[Gasification] Biomass Ethanol

[Mark & Elena Gallmeier]

Dear Drew & All,

>>I have been trying to get a handle on this as well.<<

You're welcome to use the handle I have, for what it's worth.

>>It is my understanding that clean wood gas consists mostly of nitrogen, CO
>>and Hydrogen.

Basically yes.  There is - usually - a small percentage of CH4 methane, some
H2O water, CO2 carbon dioxide, plus a chemistry lab of 'tars' and
'volatiles'. This gas mixture is also called "producer gas".  On this list,
anyway, 'producer gas' is made by the basic process of:

Biomass + Air ===> Biomass Gasifier ====> 'Woodgas' (or producer gas).

The optimum scientific, engineering and economic mechanics of doing this are
a main topic in the archives, hundreds of websites and long shelves of
scientific and engineering books and papers.

>>There is very little methane to convert to methanol.<<

Methane (CH4) is not converted directly to methanol (CH3OH) using
'gasification' & catalytic processes.  *Synthesis Gas* is used.
That reaction is:

Biomass + Oxygen ===> Gasifier ===> Catalytic Reactor (heat, pressure and
specially formulated 'catalyst')  ===> "Methanol".

The major gasification difference is the use of oxygen, O2, in place of
'air' (78% Nitrogen 21% Oxygen, .97% Argon and trace gasses) as the
oxyidizer of the gasification process.  The resulting 'syngas' is CO + H2.
Nitrogen can also inactivate methanol catalysts.  The CO + H2 synthesis gas
is then put through the catalytic reactor to reform it to CH3OH, methanol
using different combinations of pressure, heat and formulations of
'catalyst'.

This is very simplified and plenty of vital details lurk within.

>>Methanol was commonly produced from wood, via destructive
distillation (also known as charcoal making) which took place at lower
temperatures  (600 C or less I believe).<<

Yes.  About a 2% yield of methanol can be obtained from destructive
distillation, or retorting wood.  This means heating wood in an oxygen
deprived atmosphere.  Retorting is different from charcoal *kilning*, FYI.
*Kilning* involves the admission of controlled amounts of air into a kiln to
partially combust the wood.  Retorting applies heat from outside the
chamber, which is usually a metal container of some kind.  Both
retorting and kilning are different than 'gasifying' as discussed here.

Kilning and gasifying are more closely related in process and resulting gas,
with retorting being a second cousin.  Because of the oxygen/nitrogen
deprived environment and the typically lower temperatures, retort gas is 
very
different in composition from producer gas or synthesis gas.

Retorts do make charcoal.  Historically "kilning" has been more widely used
by pure charcoal making operations.  'Retorts' historically were used more
by operations seeking chemicals recovery of products like acetic acid and
methanol, with charcoal being a byproduct.

>>An issue then is the tars associated may poison or coat the catalysts
>>(reducing surface area).   I believe this is also where other very toxic
>>things like dioxins can be
easily produced via salty wood).<

With retorting, about 200 other chemicals are produced.  Most are on the
EPA's controlled chemical emissions list in varying amounts.

>>(easy is relative, cleaning wood tar is nasty and likely toxic), where the
>>tars would have congealed (stockholm tar)<<

Certainly a clean synthesis gas is required.

>>the resulting gasses then might be safely run through a catalyst bed
>>(copper
seems like an inexpensive choice).<<

This has been done as simply as using producer gas ducted into copper tubing
packed with pieces of copper "Chore Girl" scrub pads.  A major practical
issue is the methanol yield per ton of feedstock.  Destructive distillation
yields about 2%.   More advanced biomass - synthesis gas - catalytic
reformation can yield 187 gallons per ton.

Methanol plants come in all sizes and efficiencies.  Whether a particular
size and design is considered 'economic' depends on a lot of local variables
and assumptions.  These include:

--- Cost of other available liquid fuels (and buyer's ability to pay some
kind of exchange for them)

--- Cost of available 'biomass' feedstocks and their currrent uses.   In
2006 North America the primary use is making compost, whether wanted or not.

--- Cost of electricity and/or oxygen.

--- Goals of the owners/operators.

--- Basic technical ability of the owners/operators and the amount of local
fabrication of plant components they can engage in.

--- Desire and need of external 'venture capitalists', 'consultants' and
'governments' to extract fees and taxes from a particular project in
exchange for supplying printed paper of different types.

These economic factors are so variable, and existing biomass methanol
production so nano-scaled, that blanket statements about the
'economic feasibility' of different plant sizes and efficiencies cannot be
made.

Healthy skepticism should be applied to both wild optimism and excessive
pessimism over the potential for making biomass methanol at smaller scales.

Best Wishes,

Mark

------------------------------

Message: 3
Date: Sat, 09 Dec 2006 11:18:41 -0800
From: drew <drew at artforging.com>
Subject: [Gasification] Ethanol
To: gasification at listserv.repp.org, dhansen at uniserve.com
Message-ID: <457B0C11.20204 at artforging.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

   I have been trying to get a handle on this as well.    It is my
understanding that clean wood gas consists mostly of nitrogen, CO and
Hydrogen.    There is very little methane to convert to methanol.   The
biomass may give off plenty of methane as it decomposes via the heat,
but the methane is one of the first things to crack in the tar cracking
bed.    Methanol was commonly produced from wood, via destructive
distillation (also known as charcoal making) which took place at lower
temperatures  (600 C or less I believe).   An issue then is the tars
associated may poison or coat the catalysts (reducing surface area).   I
believe this is also where other very toxic things like dioxins can be
easily produced via salty wood).   I believe that the gases from
destructive distillation would normally have been lead to a large easy
to clean condenser (easy is relative, cleaning wood tar is nasty and
likely toxic), where the tars would have congealed (stockholm tar), the
resulting gasses then might be safely run through a catalyst bed (copper
seems like an inexpensive choice).     I am not sure if gas acidity
would be an issue, if it were the produced gas would have likely been
bubbled through a buffering fluid, to further clean and balance the
ph.     This seems likely to produce the toxic soups so common back in
the day, where if you found you had produced something deadly to plant
life, you likely painted on your house or rubbed it on your skin to keep
the bugs away.