Formation of Nanocarbon Spheres by Thermal Treatment of Woody Char from Fast Pyrolysis Process

Influences of thermal treatment conditions of temperature, reaction cycle and time, and purge gas type on nanocarbon formation over bio-chars from fast pyrolysis and effects of thermal reaction cycle and purge gas type on bio-char surface functional groups were investigated by temperature-programmed desorption (TPD) and temperature-programmed reduction methods. Nanospheres occurred on bio-chars under the activation temperature of 700°C; more nanospheres occurred when temperature increased to 900°C. Further increase of temperature to 1100°C yielded bio-char surfaces covered with a layer of nanospheres between 20 and 50 nm. More carbon nanospheres formed by increasing thermal cycles and reaction time. Scanning electron microscope images of char surfaces showed there were fewer or no nanoparticles produced using H2 as the purge gas and they were porous. TPD results indicated that H2, H2O, CH4, CO, and CO2 in gas phases evolved from chars heated to 1000°C during the first heating cycle. H2 and CH4 peaked at 750 and 615°C, respectively. Both H2O and CO had two peaks, and CO2 had a broad peak. Only trace amounts of H2 and CO were detected in the second cycle. There was no detection for CH4, H2O, and CO2 after the second cycle

Synthesis and Characterization of Carbon Nanospheres Obtained by Hydrothermal Carbonization of Wood-derived and Other Saccharides

Carbon nanospheres were synthesized by hydrothermal carbonization (HTC) of four different carbon sources: xylose, glucose, sucrose, and pine wood derived saccharides. The obtained carbon nanospheres were characterized for particle morphology and size, and surface functional groups. Morphological and structural differences among these saccharides derived HTC carbons were clearly observed. Scanning electron microscopy images of carbon nanospheres from HTC of xylose showed uniform spherical particles with diameters around 80 nm, while carbon nanospheres obtained from glucose, sucrose, and pine-derived saccharides had particle size  in the range of 100-150 nm, 300-400 nm, and 50-100 nm, respectively. Carbon dioxide and carbon monoxide were primary gaseous phase products during the HTC process. In addition, methane, propane, hydrogen, and benzene were detected in the gas phase.Citation: Yan, Q., Li, R., Toghiani, H., Cai, Z., and Zhang, J. (2015). Synthesis and Characterization of Carbon Nanospheres Obtained by Hydrothermal Carbonization of Wood-derived and Other Saccharides. Trends in Renewable Energy, 1(2), 119-128. DOI: 10.17737/tre.2015.1.2.001

Catalytic thermal conversion of kraft lignin to multi-layer graphene materials

The objective of this research is to develop a scalable manufacturing process for high-volume production of low-cost graphene materials from lignin. The process includes preparation of catalyst-lignin precursors, pretreatment of precursors, and catalytic graphitization of kraft lignin to graphene materials. A growth concept, “catalytic thermal molecular welding (CTMW)” technique is proposed and validated to produce graphene materials from solid carbon resources. CTMW technique is a single process with two stages, i.e., the carbon-encapsulated metal nanostructures are first prepared. Then in the second stage these core-shell structures are opened by “scissoring molecules”, the cracked carbon shell units are welded and reconstructed to multilayer graphene materials under high temperature with selected “welding reagent gases” like light hydrocarbons (methane, natural gas, etc.) and hydrogen. Multi-layer nano-shell structure-based graphene materials, such as fluffy graphene, graphene chains, multi-layer graphene nanoplatelets, flatten or curved sheet-like graphene can be produced through altering fabrication conditions. The effects of transitional metal catalysts (Ni, Cu, Fe, and Mo) on the yields and structures of multi-layer nano-shell structure-based graphene materials from lignin are compared. The effects of the iron chemical resources (Fe(NO3)3, FeCl2, FeCl3, and Fe2O3 (nano)), iron loading on the yields and structures of multi-layer graphene materials from lignin are also examined. The influences of temperature, heating rate, heating time, metal-lignin precursor particle size, and welding reagent gas types on the yield of multi-layer graphene materials from lignin resources are investigated. Welding temperatures are optimized as1,000°C or above, with heating rates of 10°C or above. Welding gases including, argon (Ar), hydrogen (H2), methane (CH4), natural gas (NG), and mixed of these gases, are used at flow rates from 20 to 300 mL/min. Heating time is controlled between 0 to 5 hours. The effect of precursor particle size on final products is examined between 44 to 426 microns (Delta-m)

Production of COx-Free Hydrogen and Few-Layer Graphene Nanoplatelets by Catalytic Decomposition of Methane over Ni-Lignin-Derived Nanoparticles

Nickel (Ni)-lignin nanocomposites were synthesized from nickel nitrate and kraft lignin then catalytically graphitized to few-layer graphene-encapsulated nickel nanoparticles (Ni@G). Ni@G nanoparticles were used for catalytic decomposition of methane (CDM) to produce COx-free hydrogen and graphene nanoplatelets. Ni@G showed high catalytic activity for methane decomposition at temperatures of 800 to 900 °C and exhibited long-term stability of 600 min time-on-stream (TOS) without apparent deactivation. The catalytic stability may be attributed to the nickel dispersion in the Ni@G sample. During the CDM reaction process, graphene shells over Ni@G nanoparticles were cracked and peeled off the nickel cores at high temperature. Both the exposed nickel nanoparticles and the cracked graphene shells may participate the CDM reaction, making Ni@G samples highly active for CDM reaction. The vacancy defects and edges in the cracked graphene shells serve as the active sites for methane decomposition. The edges are continuously regenerated by methane molecules through CDM reaction

Thermal Decomposition of Kraft Lignin under Gas Atmospheres of Argon, Hydrogen, and Carbon Dioxide

The behaviors of thermal decomposition of kraft lignin under three different gases (Ar, CO2, or H2) were analyzed and compared using a temperature-programmed decomposition-mass spectrometry (TPD-MS) system. Experimental results indicated that Ar atmosphere produced the highest yield of solid chars, while H2 atmosphere generated the highest yield of liquids and CO2 atmosphere had the highest yield of gases. TPD-MS results showed that H2 atmosphere was consumed at the temperature range from 205 to 810 °C and CO2 atmosphere was consumed at the temperature range from 185 to 1000 °C. The H2 promoted the cleavage of lignin side chains and significantly enhanced the formation of CH4, C6H6, HCHO, C6H5OH, CH3OH, and tars. The percentages of water in produced liquids were 90.1%, 85.3%, and 95.5% for Ar, H2, and CO2 as atmosphere, respectively. The H2 yielded more organic chemicals in produced liquids compared to the other two gases. The observed organic chemicals were mainly acetic acid, phenols, ketones, alcohols, aldehydes, and esters. BET surface areas of solid products were 11.3, 98.5, and 183.9 m2/g for Ar., H2, and CO2 as the atmosphere, respectively. C–H–O–N–S elemental and morphology analyses on solid products indicated that the lowest carbon content and the highest oxygen content were obtained if Ar atmosphere was used, while H2 and CO2 yielded more carbon in final solid products. Solid products obtained under CO2 or H2 atmosphere contained sphere-shaped nanoparticles

Synthesis, Characterization and Catalytic Studies of Carbon-Based Nano Materials

Nano-scaled carbons were produced by thermal treatment of pine wood chips and bio-char. The influence of temperature, heating rate, pyrolysis time, and type and flow rate of purge gas on the production of nano-carbons was investigated. Using TEM and SEM, different carbon-based nanomaterials were observed in the prepared samples. The effect of metal ion doping on the bio-char was also investigated. Highly functionalized nano carbonaceous materials were synthesized by low temperature hydrothermal carbonization (HTC) using glucose, sucrose, xylose, and cellulose. Carbon-encapsulated iron (Fe@C) core-shell particles were also synthesized by the HTC method and used as catalyst for Fischer-Tropsch synthesis to produce liquid hydrocarbons from syngas; it showed excellent activity. Nano-structured Co-Mo carbides over several nano-sized carbon materials were prepared using the carbothermal reduction and carbothermal hydrogen reduction methods. Nano-structured Co-Mo carbides derived from Vulcan® XC-72 were used as the catalyst to produce higher alcohols

Effect of Solvents on Fe–Lignin Precursors for Production Graphene-Based Nanostructures

Kraft lignin was catalytically graphitized to graphene-based nanostructures at high temperature under non-oxidative atmospheres. To obtain the best catalytic performance, a uniform catalyst–lignin mixture must be made by bonding transitional metal (M) ions to oxygen (O), sulfur (S) or nitrogen (N)-containing functional groups in kraft lignin. One of the strategies is to dissolve or disperse kraft lignin in a suitable solvent, whereby the polymer chains in the condensed lignin molecules will be detangled and stretched out while the functional groups are solvated, and when mixing lignin solution with catalyst metal solution, the solvated metal ions in an aqueous solution can diffuse and migrate onto lignin chains to form M-O, M-S, or M-N bonds during the mixing process. Therefore, solvent effects are important in preparing M–lignin mixture for production of graphene-based nanostructures. Fe–lignin precursors were prepared by dissolving lignin with different solvents, including water, methanol, acetone, and tetrahydrofuran (THF). Solvent effects on the catalytic performance, size and morphology of graphene-based nanostructures were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HRTEM), and nitrogen sorption measurements. The sizes, morphologies, and catalytic properties of the products obtained from Fe–lignin precursors are greatly influenced by the solvents used. It was found that Fe–lignin (THF) had the highest iron dispersion and the smallest iron particle size. Furthermore, Fe–lignin (THF) exhibited the best catalytic performance for graphitization of kraft lignin while the graphitization degree decreased in the order: Fe–lignin(THF) > Fe–lignin(Acetone) > Fe–lignin(methanol) > Fe–lignin(water)

Production of COx-Free Hydrogen and Few-Layer Graphene Nanoplatelets by Catalytic Decomposition of Methane over Ni-Lignin-Derived Nanoparticles

Nickel (Ni)-lignin nanocomposites were synthesized from nickel nitrate and kraft lignin then catalytically graphitized to few-layer graphene-encapsulated nickel nanoparticles (Ni@G). Ni@G nanoparticles were used for catalytic decomposition of methane (CDM) to produce COx-free hydrogen and graphene nanoplatelets. Ni@G showed high catalytic activity for methane decomposition at temperatures of 800 to 900 °C and exhibited long-term stability of 600 min time-on-stream (TOS) without apparent deactivation. The catalytic stability may be attributed to the nickel dispersion in the Ni@G sample. During the CDM reaction process, graphene shells over Ni@G nanoparticles were cracked and peeled off the nickel cores at high temperature. Both the exposed nickel nanoparticles and the cracked graphene shells may participate the CDM reaction, making Ni@G samples highly active for CDM reaction. The vacancy defects and edges in the cracked graphene shells serve as the active sites for methane decomposition. The edges are continuously regenerated by methane molecules through CDM reaction

A Study of the Key Factors on Production of Graphene Materials from Fe-Lignin Nanocomposites through a Molecular Cracking and Welding (MCW) Method

In this work, few-layer graphene materials were produced from Fe-lignin nanocomposites through a molecular cracking and welding (MCW) method. MCW process is a low-cost, scalable technique to fabricate few-layer graphene materials. It involves preparing metal (M)-lignin nanocomposites from kraft lignin and a transition metal catalyst, pretreating the M-lignin composites, and forming of the graphene-encapsulated metal structures by catalytic graphitization the M-lignin composites. Then, these graphene-encapsulated metal structures are opened by the molecule cracking reagents. The graphene shells are peeled off the metal core and simultaneously welded and reconstructed to graphene materials under a selected welding reagent. The critical parameters, including heating temperature, heating time, and particle sizes of the Fe-lignin composites, have been explored to understand the graphene formation mechanism and to obtain the optimized process parameters to improve the yield and selectivity of graphene materials

Thermal Decomposition of Kraft Lignin under Gas Atmospheres of Argon, Hydrogen, and Carbon Dioxide

The behaviors of thermal decomposition of kraft lignin under three different gases (Ar, CO2, or H2) were analyzed and compared using a temperature-programmed decomposition-mass spectrometry (TPD-MS) system. Experimental results indicated that Ar atmosphere produced the highest yield of solid chars, while H2 atmosphere generated the highest yield of liquids and CO2 atmosphere had the highest yield of gases. TPD-MS results showed that H2 atmosphere was consumed at the temperature range from 205 to 810 °C and CO2 atmosphere was consumed at the temperature range from 185 to 1000 °C. The H2 promoted the cleavage of lignin side chains and significantly enhanced the formation of CH4, C6H6, HCHO, C6H5OH, CH3OH, and tars. The percentages of water in produced liquids were 90.1%, 85.3%, and 95.5% for Ar, H2, and CO2 as atmosphere, respectively. The H2 yielded more organic chemicals in produced liquids compared to the other two gases. The observed organic chemicals were mainly acetic acid, phenols, ketones, alcohols, aldehydes, and esters. BET surface areas of solid products were 11.3, 98.5, and 183.9 m2/g for Ar., H2, and CO2 as the atmosphere, respectively. C–H–O–N–S elemental and morphology analyses on solid products indicated that the lowest carbon content and the highest oxygen content were obtained if Ar atmosphere was used, while H2 and CO2 yielded more carbon in final solid products. Solid products obtained under CO2 or H2 atmosphere contained sphere-shaped nanoparticles