Patent Application
20090183422
1. Field of the Invention
The invention generally relates to preparation of bio-fuel and, more particularly, to a system and process that includes continuous water removal during the esterification process preceding transesterification during the preparation of the bio-fuel such as bio-diesel.
2. Related Art
Bio-fuels such as bio-diesel fuels are becoming more prevalent as an alternative source of fuel. In many aspects, the production of methyl or ethyl esters from fatty acids and triglycerides, such as found in animal and vegetable fats, has become quite central to producing the bio-fuels.
The production of bio-fuels is influenced by many factors including cost of materials such as the feedstock (e.g., unrefined vegetable oils, fats from slaughtered animals, virgin or recycled oleins and vegetable oil, and waste fats, etc.). In general, about 60-80% of the cost of producing bio-fuels is related to feedstock. Therefore, lower cost feedstock is sought to offset overall costs.
Typically, lower cost feedstock comprises triglycerides that have organic acidity due to the high quantities of free fatty acids (FFA), necessitating a robust acid-catalyzed esterfication process to reduce the FFA content. Traditional transesterfication processes cannot employ fats or oils with FFA acidity exceeding about 0.5% by weight (expressed as oleic acid) because the free acidity produces, by reacting with and consuming the basic catalyst (e.g., potassium hydroxide or sodium methoxide), soaps that interfere with the production of methylesters. This creates complications due to the necessary separation of the byproduct glycerin from the methyl esters. Thus, the potential benefits from using lower cost raw feedstock are compromised.
When employing homogeneous catalysts during the esterfication processes, concentrated sulfuric acid (H2SO4) is most often used because of high acidity activity and economics. However, using standard ratios of acid to methanol, oils of higher than 5% FFA cannot be used because of incomplete esterfication. Higher amounts of H2SO4 are possible but create difficulties because of oxidation or sulfonation of unsaturated oils and with downstream neutralization before trans-reaction and post separation of effluents.
The use of heterogeneous catalysts (e.g., sulfonic acid bonded to carbon, sulfonic acid bonded to silicon, and sulfated metal oxides) during the esterfication process provide several advantages over homogenous catalysts. Some of these advantages include:
Examples of heterogeneous catalyst sulfonic acid bonded to carbon compounds include:
An example of heterogeneous catalyst sulfonic acid bonded indirectly to silicon includes specialty chemically-modified mesoporous silicates —Si(OSi)2—R—SO3H (R is aliphatic or aromatic). This expensive catalyst gives higher esterification activity than the conventional acidic solid catalysts, but a special filtration system and much longer times and higher temperature/pressure are required than other common procedures.
Another example of a conventional heterogeneous catalyst is sulfated metal oxides, e.g., zirconia. This type of catalyst requires high temperature/pressure and/or specialized expensive countercurrent reactive columns, sometimes utilizing extraneous entraining agents which must be separated and recovered.
There are known processes for pre-esterfication of an oil containing FFA to then be used for transesterification, such as described in U.S. Pat. No. 4,698,186. This patent discloses a generic process using a sulfonated solid catalyst to esterify FFA in an oil feedstock. The feedstock oils disclosed are only 5% FFA. The reaction mixture is flash dried at 120° C. in example 1 and the dried oil and methanol are recovered separately from the main reaction. Thus, no continuous drying of the reaction mixture is disclosed, as disclosed herein, nor is dry methanol continuously returned; rather the drying is a post reaction operation.
International Patent Publication WO/2007/083213 discloses a process for preparation of bio-diesel. However, this disclosure also fails to disclose continuous drying of the reaction mixture nor is dry methanol continuously returned, as disclosed herein.
There is a need for robust homogenous and/or heterogeneous acid esterification systems for bio-fuels (e.g., bio-diesel) production utilizing high FFA feedstock (e.g., 10-100% FFA) which can be run at about 70° C. or less at atmospheric pressure, utilizing conventional and commercially available acids, and utilizing a process that can be added in a “modular” fashion to existing manufacturing facilities or installed at new plants using conventional industrial equipment.
The invention satisfies the above needs and avoids the disadvantages and provides a economical process for using lower cost feedstock that have higher percentages of free fatty acid. In one aspect, the process and system permits the esterification reaction as a first step in a bio-diesel production process, where the esterification is driven to completion by continuously removing water from the reaction mixture and returning dry methanol to the reaction vessel. Continuous drying and return of dried methanol drives the esterification reaction to completion quickly by removing water and by maintaining a constant excess of methanol. It also has an economic advantage over conventional post esterification drying, since it requires less cycle time (therefore greater throughput) and less equipment before transesterification for high FFA feedstocks and conventional set ups, where two stage esterification may ordinarily be required. The esterification product may then be transesterified by conventional techniques. This process may use commonly employed equipment and commercially available catalysts and feed stock.
According to another aspect of the invention, a process for production of a bio-fuel is provided that includes the steps of creating a esterification reaction mixture by placing one of a homogeneous catalyst and a heterogeneous catalyst in a reaction vessel so that one of the catalysts contacts methanol and a feed stock comprising free fatty acid (FFA) or a FFA-containing triglyceride in the reaction vessel, continuously drying the methanol during the reaction by removing water, and returning the dried methanol to the reaction vessel until the percentage of FFA reaches a predetermined value.
In another aspect, a process for production of bio-diesel is provided including drying methanol present during an esterification reaction by removing water, the esterification reaction including a feed stock comprising free fatty acid (FFA) or a FFA-containing triglyceride, the feedstock having an initial percentage of FFA and returning the dried methanol to the esterification reaction until the percentage of FFA reaches a predetermined value or until the reaction has run for a predetermined amount of time known to produce approximately the predetermined value.
In another aspect, an apparatus for producing bio-diesel is provided including means for creating a esterification reaction including one of a homogeneous catalyst and a heterogeneous catalyst so that one of the catalysts contacts methanol and a feed stock comprising free fatty acid (FFA) or a FFA-containing triglyceride, the feedstock having an initial percentage of FFA, means for drying the methanol during the reaction by removing water and means for returning the dried methanol to the esterification reaction until the percentage of FFA reaches a predetermined value or until a predetermined amount of reaction time has elapsed known to produce approximately the predetermined value.
The accompanying drawings, which are included to provide a further understanding of the invention, are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the detailed description serve to explain the principles of the invention. No attempt is made to show structural details of the invention in more detail than may be necessary for a fundamental understanding of the invention and various ways in which it may be practiced. In the drawings:
It is understood that the invention is not limited to the particular methodology, protocols, and reagents, etc., described herein, as these may vary as the skilled artisan will recognize. It is also to be understood that the terminology used herein is used for the purpose of describing particular embodiments only, and is not intended to limit the scope of the invention. It also is noted that as used herein and in the appended claims, the singular forms “a,” “an,” and “the” include the plural reference unless the context clearly dictates otherwise. Thus, for example, a reference to “a lesion” is a reference to one or more lesions and equivalents thereof known to those skilled in the art.
Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which the invention pertains. The embodiments of the invention and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments and examples that are described and/or illustrated in the accompanying drawings and detailed in the following description. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale, and features of one embodiment may be employed with other embodiments as the skilled artisan would recognize, even if not explicitly stated herein. Descriptions of well-known components and processing techniques may be omitted so as to not unnecessarily obscure the embodiments of the invention. The examples used herein are intended merely to facilitate an understanding of ways in which the invention may be practiced and to further enable those of skill in the art to practice the embodiments of the invention. Accordingly, the examples and embodiments herein should not be construed as limiting the scope of the invention, which is defined solely by the appended claims and applicable law. Moreover, it is noted that like reference numerals reference similar parts throughout the several views of the drawings.
In certain aspects, the invention includes providing for a process utilizing either a homogenous acid (e.g., H2SO4) or heterogeneous catalyst (e.g., solid sulfonic acids), which contacts the methanol and a free fatty acid (FFA) or FFA-containing triglyceride at a preferred temperature range of about 50° to about 70° C. and at substantially atmospheric pressure in a stirred reaction vessel or packed reaction column while water is continuously removed, and dry methanol continuously returned. In this way at least 98 to about 99.5% esterification may be accomplished within about three hours. The continuous water removal may be accomplished by any (or any combination) of:
a) water absorption on a solid desiccant (e.g., CaSO4) by contact in the esterification vessel.
b) water absorption on a solid desiccant (e.g., CaSO4) by pumping the reaction mixture through a column packed with the desiccant and returning the dried mixture to the vessel.
c) passing refluxing wet methanol vapors through a rectifying column (e.g., fractional distillation column) so that dry methanol is continuously returned to the reaction chamber.
d) water absorption on a solid desiccant (e.g., CaSO4) by refluxing wet methanol vapors up the side arm of a column packed with desiccant to a condenser positioned above the column. The wet condensed methanol falls and flows through the column, returning dry methanol to the reaction vessel (as in
In one embodiment, a heated agitated reaction vessel containing oil, methanol, and a solid sulfonated catalyst (preferably Nafion, Dowex, Amberlite 15, or Purolite) may be attached to a rectifying column so that refluxing wet methanol vapors (containing water as the esterfication progresses) can enter the column. In this way the methanol is dried, and the dry condensed methanol returned in a continuous fashion to the reaction vessel by exiting the top of the column. Water exits the bottom of the column and may be stored separately for other use or disposal.
When the percent of FFA reaches a predetermined value (e.g., about 0.5%), the oil may be pumped out of the reaction vessel, through a filter, and into the transesterification vessel for final conversion into bio-fuel (e.g., bio-diesel). The filter typically retains the original catalyst in the esterification reaction vessel for reuse with the next charge of oil and methanol. Alternatively, in a non-preferred embodiment, a temperature range of about 40-100° C. may be employed, perhaps with some added pressure.
Alternatively, the side columns may be packed with Drierite (or other suitable drying agent) and a homogeneous catalyst used the reaction vessel 1 which contacts the methanol and feedstock. Further, in another configuration only one side column might be employed for drying. The reaction mixture may be stirred with any suitable method.
Typically, all reaction vessels have a filter 30 to filter the completed reaction mixture as the liquid mixture is pumped to the transesterification vessel. Optionally, the completed reaction mixture might go to an intermediate vessel where methanol is flashed off. The filter 30 retains Drierite (and/or other solid drying agent) and/or heterogeneous catalyst when appropriate.
In general, all condensers in these embodiments may be vented (with moist air exclusion mechanisms) to atmospheric pressure 50. The reaction vessels may vary in shape but preferably horizontal or vertical cylindrical-shaped tanks. All side-columns may have filters on each end to retain their packing; where two columns are used, they may be either in series or in parallel. Moreover, reactants may be pumped upward or downward through the side columns. Further, all reaction vessels may be charged initially with pre-dried feedstock and anhydrous methanol.
The configuration and process of the embodiments herein may provide substantially continuous drying of the methanol during the esterification reaction so as to shift the esterification equilibrium to completion (e.g., a pre-determined level of FFA). Alternatively, the reactions of the embodiments may be permitted to run for a predetermined amount of time known to approximate the percentage of FFA, given a known set-up and starting mixture.
Chemicals used in one or more experiments:
A 250 ml three-necked, round-bottomed, standard taper flask was fitted with a reflux condenser (terminating in a drying tube to exclude moist air), a thermometer dipping into the flask contents, and a stirring gland/stirring shaft assembly with paddle. Into the third neck of the flask was introduced 100 g of stabilized poultry fat (SPF with a FFA content of 10%) and a solution of 0.5 g of sulfuric acid (98% H2SO4) dissolved in 29 ml of anhydrous methanol, and the neck stoppered.
The flask was heated with a water bath, with stirring (120 rpm), where the internal temperature of the reaction mixture was maintained at about 60° C. A sample of the oil phase was removed after one hour and found to be 1.1% by titration with 0.1% aqueous sodium hydroxide to a phenolphthalein endpoint.
Using the same set up and procedure as Exp. #1, the following were introduced to the flask:
A 250 ml three-necked, round bottom, standard taper flask was equipped with a reflux condenser and thermometer (as above) and a magnetic stirring bar. The following were introduced to the flask, through the third neck, which was then was stoppered:
The flask of Experiment #3 was fitted with a thermometer, a magnetic stirring bar, and a side-armed, standard taper addition funnel. The top joint of the funnel was fitted with a reflux condenser and drying tube. Into the flask was introduced 58.5 g SPF (10% FFA), 44 ml methanol, and 17.5 g Hi-cat. Into the addition funnel was introduced 10 g of Drierite, retained by a small-bored stopcock. The contents were heated to 65° C. with an oil bath and hot plate stirrer as in the last example. The refluxing methanol was allowed to condense in the condenser, drain through the Drierite, and return through the open stopcock to the flask. After 1 hour at reflux, a sample of the oil phase was found to be 0.50% FFA.
Using the set up of Experiment #4, the following were introduced to the flask, which was then re-stoppered:
Using the set up of Experiment #4, the following were introduced to the flask, which was then re-stoppered:
Table 1 summarizes additional experiments 6A-11C. The experiments each have a CONTROL experiment always designated as the “B” experiment (e.g., 6B or 7B, etc.), which are the experiments that employed no continuous drying of the esterification reaction. The other experiments (e.g., 6A, 7A, 7C, 8A, 9A, 10A, 11A, 11C) employ a technique of continuous drying performed according to principles of the invention.
In Table 1, the column labeled “REACTION CONDITION” shows the parameters of the reaction for the experiments as denoted under the column “EXPERIMENT.” The reaction condition may include the temperature in ° C., reaction time duration in hours, reflux, and if an inert gas (e.g., helium) was used to add additional drying. The column labeled “Feedstock” shows the amount of feedstock, e.g., stabilized poultry fat (SPF) or soy bean oil (SBO), in grams. The column labeled “Initial % FFA” shows the initial percentage of FFA by weight of the feedstock. The column labeled “CH3OH” shows the amount of methanol used for each experiment. The column labeled “CAT” shows the type and amount of catalyst used such as Hicat 1100, Amberlite 15 or Dowex DR 2030. The column labeled “Other” shows the amount of drying agent (e.g., Drierite) or other technique of drying. The column labeled “Final % FFA” shows the final percent of FFA remaining after the experiment time period. As can be seen in these results, the final % FFA is always higher in the CONTROL experiment which uses no drying of the methanol. Therefore, it may be concluded that continuous drying of the methanol improves effectiveness of the esterification reaction.
The examples given above are merely illustrative and are not meant to be an exhaustive list of all possible embodiments, applications or modifications of the invention. Thus, various modifications and variations of the described methods and systems of the invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in the cellular and molecular biology fields or related fields are intended to be within the scope of the appended claims.
The disclosures of any patents, references and publications cited above are expressly incorporated by reference in their entireties to the same extent as if each were incorporated by reference individually.
This application claims benefit and priority under 35 U.S.C. §119(e) from U.S. Provisional application No. 61/022,032 filed Jan. 18, 2008, entitled “Process and System for Preparation of Bio-fuels,” the disclosure of which is incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61022032 | Jan 2008 | US |
