(compressed under high pressure) is also manufactured, often as small pellets a few mm long. Powdered charcoal is mixed with a binding agent and compressed under high pressure. Here, the macro pores are formed in the cracks between the powder particles. This type of activated carbon is not good for alcohol purification: the pellets are too big, the contact surface is too small, and the contact time is too short.Ash content and after-treatment of activated carbon The ash content of activated carbon is a measure of the mineral content (Ca, Mg, Si, Fe, salts, etc.) left in the carbon after the manufacturing process. We are only interested in the soluble (in water and alcohol) substances that remain. We don’t want to drink them, and they often leave a deposit in the alcohol. Therefore, activated carbon used for purification of water, alcohol, and other foodstuffs is cleaned with acid, often followed by water, to get rid of most of these substances.But – all this carbon is meant to be used in carbon beds that are started up in the correct way. This includes wetting and washing (or rinsing) the carbon. No carbon bed in an industrial filter is started unless the carbon has been saturated for 24 hours and thereafter rinsed for some hours. In this way all the remaining soluble substances arewashed out.The amateur distiller, who often pours dry carbon into a pipe and then directly filters the alcohol through it, releases the substances from the carbon and then drinks them. Carbon made from coconut shells usually leaves a white deposit in the alcohol. The carbon almost exclusively contains micro pores and is difficult to clean: hence the deposits. If you start up the carbon in the way recommended here, this problem will disappear by itself. In difficult cases an extra 10 liters of water is filtered through the carbon bed before alcohol is filtered.Effectiveness of purification and pore size
Only a small part of the carbon’s absorption surface is such that impurities can get stuck in them. The largest surface area is made up of micro pores, normally 90-98%. One to ten percent are meso pores and ca. 1% are macro pores. Many of the impurities we want to separate from the alcohol have molecules 2-10 nm in size, and are too large to be caught in the micro pores. We also need meso pores. Ideally, the pores in the carbon are slightly larger than the impurities that are to be caught in them. Smaller pores are not
found, and there are few larger pores.