Utilizing 3-Diethylaminopropylamine for CO2 Capture Solvent Development

Utilizing 3-Diethylaminopropylamine for CO₂ Capture Solvent Development

Introduction

Carbon dioxide (CO₂) emissions from fossil fuel combustion and industrial processes are among the primary contributors to global climate change. As a result, carbon capture, utilization, and storage (CCUS) technologies have become critical components in mitigating greenhouse gas emissions. Among various carbon capture approaches, post-combustion CO₂ capture using chemical solvents has gained widespread attention due to its compatibility with existing power plant infrastructure.

Amine-based solvents remain the most widely studied and deployed technology for post-combustion CO₂ capture. Traditional solvents such as monoethanolamine (MEA), diethanolamine (DEA), and methyldiethanolamine (MDEA) exhibit high reactivity with CO₂ but suffer from drawbacks including high regeneration energy, solvent degradation, and equipment corrosion. To overcome these limitations, researchers have explored alternative amines with improved performance characteristics. One promising candidate is 3-diethylaminopropylamine (DEAPA), a tertiary diamine that demonstrates favorable kinetics, capacity, and stability under CO₂ absorption conditions.

This article provides an in-depth analysis of DEAPA’s role in CO₂ capture solvent development, covering its chemical properties, reaction mechanisms, performance metrics, comparative advantages, and integration into advanced solvent systems. The discussion is supported by data from international research institutions and peer-reviewed studies, offering a comprehensive perspective on DEAPA’s potential in next-generation carbon capture technologies.

Chemical Structure and Physical Properties of 3-Diethylaminopropylamine

3-Diethylaminopropylamine (C₉H₂₂N₂), also known as N,N-diethyl-1,3-propanediamine, is an organic compound belonging to the class of aliphatic amines. It features a primary amine group (-NH₂) at one end and a tertiary amine group (-N(CH₂CH₃)₂) at the other, separated by a three-carbon propyl chain. This structural duality enables DEAPA to participate in both carbamate formation and bicarbonate pathways during CO₂ absorption.

Molecular Formula and Key Parameters

Source: PubChem, Sigma-Aldrich Technical Data Sheet

The presence of both primary and tertiary amine functionalities allows DEAPA to act as a bifunctional absorbent. The primary amine reacts rapidly with CO₂ to form carbamates, while the tertiary amine enhances CO₂ solubility through physical absorption and facilitates bicarbonate formation in aqueous environments.

Mechanism of CO₂ Absorption with DEAPA

In aqueous solutions, DEAPA undergoes complex reactions with CO₂, which can be broadly categorized into two pathways: the zwitterion mechanism (for primary amines) and base-catalyzed hydration (for tertiary amines).

Primary Amine Reaction (Carbamate Formation)

$$
RNH₂ + CO₂ rightleftharpoons RNHCOO⁻ + H⁺
$$
$$
RNHCOO⁻ + H₂O rightleftharpoons RNH₃⁺ + HCO₃⁻
$$

The primary amine group in DEAPA readily forms a zwitterionic intermediate upon reacting with CO₂, which is then deprotonated by water or another amine molecule to yield a stable carbamate ion.

Tertiary Amine Reaction (Bicarbonate Pathway)

$$
R₃N + CO₂ + H₂O rightleftharpoons R₃NH⁺ + HCO₃⁻
$$

Tertiary amines cannot form carbamates directly due to the absence of a hydrogen atom on nitrogen. Instead, they catalyze the hydrolysis of CO₂ into bicarbonate ions, increasing the overall CO₂ loading capacity without forming thermally stable carbamates that require high energy for regeneration.

Due to its dual functional groups, DEAPA operates via a hybrid mechanism—offering fast initial absorption kinetics from the primary amine and higher theoretical capacity from the tertiary amine’s participation in bicarbonate equilibrium.

Performance Evaluation of DEAPA-Based Solvents

Several experimental studies have evaluated DEAPA’s effectiveness in CO₂ capture systems. Key performance indicators include CO₂ absorption rate, cyclic capacity, regeneration energy, thermal and oxidative stability, and corrosion behavior.

Table 1: Comparative CO₂ Absorption Performance of Common Amines (5 wt% aqueous solution, 40 °C, 15% CO₂ in N₂)

Sources: Zhang et al., International Journal of Greenhouse Gas Control, 2018; Liang et al., Chemical Engineering Journal, 2020; Rochelle et al., AIChE Journal, 2011

As shown in Table 1, DEAPA exhibits a higher CO₂ loading than MEA and MDEA, though slightly lower than piperazine (PZ). Its absorption rate surpasses MDEA significantly and approaches that of MEA, indicating good kinetic performance. Notably, DEAPA requires approximately 15–20% less regeneration energy than MEA, making it more energy-efficient.

Advantages of DEAPA in CO₂ Capture Applications

1. High CO₂ Capacity and Fast Kinetics

DEAPA’s primary amine group ensures rapid reaction initiation, while the tertiary amine contributes to additional CO₂ uptake through bicarbonate formation. This dual functionality results in a balanced profile between speed and capacity.

Studies conducted at Tsinghua University demonstrated that 30 wt% aqueous DEAPA achieved a maximum CO₂ loading of 1.02 mol CO₂/mol amine at 40 °C under flue gas conditions, outperforming 30 wt% MEA (0.52 mol/mol) and approaching the performance of concentrated piperazine blends (Zhou et al., Energy & Fuels, 2019).

2. Lower Regeneration Energy

Regeneration accounts for 60–80% of the total operating cost in amine-based CO₂ capture. DEAPA’s lower heat of reaction compared to MEA reduces steam consumption in the stripper. According to thermogravimetric analysis (TGA) data from SINTEF (Norway), the enthalpy of CO₂ desorption for DEAPA is approximately 52 kJ/mol, compared to 78 kJ/mol for MEA.

3. Improved Thermal Stability

Thermal degradation occurs when amines decompose at elevated temperatures in the regenerator. DEAPA shows superior resistance to thermal breakdown due to the steric protection offered by ethyl groups on the tertiary nitrogen. In accelerated aging tests (120 °C, 7 days), DEAPA retained over 92% of its original concentration, whereas MEA degraded by nearly 35% under identical conditions (Wang et al., Industrial & Engineering Chemistry Research, 2021).

4. Reduced Corrosivity

Corrosion of carbon steel equipment is a major operational concern in amine plants. DEAPA’s lower volatility and moderate basicity reduce vapor-phase corrosion. Electrochemical impedance spectroscopy (EIS) tests at Shanghai Jiao Tong University indicated that carbon steel exposed to 30% DEAPA at 80 °C exhibited a corrosion rate of 0.18 mm/year, significantly lower than MEA’s 0.45 mm/year under the same conditions.

5. Compatibility with Promoters and Blends

DEAPA functions effectively in blended solvents, where it can be combined with activators like piperazine or inhibitors to enhance performance. For example:

• DEAPA + Piperazine (PZ): Increases CO₂ absorption rate and capacity.
• DEAPA + Methanol: Improves mass transfer in non-aqueous systems.
• DEAPA + Phase-Change Solvents: Enables liquid-liquid phase separation upon CO₂ loading, reducing regeneration energy.

A study published in Separation and Purification Technology (Liu et al., 2022) reported that a 2:1 molar blend of DEAPA:PZ achieved a CO₂ capacity of 1.15 mol/mol with a 30% reduction in regeneration energy compared to conventional MEA.

Challenges and Limitations

Despite its advantages, DEAPA faces several challenges that must be addressed before large-scale deployment.

1. Higher Viscosity Compared to MEA

While DEAPA has acceptable viscosity at ambient temperatures, its viscosity increases significantly upon CO₂ loading, potentially affecting pumpability and mass transfer efficiency.

High viscosity may necessitate dilution or blending with low-viscosity co-solvents to maintain fluid dynamics in absorber columns.

2. Oxidative Degradation

Although DEAPA is more stable than MEA, it remains susceptible to oxidation in the presence of O₂, especially at elevated temperatures. Oxidative degradation leads to the formation of organic acids (e.g., formic, acetic) and ammonia, which can lower pH and increase corrosivity.

Research from the University of Kentucky showed that adding antioxidants such as ethylenediaminetetraacetic acid (EDTA) or N-(2-aminoethyl)piperazine (AEP) can suppress oxidative degradation of DEAPA by up to 60%.

3. Foaming Tendency

Like many long-chain amines, DEAPA can promote foaming in absorber units, particularly when impurities such as fly ash or SOₓ are present in flue gas. Foam control agents (e.g., polyglycol ethers) are typically required in pilot-scale systems using DEAPA-based solvents.

Pilot-Scale Testing and Industrial Relevance

Several pilot-scale demonstrations have validated DEAPA’s performance in real-world conditions.

Case Study: National Carbon Capture Center (NCCC), USA

At the NCCC in Alabama, a 0.5 MWₑ pilot plant tested a 35 wt% DEAPA solution over a 6-month campaign. Key outcomes included:

• Average CO₂ capture efficiency: 90.3%
• Specific reboiler duty: 3.2 GJ/tonne CO₂ (vs. 3.8 GJ/tonne for MEA)
• Solvent loss: <2 kg/tonne CO₂
• No significant fouling observed

These results suggest that DEAPA can meet industrial performance benchmarks while reducing energy penalties.

Case Study: Huaneng Group, China

China Huaneng Group conducted trials at the Beijing Gaobeidian coal-fired power station using a DEAPA/MDEA blend. The system achieved 88% CO₂ removal with a 22% reduction in steam consumption compared to a baseline MEA system. Long-term monitoring confirmed minimal degradation after 1,200 hours of continuous operation.

Environmental and Economic Considerations

From a lifecycle assessment (LCA) perspective, DEAPA offers environmental benefits due to reduced energy demand and lower solvent make-up requirements. However, its synthesis involves multi-step organic reactions starting from acrylonitrile and diethylamine, which entail energy input and waste generation.

Table 3: Estimated Cost Comparison of Solvent Systems (per tonne CO₂ captured)

Estimates based on data from IEAGHG (2023) and techno-economic models from MIT Energy Initiative

While DEAPA has a higher upfront solvent cost than MEA, its lower operating costs—driven by energy savings and durability—make it economically competitive over time.

Future Directions and Research Opportunities

Ongoing research focuses on optimizing DEAPA-based formulations for commercial viability. Key areas include:

• Hybrid Solvent Design: Combining DEAPA with ionic liquids or amino acid salts to further reduce volatility and improve selectivity.
• Nanostructured Catalysts: Incorporating nanoparticles (e.g., TiO₂, SiO₂) to accelerate CO₂ hydration and desorption kinetics.
• Process Integration: Coupling DEAPA systems with advanced configurations such as intercooled absorption, rich-split stripping, or membrane-assisted regeneration.
• Digital Monitoring: Using online sensors and machine learning to predict degradation and optimize solvent management.

Additionally, DEAPA is being investigated for direct air capture (DAC) applications, where its strong affinity for dilute CO₂ and resistance to humidity fluctuations could offer advantages over conventional sorbents.

Summary of Key Features

Conclusion of Analysis

3-Diethylaminopropylamine represents a promising advancement in the evolution of CO₂ capture solvents. Its molecular architecture enables a synergistic combination of rapid absorption, high capacity, and moderate regeneration energy, addressing key limitations of first-generation amines. Supported by extensive laboratory testing and pilot-scale validation, DEAPA-based systems demonstrate technical feasibility and economic potential for deployment in coal-fired power plants, cement kilns, and steel manufacturing facilities.

Further innovation in solvent formulation, process engineering, and system integration will likely expand DEAPA’s applicability across diverse emission sources. As global decarbonization efforts intensify, DEAPA stands as a viable component of the next generation of sustainable carbon capture technologies.