from the spirit and scope of the invention. Accordingly, it is expressly intended that all such modifications, variations, substitutions and equivalents which fall within the spirit and scope of the invention as defined in the appended claims to be embraced thereby.
The preferred embodiments have been described, herein. It will be apparent to those skilled in the art that the above methods may incorporate changes and modifications without departing from the general scope of this invention. It is intended to include all such modifications and alterations in so far as they come within the scope of the appended claims or the equivalents thereof.
This application claims the benefit of U.S. provisional application Ser. No. 61/267,900 filed Dec. 9, 2009, the contents of which are incorporated herein in their entirety by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61267900 | Dec 2009 | US |
