Effect of Porosity and Surface Chemistry on CO2 and CH4 Adsorption in S-Doped and S-/O-co-Doped Porous Carbons

The aim of this study was to determine the adsorption performance of a petroleum pitch-based activated carbon (PPAC1:3) before and after a post-treatment with H2S. In the first step, a microporous activated carbon (PPAC1:3) with a highly developed porous structure was produced through a chemical activation route with KOH. Afterward, the synthesized activated carbon was thermally treated yielding two different series of functionalized activated carbons: (i) a series of carbons were treated directly with H2S at elevated temperatures (600 °C and 800 °C), and (ii) a series of carbons were generated by combining an oxidation treatment with plasma followed by H2S treatment at elevated temperatures (600 °C and 800 °C). The chemical and structural characteristics of the S-doped and S-/O-co-doped porous carbons were investigated by means of different experimental techniques, such as XRD, RAMAN, FESEM, XPS, TPD, N2, and CO2 adsorption, and finally tested in CO2 and CH4 adsorption at atmospheric and high pressure. The functionalized porous carbons possessed specific surface areas of 2420–2690 m2/g, total pore volume of 1.05–1.18 cm3/g, and sulfur content up to 2.55 atom % (the sulfur content of the original carbon was 0.19%). After a careful analysis of the carbon dioxide and methane uptake at atmospheric (0.1 MPa) and high pressure (4 MPa), adsorption results confirm that the microporous structure is the main structural parameter defining the adsorption performance and, to a lower extent, the surface chemistry. Overall, a significant improvement in the total uptake can be appreciated after the H2S treatment.This research was funded by MCIN, and NATO. The authors would like to acknowledge financial support from the Ministerio de Ciencia e Innovación—MCIN (projects PID2019-108453GB-C21, MCIN/AEI/10.13039/501100011033 and EU “NextGeneration/PRTR” (project PCI2020-111968/3D-Photocat)), and NATO SPS program (project G5683)

Effect of the porous structure in carbon materials for CO2 capture at atmospheric and high-pressure

Activated carbons prepared from petroleum pitch and using KOH as activating agent exhibit an excellent behavior in CO2 capture both at atmospheric (∼168 mg CO2/g at 298 K) and high pressure (∼1500 mg CO2/g at 298 K and 4.5 MPa). However, an exhaustive evaluation of the adsorption process shows that the optimum carbon structure, in terms of adsorption capacity, depends on the final application. Whereas narrow micropores (pores below 0.6 nm) govern the sorption behavior at 0.1 MPa, large micropores/small mesopores (pores below 2.0–3.0 nm) govern the sorption behavior at high pressure (4.5 MPa). Consequently, an optimum sorbent exhibiting a high working capacity for high pressure applications, e.g., pressure-swing adsorption units, will require a poorly-developed narrow microporous structure together with a highly-developed wide microporous and small mesoporous network. The appropriate design of the preparation conditions gives rise to carbon materials with an extremely high delivery capacity ∼1388 mg CO2/g between 4.5 MPa and 0.1 MPa. Consequently, this study provides guidelines for the design of carbon materials with an improved ability to remove carbon dioxide from the environment at atmospheric and high pressure.Financial support from MINECO: Strategic Japanese-Spanish Cooperative Program (PLE2009-0052) and Generalitat Valenciana (PROMETEO/2009/002)

Very high methane uptake on activated carbons prepared from mesophase pitch: A compromise between microporosity and bulk density

Two petroleum residues were pyrolyzed under two different conditions to obtain pitches with low or high mesophase content. The effect of the KOH: precursor ratio and the activation temperature on the packing density and porous texture of the carbons have been studied and optimized. Activated carbons combining high micropore volume (>1 cm3/g) and high packing density (0.7 g/cm3) have been successfully prepared. Regarding excess methane adsorption capacities, the best results (160 cm3 (STP)/cm3 at 25 °C and 3.5 MPa) were obtained using the pitch with the higher content of the more organized mesophase, activated at relatively low temperature (700 °C), with a medium KOH: precursor ratio (3:1). Some of the activated carbons exhibit enhanced adsorption capacity at high pressure, giving values as high as 175 cm3 (STP)/cm3 at 25 °C and 5 MPa and 200 cm3 (STP)/cm3 at 25 °C and 10 MPa (the same amount as in an empty cylinder but at half of the pressure), indicating a contribution of large micropores and narrow mesopores to adsorption at high pressure. The density of methane in pores between 1 and 2.5 nm at pressure up to 10 MPa was estimated to understand their contribution to the total adsorption capacity.Authors acknowledge financial support from MINECO: Project MAT2013-45008-p and CONCERT Project-NASEMS (PCIN-2013-057) and Generalitat Valenciana (PROMETEO/2009/002)

Improved thermal management in HKUST-1 composites upon graphite flakes incorporation: Hydrogen adsorption properties

HKUST-1-based composites have been synthesized through the incorporation of synthetic graphite flakes in the MOF synthesis media. The presence of flakes gives rise to high quality HKUST-1 crystals, combining different morphologies (octahedral-shape crystals, cauliflower-shape crystals and truncated pyramids). The incorporation of graphite in the composites improves the structural stability of the embedded nanocrystals upon a conforming step at 377 kg/cm2 (0.5 tons), with limited structural damage (below 10% BET surface area reduction as compared to the 40% observed for pure HKUST-1). Furthermore, composites exhibit a significant improvement in thermal management, associated with the excellent thermal and electrical properties of the graphite microdomains incorporated. The improved stability of the composites is also reflected in the adsorption performance for hydrogen at atmospheric pressure and cryogenic temperatures, with a significant preservation of the adsorption properties (gravimetric capacity, <15% decrease vs powders) in the monoliths containing graphite. The best adsorption performance is achieved with sample HKUST-1@10GF, in monolithic form, with a volumetric excess uptake at 0.1 MPa and −195 °C close to 18.7 g/L. This value is among the best described in the literature for monolithic MOFs under similar adsorption conditions.Authors would like to acknowledge financial support from Ministerio de Ciencia e Innovación (Project PID2019-108453GB-C21), Conselleria de Innovación, Universidades, Ciencia y Sociedad Digital, Generalitat Valenciana (project CIPROM/2021/022) and European Union: Horizon Europe (project MOST-H2; Grant agreement no. 101058547). M. R.-C. and M. M. thank the project PID2019-104379RB-C22 funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe” for financial support. Authors would like to thank Imerys Graphite & Carbon Ltd. (Dr. Raffaele Gilardi) for the supply of the graphite flakes

The scientific impact of Francisco Rodríguez-Reinoso in carbon research and beyond

This review article is dedicated to the memory of Francisco (Paco) Rodríguez-Reinoso (Granada 1941 - Alicante 2020). Paco dedicated more than 56 years of his life to research on carbon materials, covering from their synthesis and characterization, to their evaluation using a range of processes such as gas adsorption/separation, heterogeneous catalysis, and drug delivery, among others. His extensive research was mainly performed in the Advanced Materials Laboratory (LMA) located at the University of Alicante, Spain. This research has been reflected in more than 400 research articles in high quality international journals. This review article summarizes some of Paco’s main achievements in carbon-related research emphasizing his main contributions and perspectives in the field

Preparation of Porous Carbons from Petroleum Pitch and Polyaniline by Thermal Treatment for Methane Storage

The methane storage capacity of two series of activated carbons, obtained from a graphitizable (petroleum pitch) and a nongraphitizable precursor (polyaniline), has been evaluated after different thermal treatments. Both samples have been pyrolyzed and subsequently activated with KOH to obtain a highly developed microporous structure. After the synthesis, samples have been heat-treated at different temperatures, between 1000 and 1500 °C, to introduce structural changes that could have an effect on two parameters defining the methane adsorption capacity: the porosity and the density. The physicochemical characterization of the samples has shown that the activation process destroys the pregraphitic structure, with a development of microporosity. However, during the subsequent thermal treatment, the graphitic order can be partially recovered, especially with the graphitizable material, together with a decrease in the micropore volume and an enhancement of the density. The electrical conductivity of the activated carbon obtained from a graphitizable precursor improves much more with an increase in the temperature of the thermal treatment than that of the activated carbon obtained from a nongraphitizable precursor. It is worth highlighting that the high methane adsorption capacities achieved with some of these samples, reaching values as high as 180 V/V. These values are among the highest reported in the literature so far.The authors would like to acknowledge financial support from MINECO (MAT2016-80285-p)

High-Pressure Methane Storage in Porous Materials: Are Carbon Materials in the Pole Position?

Natural gas storage on porous materials (ANG) is a promising alternative to conventional on-board compressed (CNG) or liquefied natural gas (LNG). To date, Metal–organic framework (MOF) materials have apparently been the only system published in the literature that is able to reach the new Department of Energy (DOE) value of 263 cm3 (STP: 273.15 K, 1 atm)/cm3; however, this value was obtained by using the ideal single-crystal density to calculate the volumetric capacity. Here, we prove experimentally, and for the first time, that properly designed activated carbon materials can really achieve the new DOE value while avoiding the additional drawback usually associated with MOF materials (i.e., the low mechanical stability under pressure (conforming), which is required for any practical application).Authors acknowledge financial support from MINECO: Strategic Japanese−Spanish Cooperation Program (No. PLE2009-0052), Concert Project-NASEMS (No. PCIN-2013-057) and Generalitat Valenciana (No. PROMETEO/2009/002)

Activated carbon from polyurethane residues as molecular sieves for kinetic adsorption/separation of CO2/CH4

Activated carbon-based molecular sieves were synthetized, characterized and their kinetics of adsorption were evaluated to be used in separation processes of CO2/CH4 mixtures. Polyurethane (PU) foams were used as carbon precursors and the PU-derived carbons were physical activated with CO2. All the samples present a preferential adsorption of CO2 over methane in kinetic adsorption experiments. Samples activated at 800 ºC during 6 h exhibited the highest selectivity due to the absence of methane adsorption at lower resident times, which makes those samples very interesting for industrial processes of natural gas purification. Kinetic studies were performed to explain the kinetic profiles obtained, confirming that in the samples with smallest pore size, intraparticle diffusion was the limiting step, evidencing that certain oxygen groups favour CO2 adsorption, whereas adsorption was the limiting step in the samples with wider pores.This research was funded by MINECO (MAT2016-80285-p), GV (PROMETEOII/2014/004), H2020 (MSCA-RISE-2016/NanoMed Project). Financial support from the National Council for Scientific and Technological Development (CNPq-Brazil) is also acknowledged

Non-porous reference carbon for N2 (77.4 K) and Ar (87.3 K) adsorption

A new non-porous carbon material from granular olive stones has been prepared to be used as a reference material for the characterization of the pore structure of activated carbons. The high precision adsorption isotherms of nitrogen at 77.4 K and argon at 87.3 K on the newly developed sample have been measured, providing the standard data for a more accurate comparative analysis to characterize disordered porous carbons using comparative methods such as t- and αS-methods.Financial support from a Strategic Japanese–Spanish Cooperative Program: Nanotechnologies and New Materials for Environmental Challenges (PLE2009-0052). K.K. was supported by Exotic Nanocarbons, Japan Regional Innovation Strategy Program by the Excellent, JST

Activated carbon materials with a rich surface chemistry prepared from L-cysteine amino acid

A series of activated carbon materials have been successfully prepared from a non-essential amino acid, such as L-cysteine. The synthesized carbons combine a widely developed porous structure (BET surface area up to 1000 m2/g) and a rich surface chemistry (mainly oxygen, nitrogen and sulphur functionalities). These surface functional groups are relatively stable even after a high temperature thermal treatment (O>N∼S). Experimental results show that these samples with a rich surface chemistry exhibit a significant improvement in their hydrophilic character. Although the role of the surface functional groups is less pronounced for the adsorption of non-polar molecules such as CO2, CH4 and C2H4, their adsorption at atmospheric pressure is to some extend conditioned by the characteristics of the adsorbent-adsorbate interactions. The synthesized carbons exhibit an excellent adsorption performance for CO2 (up to 3 mmol/g at 0°C). Furthermore, samples with a low activation degree exhibit molecular sieving properties with very promising CO2/CH4 (up to 4.5) and C2H4/CH4 (up to 6) selectivity ratios. These results anticipate that non-essential amino acids are a versatile platform to obtain carbon materials combining a tailored porous structure and rich multifunctional surface chemistry and with potential application for gas adsorption/separation processes.Authors would like to acknowledge financial support from the MINECO (Projects PID2019-108453GB-C21 and PCI2020-111968/ERANET-M/3D-Photocat) and NATO SPS program (Project G5683)