슬러지 마이크로파 열분해 온도에 따른 가스 조성의 영향

김가빈(Gabin Kim),박영호(Young Ho Park),김주형(Joohyeong Kim),김대기(Daegi Kim),박기영(Ki Young Park) 한국열환경공학회 2019 한국열환경공학회 학술대회지 Vol.2019 No.춘계

현재 화석연료에 대한 높은 의존도로 인해 지속가능한 에너지원의 구축이 필요하다. 이에 폐기물을 이용해 에너지를 생산하는 폐기물자원화 기술이 주목을 받고 있다. 폐기물 중 하수슬러지는 발생량이 많고 유기물 함량이 높아 에너지원으로 활용될 가능성이 높다. 다양한 자원화 방법 중 열분해는 고분자 유기물질을 열적 분해하여 고체, 액체, 기체상의 생성물로 회수할 수 있는 방법으로, 보다 환경적인 슬러지 처리가 가능하게 된다. 하지만 외부 열원을 에너지원으로 이용하는 기존 열분해 방법의 경우에는 온도 상승에 많은 시간이 소요되고 직접적인 내부 가열이 어렵다는 단점이 있다. 이를 극복하기 위해 유전 가열을 통해 유기물의 내부를 직접적으로 분해하는 마이크로파 열분해 방법이 고안되었다. 마이크로파를 이용한 열분해는 기존 열분해와 비교 시 최종 온도에 도달하는 시간이 단축되며 높은 수소가스 성분 생성이 가능하다는 장점을 가진다. 본 연구에서는 하수슬러지의 효율적인 에너지화 공정으로 마이크로파 열분해 방법을 제시하고, 슬러지의 마이크로파 열분해 시 최종 온도 변화에 따른 가스 생성물의 조성을 관찰하였다. 마이크로파 열분해 온도는 각각 400, 600, 800, 1000℃로 설정하였다. 1시간동안 최종 온도를 유지하며 열분해 실험을 진행하였고, 생성되는 열분해 가스를 포집하였다. 온도 상승 추이와 가스 생성물 중 수소가스의 발생을 중점적으로 분석하여 슬러지 열분해에 있어서 마이크로파가 미치는 영향을 도출하였다.

New 4V-Class and Zero-Strain Cathode Material for Na-Ion Batteries

Kim, Jongsoon,Yoon, Gabin,Lee, Myeong Hwan,Kim, Hyungsub,Lee, Seongsu,Kang, Kisuk American Chemical Society 2017 Chemistry of materials Vol.29 No.18

<P>Here, we introduce Na<SUB>3</SUB>V(PO<SUB>3</SUB>)<SUB>3</SUB>N as a novel 4V-class and zero-strain cathode material for Na-ion batteries. Structural analysis based on a combination of neutron and X-ray diffraction (XRD) reveals that the Na<SUB>3</SUB>V(PO<SUB>3</SUB>)<SUB>3</SUB>N crystal contains three-dimensional channels that are suitable for facile Na diffusion. The Na (de)intercalation is observed to occur at ∼4 V vs Na/Na<SUP>+</SUP> in the Na cell via the V<SUP>3+</SUP>/V<SUP>4+</SUP> redox reaction with ∼67% retention of the initial capacity after over 3000 cycles. The remarkable cycle stability is attributed to the near-zero volume change (∼0.24%) and unique centrosymmetric distortion that occurs during a cycle despite the large ionic size of Na ions for (de)intercalation, as demonstrated by <I>ex situ</I> XRD analysis and first-principles calculations. We also demonstrate that the Na<SUB>3</SUB>V(PO<SUB>3</SUB>)<SUB>3</SUB>N electrode can display outstanding power capability with ∼84% of the theoretical capacity retained at 10C, even though the particle sizes are on the micrometer scale (>5 μm), which is attributed to its intrinsic three-dimensional open-crystal framework. The combination of this high power capability and extraordinary cycle stability makes Na<SUB>3</SUB>V(PO<SUB>3</SUB>)<SUB>3</SUB>N a new potential cathode material for Na-ion batteries.</P> [FIG OMISSION]</BR>

Highly Stable Iron- and Manganese-Based Cathodes for Long-Lasting Sodium Rechargeable Batteries

Kim, Hyungsub,Yoon, Gabin,Park, Inchul,Hong, Jihyun,Park, Kyu-Young,Kim, Jongsoon,Lee, Kug-Seung,Sung, Nark-Eon,Lee, Seongsu,Kang, Kisuk American Chemical Society 2016 Chemistry of materials Vol.28 No.20

<P>The development of long-lasting and low-cost rechargeable batteries lies at the heart of the success of large-scale energy storage systems for various applications. Here, we introduce Fe- and Mn-based Na rechargeable battery cathodes that can stably cycle more than 3000 times. The new cathode is based on the solid-solution phases of Na4MnxFe3-x(PO4)(2)-(P2O7) (x = 1 or 2) that we successfully synthesized for the first time. Electrochemical analysis and ex situ structural investigation reveal that the electrodes operate via a one phase reaction upon charging and discharging with a remarkably low volume change of 2.1% for Na4MnFe2(PO4)(P2O7), which is one of the lowest values among Na battery cathodes reported thus far. With merits including an open framework structure and a small volume change, a stable cycle performance up to 3000 cycles can be achieved at 1C and room temperature, and almost 70% of the capacity at C/20 can be obtained at 20C. We believe that these materials are strong competitors for large-scale Na-ion battery cathodes based on their low costs, long-term cycle stability, and high energy density.</P>

Extremely large, non-oxidized graphene flakes based on spontaneous solvent insertion into graphite intercalation compounds

Kim, Jungmo,Yoon, Gabin,Kim, Jin,Yoon, Hyewon,Baek, Jinwook,Lee, Joong Hee,Kang, Kisuk,Jeon, Seokwoo Elsevier 2018 Carbon Vol.139 No.-

<P><B>Abstract</B></P> <P>Demand for an effective strategy for exfoliating layered materials into flakes without perturbing their intrinsic structure is growing. Herein, we introduce an effective fabrication method of large-sized non-oxidized graphene flakes (NOGFs) as a representative example of a general strategy using spontaneous insertion of exfoliating medium into a layered material. We fabricated a ternary graphite intercalation compound (t-GIC) with stoichiometry of KC<SUB>24</SUB>(THF)<SUB>2</SUB>, and analyzed its morphology and electronic structure through experimental and computational approach. Interactions between the t-GIC and aprotic organic solvents with different polarities were investigated, where a unique swelling behavior was observed with dimethyl sulfoxide (DMSO). Based on the analysis of the phenomena, we demonstrate facile exfoliation of the t-GIC in polyvinyl pyrrolidone (PVP)-DMSO solution for fabrication of highly crystalline and large-sized NOGFs. The lateral size of the NOGFs ranges over 30 μm, while the 98% having thickness below 10 layers. The NOGF film exhibits supreme electrical conductivity of 3.36 × 10<SUP>5</SUP> S/m, which is, to our best knowledge, the highest value for a thin conductive film made of graphene flakes.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Anomalous Jahn–Teller behavior in a manganese-based mixed-phosphate cathode for sodium ion batteries

Kim, Hyungsub,Yoon, Gabin,Park, Inchul,Park, Kyu-Young,Lee, Byungju,Kim, Jongsoon,Park, Young-Uk,Jung, Sung-Kyun,Lim, Hee-Dae,Ahn, Docheon,Lee, Seongsu,Kang, Kisuk The Royal Society of Chemistry 2015 ENERGY AND ENVIRONMENTAL SCIENCE Vol.8 No.11

<P>We report a 3.8 V manganese-based mixed-phosphate cathode material for applications in sodium rechargeable batteries; i.e., Na4Mn3(PO4)(2)(P2O7). This material exhibits a largest Mn2+/Mn3+ redox potential of 3.84 V vs. Na+/Na yet reported for a manganese-based cathode, together with the largest energy density of 416 W h kg (1). We describe first-principles calculations and experimental results which show that three-dimensional Na diffusion pathways with low-activation-energy barriers enable the rapid sodium insertion and extraction at various states of charge of the Na4-xMn3(PO4)(2)(P2O7) electrode (where x = 0, 1, 3). Furthermore, we show that the sodium ion mobility in this crystal structure is not decreased by the structural changes induced by Jahn-Teller distortion (Mn3+), in contrast to most manganese-based electrodes, rather it is increased due to distortion, which opens up sodium diffusion channels. This feature stabilizes the material, providing high cycle stability and high power performance for sodium rechargeable batteries. The high voltage, large energy density, cycle stability and the use of low-cost Mn give Na4Mn3(PO4)(2)(P2O7) significant potential for applications as a cathode material for large-scale Na-ion batteries.</P>

Sodium intercalation chemistry in graphite

Kim, Haegyeom,Hong, Jihyun,Yoon, Gabin,Kim, Hyunchul,Park, Kyu-Young,Park, Min-Sik,Yoon, Won-Sub,Kang, Kisuk The Royal Society of Chemistry 2015 ENERGY AND ENVIRONMENTAL SCIENCE Vol.8 No.10

<P>The insertion of guest species in graphite is the key feature utilized in applications ranging from energy storage and liquid purification to the synthesis of graphene. Recently, it was discovered that solvated-Na-ion intercalation can occur in graphite even though the insertion of Na ions alone is thermodynamically impossible; this phenomenon enables graphite to function as a promising anode for Na-ion batteries. In an effort to understand this unusual behavior, we investigate the solvated-Na-ion intercalation mechanism using <I>in operando</I> X-ray diffraction analysis, electrochemical titration, real-time optical observation, and density functional theory (DFT) calculations. The ultrafast intercalation is demonstrated in real time using millimeter-sized highly ordered pyrolytic graphite, in which instantaneous insertion of solvated-Na-ions occurs (in less than 2 s). The formation of various stagings with solvated-Na-ions in graphite is observed and precisely quantified for the first time. The atomistic configuration of the solvated-Na-ions in graphite is proposed based on the experimental results and DFT calculations. The correlation between the properties of various solvents and the Na ion co-intercalation further suggests a strategy to tune the electrochemical performance of graphite electrodes in Na rechargeable batteries.</P> <P>Graphic Abstract</P><P>The solvated-Na-ion intercalation in graphite is investigated in terms of stoichiometry, staging structure, and solvated ion configuration using combined experimental and theoretical studies. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5ee02051d'> </P>

Microwave-pyrolysis of Sewage Sludge at High Temperature

( Gabin Kim ),( Young Ho Park ),( Sung Wan Cho ),( Ki Young Park ) 한국폐기물자원순환학회(구 한국폐기물학회) 2019 ISSE 초록집 Vol.2019 No.-

The influence of temperature and moisture content on microwave-pyrolysis was investigated at high temperature. It was explained by the change of product yield and gas component. The dried sludge and dewatered sludge that its moisture content is 80.42 wt. % were used as substances for pyrolysis experiment. It aims to analyze the effect of moisture content. As the organic matter is poor microwave-absorbent (poor dielectric properties), it is necessary to mix a substance that has high capacity to absorb microwave energy and convert it into heat. In this study, graphite was used as microwave-absorber (MWA). High temperature pyrolysis of sewage sludge was carried out at 800, 1000 ℃. The products were quantitatively, qualitatively analyzed. As temperature increasing, gas yield increased and oil, solid yield decreased. The highest gas yield was observed at 1000 ℃ with the highest hydrogen gas production. In the case of dewatered sludge, pyrolysis efficiency was higher than the case of dried sludge. It is because that the moisture content of dewatered sludge has a role that absorbing the microwave energy. In case of microwave-pyrolysis, the time to reach the setting temperature was shortened and the gas yield increased by comparison with the case of conventional pyrolysis. In this study, it was proven that the microwave-pyrolysis is an economicefficiency method that occurs drying, pyrolysis and gasification at the same time.

Recent Progress in Electrode Materials for Sodium-Ion Batteries

Kim, Hyungsub,Kim, Haegyeom,Ding, Zhang,Lee, Myeong Hwan,Lim, Kyungmi,Yoon, Gabin,Kang, Kisuk Wiley-VCH 2016 ADVANCED ENERGY MATERIALS Vol.6 No.19

<P>Grid-scale energy storage systems (ESSs) that can connect to sustainable energy resources have received great attention in an effort to satisfy ever-growing energy demands. Although recent advances in Li-ion battery (LIB) technology have increased the energy density to a level applicable to grid-scale ESSs, the high cost of Li and transition metals have led to a search for lower-cost battery system alternatives. Based on the abundance and accessibility of Na and its similar electrochemistry to the well-established LIB technology, Na-ion batteries (NIBs) have attracted significant attention as an ideal candidate for grid-scale ESSs. Since research on NIB chemistry resurged in 2010, various positive and negative electrode materials have been synthesized and evaluated for NIBs. Nonetheless, studies on NIB chemistry are still in their infancy compared with LIB technology, and further improvements are required in terms of energy, power density, and electrochemical stability for commercialization. Most recent progress on electrode materials for NIBs, including the discovery of new electrode materials and their Na storage mechanisms, is briefly reviewed. In addition, efforts to enhance the electrochemical properties of NIB electrode materials as well as the challenges and perspectives involving these materials are discussed.</P>

Hyrothermal carbonization of sewage sludge for energy recovery

( Gabin Kim ),( Donghwan Sohn ),( Jongkeun Lee ),( Seunghyun Lee ),( Kyung Jin Min ),( Ki Young Park ) 한국폐기물자원순환학회(구 한국폐기물학회) 2019 한국폐기물자원순환학회 심포지움 Vol.2019 No.1

One way to recover energy from sewage sludge is to use it as fuel through drying and carbonization. Although this method accounts for 43.8% (w/w)of sludge recycling rate, however, it consumes much energy in the fueling process due to the high water content of sewage sludge. In order to overcome this problem, a hydrothermal carbonization method which can carbonize sewage sludge at a lower temperature by using water in sewage sludge is being used as a new treatment method. In this study, to increase the efficiency of the sewage sludge fueling method for the energy independence of the sewage treatment plant, the primary sludge generated in the sewage treatment plant and the digested sludge are converted into fuel through hydrothermal carbonization, and the solid fuel characteristics of the product are analyzed Sludge selection and optimum treatment conditions for solid fuel production. In this study, sludge generated in J wastewater treatment plant in Seoul was used. Experimental conditions were as follows: 300 mL of feedstock and the same amount of distilled water was added to the reactor and heated to 180~270℃. The reaction time was the same for 30 minutes and aimed at the optimum temperature was obtained. Both the primary sludge and the digested sludge showed an increase in carbon content, a decrease in oxygen and hydrogen content, and an improvement in coal quality as the water temperature increased. However, as the treatment temperature increased, the calorific value of the primary sludge improved, but the calorific value of the digested sludge decreased. This phenomenon is considered to be the result of increased ash content in the carbonization process. In order to use sewage sludge generated from sewage treatment facilities as solid fuel, primary sludge with high heating value is more suitable than digestion sludge and 210℃ with high energy recovery efficiency is suitable because the treatment temperature is the highest.

Syngas production from digested sludge and its application to anaerobic digestion

Gabin Kim,Young Ho Park,Ki Young Park 대한환경공학회 2019 대한환경공학회 학술발표논문집 Vol.2019 No.-