Lignin‐derived heteroatom‐doped porous carbons for supercapacitor and CO2 capture applications

The present study reports the economic and sustainable syntheses of functional porous carbons for supercapacitor and CO₂ capture applications. Lignin, a byproduct of pulp and paper industry, was successfully converted into a series of heteroatom‐doped porous carbons (LHPCs) through a hydrothermal carbonization followed by a chemical activating treatment. The prepared carbons include in the range of 2.5 to 5.6 wt% nitrogen and 54 wt% oxygen in its structure. All the prepared carbons exhibit micro‐ and mesoporous structures with a high surface area in the range of 1788 to 2957 m² g^?1. As‐prepared LHPCs as an active electrode material and CO₂ adsorbents were investigated for supercapacitor and CO₂ capture applications. Lignin‐derived heteroatom‐doped porous carbon 850 shows an outstanding gravimetric specific capacitance of 372 F g^?1 and excellent cyclic stability over 30,000 cycles in 1 M KOH. Lignin‐derived heteroatom‐doped porous carbon 700 displays a remarkable CO₂ capture capacity of up to 4.8 mmol g^?1 (1 bar and 298 K). This study illustrates the effective transformation of a sustainable waste product into a highly functional carbon material for energy storage and CO₂ separation applications.     

Nitrogen-doping activated biomass carbon from tea seed shell for CO2 capture and supercapacitor

Activated carbon is a promising material that has a broad application prospect. In this work, biomass (tea seed shell) was used to prepare activated carbon with KOH activation (referred to as AC), and nitrogen was doped in activated carbon using melamine as the nitrogen source (referred to as NAC-x, where x is the mass ratio of melamine and activated carbon). The obtained activated biomass carbon (activated bio-carbon) samples were characterized by Brunauer–Emmett–Teller (BET)-specific surface area analysis, ultimate analysis, X-ray photoelectron spectroscopy (XPS) analysis, Raman spectrum analysis, and X-ray diffraction (XRD) patterns. The specific surface areas of activated bio-carbons were 1503.20 m²/g (AC), 1064.54 m²/g (NAC-1), 1187.93 m²/g (NAC-2), 1055.32 m²/g (NAC-3), and 706.22 m²/g (NAC-4), revealing that nitrogen-doping process leads to decrease in specific surface area. XPS analysis revealed that the main nitrogen-containing functional groups were pyrrolic-N and pyridinic-N. The capacity of CO₂ capture and electrochemical performance of activated bio-carbon samples were investigated. The CO₂ capturing capacity followed this order: AC (3.15 mmol/g) > NAC-2 (2.75 mmol/g) > NAC-1 (2.69 mmol/g) > NAC-3 (2.44 mmol/g) > NAC-4 (1.95 mmol/g) at 298 K at 1 bar, which is consistent with the order of specific surface area. The specific surface area played a dominant role in CO₂ capturing capacity. As for supercapacitor, AC-4 showed the highest specific capacitance (168 F/g) at the current density of 0.5 A/g, but NAC-2 showed the best electrochemical performance (89 F/g) at 2 A/g. Nitrogen-containing functional groups and specific surface area both had an important impact on electrochemical performance. In general, NAC-3 and NAC-2 produced excellent electrochemical performance. Compared with NAC-3, less melamine was used to prepare NAC-2; therefore, NAC-2 was considered as the best activated bio-carbon for supercapacitor for 141 F/g (at 0.5 A/g), 108 F/g (at 1 A/g), and 89 F/g (at 2 A/g) in this work.     

Preparation of activated biomass carbon from pine sawdust for supercapacitor and CO2 capture

Biomass based carbon has captured more and more attention because it is environmentally friendly and has properties of low cost and ideal sustainability. In this study, three kinds of activated biomass carbons (ie, ABC-700, ABC-800 and ABC-900) were first carbonized through pine sawdust pyrolysis and then activated using KOH under three different activation temperatures (ie, 700°C, 800°C and 900°C). The structure properties of the prepared activated biomass carbons were characterized by N₂-adsorption/desorption, SEM, TEM, XRD, Raman, XPS, TG and ultimate analysis. To clarify the activation mechanism, the gas products produced during KOH activation process were measured online with an ETG gas analyzer. The performance of the activated biomass carbons derived from pine sawdust for supercapacitor and CO₂ capture was then evaluated. The predominant gas products during the activation process are H₂ and CO. It indicates that the porous structure was created by using an enhanced etching reaction between carbon atoms and KOH. An increment of the activation temperature from 700 to 900°C results in the increase of surface area (from 1728.66 to 2330.89 m²/g) and total pore volume (from 0.671 to 1.914 cm³/g). Among the three samples, ABC-900 exhibits the maximal specific capacitance of 175.6 F·g⁻¹ and high energy density of 24.39 Wh·kg⁻¹ at the 0.5 A·g⁻¹. And the ABC-700 shows the maximal CO₂ capture capacity of 4.21 mmol/g and high selectivity of CO₂ over N₂ at 298 K and 1 bar. In addition, ABC-700 also has excellent stability and reproducibility after 15 times adsorption-desorption cycles. The unexceptionable electrochemical performance and adsorption capacity of the biomass-carbons show its broad application prospects in the field of supercapacitors and CO₂ capture.     

双流化床生物质气化及CO2捕获的模拟

用Aspen Plus建立了双流化床气化和燃烧模型,对生物质在双流化床中气化及CaO吸收合成气中的CO2过程进行了模拟研究;探讨不同反应条件:气化温度、蒸汽与生物质的质量配比(S/B)以及CaO循环量与生物质的质量配比(Ca/B)对合成气成分的影响,为该类型工业反应器的研发提供了理论依据.模拟分析结果表明:气化温度低于700℃时,CaO能很好地吸收气化过程中产生的CO2并促进平衡反应向产氢方向进行;在温度为650℃及CaO作用下,S/B在0.6～1.7内对合成气成分的影响不大;CaO的加入能够有效地改善合成气的组成,合成气中氢气浓度能达到95％以上,氢气产量达到52 mol/kg.     

Nitrogen-doped porous carbons derived from sustainable biomass via a facile post-treatment nitrogen doping strategy: Efficient CO2 capture and DRM

Nitrogen (N)-doped carbon materials have become promising candidates for many applications. In this paper, the biomass activated carbon (BC) was obtained by carbonization and activation of soybean meal. Using soybean meal as the precursor, potassium hydroxide (KOH) as the activator and melamine as the nitrogen source, a series of N-doped porous biomass carbons (H-NC-X) with different N contents were achieved via a facile post-treatment nitrogen doping strategy. Then these samples were used as a catalyst for dry reforming of methane (DRM) reaction and an adsorbent for CO₂ capture. Among all the investigated samples, BC has the largest specific surface area and the best pore structure characteristics, showing the best CO₂ adsorption capacity. However, when BC was used as a catalyst for DRM reaction, it showed the worst catalytic performance. After nitrogen doping treatment, the CO₂ adsorption capacity of the prepared N-doped biomass porous carbon decreased gradually with the increase of the introduced N content. This is mainly due to the destruction of the microporous structure of porous carbon by post-processing nitrogen doping. In contrast, when nitrogen-doped porous carbon was used as the reforming catalyst, the catalytic activity increased with the increase of the introduced N content. The order was: H-NC-30>H-NC-20>H-NC-10. This indicates that when nitrogen-doped porous carbon was used as an adsorbent, the pore structure plays a major role; while when it was used as a reforming catalyst, nitrogen functional groups are the major active sites. This study provides a promising N-doped carbon material for effect CO₂ adsorption and DRM reactions.     

Comparison of MEA and DGA performance for CO2 capture under different operational conditions

Carbon capture and storage from flue gases is the most common method to reduce greenhouse gas emissions. Using a primary amine as the solvent of CO₂ capture unit is popular because of its high activity and ability to be used for streams with low concentration and low partial pressure of CO₂. Monoethanolamine(MEA) and Diglycolamine(DGA) are the most common kinds of primary amines which have been traditionally used in many natural gas sweetening plants. In this research, the capture plant has been designed for these two solvents at various CO₂ concentrations in the feed flue gas. This paper proposes different possible alters to overcome the high energy requirements of capture plant. It also presents the results of technical evaluation of different parameters, in order to design an actual plant with minimum energy requirement. The results of different parameters show that for DGA solvent, there will be an improvement in overall energy usage in the capture plant rather than MEA for some special cases. To gain the practical results, actual stages have been used for absorber and stripper instead of equilibrium stages. Copyright © 2011 John Wiley & Sons, Ltd.     

Analysis of equilibrium CO2 solubility in aqueous APDA and its potential blends with AMP/MDEA for postcombustion CO2 capture

The utility of polyamine-based solvent-activators for the possible application in postcombustion CO₂ capture technology has drawn considerable attention recently owing to its higher loading capacity as well as superior kinetics. The current work involves a comprehensive experimental cum theoretical investigation on the equilibrium solubility of CO₂ pertaining to aqueous N-(3-aminopropyl)-1,3-propanediamine and its blends with N-methyldiethanolamine and 2-amino-2-methyl-1-propanol. The analysis was conducted within the operating temperature and CO₂ partial pressure range of 303.2-323.2 K and 2-200 kPa, respectively. Two different mathematical models based on nonrigorous approaches such as equilibrium based modified Kent-Eisenberg (KE) model and a multilayer feedforward neural network model have been developed to correlate the CO₂ solubility data over a wide range of experimental conditions. Both the model predictions are well-validated with the experimental results. The reaction scheme as well as the prevalence of important reaction products was further confirmed with qualitative ¹³C NMR as well as ATR-FTIR analysis. Apart from these some of the important thermally induced transport properties viz, density, viscosity, and surface tension of the aqueous single and blended systems were measured and correlated with various consistent empirical models such as Redlich-Kister and Grunberg-Nissan model while surface tension data are modeled using temperature-based multiple linear regression technique.     

A coal-fired power plant integrated with biomass co-firing and CO2 capture for zero carbon emission

A promising scheme for coal-fired power plants in which biomass co-firing and carbon dioxide capture technologies are adopted and the low-temperature waste heat from the CO₂ capture process is recycled to heat the condensed water to achieve zero carbon emission is proposed in this paper. Based on a 660 MW supercritical coal-fired power plant, the thermal performance, emission performance, and economic performance of the proposed scheme are evaluated. In addition, a sensitivity analysis is conducted to show the effects of several key parameters on the performance of the proposed system. The results show that when the biomass mass mixing ratio is 15.40% and the CO₂ capture rate is 90%, the CO₂ emission of the coal-fired power plant can reach zero, indicating that the technical route proposed in this paper can indeed achieve zero carbon emission in coal-fired power plants. The net thermal efficiency decreases by 10.31%, due to the huge energy consumption of the CO₂ capture unit. Besides, the cost of electricity (COE) and the cost of CO₂ avoided (COA) of the proposed system are 80.37 $/MWh and 41.63 $/tCO₂, respectively. The sensitivity analysis demonstrates that with the energy consumption of the reboiler decreasing from 3.22 GJ/tCO₂ to 2.40 GJ/ tCO₂, the efficiency penalty is reduced to 8.67%. This paper may provide reference for promoting the early realization of carbon neutrality in the power generation industry.     

气化参数对高温空气气化的影响

介绍了生物质高温空气气化思想和系统的工作原理及其过程，并就气化参数对生物质高温空气气化的影响进行了深入的分析，结畏发现：随蒸汽消耗率的增加气化温度降低，而气化所得的煤气热值增大；气化温度随氮碳比的增大而升高，而气化所得的煤气热值却随氮碳比的增加而降低；煤气热值随气化温度的增加而增大，但是增加量不大。     

Reduction of CO2 capture plant energy requirement by selecting a suitable solvent and analyzing the operating parameters

Among various developed methods for CO₂ capturing from industrial flue gases, chemical absorption system is still considered as the most efficient technique, because of its lower energy requirement and also its applicability for low concentration of CO₂ in the inlet gas stream. Also, it can be used to retrofit the existed power plants, which are the major industrial CO₂ emission sources, without changing their design condition. Selection of a suitable solvent is the first parameter that should be considered in the design of capture plants that use absorption technology. The most important challenge for using chemical solvents is finding the optimum operating conditions to minimize the energy requirement. Study of technical parameters can be helpful to improve the overall capture plant efficiency. In this paper, CO₂ capture plant has been simulated for different solvents to compare their performance and energy requirement. To improve the plant overall efficiency, effect of the main operating factors such as amine flow rate, temperature, inlet gas temperature, and pressure has been studied in this paper. This analysis indicates the best chemical solvent for various cases of inlet flue gas. This parametric study reduces the overall energy requirement and helps design a cost‐effective plant. Copyright © 2012 John Wiley & Sons, Ltd.     

Influence of pyrolysis temperature and residence time on available nutrients for biochars derived from various biomass

To study the effect of pyrolysis temperature and residence time on properties and nutrient values, biochars were produced from corn stalk, rice hull, peanut hull and tobacco stalk at 200°C–700°C for one minute and 60 minutes, respectively. When temperatures and residence times increase, yields of biochars decrease accompany with higher pH values of biochars, changing the acidity of biochars from acidic to alkaline, and increasing total C and parts of the available N and K contents of biochars. These results indicate that feedstock and preparation technology are important factors affecting available nutrients of biochars.     

Rapid synthesis of chitin-based porous carbons with high yield,high nitrogen retention,and low cost for high-rate supercapacitors

It is a great challenge to simultaneously achieve high yield, high nitrogen retention, and low cost for chitin-based porous carbons (PCs) while obtaining highly porous structure. Herein, copper (II) chloride dihydrate (CuCl₂ 2H₂O) is innovatively used as the microwave absorber and also porogen for direct synthesis of PCs from chitin via microwave heating. A very short duration of 10 minutes is achieved for this synthesis, because microwave irradiation renders a rapid heating rate of 126°C min⁻¹ during the initial 5 minutes. In addition, the melted CuCl₂ wraps the chitin to preserve its overall structure during synthesis, thus obtaining a yield as high as 36% and a nitrogen retention up to 5.2%. Furthermore, a low temperature of about 600°C that triggers the redox reactions of CuCl₂ into Cu to achieve well-developed porous structure (specific surface area up to 1535 m² g⁻¹) is observed, suggesting a merit of low cost for this synthesis. The PC-based electrode exhibits not only a high specific capacitance of 227 F g⁻¹ at 0.5 A g⁻¹ in 6 mol L⁻¹ KOH electrolyte but also a good rate capability with a high capacitance retention of 67.7% even at an ultra-high current density of 50 A g⁻¹. Owing to these promising capacitive performances of PCs, the fabricated supercapacitor can remain 70.1% of the energy density when the power density was dramatically increased by 20 times.     

Experimental investigation on heat recovery from condensation of thermal power plant exhaust steam by a CO2 vapor compression cycle

In this paper, a method that utilizes CO₂ vapor compression thermodynamic cycle to recover low‐temperature heat from exhausted water steam of fossil fuel thermal power plants is reported. Experimental investigation was carried out to study the characteristics of low‐temperature heat recovery by liquid CO₂ evaporation process from vacuum exhausted steam condensation occurring at the turbine exit. Furthermore, measured heat recovery performances over one whole year are presented and discussed. Experimental results show that the present heat recovery process by CO₂ vapor compression cycle is able to operate stably. The yearly averaged water temperature at the CO₂ condenser outlet was measured at 87.5 °C with a COP value above 5.0. This high energy efficiency ratio is found to be mainly due to two factors: the transcritical CO₂ vapor compression and steam condensation phase change occurring on the CO₂ evaporator. The findings from this paper provide helpful guidelines for low‐temperature heat recovery system design and improving fossil fuel utilization efficiency. Copyright © 2013 John Wiley & Sons, Ltd.     

Thermodynamic performance evaluation of the CO2 parallel compression supermarket refrigeration system with a subcooler

Commercial refrigeration systems in supermarkets are intensive users of energy and CO₂ is recognized as the most promising refrigerant such systems. The CO₂ parallel compression system has been considered in medium- and low-temperature supermarket refrigeration systems, with auxiliary compressors to enhance system performance. This study is intended to investigate the effects of adding a subcooler in a CO₂ trans-critical supermarket refrigeration system with parallel compression (SPR system). Mathematical models based on mass and energy conservation are built. Optimization is performed for the gas cooler pressure and the receiver pressure for maximizing the coefficient of performance (COP). The performance of the parallel compression system with a subcooler is analyzed and compared to a baseline parallel compression system in different cities of China. A 6.8% average promotion at least in seasonal energy efficiency ratio (SEER) is predicted, and the energy consumption of the whole system decreases 7.1% totally in Haikou. Gas cooler, taking up 63.3% of the total exergy destruction rate, is the key component to increase efficiency through exergy analysis.     

Microbial electrolysis cells for production of methane from CO2: long‐term performance and perspectives

A methane‐producing microbial electrolysis cell (MEC) is a technology to convert CO₂ into methane, using electricity as an energy source and microorganisms as the catalyst. A methane‐producing MEC provides the possibility to increase the fuel yield per hectare of land area, when the CO₂ produced in biofuel production processes is converted to additional fuel methane. Besides increasing fuel yield per hectare of land area, this also results in more efficient use of land area, water, and nutrients. In this research, the performance of a methane‐producing MEC was studied for 188 days in a flat‐plate MEC design. Methane production rate and energy efficiency of the methane‐producing MEC were investigated with time to elucidate the main bottlenecks limiting system performance. When using water as the electron donor at the anode during continuous operation, methane production rate was 0.006 m³/m³ per day at a cathode potential of ?0.55 V vs. normal hydrogen electrode with a coulombic efficiency of 23.1%. External electrical energy input was 73.5 kWh/m³ methane, resulting in a voltage efficiency of 13.4%. Consequently, overall energy efficiency was 3.1%. The maximum achieved energy efficiency was obtained in a yield test and was 51.3%. Analysis of internal resistance showed that in the short term, cathode and anode losses were dominant, but with time, also pH gradient and transport losses became more important. The results obtained in this study are used to discuss the possible contribution of methane‐producing MECs to increase the fuel yield per hectare of land area. Copyright © 2011 John Wiley & Sons, Ltd.     

Green synthesis of MCM-41 derived from renewable biomass and construction of VOx-Modified nickel phyllosilicate catalyst for CO2 methanation

In order to achieve green synthesis of MCM-41 and address the sintering problem of Ni-based catalyst supported on silica material, MCM-41 with regular spherical morphology was prepared using sodium silicate extracted from renewable equisetum fluviatile as silicon source, and then a group of nickel phyllosilicates were synthesized via the reaction of MCM-41 sphere and nickel nitrate under hydrothermal condition. Much denser nanosheets corresponding to lamellar nickel phyllosilicate were formed on the surface of MCM-41 sphere with the raise of hydrothermal temperature in the range of 180–220 °C, resulting in the nickel content varying from 17.2 to 41.8 wt%. Fine Ni particles with size smaller than 6 nm could be obtained on the 750^oC-reduced catalyst owing to the strong nickel-silica interaction derived from Ni-phyllosilicate. After the addition of V₂O₅ promoter, Ni particle size was further reduced to around 4.5 nm at high Ni loading above 30 wt%. Vanadium species was in the mixed valence state of V(III), V(IV) and V(V) after reduction, which increased the electron cloud density of Ni⁰, resulting in high catalytic activity of the VO_x-modified Ni-phyllosilicate catalyst for CO₂ methanation. In a 100 h-400^oC-lifetime test and 600 °C-steam hydrothermal treatment, the VO_x-modified Ni-phyllosilicate catalyst also showed high long-term stability, excellent sintering resistance of metallic nickel particles and high hydrothermal stability due to the strong surface confinement effect of nickel phyllosilicate and promotion of VO_x species. In all, this work provided a green synthesis of MCM-41 as well as an efficient Ni/SiO₂ catalyst derived from nickel phyllosilicate for CO₂ methanation.     

Integration of gas switching combustion in a humid air turbine cycle for flexible power production from solid fuels with near-zero emissions of CO2 and other pollutants

This work presents a novel plant configuration for power production from solid fuels with integrated CO₂ capture. Specifically, the Gas Switching Combustion (GSC) system is integrated with a Humid Air Turbine (HAT) power cycle and a slurry fed entrained flow (GE-Texaco) gasifier or a dry fed (Shell) gasifier with a partial water quench. The primary novelty of the proposed GSC-HAT plant is that the reduction and oxidation reactor stages of the GSC operation can be decoupled allowing for flexible operation, with the oxygen carrier serving as a chemical and thermal energy storage medium. This can allow the air separation unit, gasifier, gas clean-up, CO₂ compressors and downstream CO₂ transport and storage network to be downsized for operation under steady state conditions, while the reactors and the power cycle operate flexibly to follow load. Such cost-effective flexibility will be highly valued in future energy systems with high shares of variable renewable energy. The GSC-HAT plant achieves 42.5% electrical efficiency with 95.0% CO₂ capture rate with the Shell gasifier, and 41.6% efficiency and 99.2% CO₂ capture with the GE gasifier. An exergy analysis performed for the GE gasifier case revealed that this plant reached 38.9% exergy efficiency, only 1.6%-points below an inflexible GSC-IGCC benchmark configuration, while reaching around 5%-points higher CO₂ capture rate. Near-zero SO_x and NO_x emissions are achieved through pre-combustion gas clean-up and flameless fuel combustion. Overall, this flexible and efficient near-zero emission power plant appears to be a promising alternative in a future carbon constrained world with increasing shares of variable renewables and more stringent pollutant (NO_x, SO_x) regulations.     

Low temperature sugar cane bagasse pyrolysis for the production of high purity hydrogen through steam reforming and CO2 capture

Biomass pyrolysis offers a fast route to produce elevated yields towards highly valued liquid products. This research aims the determination of optimal experimental conditions for a slow and low temperature pyrolysis to produce the highest yield towards condensable (CVM) and non-condensable (NCVM) volatile matter from Mexican cane bagasse and to quantify and characterize the compounds that constitute CVM and NCVM obtained. Results indicate that yield towards volatiles is strongly dependent on temperature. The highest yield was achieved at temperatures greater than 500 °C at a heating rate of 10 °C/min, residence time of 60 min and a particle size between of 420 and 840 μm. Product quantification under isothermal conditions determined that at 550 °C the NCVM, CVM and solid residue was of 26, 57 and 16%, respectively. Preliminary thermodynamic analysis of steam reforming and CO₂ absorption reactions using one of the main CVM products resulted in a potential high hydrogen production yield.     

Parametric study of chemical looping combustion for tri‐generation of hydrogen,heat, and electrical power with CO2 capture

In this article, a novel cycle configuration has been studied, termed the extended chemical looping combustion integrated in a steam‐injected gas turbine cycle. The products of this system are hydrogen, heat, and electrical power. Furthermore, the system inherently separates the CO₂ and hydrogen that is produced during the combustion. The core process is an extended chemical looping combustion (exCLC) process which is based on classical chemical looping combustion (CLC). In classical CLC, a solid oxygen carrier circulates between two fluidized bed reactors and transports oxygen from the combustion air to the fuel; thus, the fuel is not mixed with air and an inherent CO₂ separation occurs. In exCLC the oxygen carrier circulates along with a carbon carrier between three fluidized bed reactors, one to oxidize the oxygen carrier, one to produces and separate the hydrogen, and one to regenerate the carbon carrier. The impacts of process parameters, such as flowrates and temperatures have been studied on the efficiencies of producing electrical power, hydrogen, and district heating and on the degree of capturing CO₂. The result shows that this process has the potential to achieve a thermal efficiency of 54% while 96% of the CO₂ is captured and compressed to 110 bar. Copyright © 2005 John Wiley & Sons, Ltd.     

Perspectives for the direct firing of biomass as a supplementary fuel in combined cycle power plants

An analysis of the performance of a gas turbine–steam turbine combined cycle with supplementary firing has been carried out. Natural gas is fired in the main combustor of the cycle, whereas biomass fuel is considered as the supplementary fuel. Although, supplementary firing is found to reduce the overall cycle efficiency, the low cost of biomass and the CO₂‐neutral attribute of its combustion reduce the specific fuel cost and specific CO₂ emission. The effects of pressure and temperature ratios of the topping cycle and main steam conditions of the bottoming cycle on the performance parameters of the combined cycle have been studied at different degrees of supplementary firing. The topping cycle temperature ratio is found to be the most critical parameter and its low value gives substantial advantages in lowering the fuel cost and CO₂ emission. Marginal advantages are also achieved at higher pressure ratio and better bottoming cycle main steam conditions. Copyright © 2008 John Wiley & Sons, Ltd.