Your company is considering developing a process to make ammonia. There are 2
processes that can be used. The first process is the Haber process and the second is the
KAAP process. Both of these have various pros and cons. Your supervisor wants you to
develop an LCA for these two processes. This will be one of the key factors in
determining which process you will make. The processes are given below in diagram 1:
Diagram 1
The only difference in the processes is the catalyst that is used. The Haber
process uses an iron oxide based catalyst and operates at 150 atm. The KAAP process
operates at 40 atm and has a ruthenium based catalyst. In both processes there is a 2022% yield. Your target is to produce 50 tons/hour. For the Haber process you will need
7,000 tons of catalyst and for the KAAP process you will need 2,800 tons of catalyst.
1) Intuitively, which process would you chose? And why?
2) Research these 2 processes to find other factors, such as catalyst cost and toxicity
which my affect the decision
3) If available, develop a simple Aspen or Hysis model for a compressor to or size a
compressor by hand determine the energy usage for both processes
4) What are your final conclusions
Solution
1) The KAPP process looks better because it should use less energy to compress the
material.
2) The ruthenium oxide catalyst costs 25 times more than the iron oxide catalyst.
But you will only need 1/3 of the catalyst for the KAAP process. This amounts to
8.3 times the cost to fill the reactor. The cost of the iron catalyst is $1.8/lb. It will
cost 25 million for the catalyst for the Haber process and 210 million for the
catalyst for the KAAP process. Iron oxide is not known to be a potential
carcinogen and the ingestion is 5 g/kg. Ruthenium IV oxide does not have any
data listed for toxicity other than ingestion and it has an LD50 of 5.5 grams/kg.
There does not appear to be any large difference in the toxicity. To put this
ingestion toxicity into perspective, a 180 lb person would have to eat about a 1 lb
to have a 50% chance of being poisoned assuming the person is “average” and has
no conditions where they would be considered outliers in a distribution curve.
3) The KAAP process is going to require less energy for compression than is going
to be required for the Haber process. All other energy inputs are going to be the
same for the process. The other energy inputs are going to be negligible
compared to the compressors for this two processes. The horsepower for the
Haber process is 73,000 and for the KAAP process 43,000. This was found by
using the compressor icon in Aspen. The KAAP process requires 1.0 * 109
MJ/year. The Haber process requires 1.7 * 109 MJ /year.
4) Regardless of the process, both processes are using the same raw materials and
are making the same product. There are 2 green engineering factors that should
be considered for this process. The first is the use of a precious/rare metal in the
KAAP process. Typically most precious metal catalysts are typically recycled
after fouling. For the Haber process, it may not be worth regenerating the catalyst
or recycling the iron because of the low cost of iron. The other factor is energy.
The CO2 output is going to be 1.7 times greater for the Haber process. When all
the factors are considered it would be best to use the KAAP process if there is
funding available since it will save in energy.