Methanol and the Home-Brewer

In June 2013, a young man in Queensland died as a result of drinking homemade liquor. It is believed that the liquor contained a toxic level of methanol (also known as wood alcohol). Drinking 10 mL of pure methanol can cause permanent blindness, drinking 30 mL of methanol can kill you.

The first step in the production of homemade liquors, is the fermentation of sugar.
Methanol, CH₃OH,is formed during fermentation.
When fermenting 6 kg of sugar dissolved in water for the production of distilled spirits such as whiskey or vodka, the home-brewer (and home-distiller) will typically find that the concentration of methanol in their brew is about 3 parts per million.

Many fruits are used by the home-brewer as the source of sugar to be fermented. Each fruit will lend a distinctive flavour to the final product. But fruits that are high in pectin will produce greater concentrations of methanol. Apples, apricots, guavas, quinces, plums, gooseberries, and citrus fruits like oranges, all contain high levels of pectin, typically more than 1% by mass pectin. Grapes, cherries and strawberries contain low levels of pectin, less than 1% by mass pectin.

Pectin contains  galacturonic acid which has the structural formula shown below:

In pectin, about 80% of the carboxyl groups in galacturonic acid are esterified with methanol. The remaining non-esterified carboxyl groups exist as the acid, or as salts with sodium, potassium or calcium. When pectin is broken down by enzymes during the brewing process, the methyl esters react with water to produce methanol.

The second step in the production of homemade liquor is the distillation step.
This is the crucial step in removing as much of the toxic methanol as possible.
The boiling point of methanol is about 65^oC, but the boiling point of ethanol (the desired product) is about 78^oC. During the distillation process, the first fraction collected should contain the methanol. This fraction should be collected and discarded. The next fraction should contain the desired liquor. It is highly recommended that any distillate collected after about 96^oC also be discarded.


Reference:
http://www.couriermail.com.au/news/queensland/ballandean-man-bill-lynam-who-lost-his-son-joel-to-homemade-liquor-poisoning-is-thankful-that-other-son-joshua-survived/story-fnihsrf2-1226664893229

Further Reading
http://ausetute.com.au/members/alkanolp.html (members only tutorial on alkanols)
http://ausetute.com.au/members/carboxyl.html (members only tutorial on alkanoic acids) 
http://ausetute.com.au/partspm.html 
http://ausetute.com.au/density.html 

Suggested Study Questions:

1. Draw the structural formula for methanol.
2. Locate the functional group present in methanol on the structural formula above. Name the functional group. 
3. At 25^oC methanol has a density of  0.79 g mL^-3. Calculate the mass of methanol present in a lethal dose of pure methanol .
4.  Convert the concentration of methanol given for homemade whiskey into a concentration in g mL^-1.
5. Assume the young man who died drank homemade whiskey. What minimum volume of homemade whiskey did he drink?
6. For galacturonic acid given the:
   • molecular formula
   • molar mass
7.  On the structural formula for galacturonic acid identify and name the functional groups present.
8. Draw the structure for the sodium salt of galacturonic acid.
9. Draw the structure for galacturonic acid esterified with methanol.
10. Give the molecular formula and molar mass for the structure above.
11. Apples contain about 1% by mass pectin. 10 kg of apples are to be used in the production of a homemade liquor. What mass of pectin will be present?
12. Assume exactly 100% of the carboxyl groups in galacturonic acid are esterified with methanol. How many moles of the ester are present in 10 kg of apples?
13. Write an equation representing the reaction between this ester and water to form methanol  and galacturonic acid.
14. How many moles of methanol could be produced by the break down of pectin in 10 kg of apples?
15. Assuming the young man who died had drunk this apple concoction without distilling and removing the methanol, what minimum volume of fermented apple-drink would he have had to have drunk?
16. Why do you think most countries have outlawed home-distilling?

Making Methanol

Methanol as an energy source can be used as a fuel in the same way as petrol (gasoline), or it can be used in fuel cells. About 90% of the worldwide production of methanol is derived from methane, the main component of natural gas. Current methods for producing this methanol involve converting methane into syngas, a mixture of carbon monoxide and hydrogen, and then converting this syngas into methanol. Eliminating the syngas stage would dramatically reduce the cost of producing methanol.
But methane is not very reactive, and combines readily with oxygen only at high temperatures. A catalyst helps, but commonly used catalysts themselves work only at 300^oC or higher. At these temperatures, most of the methanol produced is oxidized to carbon dioxide and water. Indeed, methanol yields from such reactions can be as low as 2%.

A lower temperature catalyst such as platinum dissolved in concentrated sulfuric acid at 200^oC, has achieved a methanol yield of more than 70% in the laboratory, but platinum is an expensive metal.

Methane can also be converted to methanol in the laboratory using a halogen such as bromine. Using a suitable catalyst at 250^oC methane reacts with bromine to form bromomethane (methylbromide) and hydrogen bromide. Bromomethane (methyl bromide) then reacts with water to form methanol. The bromine from the hydrogen bromide can be recovered by reaction with air, and reused.

Methanol can be made by combining carbon dioxide and hydrogen. Such a process requires considerable energy just to harvest the hydrogen from water, for example. The carbon dioxide could be captured from flue gases, and even directly from the atmosphere.

Further Reading
Nomenclature
Alcohols
Balancing Chemical Equations
Combustion of Hydrocarbons
Halogenation of Hydrocarbons
Fuel Cells and Batteries
Temperature Conversions
Ideal Gas law
Yield

Study Questions

1. Write the chemical formula for each of the following:
   
   • methanol
   • methane
   • carbon monoxide
   • hydrogen gas
   • oxygen gas
   • carbon dioxide
   • water
   • bromine liquid
   • bromomethane (methylbromide)
   • hydrogen bromide
2. Write balanced chemical equations for each of these reactions:
   
   • carbon monoxide + hydrogen gas → methanol
   • carbon dioxide + hydrogen gas → methanol
     
   • methane + oxygen gas → carbon dioxide gas + water
   • methane + oxygen gas → methanol
   • methane + bromine liquid → bromomethane + hydrogen bromide
   • bromomethane + water → methanol + hydrogen bromide
     
   • water → hydrogen gas + oxygen gas
3. Convert the following temperatures in ^oC to Kelvin
   • 200^oC
   • 250^oC
   • 300^oC
   
   
4. For the reaction between methane and oxygen to produce methanol, calculate the theoretical yield of methanol that could be produced from 100kg of methane.
5. Using the platinum-based sulfuric acid catalyst at 200^oC, yields of 70% have been achieved for the above reaction.
   • What mass of methanol is actually produced during this reaction if you start with 100kg of methane?
   • Convert this mass to moles.
   • Calculate the volume of methanol gas produced.
     
6. At 300^oC the yield of methanol produced from the reaction between methane and oxygen is 2%. Assume the reaction starts with 100L of methane gas
   • Calculate the moles of methane gas in the reaction mixture
   • Calculate the theoretical yield of methanol that could be produced
   • Calculate the actual yield of methanol
7. Why do you think it is important for Chemists to continue to search for inexpensive catalysts for the methane to methanol reaction?