Accelerating Net Zero
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ACCELERATING NET ZERO
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ACCELERATING NET ZERO
In principle, the captured CO2 could be converted into fuels or
chemicals which would help cut down the requirements of fresh fossil
fuels. And if all the emitted CO2 is captured, one day there would be
no requirement of fossil fuel exploitation. Gaseous fuels to liquid fuel/
chemical (GTL) has been an age old research topic, idea of GTL was to
convert methane rich natural gas to liquid fuel like gasoline which could
be transported easily thus cutting down on CO2 emission associated with
natural gas storage and transport. However, challenge in conversion of CO2
to a fuel or chemical has one additional bottleneck, fresh source of green
hydrogen which could technically convert CO2 into a useful hydrocarbon
for utilization as a fuel. One has to thus identify what works better, a pure
hydrogen economy (where no hydrogen would be wasted on CO2 to create
a circular economy), or integrate hydrogen economy to circular economy
where captured CO2 is converted back to a value-added chemical or fuel.
Hydrogen for both these economies will essentially come from the same
source, a possible solution is simultaneously running both the economies.
As of today, there are many demonstration plants which exist around
the world to convert CO2 (or CO) to methanol and DME, or aviation fuel.
However, production cost is prohibitively high and these plants operates
for demonstration purpose alone.
Tons of CO2 however being captured in step-1 can’t be converted
into useful chemicals, one has to look at the thermodynamics of the
conversion process to understand the energy requirements to convert
all these CO2 into a chemical. Further, the cost of CO2 coming out of DAC
could be as high as 200 - 1000 USD per ton and considering that when one
adds similarly priced green hydrogen in the mix to produce a commodity,
the end product can’t be used for mass market application. This perhaps
suggests that it could be more economical to sequester the captured CO2
rather converting the same to a chemical/commodity.
3. Majority of the CO2 which could not be converted (in step-2) has to
be transported to the sequestration sites. While this step may look costly
as there is no value addition, it is a fact that there is no use of such a large
quantity of CO2 and one has to invest in CO2 pipelines for transportation of
these to sequestration sites.
The sequestration sites could be one of these; deep coal bed
reserves, depleted oil and gas field, saline aquifers, basalt rocks under
the earth or unconsolidated sediments deep inside the sea-bed where the
existing water in the pores of these sediments would convert into solid
CO2 hydrates making it thermodynamically stable for geological time
scale. Each of these sites have certain advantages and disadvantage and
a significant research efforts and field trials has to be done to identify
the challenges which would allow one to come-up with a well-informed
solution. Any solution should be full proof (with continuous monitoring of
sequestered CO2) and should have sufficient capacity to sequester billions
of tons of CO2 for geological time scale. Currently most of the CO2 pipelines
are being used to transport CO2 for EOR application which basically
allows one to scale-up the process for sequestration of tons of these CO2 in
geological sites.
PATH FORWARD:
Since the amount of CO2 utilized and sequestrated is directly proportional
to the amount of CO2 captured. Thus, the first step i.e. CO2 capture should
be the prime focus and looking at the scale, measuring sustainability of the
process should be the prime importance. The materials/chemicals which
are supposed to capture tons of these CO2 are very few, one such molecule
mono-ethanolamine (MEA, or a variation of this material), which has been
proven at large scale through demonstration units, industries who have
implemented these solutions for demonstration should come out with a
report on challenges which were faced. Other processes which are directly
or indirectly not related to MEA have only been demonstrated at lab scale.
Due to lack of investment and insufficient focus, scale-up of the material
synthesis has not been demonstrated, this is perhaps the other bottleneck
of step-1 as far as point source capture is concerned.
Any solution should
be full proof (with
continuous monitoring
of sequestered CO2)
and should have
sufficient capacity
to sequester billions
of tons of CO2 for
geological time scale
Talking about step-2, public perception for CO2 utilization is very
positive, this makes one to believe that we can emit as much CO2 as we
want, all of these could be converted into useful products. In reality,
90% of CO2 utilization solution has been demonstrated to work with
pure CO2, and pure CO2 could only be made available once it has been
captured from point sources (or directly from the air) as discussed in
step-1. CO2 utilization if possible could lead to a circular economy where
CO2 being emitted from industries would be converted to make chemicals
and fuels, thus, reducing the demand of fresh fossil fuel. A mature
circular economy envisions that all the process energy requirements
for conversion of CO2 to hydrocarbon would come from solar or other
renewable energy resources. In theory this is possible, however, in
reality, time and investment required to achieve renewable energy based
economy may not be realistic. Step-3, CO2 sequestration has very poor
public perception, significant work is required to build a positive public
perception for this step. Even in industry, sequestration is looked upon as
money down the drain, and industries are reluctant to invest sufficient
money on this crucial step of CO2 sequestration without which net zero
by 20XX would remain a dream. In absence of positive public perception,
and poor encouragement from industry (and government) around
the world, research on CO2 sequestration has suffered significantly.
Further, not many field trial has been done to study CO2 sequestration,
as investment is prohibitively high and land lease or site lease for such
activities are mired with multi-level govt. and non-govt. clearances. In
short, a holistic road map to achieve mini targets are necessary, and a
significant investment in all the three steps discussed at the start of this
document would be necessary.
IITM EFFORTS FOR CCUS:
IITM has been working with solid adsorbent as active ingredient for
the removal of CO2 from flue gases, basically from a point source which
typically is 10-15% CO2 mixture along with N2 and O2. Such point source
capture of CO2 is relevant for coal fired power plants, cement industries,
steel manufacturing etc. One of the focus of such studies are the kinetics
of CO2 capture and separation efficiency of carbon dioxide from flue gas
mixture. Kinetics of such capture does not get much attention; however,
this is one of the biggest bottlenecks in scale-up of any laboratory process
to pilot plant scale and eventually for commercialization. Next biggest
challenge which pertains to regeneration of the absorber/adsorber has
been studied in detail using state of the art analytical facilities like SEM,
PXRD, and FTIR spectroscopy to gain mechanistic insights. Such detailed
analysis on regeneration and reusability of active ingredient is essential
for a robust process. Some of these active ingredients were eventually used
for a pilot scale demonstration which is currently running.
A number of methods can be used to capture carbon dioxide (CO2)
from its mixture; adsorption, absorption, and membrane separation etc.
However, when it comes to capturing CO2 from a rich mixture of CO2 (more
than 25% CO2 in the stream), such mixtures are typically available after
gasification of coal, in bio-methane production and could also be very
relevant to future cement industries, one prefers a physical absorption/
adsorption. One such physical and novel process is gas separation using
gas hydrates formation and dissociation cycle. One of the major advantages
of using gas hydrates process is use of water as a working medium
to separate gases. Water needed in this process could be saline water,
effluent water or fresh water. Hydrate based process for CO2 separation
from its mixture has been studied extensively. However, a commercially
viable hydrate based CO2 separation process demands a rapid hydrate
formation rate. Higher solubility of hydrate forming guest in water and
larger contact area between the hydrate formers and water. These factors
reduces the mass transfer resistance, resulting in faster hydrate formation
rate (faster kinetics) and allows one to scale-up the process for pilot plant
demonstration. Research groups at IITM has given new patented reactor
designs and suitable additives to ensure scale-up of the process of gas
One of the major
advantages of using
gas hydrates process
is use of water as
a working medium
to separate gases.
Water needed in
this process could
be saline water,
effluent water or
fresh water. Hydrate
based process for
CO2 separation from
its mixture has been
studied extensively
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