Beyond Amines: A Comparative Analysis of Bio-Sequestration vs. PET-Derived Sorbents in Carbon Capture

Abstract

The mitigation of anthropogenic climate change necessitates the rapid deployment of Carbon Capture, Utilization, and Storage (CCUS) technologies to manage the annual emission of over 36 billion tons of carbon dioxide (CO_2). This comprehensive research report evaluates three distinct paradigms in carbon management: the mature, industrial standard of chemical absorption using Liquid Amines (specifically Monoethanolamine, MEA); the biological approach leveraging photosynthetic Microalgae; and the emerging material science innovation of Bis(2-aminoethyl)terephthalamide (BAETA), a solid sorbent derived from the upcycling of Polyethylene Terephthalate (PET) plastic waste. Through a rigorous analysis of reaction kinetics, thermodynamic penalties, lifecycle costs, and environmental impacts, this report establishes that while liquid amines currently dominate due to technological readiness, they suffer from prohibitive energy intensities (3.5–4.2 GJ/ton CO_2) and toxicity risks. Microalgal systems, while offering a pathway to carbon-neutral biofuels, are constrained by the catalytic inefficiencies of the enzyme RuBisCO and immense land-use requirements. Conversely, BAETA emerges as a transformative "closed-loop" solution. By converting a persistent waste pollutant into a thermally stable (<250°C), high-capacity (3.4 mmol/g) sorbent, BAETA addresses both the atmospheric carbon crisis and the terrestrial plastic burden, offering a thermodynamically superior alternative for high-temperature industrial exhaust streams.

1. Introduction: The Dual Crisis of Carbon and Waste

1.1 The Atmospheric Imperative

The trajectory of global civilization is currently on a collision course with the planetary boundaries governing climate stability. The concentration of atmospheric carbon dioxide (CO_2) has risen from pre-industrial levels of 280 parts per million (ppm) to over 420 ppm, driving global mean temperature rise, ocean acidification, and extreme weather events.¹ To adhere to the Paris Agreement's goal of limiting warming to 1.5–2.0°C, the Intergovernmental Panel on Climate Change (IPCC) indicates that emissions reduction alone is insufficient. Active removal of CO_2—at a scale of 1.5 to 2.6 billion metric tons annually—is required by mid-century.²

This challenge is compounded by the nature of industrial emissions. While renewable energy is decarbonizing the electrical grid, "hard-to-abate" sectors such as cement, steel, and chemical manufacturing continue to produce concentrated streams of CO_2 that cannot be easily electrified. For these point sources, post-combustion carbon capture represents the only viable bridge to a net-zero future.

1.2 The Terrestrial Burden of Plastics

Parallel to the invisible accumulation of atmospheric carbon is the highly visible accumulation of synthetic polymers. Polyethylene Terephthalate (PET), a semi-crystalline thermoplastic polyester, is the backbone of the global packaging and textile industries. Despite its theoretical recyclability, the actual recycling rate for PET remains stagnantly low, often cited between 10% and 15% globally.³ The remainder—millions of tons annually—is relegated to landfills, incineration (which converts solid carbon back into gaseous CO_2), or environmental leakage, where it degrades into microplastics that permeate marine and terrestrial ecosystems.⁴

The intersection of these two crises—carbon emissions and plastic waste—has catalyzed a new avenue of materials science research. The traditional linear economy treats waste PET as a liability. However, emerging chemical upcycling strategies propose treating waste PET as a feedstock for advanced materials, specifically carbon capture sorbents.

1.3 The Scope of Inquiry

This report provides a comparative deep-dive into three competing methodologies for capturing CO_2:

1. Liquid Amine Scrubbing: The incumbent technology, relying on aqueous solutions of organic amines (e.g., MEA) to chemically absorb CO_2. It is the benchmark against which all other technologies are measured.

2. Microalgal Bio-Sequestration: A biological approach utilizing the natural photosynthetic machinery of algae to fix carbon into biomass. This method promises "green" capture and the production of value-added biofuels.

3. BAETA (Waste-Derived Solid Sorbents): A novel chemical approach where waste PET is depolymerized via aminolysis to create high-performance solid sorbents. This represents a "waste-to-value" paradigm.

The following sections will dissect the fundamental chemistry, engineering challenges, economic realities, and environmental footprints of each approach to determine their viability in a decarbonized world.

2. Liquid Amine Scrubbing: The Thermodynamic Titan and Its Flaws

2.1 Historical Context and Industrial Dominance

The use of alkanolamines for gas treating dates back to the 1930s, originally developed for "sweetening" natural gas by removing acidic impurities like hydrogen sulfide (H_2S) and CO_2. Because of this eighty-year operational history, amine scrubbing is the only carbon capture technology considered to be at a high Technology Readiness Level (TRL 9). It is the default choice for retrofitting existing coal and gas power plants because the process engineering is well-understood, and the supply chains for chemicals are established.¹

2.2 The Chemistry of Capture: Monoethanolamine (MEA)

Among the various amines employed, Monoethanolamine (MEA) is the standard solvent. It is a primary amine (R-NH_2) characterized by high reactivity and relatively low cost.

2.2.1 The Zwitterion Mechanism

The reaction between MEA and CO_2 in an aqueous solution is a complex interplay of diffusion and chemical kinetics. The widely accepted mechanism proceeds via the formation of a zwitterionic intermediate:

1. Nucleophilic Attack: The lone pair of electrons on the nitrogen atom of the MEA molecule attacks the electrophilic carbon atom of the CO_2 molecule. This forms a zwitterion (RNH_2^+COO^-).

2. Deprotonation (Base Catalysis): The zwitterion is unstable and must be deprotonated to form a stable carbamate. A base (B)—which can be another amine molecule, water, or a hydroxyl ion—accepts the proton.

3. Equation: RNH_2 + CO_2 <-> RNH_2^+COO^-

4. Equation: RNH_2^+COO^- + B <-> RNHCOO^- + BH^+

This mechanism reveals a fundamental stoichiometric limitation of primary amines: Two moles of amine are required to capture one mole of CO_2 (one to form the carbamate, one to act as the base/proton acceptor). This limits the theoretical loading capacity to 0.5 mol CO_2/mol amine.⁵ While hydrolysis of the carbamate can theoretically allow for bicarbonate formation (1:1 stoichiometry), the kinetics of that pathway are too slow for the rapid residence times required in industrial absorbers.

2.3 Process Engineering and Energy Penalties

The industrial implementation of MEA capture involves a continuous loop between two massive columns: the Absorber (operating at 40-60°C) and the Stripper/Regenerator (operating at 100-120°C).

2.3.1 The Parasitic Energy Load

The Achilles' heel of liquid amine systems is the energy required to reverse the reaction and regenerate the solvent. This energy, supplied as steam from the power plant's cycle, is known as the "reboiler duty." For a standard 30 wt% MEA solution, the regeneration energy is typically 3.5 to 4.2 GJ per ton of CO_2 captured.⁶

This energy consumption can be broken down into three components:

1. Sensible Heat (Q_{sens}): The energy required to heat the massive volume of solvent (which is 70% water) from the absorber temperature to the stripper temperature. Because water has a high specific heat capacity (4.18 J/g·K), this is a major thermodynamic penalty.

2. Heat of Vaporization (Q_{vap}): The energy consumed to vaporize water in the stripper to create the steam stripping vapor that acts as a sweep gas to lower the partial pressure of CO_2.

3. Heat of Desorption (Q_{rxn}): The chemical energy required to break the strong covalent bond of the carbamate. For MEA, the heat of absorption is high (~85 kJ/mol), meaning an equal amount of heat must be injected to release the gas.⁸

These factors combine to reduce the electrical output of a power plant by 20-30%, a "parasitic load" that fundamentally alters the economics of energy production.⁹

2.4 Degradation: The Hidden Economic and Environmental Cost

While the energy penalty is the most cited drawback, solvent degradation represents a critical operational challenge that drives up Operating Expenses (OPEX) and creates environmental liabilities.

2.4.1 Oxidative Degradation

Flue gases from coal and natural gas combustion contain significant amounts of oxygen (3-15%). When MEA is exposed to O_2 at absorber temperatures, it undergoes oxidative fragmentation. This free-radical mechanism, often catalyzed by dissolved metals (Fe, Cu from corrosion) or fly ash, cleaves the amine backbone.¹⁰

• Products: This generates volatile ammonia (NH_3), which can escape the stack, and organic acids (formic, acetic, oxalic acids).

• Consequence: The acids react with the amine to form "Heat Stable Salts" (HSS). These salts do not regenerate in the stripper; they permanently deactivate the amine, reducing the plant's capture capacity over time and necessitating constant solvent bleed-and-feed (replacing old solvent with fresh MEA).⁹

2.4.2 Thermal Degradation

In the high-temperature environment of the stripper (>120°C), MEA undergoes thermal degradation via carbamate polymerization.

• Mechanism: The carbamate cyclizes to form 2-oxazolidinone (OZD). OZD reacts with free MEA to form N-(2-hydroxyethyl)ethylenediamine (HEEDA), which further polymerizes.¹²

• Consequence: These high-molecular-weight polymers increase the viscosity of the solvent, reducing heat transfer efficiency and causing fouling in heat exchangers and packing materials.

2.4.3 Toxicity and Emissions

The environmental impact of amine emissions is a subject of intense scrutiny. The atmospheric degradation of emitted amines can lead to the formation of Nitrosamines and Nitramines.¹³

• Nitrosation: Secondary amines (degradation products) can react with NO_x in the flue gas or atmosphere to form N-nitrosamines.

• Health Risk: Many nitrosamines are classified as probable human carcinogens. This risk necessitates the installation of expensive multi-stage water wash sections and acid wash sections at the top of the absorber to scrub amine vapors, further increasing CAPEX and water usage.¹⁴

3. Microalgal Bio-Sequestration: The Biological Paradox

3.1 The Promise of Photosynthesis

Microalgae represent a fundamentally different approach to carbon capture. Rather than viewing CO_2 as a waste product to be buried (Geological Storage), algal systems view it as a nutrient for growth. Through photosynthesis, algae utilize solar energy to convert inorganic carbon (CO_2) and water into organic biomass (lipids, proteins, carbohydrates) and oxygen. This pathway is attractive because it offers the potential for Carbon Capture and Utilization (CCU)—turning emissions into biofuels, animal feed, or bioplastics.¹⁵

3.2 The Biochemistry of Inefficiency: RuBisCO

The core limitation of algal carbon capture lies within the enzyme Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). It is the primary engine of the Calvin-Benson-Bassham (CBB) cycle, responsible for fixing CO_2 into organic sugars. However, RuBisCO is evolutionarily imperfect.

3.2.1 The Specificity Problem

RuBisCO cannot perfectly distinguish between carbon dioxide and oxygen.

• Carboxylation: RuBisCO + CO_2 -> 2 molecules of 3-phosphoglycerate (Productive photosynthesis).

• Oxygenation: RuBisCO + O_2 -> 3-phosphoglycerate + 2-phosphoglycolate (Photorespiration).

Photorespiration is a metabolic "waste" process. It consumes energy (ATP and NADPH) and releases previously fixed CO_2 back into the cell, reducing the net carbon fixation efficiency by up to 30-50% under ambient conditions.¹⁶ While many algae have evolved Carbon Concentrating Mechanisms (CCMs) to pump bicarbonate into the cell and saturate RuBisCO with CO_2, the energy cost of these pumps further reduces the overall thermodynamic efficiency of the system.¹⁸

3.2.2 The Kinetic Trade-off

Evolutionary studies suggest a rigid trade-off in RuBisCO mechanics: variants of the enzyme that have higher specificity for CO_2 tend to have slower catalytic turnover rates (k_{cat}).¹⁹ This means that to achieve high growth rates, algae must synthesize massive amounts of RuBisCO (often 30-50% of total soluble protein), creating a high biological demand for Nitrogen fertilizer—the production of which generates its own CO_2 emissions.²⁰

3.3 Cultivation Engineering: Ponds vs. Bioreactors

Scaling algal capture to industrial relevance faces severe engineering constraints regarding mass transfer and land use.

3.3.1 Open Raceway Ponds

• Design: Shallow loops of water driven by paddlewheels.

• Economics: Lowest Capital Expenditure (CAPEX) and Operating Expenditure (OPEX).

• Limitations: Poor CO_2 utilization. Bubbling flue gas through a shallow pond results in short gas-liquid contact times; much of the CO_2 simply bubbles out to the atmosphere before the algae can absorb it. Additionally, open ponds suffer from high evaporative water losses and are vulnerable to contamination by invasive species or grazers.¹⁵

3.3.2 Closed Photobioreactors (PBRs)

• Design: Tubular or flat-panel systems that enclose the culture to maximize light exposure and gas retention.

• Performance: Higher biomass densities and better CO_2 capture efficiency due to controlled mixing and longer gas retention times.

• Limitations: The CAPEX for PBRs is prohibitive (glass/plastic tubing costs). Furthermore, they suffer from the accumulation of dissolved oxygen (produced by photosynthesis), which inhibits growth and must be actively degassed. The energy required to pump fluids through narrow tubes significantly increases the parasitic load.¹⁵

3.4 The Land Use and Water Footprint

The most damning metric for algal carbon capture at the gigaton scale is spatial intensity.

• Land Requirement: To capture the emissions from a standard 500 MW coal power plant (approx. 3-4 million tons CO_2/year), an algal system would require between 3,500 and 15,000 hectares of land, depending on the productivity assumptions.²⁰ This is orders of magnitude larger than the footprint of a chemical capture plant (approx. 1-2 hectares).

• Water Requirement: Algae are aquatic. While they can grow in wastewater or saline water, the sheer volume required for evaporation replacement in open ponds is a massive logistical constraint in water-scarce regions.

3.5 Economic Viability

Current techno-economic analyses (TEA) place the cost of algal carbon capture between 300 and 1,600 per ton of CO_2.²¹ While some pilot projects claim costs closer to 50/ton, these models invariably rely on selling the biomass for high-value applications (e.g., Omega-3 supplements, cosmetics) rather than bulk commodities like fuel or pure sequestration.²² Once the market for high-value nutraceuticals is saturated, the economics collapse back to the energy commodity price, which is too low to support the high cultivation costs.

4. BAETA and Plastic Upcycling: The Circular Frontier

4.1 Concept: Turning a Liability into an Asset

The third paradigm examined in this report breaks the linear model of resource consumption. BAETA (Bis(2-aminoethyl)terephthalamide) is a solid amine sorbent synthesized directly from waste PET bottles. This approach aligns with the principles of the Circular Economy: rather than extracting fossil resources to synthesize amines (like MEA) or using arable land for algae, it utilizes the megatons of plastic waste currently clogging landfills as a raw material for climate tech.²

4.2 Synthesis: The Chemistry of Upcycling

The synthesis of BAETA is an elegant application of aminolysis, a reaction that depolymerizes the long PET chains into monomeric diamides.

4.2.1 Reaction Pathway

The process involves reacting waste PET (bottles, textiles, packaging) with 1,2-ethylenediamine (EDA).

• Reactants: Polyethylene Terephthalate ([-CO-C_6H_4-CO-O-CH_2-CH_2-O-]_n) + Ethylenediamine (NH_2-CH_2-CH_2-NH_2).

• Conditions: The reaction proceeds under mild conditions—typically 60°C for 24 hours or even room temperature for extended periods. It does not require high pressures or expensive noble metal catalysts.⁸

• Mechanism: The amine groups of the EDA act as nucleophiles, attacking the carbonyl carbons of the ester linkages in the PET backbone. This cleaves the polymer chain.

• Products:

• BAETA: A white, powdery solid (yields up to 83-90% based on reaction optimization).

• Ethylene Glycol (EG): A valuable byproduct used in antifreeze and polymer synthesis.

• Oligomers: Short-chain residues that can also function as sorbents.⁸

4.2.2 Atom Economy and Tolerance

A critical advantage of this synthesis is its robustness. Research at the University of Copenhagen demonstrated that the process works effectively even with dirty, colored, or mixed plastic waste streams. The presence of additives, labels, or food residue does not significantly inhibit the aminolysis, and the resulting BAETA can be purified via simple filtration and washing steps.²⁴ This implies that BAETA production could serve as a sink for "low-grade" PET that is currently rejected by mechanical recyclers.

4.3 Material Properties and Sorption Performance

BAETA functions as a solid-state chemisorbent, distinct from both liquid amines and biological systems.

4.3.1 Capacity and Selectivity

BAETA features a terephthalamide core with two pendant amino-ethyl groups. These primary amines interact with CO_2 similarly to liquid amines but within a solid crystal lattice.

• Capture Capacity: Experimental data indicates a CO_2 uptake of 3.17 to 3.41 mmol/g.²³ This is highly competitive with commercial solid sorbents like zeolites or MOFs.

• Selectivity: The chemical nature of the amine-CO_2 bond ensures extremely high selectivity for CO_2 over Nitrogen (N_2) and Oxygen (O_2), a critical requirement for flue gas separation where N_2 is the dominant species.⁸

4.3.2 Thermal Stability and the "Hot Gas" Advantage

One of the most disruptive features of BAETA is its thermal resilience.

• Degradation Point: TGA (Thermogravimetric Analysis) shows that BAETA is stable up to 250°C.⁸

• Operational Implication: Liquid MEA degrades rapidly above 120°C. Industrial flue gases typically exit stacks at 130-150°C. To use MEA, this gas must be cooled (requiring water and heat exchangers). BAETA, however, can capture CO_2 directly at 150°C.²⁵ This capability allows for "hot capture," significantly reducing the thermal management equipment required and integrating more efficiently with industrial heat balances.

4.3.3 Moisture Tolerance

Unlike physical adsorbents (e.g., activated carbon, zeolites) which lose capacity in humid streams because water competes for adsorption sites, BAETA performs well in humid conditions (0-100% Relative Humidity). The water vapor facilitates the zwitterion transfer mechanisms in the solid state, preventing the sorbent from becoming "poisoned" by the moisture naturally present in combustion exhaust.²⁵

4.4 Regeneration and Lifecycle

The regeneration of BAETA is achieved by heating the saturated sorbent to release the stored CO_2.

• Energy of Regeneration: The enthalpy of desorption is estimated to be significantly lower than liquid amines. While MEA requires ~3.5-4.0 GJ/ton, solid amines like BAETA benefit from the absence of water solvent. There is no massive heat penalty for vaporizing water. Estimates for solid amine regeneration energy hover around 1.8–2.6 GJ/ton CO_2.⁶

• Durability: Laboratory cycling tests have demonstrated stability over 150 adsorption-desorption cycles with minimal loss of capacity.²⁵ While this is promising, industrial applications require stability over thousands of cycles, an area for future long-duration testing.

5. Comparative Technoeconomic Analysis

To provide a structured comparison, we evaluate the three technologies across four critical dimensions: Thermodynamic Efficiency, Economic Feasibility, Environmental Impact, and Scalability.

5.1 Thermodynamic Efficiency Comparison

Parameter	Liquid Amines (MEA)	Microalgae (PBR/Ponds)	BAETA (Solid Sorbent)
Capture Mechanism	Chemical Absorption (Liquid)	Photosynthesis (Biological)	Chemical Adsorption (Solid)
Reaction Kinetics	Very Fast (Seconds)	Slow (Hours/Days)	Moderate (Minutes)
Heat of Regeneration	High (~3.5–4.2 GJ/ton CO_2)	N/A (Solar driven)	Low-Medium (~1.8–2.6 GJ/ton)
Operating Temp	Absorber: 40°C / Stripper: 120°C	Ambient (20-30°C)	Broad (25°C – 170°C)
Pre-treatment	Requires cooling & extensive cleaning	Requires cooling & nutrient mixing	Minimal (High tolerance)
Water Usage	High (Cooling + Solvent make-up)	Very High (Evaporation)	Low (No solvent loop)

Analysis:

The thermodynamic data clearly favors solid sorbents like BAETA. Liquid amines are penalized by the specific heat capacity of water. Algae are penalized by the inefficiency of biological energy conversion (photosynthesis is typically <3% efficient at converting solar energy to biomass energy). BAETA strikes the optimal balance: chemical binding strength sufficient for low-concentration capture, but without the thermal mass of a liquid solvent carrier.

5.2 Economic Feasibility (CAPEX and OPEX)

5.2.1 Liquid Amines

• Status: Commercially available.

• Cost: Estimates for mature Nth-of-a-kind plants range from 57 to 80 per ton of CO_2.²⁸

• Drivers: High OPEX due to steam consumption and solvent degradation (replacement costs). High CAPEX due to stainless steel requirements to resist corrosion.

5.2.2 Microalgae

• Status: Demonstration/Pilot scale.

• Cost: Highly variable, generally 300 to 1,500 per ton CO_2 for strict sequestration.²¹

• Drivers: Massive CAPEX for land preparation and bioreactors. High OPEX for harvesting (centrifugation/filtration) and drying. The economics only work if the biomass is sold as high-value product (e.g., 100/kg nutraceuticals), which is a niche market not scalable to gigaton climate needs.

5.2.3 BAETA

• Status: Laboratory/Pilot scale (TRL 4-5).

• Cost: Projected to be lower than liquid amines, potentially targeting 40–60 per ton CO_2.

• Drivers:

• Feedstock Advantage: The raw material (waste PET) has negative value (gate fees for waste disposal). This is a massive economic lever compared to synthesizing virgin amines.

• Energy Savings: The reduction in regeneration energy directly lowers OPEX.

• Uncertainty: The CAPEX for solid-handling machinery (fluidized beds, moving beds) can be higher than liquid pumps. Scale-up is the primary risk factor.

5.3 Environmental Lifecycle Assessment (LCA)

Liquid MEA poses significant ecotoxicity risks. The production of MEA is fossil-intensive (derived from ammonia and ethylene oxide). Its degradation releases ammonia and nitrosamines, requiring strict emissions control. The "sludge" from reclaimer units is hazardous waste.¹⁴

Algae offer a potential environmental benefit by treating wastewater (removing nitrates/phosphates). However, if grown in open ponds, the "water footprint" is unsustainable in arid regions. Furthermore, if the algal biomass is merely burned for fuel, the CO_2 is re-released. Permanent sequestration requires burying the biomass (biochar), which generates no revenue.²⁰

BAETA offers the strongest LCA profile via Avoided Emissions. By diverting PET from incineration, it prevents CO_2 release. By using it to capture industrial CO_2, it doubles the benefit. The primary environmental concern is the handling of Ethylenediamine (EDA) during synthesis. EDA is a volatile, corrosive, and sensitizing liquid that requires strict safety protocols during the manufacturing phase.²⁹ However, once reacted into the BAETA polymer, the material is a stable solid, eliminating the risk of volatile emissions during the capture operation.

6. Discussion: Limitations and Technical Challenges

6.1 The "Solids Handling" Challenge for BAETA

While BAETA wins on thermodynamics, moving tons of solid powder is mechanically harder than pumping liquid. Liquid amines flow easily through pipes. Solids are abrasive, can attrition (break down into dust), and are difficult to heat and cool rapidly due to poor heat transfer coefficients in packed beds. Future engineering must focus on fluidized bed reactors or rotary contactors that allow for rapid heat exchange and minimizing mechanical attrition of the BAETA pellets.

6.2 Algae's Niche: Utilization, Not Just Capture

It is becoming clear that algae are ill-suited for the role of a primary "scrubber" for a coal plant. They simply cannot grow fast enough to eat the CO_2 output of a gigawatt-scale facility without consuming a city-sized area of land. However, algae have a vital role in decentralized capture and utilization. They can serve as a "polishing" step for smaller emissions sources, creating sustainable aviation fuels (SAF) or bioplastics. They are a tool for the circular bio-economy, not necessarily the geological sequestration industry.

6.3 MEA's Entrenchment

The inertia of the energy industry favors MEA. Billions of dollars of infrastructure are designed around liquid handling. Retrofitting a plant with liquid amine scrubbers is a known quantity. Switching to solid sorbents like BAETA requires a fundamental redesign of the capture block. This "lock-in" effect suggests that MEA will dominate the first wave of CCS deployment (2025-2035), with solid sorbents like BAETA phasing in as the technology matures and cost pressures for higher efficiency mount.

7. Conclusion

The tripartite comparison of Liquid Amines, Microalgae, and BAETA reveals that there is no "silver bullet" for carbon capture, but rather an evolution of technologies tailored to specific thermodynamic and economic niches.

1. Liquid Amines (MEA) remain the pragmatic incumbent. They are the only option available today for immediate, large-scale deployment. However, their high parasitic energy load and toxicity profile make them a "necessary evil" rather than an optimized long-term solution. They will likely bridge the gap for the next decade.

2. Microalgae represent a biological utilization pathway. Constrained by the inefficiency of RuBisCO and massive land requirements, they cannot compete with chemical methods for bulk point-source capture. Their future lies in the production of high-value bioproducts and sustainable fuels, rather than pure carbon sequestration.

3. BAETA represents the disruptive future. It fundamentally alters the economics of CCS by leveraging the global waste crisis. Its high thermal stability (150°C+), low regeneration energy, and immunity to water poisoning address the specific failings of liquid amines. By transforming the PET waste liability into a climate asset, BAETA exemplifies the principles of the circular economy.

Recommendation: Future research and investment should prioritize the scaling of BAETA synthesis and the development of efficient gas-solid contactor reactors. While liquid amines will carry the baton for the first leg of the decarbonization race, innovative materials like BAETA are required to cross the finish line of a net-zero 2050.

Appendix: Summary of Key Technical Parameters

Feature	Monoethanolamine (MEA)	Microalgae	BAETA (PET-Derived)
State	Liquid (Aqueous Solution)	Biological Suspension	Solid (Powder/Pellet)
Sorption Type	Chemisorption (Carbamate)	Photosynthesis (Biomass)	Chemisorption (Surface Amine)
Capacity	~0.5 mol CO_2/mol amine	Low (Growth rate limited)	~3.4 mmol CO_2/g sorbent
Regen. Energy	High (3.5–4.2 GJ/ton)	Solar (Requires harvesting energy)	Low (1.8–2.6 GJ/ton)
Max Temp	<120°C (Degradation)	<40°C (Cell death)	250°C (Stable)
Toxicity	High (Ammonia, Nitrosamines)	Low (Benign biomass)	Low (Stable polymer)
Feedstock	Ammonia/Ethylene Oxide (Fossil)	CO_2, Sunlight, Nutrients	Waste PET Plastic + EDA
Cost Est.	60–80 / ton CO_2	300+ / ton CO_2	40–60 / ton CO_2 (Proj.)

Works cited

1. Liquid CO2-Capture Technologies: A Review - PMC - PubMed Central, accessed December 19, 2025, https://pmc.ncbi.nlm.nih.gov/articles/PMC11643708/

2. Chemists turn plastic waste into carbon capture material - Anthropocene Magazine, accessed December 19, 2025, https://www.anthropocenemagazine.org/2025/09/chemists-turn-plastic-waste-into-carbon-capture-material/

3. (PDF) Repurposing polyethylene terephthalate plastic waste to capture carbon dioxide, accessed December 19, 2025, https://www.researchgate.net/publication/395304158_Repurposing_polyethylene_terephthalate_plastic_waste_to_capture_carbon_dioxide

4. Scientists Find Way To Turn Plastic Waste Into Carbon Capture Materials, accessed December 19, 2025, https://carbonherald.com/scientists-find-way-to-turn-plastic-waste-into-carbon-capture-materials/

5. Comparative Review for Enhancing CO2 Capture Efficiency with Mixed Amine Systems and Catalysts - PMC - NIH, accessed December 19, 2025, https://pmc.ncbi.nlm.nih.gov/articles/PMC11477971/

6. Experimental study on CO2 capture by MEA/n-butanol/H2O phase change absorbent - NIH, accessed December 19, 2025, https://pmc.ncbi.nlm.nih.gov/articles/PMC10797326/

7. Energy Reduction of CO2 Capture by New Absorbents Development - China Steel Corporation, accessed December 19, 2025, https://www.csc.com.tw/csc/ts/ena/pdf/no26/13--Energy%20Reduction%20of%20CO2%20Capture%20by%20New%20Absorbents%20Develo.pdf

8. Repurposing polyethylene terephthalate plastic waste to capture carbon dioxide - NIH, accessed December 19, 2025, https://pmc.ncbi.nlm.nih.gov/articles/PMC12412650/

9. IECM Technical Documentation: - Amine-based Post-Combustion CO2 Capture - University of Wyoming, accessed December 19, 2025, https://www.uwyo.edu/iecm/_bfiles/documentation/201901_iecmtd_amine-based-co2-cap.pdf

10. Thermal degradation of monoethanolamine and its effect on CO2 capture capacity - ORCA – Online Research @ Cardiff, accessed December 19, 2025, https://orca.cardiff.ac.uk/id/eprint/49117/1/49117%20Sapsford%202013%20Thermal.pdf

11. Prediction of Thermal and Oxidative Degradation of Amines to Improve Sustainability of CO 2 Absorption Process - MDPI, accessed December 19, 2025, https://www.mdpi.com/2071-1050/17/22/10311

12. Modeling the Formation of Degradation Compounds during Thermal Degradation of MEA | Industrial & Engineering Chemistry Research - ACS Publications, accessed December 19, 2025, https://pubs.acs.org/doi/10.1021/acs.iecr.1c04496

13. Environmental assessment of amine-based carbon capture Scenario modelling with life cycle assessment (LCA) - Norsus, accessed December 19, 2025, https://norsus.no/wp-content/uploads/1712.pdf

14. Emissions and formation of degradation products in amine- based carbon capture plants - FORCE Technology, accessed December 19, 2025, https://forcetechnology.com/-/media/force-technology-media/pdf-files/5501-to-6000/5796-rapport-omkring-emissioner-fra-carbon-capture-final.pdf

15. A Review of Algae-Based Carbon Capture, Utilization, and Storage (Algae-Based CCUS), accessed December 19, 2025, https://www.mdpi.com/2673-5628/4/4/24

16. Engineering photoautotrophic carbon fixation for enhanced growth and productivity, accessed December 19, 2025, https://pubs.rsc.org/en/content/articlehtml/2018/se/c8se00281a

17. Algal Mechanisms | RIPE - University of Illinois, accessed December 19, 2025, https://ripe.illinois.edu/objectives/algal-mechanisms

18. Role of Microalgae in Global CO2 Sequestration: Physiological Mechanism, Recent Development, Challenges, and Future Prospective - MDPI, accessed December 19, 2025, https://www.mdpi.com/2071-1050/13/23/13061

19. Directions for Optimization of Photosynthetic Carbon Fixation: RuBisCO's Efficiency May Not Be So Constrained After All - PMC - PubMed Central, accessed December 19, 2025, https://pmc.ncbi.nlm.nih.gov/articles/PMC5838012/

20. Carbon Capture from Biomass Boiler Flue Gas Emissions using Microalgae - DiVA portal, accessed December 19, 2025, https://www.diva-portal.org/smash/get/diva2:1773491/FULLTEXT01.pdf

21. Liquid Trees: Carbon Capture and Sequestration Via Mass Algae Farming and Marine Spatial Planning - Joseph Gabris • Environmental, Natural Resources, & Energy Law, accessed December 19, 2025, https://law.lclark.edu/live/blogs/253-liquid-trees-carbon-capture-and-sequestration-via

22. Growing Algae In The Desert to Capture Carbon - CarbonCredits.com, accessed December 19, 2025, https://carboncredits.com/brilliant-planet-carbon-capture-with-algae/

23. Supplementary Materials for, accessed December 19, 2025, https://www.sdu.dk/-/media/files/forskning/sdu-climate-cluster/climate+thursdays+2025/sciadv_adv5906_supporting_material_margarita_poderyte.pdf

24. How PET Waste Captures CO 2 from the Air - Plastics Insights, accessed December 19, 2025, https://en.kunststoffe.de/a/news/how-pet-waste-captures-colesssubgreater2-7145758

25. Turning plastic waste into a way to capture CO₂ - Science News, accessed December 19, 2025, https://sciencenews.dk/en/turning-plastic-waste-into-a-way-to-capture-co

26. Scientists transform plastic waste into efficient CO2 capture ..., accessed December 19, 2025, https://science.ku.dk/english/press/news/2025/scientists-transform-plastic-waste-into-efficient-co2-capture-materials/

27. Comparative Review for Enhancing CO2 Capture Efficiency with Mixed Amine Systems and Catalysts - MDPI, accessed December 19, 2025, https://www.mdpi.com/1420-3049/29/19/4618

28. Comparative techno-economic analysis of the integration of MEA-based scrubbing and silica PEI adsorbent-based CO2 capture processes, accessed December 19, 2025, https://pure.ulster.ac.uk/files/121039922/1_s2.0_S0959652623018243_main.pdf

29. Common Name: ETHYLENEDIAMINE HAZARD SUMMARY IDENTIFICATION REASON FOR CITATION HOW TO DETERMINE IF YOU ARE BEING EXPOSED WORKPLA - NJ.gov, accessed December 19, 2025, https://www.nj.gov/health/eoh/rtkweb/documents/fs/0875.pdf