The University of Akron IdeaExchange@UAkron The Dr. Gary B. and Pamela S. Williams Honors Honors Research Projects College Spring 2016 Investigation of Degradation of Amine Sorbent Elijah Arendt University of Akron, [email protected] Please take a moment to share how this work helps youthrough this survey. Your feedback will be important as we plan further development of our repository. Follow this and additional works at:http://ideaexchange.uakron.edu/honors_research_projects Part of theOther Chemical Engineering Commons Recommended Citation Arendt, Elijah, "Investigation of Degradation of Amine Sorbent" (2016).Honors Research Projects. 312. http://ideaexchange.uakron.edu/honors_research_projects/312 This Honors Research Project is brought to you for free and open access by The Dr. Gary B. and Pamela S. Williams Honors College at IdeaExchange@UAkron, the institutional repository of The University of Akron in Akron, Ohio, USA. It has been accepted for inclusion in Honors Research Projects by an authorized administrator of IdeaExchange@UAkron. For more information, please [email protected], [email protected]. Investigation of Degradation of Amine Sorbent Elijah Arendt Honors Research Project Department of Chemical and Biomolecular Engineering Executive Summary Problem Statement Global warming is a phenomena that has been increasing in severity over the past few decades. To mitigate the effects and protect future generations, world leaders have vowed to decrease their greenhouse gas emissions. Carbon dioxide is the primary greenhouse gas emitted in the world, and one major source of it is coal-fired power plants. Solid sorbents are used to reduce the amount of CO emitted from power plants. These amine-grafted sorbents adsorb CO from 2 2 the flue gas of power plants. This study investigates the performance of amine-grafted sorbents, specifically when they are degraded at 120°C. Results Amine-grafted sorbents consist of an amine source, additive, crosslinker (EPON resin), spacer (polyethylene glycol), and support material (silica). This study varied the amine source (tetraethylenepentamine [TEPA] or polyethylenimine [PEI]) and the amount of it in the sorbent. The additive type (potassium carbonate, sodium carbonate, rubidium carbonate, or sodium chloride) and the amount of it was also manipulated. The performance of sorbents is characterized by CO capture capacity, which is the amount (in mmol) of CO captured per gram 2 2 of sorbent at 40°C. When the amount of additive was manipulated, potassium carbonate was used for the batch. The maximum CO was captured with the fresh (not degraded) sorbent 2 containing 0.5wt% potassium carbonate. However when the sorbents were degraded, there was a 38% loss in the CO capture capacity. The best performing sorbents are ones that maintain their 2 performance after degradation. For this reason, the sorbents containing 2wt% and 5wt% were the best. When the type of additive was manipulated, 0.5wt% was used because previous research involved that amount. Potassium carbonate had the highest CO capture capacity, but 2 again this was before degradation. Sorbents containing sodium carbonate and rubidium carbonate performed the best after degradation. Lastly, the amine source and amount of that source in the sorbent was manipulated. The sorbent containing 30wt% TEPA outperformed the other sorbents by a large amount. Overall, sorbents with TEPA captured more CO than those 2 with PEI and 30wt% was the optimal amount. It should be noted that the sorbents containing 50wt% TEPA and 50wt% PEI had an increasing CO capture capacity with an increase in 2 degradation time. This phenomena can be attributed to the isolation of the amine groups with heat. All relevant data is located in the Data and Results section of this report. Conclusions Although the CO capture capacity is important when selecting a sorbent, the integrity of the 2 sorbent after thermal degradation must be considered. Therefore, the change in CO capture 2 capacity after degradation is an indicator of sorbent performance. An additive type of rubidium carbonate had the best performance and an amount of 5wt% should be used. The amine source and amount that achieved the most CO capture was 30wt% TEPA. 2 Broader Implications As a result of this research project, I gained the skill of designing a set of experiments. I created 15 sorbents and degraded them for 6 increments of time, totaling 90 samples. After measuring the CO capture capacity of these samples, I improved my ability to use various pieces of 2 equipment by characterizing the samples. I obtained infrared (IR) spectra, used an optical microscope, and used a scanning electron microscope (SEM) with energy-dispersive x-ray 2 spectroscopy (EDS) capability. Doing this research within an 8 month timeframe required prominent project management skills. I feel confident that completing this project improved my project and time management abilities, since I conducted research while working part-time and maintaining a full course load. The results I obtained not only benefits the group I worked in but also benefits the energy industry. Investigating the performance of degraded sorbents is a stepping stone to the overall goal of retrofitting CO capture systems to existing power plant flue 2 stacks. Recommendations Moving forward, the scaled-up performance of amine-grafted sorbents must be investigated. The sorbents created in this study were in powder form, but the sorbents used in industry are in pellet form. It is recommended to replicate the top-performing sorbents of each batch in pellet form. Additionally, the sorbents in this study captured pure CO at 40°C. Future studies should 2 replicate the composition and temperature of industry’s flue gas and test under those conditions. I recommend this type of project for future students because it teaches research and development (R&D). R&D is an important sector in all chemical industries because it delivers the products of the future. In conclusion, I am glad I conducted research in the Department of Chemical and Biomolecular Engineering as part of the Honors College curriculum. 3 Introduction In a fast-developing world, the need for power and energy is currently at its highest point. As lesser developed countries build their infrastructure, the demand on fossil fuels will become too great. In 2013, coal was 11.5% of the fuel consumed in the world1. The top producer of coal in the People’s Republic of China, followed by the United States. Coal generated 41.3% of the world’s electricity in 2013, which is the most of all fuel types. However, coal also produces the most carbon dioxide of all fuel types. Coal is responsible for 46% of the CO emissions in 2 20131. CO is the primary greenhouse gas emitted, accounting for 82% of all United States 2 greenhouse gas emissions in 20132. The United States is taking measures to reduce the amount of CO released through the Environmental Protection Agency’s Clean Air Act. Specifically, the 2 Clean Power Plan was created in 2015, which mandates to cut carbon pollution from the power sector by 32% by 20303. It also sets carbon pollution emission performance rates for coal-fired power plants. For this reason, power plants must find a way to reduce their CO emissions while 2 still maintaining their business production levels. There are many ways to reduce the CO emitted from power plants. They can be categorized 2 into location: post-combustion, pre-combustion and oxyfuel combustion. In post-combustion CO capture, the CO is removed from the flue gas after combustion has taken place. This is the 2 2 most preferred method because the process can be retrofitted onto the existing power-production process. It is also the most mature process for CO capture. In pre-combustion, the fuel is pre- 2 treated before combustion to reduce the CO emitted. Lastly, in oxyfuel combustion, oxygen is 2 used for combustion instead of air. This reduces the amount of nitrogen present in the exhaust gas4. This study covers the post-combustion CO capture process of adsorption. Unlike absorption, 2 which uses a liquid absorbent, a solid sorbent is used in adsorption to bind the CO on its 2 surfaces. When selecting a sorbent, a large surface area, high selectivity, and high regeneration ability are the main criteria5. This report discusses the CO capture capacity of degraded amine 2 sorbents. The surface area and selectivity of the sorbent is out of the scope of this project. Background The oxidative degradation of amine sorbents has previously been studied by Srikanth and Chuang. The amount of tetraethylenepentamine(TEPA) and polyethylene glycol(PEG) were varied and the characteristics post-degradation were studied. The silica-supported sorbents were subjected to 100°C for 12 hours and then characterized via IR and NMR spectroscopy. The researchers compared the ability of the sorbents to capture CO to the spectral analysis6. 2 Additionally, the group Khatri, Chuang, Soong, and Gray studied the thermal and chemical stability of amine sorbents. In their study, the adsorption and desorption of CO as well as SO 2 2 was investigated. The group found that water played a role in the adsorption capacity of the amine-grafted sorbents. The degradation of the sorbent was also studied7. In this project, the CO capture capacity of thermally degraded sorbents is studied. 2 1 Experimental Methods The sorbent consists of an amine source, additive, cross-linker, spacer, and support material. For this project, the support material used was silica (SiO ), the cross-linker is EPON resin, and the 2 spacer is polyethylene glycol (PEG) with a molecular weight of 200. Four variables were manipulated to determine the optimum recipe for amine sorbent: amount and type of additive and amine. The amine sources studied are tetraethylenepentaamine (TEPA) and polyethylenimine (PEI). The additives studied are potassium carbonate, sodium carbonate, rubidium carbonate, and a standard salt (NaCl). Figure 1 shows the breakdown of the batches of sorbent created and tested. When the amount of additive was varied, potassium carbonate was used with 30% b.w. TEPA. When the type of additive was manipulated, 0.5% b.w. of additive amount and 30% b.w. PEI was used. Lastly, when the amount and type of amine was varied, 0.5% b.w. of potassium carbonate was used. Amount/Type of Additive Amount/Type of Amine K CO3 Na CO Ru CO NaCl TEPA PEI 2 2 3 2 3 0% 10% 10% 0.5% 30% 30% 2% 50% 50% 5% 10% Figure 1: Breakdown of manipulated variables for this project. Figure 2 shows the process flow for the experimental procedure of this project. The sorbent powder was prepared by combining a solution of amine source, polyethyleneglycol (PEG), and EPON resin with a solution of additive (carbonate/salt) and silica. Once a homogeneous mixture was achieved, the sorbent was placed in a 100°C oven to dry. 2 Degradation Characterization •0.5 hr •SEM/EDS CO Sorbent 2 •1 hr CO Capture •Optical Capture 2 Preparation •3 hr Capacity Microscope Capacity •5 hr •IR •Overnight Figure 2: The process flow for this project The carbon dioxide capture capacity was found by measuring the amount of carbon dioxide captured in 10 minutes. To do so, approximately 1g of sorbent was subjected to heat at 100°C for 10 minutes to desorb any water or other impurities. Then the sorbent was weighed and placed in a carbon dioxide-filled bag at 40°C for 10 minutes. The sorbent was weighed again to determine the amount of CO absorbed. The sorbent was regenerated by placing it back into the 2 100°C oven for 10 minutes. This process was done 4 times and the average CO capture 2 capacity was calculated. Following initial CO capture capacity measurement, the remaining sorbent was degraded in air 2 using a 120° oven for 5 time groups: 30 minutes, 1 hour, 3 hours, 5 hours, and overnight (12-15 hours). The CO capture capacity was measured again to determine the loss of capture capacity 2 due to degradation. Images were obtained for all samples using an optical microscope and a scanning electron microscope (SEM). Using the SEM, the existing elements and their amounts were determined. The sorbent was also examined using infrared spectroscopy (IR) to verify the presence of various chemical bonds. 3 Data and Results Amount of Additive As seen in Figure 3, the amount of K CO additive impacted the CO capture capacity of the 2 3 2 sorbents. Of the non-degraded (“fresh”) sorbents, the sorbent containing 0.5% of K CO 2 3 performed the best. However after 5 hour degradation, the CO capture capacity dropped. 2 3.5 ) 3 g / lo m 2.5 m ( y tic 2 a p a C Fresh e 1.5 r u 5 hour degradation t p a 1 C 2 O C 0.5 0 0% 0.5% 2% 5% 10% K2CO3 Amount (Weight %) Figure 3: Effect of K2CO3 Amount on CO2 Capture Capacity As seen in Table 1, the sorbents containing 2% and 5% K CO had the least change in CO 2 3 2 capture capacity with total degradation time. Figure 4 shows the trend of CO capture capacity 2 versus amount of degradation for each sorbent. The sorbents containing 2% and 5% K CO had 2 3 an increase in CO capture capacity within the first 3 hours of degradation, and then a decrease 2 after 3 hours, which accounts for the smaller change in performance with total degradation. Table 1: Percent change in CO2 capture capacity for additive amount Fresh 14 Hour Degradation Additive CO2 Capture CO2 Capture Amount Capacity (mmol/g) % change Capacity (mmol/g) % change 0% 2.752 0% 1.903 -31% 0.5% 3.155 0% 1.952 -38% 2% 2.233 0% 2.112 -5% 5% 2.212 0% 2.210 0% 10% 1.523 0% 0.769 -49% 4 3.5 3 ) g / lo m 2.5 m (y 0% K2CO3 t ic 2 ap 0.5% K2CO3 a C e 1.5 2% K2CO3 r u tp 5% K2CO3 a 1 C 2 10% K2CO3 O C 0.5 0 0 2 4 6 8 10 12 14 Degradation Time (hours) Figure 4: Effect of Oxidative Degradation on CO2 Capture Capacity Type of Additive When the type of additive was manipulated, various carbonates as well as a standard salt were chosen. As seen in Figure 5, the fresh sorbent containing potassium carbonate performed the best. 1.2 )g 1 / lo m m 0.8 ( y t ic a p 0.6 a C Fresh e r u 5 hour degradation t 0.4 p a C 2 O 0.2 C 0 K2CO3 Na2CO3 Rb2CO3 NaCl Additive Figure 5: Effect of Additive Type on CO2 Capture Capacity After thermal degradation, the sorbent containing potassium carbonate had a significant change in CO capture capacity, as seen in Table 2. The integrity of all sorbents in this group was 2 compromised. As seen in Table 2 and Figure 6, rubidium carbonate had the least change in CO 2 capture capacity. 5