https://doi.org/10.1016/j.petlm.2016.11.002
“The progress and prospects of blended amine solvents for CO2 capture from combustion processes has been extensively reviewed in this paper. Several studies (laboratory scale and pilot plant scale) has shown the potentials of blending amine solvents towards optimizing their CO2 absorption efficiency and decreasing their regeneration energy. Improvements are required in the degradation of blended amine solvents as well as emissions.
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Several new amine bi–solvent blends are currently being studied with the intention of out-performing the already existing single amines and bi–solvent blends. Considerable success is being achieved in this area and further studies are indeed needed.
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Amine bi–solvent blends though industrially applied have led to the study of tri–solvent and quad–solvent blends. It is believed that increasing the amine components in the blend can further improve its CO2 absorption–desorption capabilities. This has also been proven both in the laboratory and pilot plant scale where amine circulation rate has been reduced, increase in both CO2 absorption capacity and absorption rate, and regeneration energy reduced as much as 50%.
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Phase–split (phase–change or bi–phasic) solvent blends have also gained wide attention. More than a few researches have been done in this area and have reported increased cyclic capacity (bi–solvent blend) and reduction in the regeneration energy by 50% (tri–solvent). Studies are yet to be carried out in terms of their degradation rate and emissions.
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Amine volatility and emissions is integral in selecting the appropriate amine solvent for CO2 capture because most amine solvents are ecotoxic and not readily biodegradable. Amine solvents that are eco–friendly and biodegradable will go a long way towards protecting public health, environment and aquatic life from potential toxic risks. A previous study has given an indication that blending amine solvents can reduce the volatility of the amine solution. This paper also proposed that emerging amine blend formulations should be chosen in terms of their BOD and being eco–friendly. For example, a 60% BOD amine solvent can be blended with a 25% BOD amine solvent at blend ratio of 70–30% respectively, and/or an amine solvent with ecotoxicity below 10 mg/l should be blended with another amine solvent with ecotoxicity above 10 mg/l at 30–70% blend ratio respectively.
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Low boiling point amines could provide an alternative route towards reducing the energy of regeneration and also enhance amine reclaiming. A new term to be known as “simultaneous regeneration and reclaiming in the regenerator, S3R” might offer substantial benefits. Research should be carried out to specifically on this to specifically outline possible advantages and commerciality.
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Cost energy penalty indices explained and proposed in this paper will guide towards understanding the actual energy penalty and savings and cost of an amine solution for CO2 capture. When using the cost energy penalty indices, amine solvents should be compared based on a similar CO2 capture efficiency and/or same CO2 produced. The cost indices will also be very instrumental when scaling up from laboratory sized experimental set–up (e.g. semi–batch) to bench–scale pilot plants, large pilot plants and commercial CO2 capture plants.
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This review paper also proposed a new method and equations for estimating the reclaiming energy even when semi–batch experimental set–up are being used for analysis. This energy should also be compared to regeneration energy of amine solvents as this will provide vital evidence on the major contributor to the energy penalty. Future research should focus on determining this energy at small scale laboratory set up.
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A new experimental analysis is also proposed for investigating regeneration energy, reclaiming energy, amine cost and degradation rates of amine solvents towards CO2 capture. Taking into account these energy and cost penalties will be beneficial in selecting the appropriate amine solvent for CO2 capture.
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Studies conducted so far (on amine solvents) in all the CO2 capture performance metrics have given an indication that it might be ideal to synthesize a novel amine solvent that will contain all the desired structural properties (e.g. type of functional group and position). This technology can lead to the deployment of a single amine (polyamine) that can effectively compete with blended amine solution.
To enable easy transition from the already existing and industrially applied single and amine blends to newly developed blends, they must prove to be competitive (compared to 5 kmol/m3 MEA) in their average overall mass transfer coefficient, kinetics (absorption rate), cyclic capacity (CO2 production), regeneration energy, degradation, reclaiming energy and total equivalent work (as described in this paper). The success of newly developed blends for post–combustion CO2 capture will aid towards developing the ideal solvent blends for CO2 capture from natural gas processing, and pre–combustion (gas to liquids, hydrogen production etc.) and oxy–fuel processes.
The breakthrough achieved so far portends a bright future towards developing the ideal solvent blend for CO2 capture from post–combustion and pre–combustion process systems and natural gas processing.
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