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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