Activated olive mill waste-based hydrochars as selective adsorbents for CO2 capture under postcombustion conditions

Porous carbons are considered to be promising sorbents for carbon capture and sequestration. As precursors, the use of biomass materials has acquiring special interest due to its low cost and high availability. Among all the possibilities to convert low-value biomass into these interesting sorbents, hydrothermal carbonization has demonstrated several advantages such as lower energy consumption over pyrolysis. In this work, activated hydrochars using two-phase olive mill waste as precursor have been prepared through physical and chemical activation using CO2 and KOH, respectively. Additionally, with the aim to study the influence of the nitrogen on their adsorption capacity, N-doped adsorbents have been prepared through a one-step hydrothermal carbonization. The behaviour of these adsorbents has been studied in terms of CO2 uptake capacity at an absolute pressure of 15 kPa and temperatures of 0, 25 and 75 °C, apparent selectivity towards CO2 over N2, and isosteric heat of adsorption. Among all these samples, the physically activated hydrochar appears to be the best due to its higher CO2 uptakes, adsorption rates and values of selectivity at 25 °C. Therefore, considering these results, doping these materials with nitrogen does not appear to enhance their adsorption properties, contrary to what some authors have previously reported. © 2020 Elsevier B.V

Assembly and electrochemical testing of renewable carbon-based anodes in SIBs: a practical guide

Sodium-ion batteries (SIBs) are considered as a promising candidate to replace lithium-ion batteries (LIBs) in large-scale energy storage applications. Abundant sodium resources and similar working principles make this technology attractive to be implemented in the near future. However, the development of high-performance carbon anodes is a focal point to the upcoming success of SIBs in terms of power density, cycling stability, and lifespan. Fundamental knowledge in electrochemical and physicochemical techniques is required to properly evaluate the anode performance and move it in the right direction. This review aims at providing a comprehensive guideline to help researchers from different backgrounds (e.g., nanomaterials and thermochemistry) to delve into this topic. The main components, lab configurations, procedures, and working principles of SIBs are summarized. Moreover, a detailed description of the most used electrochemical and physicochemical techniques to characterize electrochemically active materials is provided

Adsorption performance of physically activated biochars for postcombustion Co2 capture from dry and humid flue gas

In the present study, the performance of four biomass-derived physically activated biochars for dynamic CO2 capture was assessed. Biochars were first produced from vine shoots and wheat straw pellets through slow pyrolysis (at pressures of 0.1 and 0.5 MPa) and then activated with CO2 (at 0.1 MPa and 800 C) up to different degrees of burn-off. Cyclic adsorption-desorption measurements were conducted under both dry and humid conditions using a packed-bed of adsorbent at relatively short residence times of the gas phase (12-13 s). The adsorbent prepared from the vine shoots-derived biochar obtained by atmospheric pyrolysis, which showed the most hierarchical pore size distribution, exhibited a good and stable performance under dry conditions and at an adsorption temperature of 50 C, due to the enhanced CO2 adsorption and desorption rates. However, the presence of relatively high concentrations of water vapor in the feeding gas clearly interfered with the CO2 adsorption mechanism, leading to significantly shorter breakthrough times. In this case, the highest percentages of a used bed were achieved by one of the other activated biochars tested, which was prepared from the wheat straw-derived biochar obtained by pressurized pyrolysis

Influence of pressure and temperature on key physicochemical properties of corn stover-derived biochar

This study focuses on analyzing the effect of both the peak temperature and pressure on the properties of biochar produced through slow pyrolysis of corn stover, which is a common agricultural waste that currently has little or no value. The pyrolysis experiments were carried out in a fixed-bed reactor at different peak temperatures (400, 525 and 650 °C) and absolute pressures (0.1, 0.85 and 1.6 MPa). The inert mass flow rate (at NTP conditions) was adjusted in each test to keep the gas residence time constant within the reactor. The as-received corn stover was pyrolyzed into a biochar without any physical pre-treatment as a way to reduce the operating costs. The properties of biochars showed that high peak temperature led to high fixed-carbon contents, high aromaticity and low molar H:C and O:C ratios; whereas a high pressure only resulted in a further decrease in the O:C ratio and a further increase in the fixed-carbon content. Increasing the operating pressure also resulted in a higher production of pyrolysis gas at the expense of water formation

Biochar production through slow pyrolysis of different biomass materials: Seeking the best operating conditions

In the last years, special attention has been focused on analyzing the effect of pyrolysis conditions (mainly peak temperature) on the yield and properties of produced biochar. Given that the nature of biomass plays a key role in the pyrolysis process, it becomes really difficult to establish generic trends and correlations, which can be used for any biomass feedstock to predict the properties of derived biochar. Thus, more experimental studies focused on a given biomass source are still needed with the aim of providing reliable data for further research goals. In addition, a number of techniques have been proposed to estimate the long-term stability of biochar in a relatively easy and fast way (e.g., recalcitrance index, percentage of aromatic carbon, H2O2 oxidation, etc.). Please click on the file below for full content of the abstract

Study on the effects of using a carbon dioxide atmosphere on the properties of vine shoots-derived biochar

This study analyzes the effects of using a different atmosphere (pure N2 or pure CO2) at two levels of absolute pressure (0.1 and 1.1 MPa) on the pyrolysis of vine shoots at a constant peak temperature of 600 °C. Recycling CO2 from residual flue gases into the pyrolysis process may be economically beneficial, since CO2 can replace the use of an expensive N2 environment. In addition, the use of a moderate pressure (e.g., 1.1 MPa) can result in higher carbonization efficiencies and an improvement in the pyrolysis gas (in terms of yield and composition). Results from our study suggest that the use of CO2 instead of N2 as pyrolysis environment led to similar carbonization efficiencies (i.e., fixed-carbon yields) and mass yields of biochar. The chemical properties related to the potential stability of biochar (i.e., fixed-carbon content and molar H:C and O:C ratios) were very similar for both pyrolysis atmospheres. Under an atmosphere of CO2, the yield of produced CO2 was drastically decreased at the expense of an increase in the yield of CO, probably as a consequence of the promotion of the reverse Boudouard reaction, especially at high pressure. The enhanced reverse Boudouard reaction can also explain the relatively high BET specific surface area and the macro-porosity development observed for the biochar produced under a CO2 environment at 1.1 MPa. In summary, the pressurized pyrolysis of biomass under an atmosphere of CO2 appears as a very interesting route to produce highly stable and porous biochars and simultaneously improving the yield of CO

Evolution of the mass-loss rate during atmospheric and pressurized slow pyrolysis of wheat straw in a bench-scale reactor

In the present study, the effects of the absolute pressure (0.1 or 0.5 MPa) and the reactor atmosphere (pure N2 or a mixture of CO2/N2) on the pyrolysis behavior of wheat straw pellets (at 500 °C) were investigated. The most interesting aspect of this work was the use of a weighing platform (with a maximum capacity of 100 kg and a resolution of 0.5 g) to monitor the real-time mass-loss data for the biomass sample (with an initial mass of 400 g). It was observed that an increased pressure considerably affects the mass-loss profiles during the pyrolysis process, leading to higher devolatilization rates in a shorter period of time. Regardless of the pyrolysis atmosphere, an increase in the absolute pressure led to higher yields of gas at the expense of produced water and condensable organic compounds. This finding could be due to the fact that an increased pressure favors the exothermic secondary reactions of the intermediate volatile organic compounds in both liquid and vapor phases. The switch from pure N2 to a mixture of CO2 and N2 at 0.1 MPa also led to a remarkable increase in the yield of produced gas at the expense of the total liquid. This could be mainly due to the promotion of the thermal cracking of the volatile organic compounds at a high partial pressure of CO2, which is also consistent with the measured higher yields of CH4 and CO. The increased yield of CO can also be seen as a direct result of the enhanced reverse Boudouard reaction, which can also explain the much higher specific surface area (and ultra-micropore volume) measured for the biochar produced under the same operating conditions (0.1 MPa and a mixture CO2/N2 as pyrolysis medium)

Evolution of the Mass Loss Rate During Atmospheric and Pressurized Slow Pyrolysis of Wheat Straw in a Bench-Scale Reactor

A deep study focused on the significant effect of the absolute pressure on the yield of produced gas during the slow pyrolysis of biomass was carried out. In addition, the evolution of the mass loss rate linked to the pyrolysis process was also analyzed

Using a Fixed-Bed of Wheat Straw-Derived Biochar to Enhance Cracking of a Mixture of Four Pyrolysis Vapor Model Compounds

The aim of this work is to test the capacity of a biochar-based porous material to enhance the cracking of pyrolysis vapors. Biochar is a sustainable material obtained from renewable resources and a relatively low cost alternative to the metal-containing catalysts used in catalytic cracking