Patent Application
20090293346
The disclosure relates to continuous reactor/separator devices and uses thereof, in particular centrifugal separator/reactors that provide improved residence time for reaction and separation of immiscible liquids from one another.
In the current method of manufacture of esterified vegetable oils or animal fats, a feed material containing triglycerides is reacted with a methoxide (typically sodium or potassium methoxide), resulting in the esterification of the glycerides into fatty acid methyl esters. The foregoing process is typically performed in reaction vessels in which the reactants, which are immiscible with one another, are dispersed in one another by stirring or sparging. Upon reaction, the reaction product is a dispersion of two new immiscible liquids, a solution of fatty acid methyl esters and glycerine. In a conventional manufacturing process, the dispersion product of esters and glycerine is separated by centrifugal separation or by the force of gravity by allowing the reaction products to sit undisturbed for approximately 24 hours. The recovered glycerine is disposed of, and the ester product is contacted with water or other aqueous solutions to remove excess reactants and/or unreacted glycerides. The water washing steps may be performed by centrifugal separation or by settling in large tanks that require extensive settling times to allow the wash and product solutions to separate from one another after mixing.
Problems with the foregoing manufacturing process are two fold. First, the effectiveness of the esterification reaction is limited by the extent to which the reactants are intimately mixed with one another and/or reaction kinetics. Consequently, the size of the reactor and the reaction times may be greater than theoretically necessary or the reaction may require a significant excess of methoxide, making purification and recovery of reactants and products more difficult. Secondly, the current state of the art includes several washing and separation steps (processes in which dispersed, immiscible solutions must be allowed to separate over time), each of which is accomplished by gravity settling in large tanks or by the use of conventional centrifugal separation techniques.
Accordingly, there is a need for a more efficient reaction and separation process that provides more intimate mixing of reactants and relatively more rapid separation of the reaction product and reactants and impurities from one another.
With regard to the foregoing, the disclosure provides a method and apparatus for producing a biodiesel product. The method includes continuously contacting a triglyceride containing component with an alcohol and a catalyst at an elevated temperature in a centrifugal reactor/separator. A less dense phase including the biodiesel product is continuously separated from a more dense phase containing glycerine in the reactor/separator.
In an exemplary embodiment, the disclosure provides an apparatus for manufacturing a biodiesel product from triglycerides. The apparatus includes a centrifugal reactor/separator having a stationary shell, a rotating hollow cylindrical component disposed in the stationary shell, a residence-time increasing component between the stationary shell and the hollow cylindrical component, a less dense phase outlet in fluid flow communication with an interior cavity of the hollow cylindrical component; and a more dense phase outlet in fluid flow communication with the interior cavity of the hollow cylindrical component. Storage vessels are provided for reactants in fluid flow communication with the centrifugal reactor/separator. A pump is used for pumping a reactant from the storage vessels to the centrifugal reactor/separator.
In yet another embodiment, the disclosure provides a centrifugal reactor/separator having a stationary shell, a rotating hollow cylindrical component disposed in the stationary shell, a residence-time increasing component between the stationary shell and the hollow cylindrical component, a first outlet in fluid flow communication with an interior cavity of the hollow cylindrical component for a less dense phase fluid, and a second outlet in fluid flow communication with the interior cavity of the hollow cylindrical component for a more dense phase fluid.
An advantage of the embodiments of the disclosure is that it provides a substantially continuous process for reacting and separating immiscible components while providing sufficient reaction time to provide relatively higher yields of product. In the case of biodiesel product manufacture, the apparatus is suitable for providing both the initial esterification reaction and the separation of the ester product and glycerine byproduct from one another in a single mixer/separator device. The apparatus and process therefore reduce the need for large vessels to provide long residence times for reaction and/or for separation of reaction products from byproducts. Multiple centrifugal separator devices may be used to provide purification of the reaction product thereby further reducing the time required for producing such products using conventional distillation, extraction, and/or settling techniques.
Further advantages of exemplary embodiments disclosed herein may become apparent by reference to the detailed description of preferred embodiments when considered in conjunction with the drawings, which are not to scale, wherein like reference characters designate like or similar elements throughout the several drawings as follows:
The production of biodiesel products from triglycerides such as vegetable oils and animal fats may be conducted in a variety of ways. However, transesterification of the triglycerides with an alcohol in the presence of an alkoxide catalyst is a useful process for making fatty acid esters that may be used as fuel. According to a particularly suitable process, the following reaction takes place:
wherein R1, R2, and R3 are hydrocarbyl groups containing from 5 to about 28 carbon atoms, R4 and R5 are selected from lower alkyl groups containing from 1 to about 4 carbon atoms, and M is a metal selected from sodium, potassium, lithium, rubidium, and cesium, or a lanthanide selected from lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. The foregoing is an equilibrium reaction. Accordingly, the reaction may be forced to the fatty acid ester product by the continuous removal of glycerine from the product.
In an alternative to the above described based-catalyzed reaction, an acid-catalyzed reaction system may be used. Acid catalysts that may be effective to catalyze the transesterification reaction may include, but are not limited to, sulfuric acid, HCl, BF3, H3PO4, and organic sulfonic acids. Although ester hydrolysis can occur by either acid or base catalysis, acid catalysis is generally believed to be more tolerant of moisture and high free fatty acid levels in the starting feedstock and, hence, more suitable for low-grade fats and grease feed stocks. A combination of based-catalyzed and acid-catalyzed reactions may also be used according to embodiments of the disclosure.
The reaction may be conducted at room temperature or at an elevated temperature, typically in the range of from about 25° C. to about 300° C., more typically from about 50° C. to about 150° C. The reaction may be conducted at atmospheric pressure or may be conducted at pressures ranging from about one atmosphere to about ten atmospheres depending on the reactants. If desired, oxygen or inert gases, such as nitrogen or argon may be co-fed with the reactants into the reactor/separator, described in more detail below.
The triglyceride reactant may be obtained from a variety of animal and vegetable sources. For example, a vegetable oil selected from soybean oil, palm oil, palm kernel oil, coconut oil, canola oil, corn oil, cottonseed oil, olive oil, peanut oil, linseed oil, tung oil, sunflower oil, safflower oil, rapeseed oil, sesame oil, Chinese tallow tree oil, Physic nut oil, Cuphea seed oil, babassu oil, perilla oil, oiticica oil, castor oil, microalgal oils, and mixtures thereof may be used as the source of the triglyceride reactant. The triglyceride reactant may also be obtained from animal fats selected from beef tallow, lard, fish oils, menhaden oil, and mixtures thereof, or from uncharacterized waste sources containing the triglycerides.
The alcohol reactant may be a lower alcohol reactant containing from about 1 to about 4 carbon atoms such as methanol, ethanol, propanol, and butanol. A particularly suitable alcohol is methanol. A ratio of alcohol to triglyceride reactant may range from about 3:1 to about 15:1 on a mole basis. However, it is desirable to maintain a nearly stoichiometric molar ratio of alcohol to triglyceride reactant so that separation of the resulting product from the reactants is easier and byproduct volumes are reduced. An advantage of the disclosed embodiments is that operation near the stoichiometric quantity of reactants may be easier to accomplish than with conventional reaction systems.
In base catalysis systems, the catalyst component may be selected from metal alkoxides wherein the alkyl group contains from about 1 to about 4 carbon atoms. Particularly suitable metal alkoxides may be prepared, for example, from sodium methoxide, potassium methoxide and lithium methoxide. An amount of catalyst ranging from about one mole percent to about three mole percent based on the total moles of alcohol plus catalyst may be used.
The fatty acid ester product that is suitable for use as a biodiesel may be a methyl or ethyl ester containing an alkyl chain having from about 8 to about 22 carbon atoms. The product may be saturated or an unsaturated product having a degree of unsaturation ranging from about one to about four.
A key aspect of the foregoing reaction is that the reactants are substantially immiscible in one another. Hence, the rate of mass transfer may be limited by the contact area between the reactant phases resulting in prolonged reaction times. In order to increase the contact area between the reactant phases, the reactants may be agitated or mixed so as to finely disperse one reactant phase into the other reactant phase. In addition, the chemical reaction rate of the components is limited by reaction kinetics. The extent of conversion of reactants into products may be improved by increasing the residence time sufficient to achieve increased conversion of reactants.
With reference to
In
In another embodiment illustrated in
With reference again to
The fatty acid ester product may be purified from unreacted materials or reaction byproducts by multiple sequential contacts with aqueous wash solutions using a similar reactor/separator 10. In the alternative, one or more conventional centrifugal separators may be used to wash and purify the product since residence time is not a factor once the reaction is complete.
Use of the reactor/separator 10 to provide reaction between the triglyceride reactant and the alcohol reactant may significantly increase the reaction efficiency, due to highly efficient mixing of the reactants in the reactor/separator 10 and the increased residence time provided by the residence-time increasing component 16. Separation of the products by centrifugation as they are formed may increase product recovery efficiency and may eliminate a need for large holding vessels, in which the reaction product and byproducts are allowed to separate from one another over extended periods of time. Accordingly, use of centrifugal separation may significantly reduce the size of a production facility required to produce biodiesel at any specific production rate. In addition, use of reactor/separator 10 to provide the various product washing operations used to purify the fatty acid ester product may increase washing efficiency (due to the mixing efficiencies of the devices) and may eliminate the need for large washing vessels. The use of the reactor/separators 10 for the reaction and product separation, and for product washings, facilitates production of biodiesel on a continuous flow basis, which may increase throughput for a facility of a given size and simplify process control during the production of biodiesel products.
While the foregoing exemplary embodiments are based, in part, on the centrifugal solvent extraction contactor, such devices may not provide sufficient residence time for fluids in a mixing zone when two immiscible liquids are contacted with one another, as in the case of biodiesel production. In fact, conventional solvent extraction contactors were designed to provide a minimum of residence time in order to minimize chemical and radiological degradation of organic extractants. However, where increased residence time is required to conduct a reaction or to provide more efficient liquid phase extraction processes, the reactor/separator device 10 as described herein may be particularly useful.
Without desiring to be bound by theoretical considerations, the reactor/separator device 10, according to the disclosure, imparts shear forces on immiscible fluids fed to a narrow annular gap 50 between the stationary shell 12 and rotor 14 enclosed in the stationary shell 12. Shear forces imparted on the fluids in the gap 50 may create a finely divided dispersion via Couette mixing, thereby promoting transfer of solute(s) between phases and reducing mass transfer residence times. The reacted dispersion then passes into the separator zone 36 within the rotor 14 where it is separated into its component liquid phases by centrifugation as described above.
Conventional annular reactors may provide control of reactant residence times by controlling the feed rate of the reaction components to the reactor through fluid inlet ports. However, the residence time in the mixing zone between a rotor and stationary housing in conventional centrifugal contactors is limited and somewhat random. Consequently, obtaining effective mass transfer or accomplishing a chemical reaction in this zone is problematic when the kinetics of the transfer of reactants and products between phases or reactions is relatively slow.
An exemplary embodiment of the disclosure may significantly improve the production of biodiesel products according to the above reaction by conducting the reaction in the centrifugal reactor/separator 10 that includes the residence-time increasing component described above. One means of increasing the residence time is by increasing a pressure drop in a region 50 where reactants flow from inlets 18 and 20 to the regions 50A and 50B between the rotor 14 and the stationary shell 12 then into the separator zone 36 in the rotor 14. Accordingly, fluid hold up in the region 50 may be controlled independent of influent feed rate, in order to provide a residence time required to achieve complete mass transfer between immiscible liquids or conversion of reactive components into products.
With reference to
The stationary, cup-shaped device 17, described with reference to
With reference to
After reaction and separation, in the reactor/separator 10, a less dense phase 74 containing the fatty acid ester product may be fed from outlet 28 to a first inlet 76A of a centrifugal separator 78A. Wash water 80 from a wash water storage vessel 82 is fed by pump 84 into the second inlet 86A of the separator 78A for contact with the fatty acid ester product 74. Byproducts and impurities 88 in the more dense phase from reactor/separator 10 are fed from outlet 30 to a byproduct storage vessel 90 for further treatment, recycle, or disposal. The washed product 92 from separator 78A is fed through outlet 94A to a first inlet 76B of a centrifugal separator 78B for further purification and the byproducts and impurities 96 are fed from outlet 98A to the byproduct storage vessel 90. As with separator 78A wash water 100 is fed into a second inlet 86B to contact the washed product 92 from separator 78A. A purified product 102 is fed from outlet 94B into a product storage vessel 104 while the impurities and byproducts 106 are fed from outlet 98B into the vessel 90.
In the foregoing embodiment, the system 60 included one reactor/separator 10 and two centrifugal separators 78. However, the disclosed embodiments are not limited to one reactor/separator 10 and two centrifugal separators 78, as more or fewer reactor/separators 10 and/or centrifugal separators 78 may be used to make a biodiesel product according to the disclosed embodiments. For example, very large reactor/separators 10 may require fewer processing steps to purify the product. Alternatively, the product may be made on a batch basis, wherein intermediate storage vessels are used for byproducts and unpurified products. The unpurified products from the storage vessel may be fed back into the same reactor/separator 10, multiple times for contact with wash water to provide a purified product that is collected in a separator product storage vessel. It will be appreciated however, that the use of the reactor/separator 10 containing the residence-time increasing component enables production of biodiesel products on a substantially continuous basis.
It is contemplated, and will be apparent to those skilled in the art from the preceding description and the accompanying drawings that modifications and/or changes may be made in the embodiments of the disclosure. Accordingly, it is expressly intended that the foregoing description and the accompanying drawings are illustrative of exemplary embodiments only, not limiting thereto, and that the true spirit and scope of the present disclosure be determined by reference to the appended claims.
This invention was made with government support under Contract No. DE-AC05-00OR22725 awarded by the U.S. Department of Energy. The government has certain rights in the invention.
