Thermodynamics/CO and H2S


QUESTION: Hi Kevin! I am doing research on coal emissions and have been performing statistical analysis graphs to determine relationships between the measured gases.  Below is a summary of the relationships.  It turns out that CO (by far) has the strongest relationship with H2S than any of the other gases.  In other words, as CO increases, H2S increases, linearly, with an average R2 (statistic) value of 0.889 (1 being highest possible).  Why is this!?  Thanks!!!

Parameters   R2 #1   R2 #2    Dif    Avg    Confidence
CO vs. H2S   0.979   0.799   0.180   0.889   High
CO vs. CH4   0.046   0.683   0.637   0.365   Low
H2S vs. CH4   0.044   0.608   0.564   0.326   Low
CO vs. T   0.516   0.036   0.480   0.276   Low
H2S vs. T   0.463   0.001   0.462   0.232   Low
CO2 vs. T   0.203   0.210   0.007   0.207   High
CO vs. CO2   0.093   0.170   0.077   0.132   High
CO2 vs. CH4   0.056   0.062   0.006   0.059   High
CO2 vs. H2S   0.047   0.014   0.033   0.031   High

ANSWER: Hi Marc,

The first thing that springs to mind is that it will depend on the type of burning.
There are two basic types. Oxidative and reductive burning.
Where fuel is in excess you will have reductive burning this will produce CO rather than CO2
and H2S will form instead of H20 + SO2. This type of burning is used in Atomic Absorption Spectroscopy.(q.v.) Oxidative burning produces higher temperatures and causes more complete oxidation i.e. CO2 not CO and H2S to steam and SO2 (SO3 ?).

I hope this helps,

Best wishes.

---------- FOLLOW-UP ----------

QUESTION: Kevin - this makes  sense! The type of combustion  occurring is incomplete combustion from wild coal mine fires… Probably less than 200° C.  

It makes sense that CO would form instead of CO2 in a reducing environment. The hydrogen probably originates from internal to the coal (there's quite a bit in the internal structure), as well as the sulfur from minerals in the coal (pyrite).  

Do the other numbers make sense to you, given the environment?

Thanks again!

Hi Marc,

Yes the other numbers make sense now.

CO v H2S  as stated.
CO2 and CO would tend to be mutually exclusive. As would CO2 and H2S.

The role of methane CH4 is more complex.

You would need a wider range of T to get meaningful data.

Best wishes,


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Thermodynamics, chemistry, chemical reactions, kinetics, chemical reaction safety, dust explosion technology, static electricity. General science.


Over 40 years experience as a practicing thermochemist in industry. Head of the fire and explosion laboratory of a major European chemical company (Ciba-Geigy). Now retired.

Institute of Chemical Engineers. Royal Society of Chemistry.

Chartered Chemist, Member of the Royal Society of Chemistry (C.Chem MRSC). Msc Sheffield.

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