The human body composition

What happens when a body is pyrolysed and what is the chemical composition of a body?

First stage

A human body consists of 70% of water. Evaporation of this water at temperatures of 80 degrees Celsius is a slow and energy efficient method. This temperature also prevents the decomposition through bacteria and the associated smells.

Pyrolysis takes place in a environment where there is no oxygen. The body is placed in a steel chamber able to withstand high temperatures and able to vent gasses that are being produced during the process. In the first stage when evaporation takes place the temperature in the pyrolysis chamber is 80 degrees Celsius provided by solar- or infrared radiation or waste heat. Typical the evaporation of water takes 2,5 MJ per kilo, thus for a body of 70 kilo by 70% = 49 kilo X 2,5 MJ = 122,5 MJ. 3,6MJ(MegaJoule) is 1 KWh(KiloWatthour) The sun provides roughly one KWh per square meter per hour.

Getting rid of most of the water content before starting the pyrolysis process also means that the gasses that are produced in the pyrolysis process have a lower water content and are more easily to handle (burn, condensed separated) and to use.

Second stage
When we look at the chemical composition of a human body we see that it’s made up for 99% from 6 basis elements. Once the water is evaporated 12% of the hydrogen atoms are still present in other chemical bonds. Breaking down the hydrogen-bonds and the carbon-hydrogen bonds releases Hydrogen-gas(H2) and other volatile CH compounds and forces the remaining carbon atoms to realign them selves in biochar. The Nitrogen is released as N2 or bound into the carbon as are most of the other elements.

By preventing oxygen to react with carbon, nearly all the carbon is locked in a chemical stable form and not released into the atmosphere as CO2.

Element
Percent by mass
Atomic percent (calc.)
Oxygen
65%
25.6%
Carbon
18%
9.5%
Hydrogen
10%
63%
Nitrogen
3%
1.3%
Calcium
1.5%
0.24%
Phosphorus
1.2%
0.24%
Potassium
0.2%
0.03%
Sulfur
0.2%
0.04%
Chlorine
0.2%
0.04%
Sodium
0.1%
0.03%
Magnesium
0.05%
0.01%
Iron
3g in men, 2.3 g in women
Cobalt Copper Zinc Iodine
0.05% each
Selenium Fluorine
0.01% each

(from Chang, Raymond (2007). Chemistry, Ninth Edition. McGraw-Hill. pp. p. 52.

Natural gas has and energy content of 32 MJ/m³. A typical cremation in a old crematorium takes up to 1200 MJ or 37m³ natural gas, resulting in the emission of 57.68 kilo CO2

Natural gas is 85% CH4 and 15% N2.
CH4 = 12+1+1+1+1 = 12 gram/Mole Carbon 4 gram/mole Hydrogen
12 x 0,85 x 41,66 = 425 gram Carbon per m³ natural gas
Carbon-dioxide = 12+16+16=44, 44/12 = 3.67
425 gram X 3.67 = 1559 gram CO2/m³
by 25C en 1 atm.

For every kilo human remains that is cremated, 660 grams of CO2 is produced. 18% = 180 gram Carbon X 3,67  = 660 Gram.

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