[Gasification] why do liquifaction proceses require nitrogen-less synthesis gas?

[Daniel Chisholm]

On Mon, 2007-29-01 at 01:23 -0800, jim mason wrote:
> that's it.  thank you.  i forgot to look in homepower.
> 
> On 1/28/07, Jeff Davis <jeff0124 at velocity.net> wrote:
> > On Sunday 28 January 2007 09:27 pm, jim mason wrote:
> > > does anyone remember that DIY liquifaction scheme i think mother earth
> > > news had on running woodgas through some copper tubing and getting
> > > some liquid fuel out?  messy but it worked.  i can't find it after
> > > much looking.  i'd really like to find it.  anyone know?
> >
> > How about Home Power:
> > http://www.homepower.com/files/woodgas.pdf?search=gas
> >
> > Page 5
> >
> > Sounds thin...

I can't quite figure out what JeffD meant by "thin," but that article
sure seemed to me to be pretty thick on some pretty misleading
"information".  A particularly bad example is the "Hydrogen Fuel"
section on page 5, in which he (the author) suggests that electrolysis
is an economically feasible way of making hydrogen for fuel purposes -
he quite clearly misses the fact that electrolysis is a less-than-100%
efficient means of converting electrical energy into chemical energy
(H2).

He (Mossberg) seems to think that an underwater arc to a submerged
aluminum wire is a promising way to generate H2 (an arc would indicate
that the electrolysis is operating particularly inefficiently).  He
neglects the consumption rate (and cost!) of the aluminum electrode per
unit of hydrogen produced.  He suggests that it would be a practical
onboard method of generating hydrogen for vehicular use.  He even steps
right off into perpetual motion machine territory, saying:

        "...the gas generator can be run by a battery which is charged
        by alternative energy methods. It is obvious that it can also be
        charged by the device it supplies, such as an engine/generator
        unit or a hydrogen fuel cell."

Enough criticism.....


With respect to the original question than JimM asked, "Is N2 a bad
thing in the feedstock for liquid fuel synthesis, and if so why?", I
still haven't figured that one out - and it's a darn good question too,
Jim.  I wonder the same thing about the processes of integrated
gasification combined cycle (IGCC) plants that I have seen, they too use
pure O2 to make synthesis gas.  Perhaps the IGCC case is similar to the
fuel synthesis case, in that it (IGCC) has a lot of chemical processing
happening in order to burn a dirty fuel (e.g. coal) cleanly enough to
power a gas turbine and also to pass emissions limits.

In liquid fuel synthesis I strongly suspect that you are right in
wondering if the problem is undesired ammonia formation, but I haven't
found out for sure yet.  I was reading through my 1962-vintage "Gas
Engineers Handbook", which had separate chapters on:

- how ammonia is mfr'd (from CH4 and atmospheric N2)
- how ethylene is mfr'd from CH4 (and it mentions that ethylene is a
principal feedstock for the chemicals industry)
- how liquid fuels are mfr'd (basically, they are built from ethylene).

Unfortunately it doesn't tie together all the questions into the big
picture, i.e. how can one proceed more directly from CH4 to liquid
fuels, or even better from producer gas to liquid fuels.  Or why this
isn't feasible.

Ethylene C2H4 has the same 1:2 carbon to hydrogen ratio as longer
chained fuel hydrocarbons, so it's not really surprising that it would
be straightforward to use ethylene as your input if you can.

Now the million dollar question of course is, how to make (CH2)n from
(CO + H2 + CH4 + CO2 + N2)......





-- 
- Daniel
Fredericton, NB  Canada