Cold biodiesel filtration process

Abstract

BIODIESEL COLD FILTRATION PROCESS. An improved biodiesel production process includes the steps of processing a feed load to produce biodiesel, cooling the biodiesel to form sediment, and filtering the biodiesel to remove the sediment. The biodiesel resulting from the cold filtration process avoids problems of sediment formation during storage and transportation.

Description

PI0705912 -4 "BIODIESEL COLD FILTRATION PROCESS" Cross Reference to Related Applications This application claims priority under 35 U.S.C. § 119 of provisional order No. of Series 60 / 764,440 filed on February 2, 2006, which application is hereby incorporated by reference in its entirety. Field of Invention The invention relates to an improved process for producing biodiesel fuel. More particularly, the quality of biodiesel fuel is improved by employing a cold filtration process to remove non-methyl ester impurities and other contaminants, such as tailings glycosides and other unsaponifiables. Background of the Invention There is significant interest in alternative non-petroleum-based fuels for many reasons, including environmental, economic, political and other reasons. Biodiesel fuel is an alternative based on renewable resources. Biodiesel is a mono-alkyl ester of long-chain fatty acids such as methyl ester derived from fats and oils and provides lower emissions when compared to petroleum-based diesel fuel. The cetane number, energy content, viscosity, and phase changes of biodiesel are similar to petroleum diesel. Biodiesel is derived from chemical transesterification processes where triglyceride feedstock deo, like vegetable fat or oil, is processed for conversion to methyl esters (biodiesel) and glycerine. The American Society for Testing Materials (ASTM) has developed standards for biodiesel fuels, with the most common being D-6751. ASTM Standard D-6751 establishes the commercial grade specifications required for biodiesel fuel. The D-6751 standard requires water and sediment to be less than 0.50% m volume, as measured by M standard D-2709. However, biodiesel that meets ASTM standards of D-6751 may still contain contaminants that tend to crystallize and / or form and fall out of solution as sediment. When such biodiesels are used at lower temperatures the precipitates create problems by slowing the flow of fuel and clogging fuel lines, filters and other engine components burning the fuel. Therefore, a primary object of the present invention is the provision of an improved biodiesel production process that utilizes cold filtration to remove impurities and contaminants from biodiesel. Still another objective of the present invention is the provision of a method for improving the quality of biodiesel by removing its particles before storage or transport. Yet another object of the present invention is the provision and process for cooling and filtering biodiesel for removing formed sediments. Another object of the present invention is the provision of an improved biodiesel production process with one or more exchangers that can be quickly and easily 1 i mno.q . -----J_--« These and other objects will become apparent from the following description of the invention. Brief Summary of the Invention The improved biodiesel production process of the present invention uses cold filtration to remove impurities and contaminants from the biodiesel. After the triglyceride feedstock is processed for separation into glycerin and methyl esters, the ethyl ester biodiesel is cooled to a temperature of less than about 38°C in order for impurities and contaminants to precipitate as particles in the biodiesel liquid. Diatomaceous earth or other filtration material is then added to the cooled biodiesel to form a slurry, which is then filtered through a pressure plate or other type of filter to remove particles. The filtered biodiesel is then passed through a polishing filter to remove any remaining diatomaceous earth and sediment in order to produce the final biodiesel product. Brief Description of the Drawings Figure 1 is a schematic view showing a preferred embodiment of the biodiesel production process according to the present invention. Figure 2 is a schematic view showing a preferred embodiment of the cold filtration step in the biodiesel production process of the present invention. Detailed Description of Preferred Mode Figure 1 shows a preferred process for producing production of improved quality biodiesel, including the new cold filtration step of the present invention. The process includes five general steps, including the pretreatment step 10, the biodiesel production step 12, the cold filtration step 14, the optional hibernation step 16, and the optional fractionation step 18. pretreatment 0, biodiesel production step 12, and hibernation and fractionation steps 16,18 are known in the industry. Improved quality biodiesel is a result of cold filtration step 14. The purpose of the pretreatment step 10 is to remove contaminants and impurities, such as phospholipid gums and free fatty acids, from the triglyceride feedstock in order to clean the feedstock in preparation for the pretreatment step. biodiesel production 12. Conventional technology is employed in this pre-treatment step 10, such as degumming, caustic refining, and silica absorbent filtration. Biodiesel production step 12 converts the triglycerides into methyl esters (also known as biodiesel) and glycerin. Conventional technology for this production step 12 uses the transesterification reaction with methanol in the presence of a sodium methoxide catalyst in order to separate the glycerine methyl esters. Hibernation step 16 is optional, depending on the climate in which the biodiesel has to be used. The purpose of hibernation is to improve the cold flow and winter performance of the fuel. Hibernation step 16 removes saturated methyl esters such as C16:0 methyl palmitate and C18:0 methyl stearate, although such removal is indiscriminate. The hibernation technology is conventional, and uses the crystallization of saturates by controlling the time, temperature and stirring of the biodiesel. The crystals are then removed by decantation and filtration. Fractionation step 18 is also optional, depending on the temperatures at which the biodiesel has to be used. Fractionation improves the cold flow and winter performance of the fuel by selectively separating the methyl esters into individual fractions or components. Individual fractionation technology is used, including urea fractionation, solvent fractionation, or thermal distillation. The biodiesel production process of the present invention improves the quality of the biodiesel by adding a new cold filtration step 14. The purpose of the cold filtration step 14 is to clean the biodiesel fuel by removing trace contaminants, including glycosides of sterol and other unsaponifiables that are naturally present, as well as non-methyl ester impurities. Cold filtration step 14 usually involves cooling the bio- diesel fuel to at least about 21°C, adding diatomaceous earth or other absorbent to the biodiesel to form a slurry, and filtering the slurry through a pressure plate or other type of filter to remove solids formed during cooling of the biodiesel. The cold filtration step 14 is shown in greater detail in Figure 2. The biodiesel 20 resulting from the production step 12 is first cooled through one or more stages 2, as indicated by arrow A. Any conventional cooling system can be used , such as hot exchangers 24. Typically, the biodiesel produced by production step 12 is approximately 143°C or higher. At the end of the cooling stage or stages 22, the temperature is preferably between about 4-38°C, with about 18-27°C being preferred, with a more preferred temperature of approximately 22°C. For example, in one embodiment, an economizer is employed in a first cooling stage in order to reduce the temperature of the biodiesel product from approximately 143°C to approximately 93-105°C, with around 99°C being preferred, transferring heat up into an extractor feed stream. In a second stage of cooling, a cooling water exchanger is employed to also reduce the temperature of the biodiesel product 20 from approximately 99°C to approximately 26-33°C, with around 30°C being preferred, transferring heat into a cooling water recirculation loop. In a third cooling stage, a cold fluid exchanger is employed to further reduce the temperature of the biodiesel product 20 from approximately 30°C to approximately about 18-24°C, with about 22°C being preferred, by transferring the heat within a chilled fluid recirculation loop, such as a glycol and water solution. The minimum final chilled temperature should be no less than 4°C, such that the oil's natural saturated fats do not crystallize. At the conclusion of the cooling stage (22), the biodiesel product is delivered to a filter feed hydraulic oscillation column 26, as indicated by arrow B, for a time sufficient to allow the impurities and contaminants to solidify and precipitate into the particle shape. Typically, the residence time in tank 26 is approximately 1-1½ hours. However, those skilled in the art would readily appreciate that the biodiesel product can remain in the tank for shorter and longer periods of time depending on a number of factors, including the degree of impurities in the product, amount of product, desired degree of purity, factors convenience, etc. Depending on the volume of tank 26, the tank can be insulated or refrigerated to maintain the temperature of the biodiesel product. After sediments have formed in the biodiesel, the biodiesel product is transferred to a body feed tank 28, as represented by arrow C, where a filter aid from a feeder 30 is added to the biodiesel (set D), with about 0.1-0.25% by weight of auxiliary filter being preferred. People versed in the technique easily understand that more or less auxiliary ire can be added based on various factors, including the source of the power load, degree of filtration desired, convenience, cost, etc. A preferred filter aid is diatomaceous earth. Diatomaceous earth is characterized by high porosity, due to the fact that up to 85% of the volume of diatomaceous earth is prepared from tiny internally connected gaps or pores. As such, diatomaceous earth has a high absorbency of 100% of its weight in liquid, while still exhibiting the properties of a dry powder. An agitator may be provided in tank 28 to facilitate mixing the biodiesel, sediment, and diatomaceous earth into a slurry. Other conventional filtration materials may also be employed instead of, or in addition to, diatomaceous earth in this step, including sand, silica, or other finely ground materials. Such filtration materials are well known to those skilled in the art, and include silica (of various grades, sizes, and either inert or chemically activated), clay (such as acid-activated bleaching clay), cellulose, mined and ground volcanic deposits , minerals of all types (including perlite), magnesium silicate (such as one sold as Magnesol, by the Dallas Group). The biodiesel mixture trapped in the tank 28 can be removed by a demixer 32 (arrow E) which is successively connected to an external opening 34 (arrow F). Such droplets of the mixture may be present in the air vapor exhaust which is opened during the drying steps of the mixture. filter cake and discharge (described below), and preferably is removed through deblender 32 or other conventional means. The biodiesel slurry is then piped to filter 36 (arrows G and H) for particulate removal. Preferably, filter 36 is a pressure plate filter whose mesh screens have preferably been pre-coated with a similar medium as that employed in the filtration step. Other types of filters suitable for this step include, but are not limited to, pressure filters such as tube and candle filters, horizontal pressure filters, or filter presses. The diatomaceous earth or other filtration material previously added to the bulk biodiesel acts as a body food that allows the construction of a filter cake on the filter sheets 36, thereby effectively removing sediment in the biodiesel at the sub-micron level. , while allowing the liquid biodiesel to pass through the cake with minimal pressure drop. With a body feed addition of 0.1-0.25% diatomaceous earth by weight of biodiesel feed, for example, the filter 36 should be expected to run from 4 to 12 hours before cleaning is required. Cleaning of the filter 36 is accomplished using any convenient method known in the industry. Other filtration equipment employing different types of media may also be used, such as carbon, activated carbon, cloth or fabric (made from natural or synthetic materials), and ion exchange resin beads. After the biodiesel product passes through filter 36, the quality can be tested. If the quality is insufficient, the product can be redirected to tank 28, as indicated by arrow I, with another mixture with the filtering material from feeder 30 and also filtering through filter 36. In a series of preliminary tests using 0.2% or less by weight of diatomaceous earth with biodiesel at a temperature chilled to at least 38°C, the pressure plate filter 36 reduced water and sediment from the biodiesel product to less than 0.01% by weight. The tests involve, and conservatively support, the use of a diatomaceous earth feed rate of about 186.6 grams / minute, with a biodiesel feed rate of approximately 554 pounds / minute for filter 36 (i.e., about 0.019 % body power of diatomaceous earth). An initial filtration run was conducted for about 6 hours at the rate of 540 pounds / minute to result in approximately 197,000 pounds of biodiesel product being fed through filtration assembly 36. No sediment and / or float during this period were observed. as being completely absent. The pressure drop across filter assembly 36 was observed to be about 5.51 kPa. After stopping the vertical plate filter 36, draining, and unloading for 3 minutes, the samples were obtained, with important tests for the residual biodiesel oil, however, the "pie" was characterized as dry The clean biodiesel product exiting the filter 36, and which does not need to be refiltered through line I, is then directed to a filter receiver pulser 38, as indicated by arrow j_. The pulsator 38 is optional, and will provide production control subsistence. The clean biodiesel is then directed to a final product filter 40, as indicated by the arrow K. In one embodiment, the filter 40 can be socket filters, which remove any final particles, including diatomaceous earth, in the biodiesel product. This final step polishes the biodiesel to final clarity and removes any residual diatomaceous earth or filter cake that may have passed through the mesh screens of the plate filter 36. The polished biodiesel is sent to storage tank 42 (arrow L ) for certification and shipment. Periodically, the plate filter 36 must be cleaned. Cleaning or changing the pressure plate filter 36 consists of taking the filter off, removing the liquid from the container, blowing the dry filter plug with air or nitrogen from the source 37 to minimize the loss of biodiesel product in the filter plug spent, and then discharge the dried filter cake from the sieves. The filter 36 should be cleaned after a preset period of time, and when excessive pressure drop across the filter is noticed during operation. After cleaning, the filter 36 must be refilled with the filter material over the mesh leaves. Such a refill can be accomplished by circulating the filtration material / biodiesel slurry from a precoat feeder 44 which supplies the filtration material to a biodiesel precoat tank 46, as indicated by arrow M. The slurry in precoat tank 46 is then circulated through filter sheet 36, as indicated by arrows P, H, and 0 until the filter sheets are sufficiently coated. Then normal filtration of biodiesel from body feed tank 28 can continue. The slurry in the precoat tank 46 will also be opened through the demixer 32, (described above) as indicated by arrow N. The plate filter pressure depends on numerous factors, such as equipment size, flow parameters and piping, and should be adjusted according to the manufacturer's design specification. A pressure relief tube (arrow Q) is provided to divert biodiesel from sheet filter 36 back to body feed tank 8 in the event of excessive pressure. Periodically, heat exchangers were employed so that the cooling process could continue during the cleaning operation by stopping one heat exchanger at the same time as employing another heat exchanger. In the present invention, cleaning the heat exchangers 24 does not require a shutdown of one exchanger to clean while the other exchanger operates. Preferably, cleaning is quickly and easily completed by employing a clean-in-place procedure by cutting off the coolant flow for a short period of time to the heat exchangers, while continuing to run the hot biodiesel product 20 through the permu- heat exchangers, and then recycling the hot biodiesel through a recycle tube 48, as indicated by the arrows R and S. Running the hot biodiesel through the heat exchangers without cooling, or any sediment formation in the exchangers is dissolved in approximately one minute or less and thereby returned to suspension in the biodiesel product. After the exchangers 24 are cleaned, the coolant flow is returned to the exchangers 24 for continued cooling of the biodiesel product 20, as described above. It is understood that the various tubes shown in Figure 2 include valves and gauges to control and monitor the flow of biodiesel during the cold filtration step 14. Clean, filtered biodiesel can be tested to determine its quality, although such testing is not a required step in the cold filtration process. One test method employed to qualitatively determine filtration efficiency and level of sediment remaining in the finished product is to replicate problematic shipping and storage conditions. This is achieved in the laboratory by chilling a 100 mL sample to 4°C for 16 hours, then centrifuging the sample (per ASTM D-2709 test method) while still cold, and visually inspecting for the presence of of sediment. Target product quality will not have any visible sediment resulting from this test method. Alternatively, a sample can be allowed to completely freeze by subjecting it to -1°C or colder for 48 hours or more, then allowed to re-freeze. bring to room temperature (approximately 24°C). The a-sample is centrifuged as before and visually inspected for sediment. In all cases, the final product should be shiny and clear with no visible sediment. A more formalized test method has been implemented in the State of Minnesota to "determine the mass of particulate contamination in a biodiesel fuel by filtration". This test method is a modified version of ASTM D-6217 and involves cold soaking a 300 milliliter sample at 4°C for 16 hours, followed by natural warming to room temperature (21°C), before filtration through a special laboratory apparatus. The technical assistant at the National Biodiesel Board facilitated modifications to this test method. All biodiesel fuel sold in Minnesota must pass this test with a filtration time of less than 360 seconds per specific customer requirements. Experience with this test has shown that the specification limits may not be adequate in identifying or preventing potential field problems, as filtered or unfiltered fuels passed this test easily. Experience suggests that the type and quality of the feedstock oil that is used to produce the biodiesel has an impact on the quality and nature of the sediment formed. Biodiesel made from refined and bleached soybean oil tends to form sediment more easily when exposed to flash cooling. Biodiesel made from less processed soybean oil (such as degummed and deodorized chilled) tends to require prolonged exposure to cooling temperatures before sediment forms. This time and temperature dependence on sediment formation could result in different field experiments with unfiltered fuel. However, it is noted that regardless of the feedstock oil employed, the cold filtration process described above is successful in removing sediment-forming materials. The invention has been shown and described above with the 1 preferred embodiments, and it is understood that many modifications, substitutions and additions can be made which are within the spirit and intended scope of the invention. From the foregoing, it can be seen that the present invention completes at least all of its stated objectives.

Claims

CLAIM 1. A method for removing impurities from biodiesel, characterized in that it comprises: converting a feedstock into biodiesel having a temperature exceeding 98°C; cooling the biodiesel to a temperature range sufficient to form impurity particles; and filtering the cooled biodiesel to remove the particles.

2. Method according to claim 1, characterized in that the biodiesel is cooled to a temperature lower than about 38°C.

3. Method according to claim 2, characterized in that the biodiesel is cooled to a temperature between 4-38°C.

4. Method according to claim 1, characterized in that the cooling step is re- realized in multiple stages employing a series of hot heat exchangers.

5. Method, according to claim 4, CHARACTERIZED in that it further comprises periodically cleaning the heat exchangers by running uncooled biodiesel through the heat exchangers without supplying cooling fluid to the exchangers.

6. Method according to claim 4, characterized in that a first cooling stage reduces the biodiesel temperature to approximately 93-105°C, a second cooling stage further... reduces the temperature of biodiesel to approximately 26- 33°C, and a third cooling stage further reduces the biodiesel temperature to at least 18-24°C.

7. Method according to claim 1, characterized by the fact that a filtration step includes multiple stages.

8. Method according to claim 7, characterized by the fact that a first filtration stage includes the addition of an absorbent to the biodiesel.

9. Method according to claim 8, characterized by the fact that the absorbent is selected from a group consisting of diatomaceous earth, silica, sand, or mixtures thereof.

10. Method according to claim 9, CHARACTERIZED in that the absorbent is diatomaceous earth.

11. Method, according to claim 10, CHARACTERIZED in that diatomaceous earth is between 0.1% and 0.25% by weight of the biodiesel.

12. Method according to claim 8, CHARACTERIZED in that the first filtration stage includes a plate filter.

13. Method according to claim 7, CHARACTERIZED in that a second filtration stage includes a socket filter.

14. Method for improving the quality of biodiesel fuel, CHARACTERIZED in that it comprises: pre-treating a supply of triglycerides to remove impurities; converting the triglycerides into methyl ethers and glycerin; cooling the methyl esters to a temperature lower than about 38°C in order to form a filter to remove non-methyl ester particles and thus produce improved biodiesel fuel.

15. Method according to claim 14, CHARACTERIZED in that the cooling is accomplished through a series of heat exchangers.

16. Method according to claim 14, CHARACTERIZED in that the filtration is accomplished through a series of filters.

17. Method according to claim 14, CHARACTERIZED in that it further comprises adding an absorbent to the methyl esters after cooling and before filtration to form a slurry.

18. Method according to claim 11, CHARACTERIZED in that the absorbent is diatomaceous earth- cea.

19. Method according to claim 11, characterized in that the sludge is filtered through A sheet metal filter to remove particles from the biodiesel.

20. Method according to claim 19, CHARACTERIZED in that the biodiesel is additionally filtered through a socket filter to remove particles.

21. Method according to claim 14, CHARACTERIZED by the fact that it additionally includes hibernate the filtered methyl esters.

22. Method according to claim 21, CHARACTERIZED in that it further comprises fractionating hibernated methyl esters.

23. Method according to claim 14, CHARACTERIZED in that the methyl esters meet the specifications of ASTM D6751 or higher before cooling.

24. Improved biodiesel production process, CHARACTERIZED in that it comprises: processing triglycerides to produce biodiesel; cooling the biodiesel with at least one heat exchanger in order to precipitate the particles; filtering the cooled biodiesel to remove the particles; and periodically cleaning the heat exchanger by passing uncooled biodiesel through the heat exchanger without supplying coolant to the heat exchanger.

25. Process, according to claim 24, CHARACTERIZED in that it further comprises returning the coolant flow to the heat exchanger after the cleaning and recycling step of the biodiesel used to clean the heat exchanger by cooling.

26. Process according to claim 24, CHARACTERIZED in that it further comprises adding an absorbent to the cooled biodiesel prior to filtration.

27. Process according to claim 26, CHARACTERIZED in that the absorbent is diatomaceous earth- cea.

28. Process according to claim 24, CHARACTERIZED in that the filtration step uses a pressure plate filter.