Abstract:
A method of converting agricultural waste to a fuel comprising adding about 5% to about 90% agricultural waste to about 10% to about 95% reaction solution of water and alcohol. The reaction solution ranges from about 100% alcohol to about 100% water. The reactants are subjected to a heat of about 230° C. to about 370° C. under a pressure of about atmospheric to about 3000 psig for three minutes or more. Another embodiment of the method of converting agricultural waste to a fuel further adds about 0.5% to about 15% of an oxidizing agent to the reactants. A further embodiment of the method of converting agricultural waste to a fuel adds about 10% to about 50% by weight of diesel fuel to the reactants.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of U.S. Provisional Patent Application Numbered 60/879,478 filed on Jan. 9, 2007. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISC APPENDIX 
       [0003]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0004]    Energy needs and the desire to protect the environment have resulted in efforts provide alternative sources of fuel. To date, in addition to the conventional fossil fuel sources and the use of nuclear energy, numerous alternative energy sources have been utilized such as the wind, or mechanical or thermal use of large bodies of water. Also, with respect to environmental considerations, low sulfur coal and methods for cleaning the exhaust from the use of fossil fuels have been utilized. 
         [0005]    The U.S. Department of Energy is faced with the immense task of balancing the energy demand of our society with the environmental consequences of generating that energy. The primary focus has been on the efficiency of conversion of fuel to a useful form of energy. Energy can simply be defined as the ability to do work. The energy value of a fuel normally is measured by temperature change as a result of oxidation. Fundamentally fuels are valued by their ability to supply heat. In the traditional sense, combustion processes produce heat from the fuel. As fuel is oxidized, heat is released. The heat is converted through some mechanical means to a more useful form of energy for application. As the efficiency of the conversion increases, the negative impact on the environment decreases. 
         [0006]    Previously, it has been shown that after reaction with water near the critical condition large portions of animal wastes, namely manures, can become soluble-. In initial experiments a blend comprised of a fifty/fifty by weight blend of agricultural waste and water was heated to nearly 360° C. and held at that temperature for about one hour. In those conditions the water reacted with parts of the agricultural waste to produce moieties that had soluble behavior when blended with diesel fuel. Although only initially partially soluble, about 35%, blending the insoluble portion with a surfactant, lecithin, and emulsifying with the diesel fuel mixture enriched the initial blend so that the final blend had compositions containing nearly 50% converted agricultural. These blends were used to operate or fuel a diesel engine. However, the reaction conditions were somewhat extreme. The vapor pressure of water at 360° C. is 2705 psia (pounds per square inch absolute). This reaction would require thick wall reactors and special training. Further one of the difficulties with this procedure was that the blend of 50% water 50% agricultural waste has a thick consistency and is difficult to handle. Finally, the heat transfer from the reactor walls to the mixture is not homogenous and some charring was seen at the reactor wall surface. 
         [0007]    In another experimental version the agricultural waste conversion water was again blended with agricultural waste to create a blend at the 50%/50% level. But to this blend diesel fuel was added to make the blend more fluid. Mixing in some diesel fuel decreased the viscosity of the blend and facilitated the reaction. The diesel fuel was also an effective solvent for the product. The procedure also facilitated a deashing of the agricultural waste material whereas the ash was prevalent in the previous method. Additionally, the remaining ash could be recovered by simple filtration or centrifugation. However, the percentage of the mixture that was soluble agricultural waste was fairly low because a significant quantity of diesel fuel was required to make the blend more fluid. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    The present invention provides for a method of converting agricultural waste to fuels under lessened conditions than previously possible. One aspect of the invention is the pretreatment of agricultural waste with an oxidizing agent. The oxidizing agent such as hydrogen peroxide could be added before the alcohol water mixture, or the addition of air bubbling through the blend could be the oxidizing agent. Additionally, even without the pretreatment a blend of agricultural waste and an improved water/alcohol reaction solution could produce a fuel under less extreme conditions than previously possible. The reaction solution could have very high concentrations of alcohol. At these different reaction solution concentrations, the addition of diesel fuel may also not be needed as it was at earlier when no alcohol was added to the reactant mixture as in previous experiments. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0009]    In this application agricultural waste can be lagoon waste, animal waste and manures, cellulose waste such as wood waste corn stover and human sewage sludge, organic wastes such as paper pulp mill black liquor waste, and animal mortalities that are a hazard in the animal production industry. 
         [0010]    Previous procedures for the conversion of agricultural waste to fuels utilized extreme conditions. The procedures required an aqueous solution to be heated to 360° C. The vapor pressure of water at this temperature is 2705 psia (pounds per square inch absolute) and additionally a gas is produced. Any gaseous products added to the total pressure inside a closed reactor and the end pressure of the procedure. Usually at a temperature around 360° C. the pressure is about 3000 psig. The procedure would be much more attractive if that pressure could be dropped significantly and the solubility of the agricultural waste could be enhanced and the fuel product could be completely deashed Since agricultural waste is mostly carbon with oxygen linkages it was felt that partially oxidized waste would produce more acids and these acids could be reacted with alcohols. 
         [0011]    In organic chemistry one of the common oxidizing agents is hydrogen peroxide. Samples of agricultural waste were placed in various concentrations of hydrogen peroxide from 5% to 50%. Reaction solutions comprised of aqueous solutions of alcohol were blended with the prereacted agricultural waste. Pretreated agricultural waste is agricultural waste that is combined with 5% hydrogen peroxide. It is suspected that the hydrogen peroxide reacted with the lignin type material. 500 grams of an alcohol/water reaction solution comprised of 40% n-propyl alcohol and 60% water was blended with 500 grams of pretreated agricultural waste and put into a closed reactor. 700 milliliters of diesel fuel was added to the blend. The reaction was completed when the mixture reached a final temperature of 360° C. but the pressure only reached 1400 psig. This is about 1000 psig less that the regular pressure of previous reactions. Further there was an enhanced solubility of agricultural waste in both the aqueous and diesel fuel fractions. Any commercial oxidizing agent such as hydrogen peroxide could potentially be used or the blend could be heated to about 200° C. and air bubbled through the blend for industrial use. The use of bubbled air would exploit the oxygen in air as the oxidizer. In this application air could be intake air from the atmosphere, air from a tank, or blends of oxygen one skilled in the art would use for optimal oxygen intake into the reaction. The cost for such a procedure would be minimal. 
         [0012]    In addition to adding oxidizing agents, the water and alcohol concentrations in the reaction solution were adjusted. A second reaction without any water composed of a blend of a 50% methyl alcohol reaction solution and 50% dried hog lagoon waste was prepared, but not pretreated. Five hundred grams of each component were mixed. The blend did not get pasty as when the dried lagoon waste was blended with water alone as a reaction solution. 350 grams of diesel fuel was added, however, it is suspected that diesel fuel may not be needed. The mixture 500 grams alcohol reaction solution/500 grams died lagoon waste/350 grams diesel fuel was heated to 360° C. The pressure in various runs of this experiment never got above 2000 psig. It is believed that the reaction conditions could be even milder with oxidation pretreatment of the agricultural waste. The system was permitted to return to room temperature. When the reactor was opened a small amount of gas evolved. The contents actually bubbled. The non-gas phase contents of the reactor were removed. There were two phases: a solid and a single-phase liquid. The phases can be separated by any means known to one skilled in the art to readily separate a solid and a liquid such as centrifugation. The solid was separated by centrifugation using about 2000 g&#39;s. The solid readily separated. The liquid remained a single phase. This is very significant because methyl alcohol has no appreciable solubility in diesel fuel. The diesel fuel did not float on top of the alcohol solution as expected. Even after centrifugation separation did not occur. The solution could be a colloidal suspension like milk but it could not be separated even at 2000 g&#39;s. Upon standing for one and a half months traces of some tar like material did separate out but it was a minimal amount. The liquid was analyzed for fuel properties. The liquid had a BTU value of 19,110 BTU/lb. Diesel fuel is about 18,500 BTU/lb. Gasoline can be about 18,000 BTU/lb. 
         [0013]    The reaction could be run under the following conditions; a temperature range of about 230° C. to about 370° C.; a solid agricultural waste to reaction solution concentration ranging from about 5% agricultural waste/95% reaction solution to about 90% agricultural waste/10% reaction solution. In addition, the reaction solution concentration could have a range of about 100% alcohol/0% water to about 0% alcohol/100% water with any water/alcohol concentrations available for use with the alcohol being a methyl, ethyl, or any other alcohol with the C n H 2n+1 OH formula. One example is a solution of about 15% alcohol to about 85% water with the alcohol being a methyl alcohol. The pressure could range from about atmospheric to about 3000 psig in a closed reactor with a reaction time between about three minutes and about one hour. Pretreatment of the agricultural waste with an oxidizing agent could make the conditions of reaction even milder. The pretreatment could be in a range of about 0.5% oxidizer/95.5% agricultural waste to about 15% oxidizer/85% agricultural waste with the oxidizer being any that one with normal skill in the art would use such as hydrogen peroxide. In addition, diesel fuel can be added to the mixture in a range of That range is probably about 10% to about 50% mixture weight, but is not essential needed. The mixture may be blended to homogeny before reaction, but could also be added unblended into a stirring reactor. 
         [0014]    Example Reaction: 
         [0015]    The experiment was a non-pretreated agricultural waste blend in a 38.5% agricultural waste/38.5% reaction solution/23% diesel fuel by weight with the reaction solution consisting of 100% alcohol. The reaction solution was 100% methyl alcohol. The charge to the reactor consisted of 500 grams of dried hog agricultural waste consisting of manure lagoon waste mixed with 500 grams of 100% pure methyl alcohol reaction solution. This was mixed and added to 300 grams of diesel fuel. The diesel fuel was in the reactor before the agricultural waste alcohol blend was prepared. The diesel fuel is added to decrease the viscosity of the blend. With the aqueous blends, the agricultural waste solution blend has the consistency of paste. To insure more complete uniform heating, diesel fuel was added to change the paste to a fluid that could be easily stirred. With the 100% methyl alcohol reaction solution the blend is very fluid and the diesel fuel was probably not needed. The mixture was heated to 360° C. at a rate of 3° C. per minute in a closed reactor although it is believed that a much faster heating rate would accomplish the same result. The pressure at this temperature was 450 psig. If there is surplus of alcohol the pressure would equal the pressure of methanol at that temperature which is greater than 1000 psia. The resultant pressure implies that there is no excess alcohol; therefore all of it must have reacted. This may not be case every time because if excess alcohol is used then the pressure would equal the pressure of the alcohol at this temperature. 
         [0016]    The reactor was cooled to room temperature. There was a pressure of 60 psia in the cooled vessel. This means that during the reaction between the alcohol and agricultural waste some gas formed. The composition of that gas is not known at this time. In earlier alcohol plus water solution reactions about 200 psia of gas was formed and that was about 97% carbon dioxide. When the depressurized contents of the reactor were removed there were two phases: a solid and a liquid. Methyl alcohol is not very soluble in diesel fuel so any unreacted alcohol would be a separate liquid phase that is denser than diesel fuel. In this case the material is completely miscible. Centrifugation did not cause two liquid phases to form so the alcohol reaction solution reacted with the agricultural waste and formed a material that mixes with the diesel fuel. The mixture may not be a true solution but a colloid like the fat in water that is called milk. 
         [0017]    After centrifugation the solid was weighted and a crude mass balance was done. Initially there were 300 grams of diesel fuel, 500 grams of methyl alcohol reaction solution and 500 grams of agricultural waste. In the product 300 grams of diesel fuel, 400 grams of agricultural waste, and 480 grams of alcohol. The 100 grams was the ash material removed as solids. Therefore the hypothesized product is about 25% diesel fuel and 75% product of the alcohol reaction solution/agricultural waste reaction. However, diesel fuel may not be needed at all. The heat of combustion of the product as measured is 19,100 BTU/lb. This is comparable to high quality diesel fuel and is a little higher than gasoline. It is further believed that the pretreatment of the agricultural waste with an oxidizing agent would make reaction conditions even milder. 
         [0018]    The initial experiments have shown that the diesel fuel may not be necessary. Second the reaction conditions are much milder than when aqueous solutions are used. The critical pressure of methyl alcohol is lower than that of water. The critical temperature of methanol is 240° C. and its critical pressure is 1146 psia water has a critical temperature of 374° C. and its critical pressure is 3200 psia. This means that the cost of equipment for the process will be less and the system will be much less dangerous. It should be also noted that although methanol was used other alcohols should also work. Further in the example, an agricultural waste material from a lagoon was used. However, other biowaste materials such as other animal waste, manures and human sewage sludge. Cellulose waste such as wood waste and corn stover should also work. 
         [0019]    These terms and specifications, including the examples, serve to describe the invention by example and not to limit the invention. It is expected that others will perceive differences, which, while differing from the forgoing, do not depart from the scope of the invention herein described and claimed. In particular, any of the function elements described herein may be replaced by any other known element having an equivalent function.