1240 Korean J. Chem. Eng., 38(6), 1240-1247 (2021) DOI: 10.1007/s11814-021-0776-6 INVITED REVIEW PAPER pISSN: 0256-1115 eISSN: 1975-7220 INVITED REVIEW PAPER † To whom correspondence should be addressed. E-mail: sdkim@hallym.ac.kr ‡ These authors contributed equally to this work. Copyright by The Korean Institute of Chemical Engineers. The role of contact time and input amount of 1,1,1,2-tetrafluoroethane (HFC-134a) on the catalyst lifetime and product selectivity in catalytic pyrolysis Ali Anus * ,‡ , Mahshab Sheraz * ,‡ , Sangjae Jeong ** , Caroline Mercy Andrew Swamidoss *** , Young-Min Kim **** , Muhammad Awais Aslam ***** , Eui-kun Kim ****** , and Seungdo Kim * ,† *Department of Environmental Sciences and Biotechnology, Hallym University, Chuncheon 24252, Korea **Department of Energy & Environmental Engineering, College of Engineering, Soonchunhyang University, Asan, Chungcheongnam-do 31538, Korea ***Department of Chemistry, Dr. M.G.R. Educational and Research Institute, Chennai, 600095, India ****Department of Environmental Engineering, Daegu University, Gyeongsan 38453, Korea *****Research Center for Climate Change and Energy, Hallym University, Chuncheon 24252, Korea ******Environment Strategy Development Institute, Hallym University, Chuncheon 24252, Korea (Received 9 November 2020 • Revised 20 February 2021 • Accepted 2 March 2021) AbstractDuring catalytic pyrolysis of HFC-134a over -alumina, the formation of HF and coke causes catalyst deac- tivation. Catalyst deactivation and product selectivity depend on the contact time during catalytic pyrolysis of HFC- 134a as reported in this paper. -Alumina calcined at 650 o C was used as the catalyst due to its higher quantity of acidic sites and larger surface area, which are crucial for catalytic pyrolysis. X-ray diffraction (XRD), scanning electron micro- scope-energy dispersive X-ray spectroscopy (SEM-EDS), and thermogravimetric analysis (TGA) of the catalysts were performed to determine the influence of contact time and flow rate of HFC-134a. 2 mL/min of HFC-134a balanced with nitrogen to 25, 50, 100, and 200 mL/min total flow rates was studied at 600 o C. 200 mL/min showed a 9.4 h cata- lyst lifetime with a small number of by-products. Shorter contact time between HFC-134a and HF with the catalyst was found to be the key to the longer lifetime of the catalyst. The catalyst lifetime was decreased with an increase in the HFC-134a input amount. Among 2, 4, and 6 mL/min input of HFC-134a, 2 mL/min showed the longest catalytic activ- ity followed by 4 and 6 mL/min, respectively. Conversion of -alumina into AlF 3 and deposition of coke were responsi- ble for the deactivation. Keywords: Catalytic Conversion, Pyrolysis, Contact Time, -Al 2 O 3 , HFC-134a INTRODUCTION The global temperature has increased rapidly in this past cen- tury. Scientists around the world have started taking action in an attempt to solve the issue of global warming, leading to thousands of publications in that arena. Most of these studies conclude that the anthropogenic activities, which laid the foundation of the mod- ern world, are the reason behind this catastrophe [1,2]. Increasing greenhouse gas (GHG) concentrations are considered to have more than 50 percent share in elevation of the global average surface tem- perature of the earth [3]. Among these GHGs, hydrofluorocarbons (HFCs) are a group of fluorine containing greenhouse gases [4,5] which replaced chlorofluorocarbons (CFCs) and hydrochlorofluo- rocarbons (HCFCs). CFCs were found to be ozone-depleting sub- stances as they generate chlorine atom by photodissociation which can react with ozone present in the stratosphere [6]. The phasing out of production and consumption of CFCs as a result of the Mon- treal Protocol [7] resulted in the usage of HFCs as a substitute for refrigerants [5]. Among these HFCs, 1,1,1,2-tetrafluoroethane (HFC- 134a) first appeared in the early 1990s as a substitute for the ozone- depleting dichlorofluoromethane (CHCl 2 F; HCFC-21). It is one of the most abundant HFCs with a global warming potential (GWP) of 1,300 [8]. The emissions of HFCs skyrocketed due to the world- wide increase in the demand for air conditioning. The rising con- centration led HFCs to the inclusion in the seven targeted GHGs by the Kyoto Protocol [4]. In 2016, the Kigali Amendment to the Montreal Protocol decided to phase down the consumption of HFCs, eager to avoid emission of 70 billion tons CO 2 equivalent (CO 2 e) by 2050 [9]. Therefore, technologies for the climate change mitigation caused by HFCs, especially HFC-134a, are of tremen- dous importance. At present, the treatment methods of HFC-134a majorly include thermal combustion, plasma decomposition, and catalytic decom- position. Thermal combustion is considered to be the most appli- cable technology for the decomposition of HFCs and Perfluoro- carbons (PFCs) so far. It is also certified by the United Nations Framework on Climate Change (UNFCC) to abate HFC-23 under clean development project [10], as it is the highly efficient and simplest treatment method for the HFCs disposal. However, being that fuel is required for this process, commercialization is difficult. It is also not easy to obtain inexpensive material for the reaction