Diffusion mechanism and effect of mass transfer limitation during the adsorption of CO₂ by polyaspartamide in a packed-bed unit

ABSTRACT

A systematic study of the diffusion mechanism and effect of mass transfer limitation during the adsorption of CO₂ onto polyaspartamide is presented using a differential adsorption bed method, carried out in a 100 × 60 × 40 mm packed-bed adsorption unit. The rate-limiting step where mass transfer limitation is dominant was studied using diffusion models. It was observed that intraparticle diffusion mechanism is the major contributor to the resistance offered to the transport of gas molecule through polyaspartamide. The behaviour of polyaspartamide, based on the intraparticle diffusion rate parameter derived from the plots of CO₂ adsorbed versus the square root of time, signified that the adsorption mechanism involved both film and intraparticle diffusion. The intraparticle diffusion parameter (kid) obtained was dependent on temperature as well as intraparticle convection effects and ranged from 1.24 × 10⁻⁴ to 2.13 × 10⁻⁴ ms⁻¹. The Biot number (Bi) values were all greater than 10 (ranged from 17.80 – 30.74), confirming that the intraparticle diffusion was the rate-limiting step and heat transfer is more by conduction from the gas film layer than convection within the pores of polyaspartamide. Results from this study provide an important basis for future scale-up and optimisation of CO₂ capture process using polyaspartamide.

KEYWORDS:

• Adsorption
• CO₂ capture
• diffusion mechanisms
• mass transfer
• Polyaspartamide

Acknowledgments

The authors are grateful to the National Research Foundation, South Africa (NRF grant numbers 107867 and 95061, respectively) and the University of the Witwatersrand, Johannesburg South Africa for the postgraduate merit awards (WITS-PMA 2017).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the National Research Foundation [grant numbers 107867 and 95061].

Notes on contributors

Kelvin O. Yoro

Kelvin O. Yoro obtained his MSc. Eng. degree in chemical engineering from University of the Witwatersrand, South Africa in 2017. He is currently a doctoral student in the school of chemical and metallurgical engineering at the same university. His main research interests are in CO₂ capture storage and utilisation as well as process modelling and optimisation, heat and mass integration as well as environmental sustainability.

Mutiu K. Amosa

Mutiu K. Amosa is an international research expert with the department for management of science and technology development and the faculty of environment and labour safety at Ton Duc Thang University in Vietnam. His main research interests are in environmental process engineering, process systems engineering, separation processes, and materials synthesis & development.

Patrick T. Sekoai

Patrick T. Sekoai completed his doctoral study in 2017 at the school of chemical Engineering, University of the Witwatersrand South Africa. His research interests are mainly in the area of sustainable and renewable energy.

Jean Mulopo

Jean Mulopo is an associate professor at the school of chemical and metallurgical engineering, University of the Witwatersrand, South Africa with interest in environmental sustainability, modelling and simulation.

Michael O. Daramola

Michael O. Daramola is an associate professor of chemical engineering at the University of the Witwatersrand, South Africa. His core research interests are in the area of CO₂ capture and storage, kinetics and catalysis, Process modelling and simulation.