We've been doing some testing on acid/base reactions lately, trying to reduce process stream "problems" when we gear up for larger volumes. The following is the outcome of some of the testing, based primarily on Aleks Kac's revised method. Rumor has it that many people seem to have problems with the process. So I thought that posting some information may be of benefit.
If anyone were to ask me, I'd say Aleks has provided a valuable service in making esterification knowledge more broadly known to the general public...deserving at minimum some healthy recognition in the Biodiesel Hall of Fame. Todd ................................... 4/25/2002 The following is a derivation of Alex Kac's revised 2 stage, acid/base catalysis of waste vegetable oil into methyl esters, presently posted at http://journeytoforever.org/biodiesel_aleksnew.html There are a few alterations of method, which include; 1) The use of potassium hydroxide (KOH) as the base, rather than NaOH, as the final intent is base recovery in the form of potassium phosphate salts. 2) An elevated processing temperature of 135*F, as this was the most easily maintained temp using lowest possible heat settings on a gas range, with a half-filled 5 gallon water bath. (This is not a brilliant maneuver and we can accept no responsibility for anyone who would be equally as "stupid" as to use an open flame heat source in the presence of alcohol or similar combustibles.) 3) A twelve hour acid stage reaction/settling period at an elevated temperature of 135* F. 4) Separation of the base stage into three distinct steps. Equipment on hand was; One generic candy thermometer, 80*F - 400*F range. One 2 liter PET soda bottle as a reaction vessel. One "pop-up" cap, easily found on sports drink and 1 liter bottled water at the grocery One 1ml pipette One 50ml beaker One 1,000ml beaker One 5 gallon stew pot as a water bath, including the following; Six quart mason jars One large dinner plate One small dinner plate Water bath preparation: Place the large dinner plate right side up in the bottom of the pot. Place the small dinner plate upside down on top of it. Fill the pot 1/3 full, removing air from beneath the inverted small plate. Place the 6 water filled mason jars (no lids) in a circle around the inside perimeter of the pot. The mason jars serve the purpose of keeping the reaction vessel upright and generally immobile in the bath. The "pop-up" cap has the unique ability of turning the 2 liter reaction vessel into a separatory funnel when inverted. Great caution and pains must be taken to not open this crude device more than a miniscule trickle. Practice should first be conducted using only water until a technique can be "perfected." Also, light but continual force must be exerted on the reaction vessel (a gentle squeeze) to prevent the uptake of air into the "separatory device," as this will re-agitate the contents and force an immediate settling period before continuation. The process: 1) Waste vegetable oil from a franchise burger joint was settled at 140*F and filtered. 2) Exactly one liter of oil was measured at 135*F and transferred to the reaction vessel. 3) 80 mililiters of MeOH was added to the oil, cap replaced, and 100 units of vertical agitation were inflicted upon the contents. 4) 1 mililiter of 98% sulfuric acid was added using the 1ml pipette, cap replaced and 100 units of vertical agitation were again inflicted upon the contents. 5) This agitation cycle was repeated every 10 minutes for one hour, while maintaining a constant temperature of 135*F. Note: A coalescence of ~1ml of dark fluid appears at the surface layer between each agitation cycle. This is almost entirely MeOH, darkened by a small bit of glycerin that is cracked by the acid. 6) The same agitation cycle was repeated every 10 minutes for a second hour, with the reaction vessel removed from the water bath for the duration. 7) The reaction vessel was inverted and placed into the 130*F water bath for a 12 hour settling period and observation. 8) The separatory feature was used to isolate the 40ml of darkened methanol that coalesced at the top of the reaction vessel. The bottom liter of oil was passed through a coffee filter during the separation to remove any particulates that may have coagulated during the acid stage. (Almost none were noted, in comparison to other acid/base sample batches where 2ml of sulfuric had been used. This filtration was done as particulates can bind up catalyst during a base reaction.) 9) Oil is returned to the reaction vessel. Note: At this point 40 of the 80ml of alcohol have been removed. 9) 5.61 grams of KOH were dissolved into 200ml MeOH. This is equivalent to 4.0 grams of NaOH. (The KOH assays out at 91%, which means that 5.61 grams is actually only equivalent to ~3.64 grams of pure NaOH.) 10) 100ml of methoxide (1.82 grams NaOH equivalent) were added to the reaction vessel's contents. 100 units of vertical agitation were inflicted upon the vessel. 11) After 15 minutes another 100 units of vertical agitation were again inflicted. Reaction vessel is inverted and returned to the water bath for 3 hours. 12) Extracted 62ml of thick, dark glycerin from the vessel using the separatory technique. 13) Added 50ml of methoxide (0.91 grams NaOH equivalent) to the reaction vessel's contents, returned cap and inflicted 100 units of agitation. 14) Repeated step #11 15) Extracted 60ml of dark, slightly less viscous glycerin from the reaction vessel. 16) Repeated step #13 17) Repeated step #14 18) Extracted 31ml of rather light colored glycerin/alcohol 19, 20, 21 & 22) Conducted four separate washes using 500 ml water each, allowing only 30 minutes settling time between each. No phosphoric acid neutralizer was applied to the fuel prior to washing. Results: When the ester was reheated to the starting temp of 135*F, 995ml of volume were recorded. Fuel was slightly hazy. This haze disipated within 24 hours, yielding 3ml water, leaving an approximate ester yield of 992ml. Yield of a single stage base reaction conducted under similar conditions two days earlier, also using KOH as the catalyst, gave a final yield of 950ml of esters at temperature, approximately 946ml after the wash haze cleared 24 hours later. Future Testing: Using the exact same feedstock and duplicating conditions of the acid/base reaction above, variations on the theme will be conducted using smaller volumes of base catalyst and reducing the total alcohol volume to a minimum or near minimum requirement, at the same time reducing the base stage from three sections to one. Targeted time for a complete reaction in the presence of minimal catalyst is arbitrarily set at not more than 6 hours. Data will be charted and used in the incremental upgrades of production volume at a later date. General Comments: The introduction of three divisions in the base stage was primarily for incremental observation of the glycerin drop under conditions of minimum catalyst. We can't see any need for anyone conducting an acid/base reaction to use anything but a 1 step base stage, with the same base amount that is suggested at http://journeytoforever.org/biodiesel_aleksnew.html We refrained from the addition of any phosphoric acid to the glycerin as a pre-treatment for washing in the attempt to produce the worste possible wash problem and potential ester loss, despite a completed reaction. However, the merit of such a pretreatment is apparent, in that it would neutralize some, if not all, of the free floating catalyst in the esters that does not settle out with the glycerin. This in turn will assist in the reduction of fuel haze resulting from the wash stages. Any benefit from step #8 may or may not exist. On the one hand it extracts alcohol from the reaction, which is why an increased total amount of alcohol was used in the base stage. The amount of sulfuric, if any, removed from the reaction by conducting this step would also reduce the amount of catalyst needed in the base reaction. Such a determination will have to wait until we've got a GC up and running. This may be in a few days or maybe not, as we have no clue at this moment if the GC's column is intact. That's about it. Todd Swearingen ------------------------ Yahoo! Groups Sponsor ---------------------~--> Buy Stock for $4 and no minimums. FREE Money 2002. http://us.click.yahoo.com/k6cvND/n97DAA/ySSFAA/FGYolB/TM ---------------------------------------------------------------------~-> Biofuel at Journey to Forever: http://journeytoforever.org/biofuel.html Please do NOT send "unsubscribe" messages to the list address. To unsubscribe, send an email to: [EMAIL PROTECTED] Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
