Adsorption of CO2 and H2 on the polymer-based membrane from High-density Polyethylene (HDPE) Plastic

Abstract

High-density polyethylene (HDPE), a widely used polymer globally, notably found in plastic bags, presents an environmental concern due to its non-biodegradable nature. Transforming non-biodegradable HDPE waste into a valuable resource presents a formidable ecological challenge. This research aims to study CO₂ and H₂ gases toward HDPE-based membranes through the adsorption process with pressure and temperature variation. The highest CO₂ and H₂ adsorption capacities of 14.19 mmol.g ^{− 1} (62.43 %wt) and 18.04 mmol.g⁻¹ (3.61 %wt) were obtained by pressure feeding 3 bar at 30°C. The adsorption capacity decrease as the temperature increase. At an adsorption temperature of 50°C, the adsorption capacity of CO₂ and H₂ decrease, respectively by 75.86 % and 69.81 %. The adsorption kinetics were evaluated using pseudo-first order, pseudo-second order, and intraparticle diffusion models. The kinetic study shows that adsorption at 30°C follows the pseudo-second order. The adsorption at elevated temperatures reveals the intraparticle diffusion mechanism, indicating that the gas is adsorbed directly into the polymer matrix. Thermodynamic results include enthalpy of adsorption (ΔH), standard entropy of adsorption (ΔS), energy Gibbs (ΔG), and energy activation (E_a). ΔH CO₂ and H₂ are -22.339 and -23.654 kJ mol⁻¹, respectively, which indicates that the process is exothermic and physisorption. The ΔS value shows that the irregularity and randomness of gas movement during the adsorption process, with the respective values for CO₂ and H₂ are -0.069 and -0.072 kJ mol⁻¹ K⁻¹, respectively. ΔG for adsorption of CO₂ and H₂ with increasing temperature becomes less spontaneous, which results in decreased adsorption capacity. E_a of CO₂ is greater than H_2, so the adsorption capacity of CO₂ is smaller than H₂. The thermodynamic study shows that the adsorption process is preferable at lower temperatures.