Hi gang! I am working with the local land grant university and our state regulators to produce a "best practices manual" for small scale biodiesel producers. Essentially we are trying to summarize all of the known safety, environmental, and regulatory issues for our state into one document, which will be distributed free to farmers and others who want to know how to produce responsibly and stay within the law. Needless to say this has been an interesting experience for an intermediate homebrewer and educator, but here I am.

Anyway I have been working on an article on tracking methanol emissions. In our state the limit is 1 ton of methanol emissions per year before you need a permit. If you would care to comment on the document below I would appreciate any input. In particular, the percentages of methanol residuals in fuel and glycerol are rough guesses based on my understanding of the stochiometry of the reaction. If you have more accurate information I would appreciate the correction! Lastly if you want a copy of the excel worksheet I sketched out for this email me at msteiman@wilson.edu and I'll send it over.

Thanks to all who have contributed to the forum and inadvertently helped me write this article.
Thanks!
Farmer

Tracking Emissions: Where does the methanol go?

Methanol is an air pollutant of concern for the Department of Environmental Protection. In Pennsylvania, facilities that emit into the air one ton (2000 lbs) or more of methanol per year are required to obtain a permit from the DEP. Facilities that emit less than one ton per year are currently exempt from permitting. As a best practice, small producers should monitor and record their methanol emissions to ensure that they fall well below the exempt levels. This section discusses some factors involved in tracking methanol emissions.

For starters, obviously no facility will emit more methanol than is purchased or used in a given year. A gallon of methanol weighs about 6.6 pounds. One ton of methanol is therefore equal to approximately 300 gallons. A facility using 300 gallons of methanol per year (with no methanol recovery) will produce between 1200 and 1500 gallons of biodiesel per year. Those who plan to produce less than this amount of fuel can be sure that they fall within the allowable levels for methanol emissions, regardless of process design. All producers are advised to carefully track their methanol usage and take steps to reduce emissions of this air pollutant.

Biodiesel chemistry: The transesterification reaction requires approximately 13% of the starting oil volume to convert oil (triglycerides) into methyl esters (biodiesel) and glycerol. However, typical base-catalyzed batch reactions use excess methanol in order to achieve full conversion of the oil into fuel. (The biodiesel reaction is reversible. Without a surplus of methanol, an equilibrium is reached, and some glycerol will remain dissolved in the biodiesel as monoglycerides and diglycerides. Excessive glycerol in the biodiesel will prevent the fuel from meeting ASTM standards, and may harm engine components with extended use). Methanol on the order of 20% to 25% of the starting oil volume is commonly used to achieve full conversion.

If we assume that methanol on the order of 13% of the oil volume is chemically incorporated into the finished biodiesel, that leaves 7% to 12% of the oil volume as residual, emission-prone methanol. If the reactor is sealed (which is strongly advised for safety and efficient production), unbound methanol amounting to approximately 2% of the oil volume will end up in the biodiesel layer. If methanol is not recovered from the fuel prior to washing, this amount will end up primarily in the water used for the first wash. (For this reason wash water, especially from the first wash, should be considered toxic and handled with care). The remaining unbound methanol, amounting to approximately 5% to 10% of the starting oil volume, will end up in the glycerol layer.

For example, consider a 50 gallon batch reaction, using 20% methanol (10 gallons), with no methanol recovery. Roughly 6.5 gallons of methanol (13% of the oil volume) will become a part of the biodiesel molecules and will be burned as fuel. That leaves about one gallon of residual methanol in the unwashed fuel, and 2.5 gallons of methanol in the glycerol byproduct.

Each production facility will follow a different set of practices for handling of post-reaction fuel and byproducts. Producers can track their methanol emissions through a record sheet such as the sample depicted below. In addition to ensuring compliance, recording methanol emissions will help inspire producers to engage in the best practice of methanol recovery.


Methanol Emissions Worksheet Facility: McDonald's Farm
Year: 2007 Sheet #: 2007-1

Methanol Usage Record
A: Batch # B: Date C: Oil Volume, gallons D: Methanol as percent of oil volume E: Methanol gallons [(C X D)/100] Estimated Total Air Emissions this year (pounds) Estimated Total Water Emissions this year (pounds)
1 10-Mar 50 22 11 37.95 13.20
2 15-Mar 50 20 10 See below
3 20-Mar 54 24 12.96
4 28-Mar 54 22 11.88
5 29-Mar 60 22 13.2

Total gallons methanol used this year 59.04

FUEL RESIDUALS WORKSHEET (Default is water)
A: Batch # F: Residual methanol in fuel, gallons [C X 0.02] G: Recovered from fuel (gallons) H: Disposition of methanol in fuel I: Estimated water emissions (pounds) [(F - G) x 6.6] J: Estimated air emissions (pounds)
1 1 0 wash water 6.6
2 1 0 wash water 6.6
3 1.08 1.08 recovered 0
4 1.08 1.08 recovered 0
5 1.2 1.2 recovered 0

Subtotals: Residual emissions from fuel 13.20 0


GLYCEROL RESIDUALS WORKSHEET
A: Batch # K: Residual methanol in glycerol (gallons) [(C X (D - 13)/100] L: Recovered from glycerol (gallons) M: Glycerol disposal N: Decomposed in disposal? (gallons) O: Estimated water emissions (pounds) P: Estimated air emissions (pounds) [(K - (L+N)) X 6.6]
1 4.5 1.25 Soap 0 0 21.45
2 3.5 0 Compost 1 0 16.5
3 5.94 5.94 Degreaser 0 0
4 4.86 0 Digester 4.86 0
5 5.4 3 digester 2.4 0

Subtotals: Residual emissions from glycerol 0 37.95

Methanol Recovery: (original text by Wallis Lloyd, adapted by MS)

Methanol in excess of the actual amount required for the trans-esterification reaction is added to drive the reaction further to completion. If the excess methanol is recovered, it can be used for processing additional batches. If not recovered, most of the excess ends up in the glycerol and some in the water wash. This is not only wasteful of a valuable component, but can further complicate the disposal of these two streams.

Methanol recovery can take place from the fuel after the glycerol is removed, and it can be distilled from the separated glycerol. In either case, it is important to have an adequate condenser to ensure that all of the methanol vapor is condensed. The condenser must have enough surface area and cooling water temperature must be low enough to do the job. Most of the methanol can be distilled at atmospheric pressure and at a temperature not much above the boiling point of methanol (148 F). Since there will usually be some water in the reaction mixture, the distilled methanol may contain a small amount of water. This may not be enough to adversely affect a subsequent reaction, but one should be aware of this. To reduce water contamination, heating of the fuel or glycerol should occur slowly, and care should be used as temperatures approach the boiling point of water (212 F). Some producers will separate their “dry” methanol recovered in the early low temperature stage from “wet” methanol recovered as the boiler temperature nears 212 F. Recovered methanol is typically blended with fresh methanol when used for making biodiesel.

Purity of recovered methanol should be assessed to provide feedback on the distillation process. Using the specific gravity of pure methanol (793 grams per liter), one can assess the purity of recovered methanol by weighing a 1 liter sample, then entering the result into the following equation:
[1000 – (weight of 1 liter in grams)] / 207 = % purity.
Example: A 1 liter sample of recovered methanol weighs 805 grams: [1000-805]/207 = .94 or 94%

The rate at which methanol will distill is a function of the temperature and the rate at which heat can be added to the liquid. Methanol exiting the condenser will collect in a vessel that must be vented to the atmosphere. It is important to keep the temperature in this vessel as low as practical to reduce the amount of vapor escaping through the vent.

Extreme caution should be used when distilling methanol to avoid fire and personal exposure. Adequate ventilation and the absence of ignition sources are a must. All fluids and gases should be transferred via tubing rated for the relevant temperatures expected. Methanol collection vessels should be vented to the outdoors to avoid vapor accumulation in the workshop, or better yet recovery gear can be located out of doors. Producers are advised to research the design of methanol recovery equipment appropriate to their operation and thoroughly think through all safety considerations.

For further information on methanol recovery see:
• Discussion forum: http://biodiesel.infopop.cc/eve/forums/a/frm/f/4441089311
• Copper condenser design: http://www.london-electronics.com/bd/still/still.htm
• Small condenser design: http://www.b100wh.com/recovery1.html#condenser
• Slide show: http://www.b100.org/presentations/MethanolRecovery/

Shoot, the worksheet columns came out all misaligned. As I said if you would like a copy of the excel spreadsheet just email me at msteiman@wilson.edu

OOPs again, looks like I forgot to subtract the 2 percent accounted for in the fuel when doing the glycerol calculations in the chart. The formula for column K: Residual methanol in Glycerol should read [(C x (D-15))/100]

Regards,
farmer