Carbon dioxide adsorption on zeolites and activated carbon by pressure swing adsorption in a fixed bed

Int J Energy Environ Eng (2014) 5:349–356 DOI 10.1007/s40095-014-0131-3 ORIGINAL RESEARCH Carbon dioxide adsorption on zeolites and activated carbon by pressure swing adsorption in a fixed bed Lalhmingsanga Hauchhum • Pinakeswar Mahanta Received: 12 February 2014 / Accepted: 10 June 2014 / Published online: 2 August 2014 Ó The Author(s) 2014. This article is published with open access at Springerlink.com Abstract Combustion of fossil fuels is one of the major sources of greenhouse gas (GHG) CO2, it is therefore necessary to develop technologies that will allow us to utilize the fossil fuels while reducing the emissions of GHG. Removal of CO2 from flue gasses has become an effective way to mitigate the GHG and adsorption is considered to be one of the methods. Adsorption of CO2 on zeolite 13X, zeolite 4A and activated carbon (AC) have been investigated at a temperature ranging from 25 to 60 °C and pressure up to 1 bar. The experimental data were fitted with isotherm models like Langmuir and Freunlich isotherm model. The Langmuir model fit well with the two zeolites and Freunlich model fit well with AC. The thermodynamics parameters were calculated and found to be exothermic in natures for all three adsorbents. Moreover, regeneration studies have been conducted in order to verify the possibility of activated carbon reutilization, to determine its CO2 adsorption capacity within consecutive cycles of adsorption–desorption. Temperature swing adsorption was employed as the regeneration method through heating up to a temperature of approximately 100 °C. There is no full reversibility for zeolites while AC can achieve complete regenerations. Keywords Adsorption  Carbon dioxide  Thermodynamic parameters  Activated carbon  Zeolite L. Hauchhum (&)  P. Mahanta Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India e-mail: P. Mahanta e-mail: Introduction The emission of gaseous products of combustion into the atmosphere, mainly Carbon dioxide (CO2) is regarded as a major cause of global warming and climate change, through the so-called greenhouse effect [1]. Currently, 85 % of total world demanded energy is supplied by thermal power plants fed by fossil fuels, including coal, oil and gas. They account for about 40 % of total CO2 emissions [2]; Yang et al. [3]; [4]. Among the ways to control, reduce or mitigate this effect, the capture of CO2 from flue gasses of industrial combustion processes and its storage in deep geological formations is now being considered as a serious option [5–7]. A number of adsorption processes are used commercially for adsorbent process, including pressure swing adsorption (PSA), vacuum pressure swing adsorption (VPSA), and thermal or temperature swing adsorption (TSA). A number of research works have been done using the processes mentioned above on different types of adsorbent materials. Recent developments have demonstrated that PSA is a promising option for separating CO2 due to its ease of applicability over a relatively wide range of temperature and pressure conditions, its low energy requirements, and its low capital investment cost (Agarwal et al. [8]). Many studies concerning CO2 removal from various flue gas mixtures by means of PSA processes have been addressed in the literature. Prior to the design of an adsorption process, selecting an appropriate adsorbent with high selectivity and working capacity, as well as a strong desorption capability, is key to separating CO2. As a result, a wide variety of adsorbents like activated carbon, zeolites, silica gel, activated alumina, urea–formaldehyde and melamine–formaldehyde resins, poly-ethyleneimine and hollow fiber carbon membranes based adsorbents, etc. have 123 350 Int J Energy Environ Eng (2014) 5:349–356 been investigated for this purpose [9]; Sircar et al. [10]; [11, 12, 17]. Recent development shows an improvement in adsorbent materials with higher adsorption capacity and selectivity like Activated carbon honeycomb monolith— Zeolite 13X hybrid system, zeolites NaKA and nanoNaKA, FAU zeolites and zeolite 13X prepared from bentonite [13–16]. The PSA process is based on preferential adsorption of the desired gas on a porous adsorbent at high pressure, and recovery of the gas at low pressure. Thus, the porous sorbent can be reused for subsequent adsorption. PSA technology has gained interest because of the low energy requirements and low capital investment costs. The low recovery rate of CO2 is one of the problems reported with the PSA process [18]. Development of regenerable sorbents that have high selectivity, adsorption capacity, and adsorption/desorption rates for CO2 capture is critical for the success of the PSA process. Cost of the sorbent is also a major factor that needs to be considered for the process to be economical [19, 20]. The adsorption method of choice for many zeolite molecular sieves is PSA, although some experiments have employed a combined pressure and temperature swing adsorption (PTSA) process (Ruthven et al. [21]; [22, 23]. It has been reported that a particular TSA and PSA cycle conditions would result in higher expected working capacity with an increase in feed temperature. Zeolites have shown promising results for the separation of CO2 from gas mixtures and can potentially be used for the PSA process. Natural zeolites are inexpensive and can be viable sorbents if they work for the process application [24]. It has also been reported that using AC as an adsorbent material, the adsorption capacity can increase till 30 Bar and become steady after 30–35 bars [25]. Based on the literatures available, PSA seems to be the best option for separating CO2 from flue gas due to its ease of applicability over a relatively wide range of temperature and pressure conditions. A number of sorbents like zeolite, activated alumina, activated carbons, etc. have been utilized and cost of the sorbents play a vital role for the process to be economical. In this paper, low cost and abundantly available locally, coconut fiber based AC was employed as the sorbent materials and compared with commercial zeolites. Work had been done to develop a process in which CO2 was adsorbed from a gas stream containing *13.8 vol. % of CO2 onto zeolite 13X, zeolite 4A and AC by means of PSA process. The system was tested for five different adsorption and desorption cycles in order to determine the adsorbent bed’s regeneration efficiencies. Kinetics and adsorption thermodynamics parameters have also been calculated. 123 Materials and methods Materials The properties of commercial zeolite 13X and Zeolite 4A which were purchased from the local chemist are given in Table 1. While the AC (coconut fiber) used was obtained from a local area. It was peeled and the fibrous part was collected and was broken into small pieces. The coconut fibre was washed with water, dried in the sun for 10 h and transferred to the furnace. The coconut pieces were bur (...truncated)