Environmental Engineering Reference
In-Depth Information
Table 11. Production Method Data
Operational
Costs
Production Method Technology Maturity
Yield
By-Products / Environmental
Diluted Acid Hydro-
lysis
Very mature technology with little
process improvements
Sugar degradation, furfural creation, and
acid neutralization
$$$
85-90%
Concentrated Acid
Hydrolysis
Very mature technology with little
process improvements
$$$$
85-90%
Acid recycling, acid neutralization
Direct Microbial Con-
version
New technology still in R&D
$$ (potential)
unknown
Produces a number of by-products
Mature process with significant im-
provements being developed
Enzyme Hydrolysis
$$$
>90%
Natural enzymes only
still unknown due to the age of this technology.
This process is still in the research and develop-
ment phase and will require many more years of
research until it is production ready.
pretreatment is shown, but there are several other
options available as stated earlier in this paper.
Each pretreatment will have a slight impact on
the process sequence as well as overall cost and
ethanol yield. This process technology is not new,
but there are still major steps that can be taken in
the commercialization of this process. Currently
ethanol production by enzyme hydrolysis is more
expensive than either acid hydrolysis method, but
there is still significant cost savings and process
improvements that can be made significantly
reducing the overall cost of ethanol (U.S. Depart-
ment of Energy, n.d.).
Enzyme Hydrolysis
This technology has been understood since World
War II when fungus was observed breaking down
tents and cheese cloths (Graf and Koehler, 2000).
This is also similar to the process cows perform
to digest grass. The biomass is broken down by
enzymes which are created by bacteria in the cow's
stomachs. This process can be performed at body
temperature and does not require any additional
pressure. In order to increase effectiveness this
process does require a pretreatment step. All other
process methods will benefit from the pretreatment
step of reducing and compacting the biomass, but
it is a requisite for this process.
As shown in this figure there are much fewer
steps in this process with less harmful inputs
and by-products. In this example a dilute acid
Evaluation of Ethanol
Production Methods
In accordance with the evaluation methodology
described above the potential product methods are
ranked and scored according to the data shown
in Table 11. These rankings are a summary of
Table 12. Weighted Values ranking of Ethanol Production Methods
Technology Matu-
rity (30)
Operational Costs
(35)
Yield
(25)
By-Products / Environ-
mental (10)
Production Method
Total
Diluted Acid Hydrolysis
5
3
4
3
385
Concentrated Acid Hydrolysis
5
1
4
3
315
Direct Microbial Conversion
1
5
1
4
270
