Koyo Norinaga

Kinetics of surface reactions in carbon deposition from light hydrocarbons

Abstract Carbon deposition from ethene, ethine and propene as a function of pressure was studied at various temperatures and two different surface area/volume ratios. Deposition rates as a function of pressure of all hydrocarbons indicate Langmuir–Hinshelwood kinetics which suggests that the deposition process is controlled by the heterogeneous surface reactions (growth mechanism). These kinetics are favored at decreasing reactivity (C3H6>C2H2>C2H4), decreasing temperature and residence time as well as increasing surface area/volume ratio. A linear rate increase at high pressures suggests that carbon is additionally or preferentially deposited by aromatic condensation reactions between polycyclic aromatic hydrocarbons large enough to be physisorbed or condensed on the substrate surface (nucleation mechanism). The results completely agree with earlier results obtained with methane.

Efficient levoglucosenone production by catalytic pyrolysis of cellulose mixed with ionic liquid

Levoglucosenone is a synthetically valuable and versatile compound that is present as a minor product of cellulose pyrolysis. Here, we report the catalytic pyrolysis of cellulose by mixing with 1-butyl-2,3-dimethylimidazolium triflate ionic liquid (IL), forming levoglucosenone in high yield. The catalysis of the IL was selectively directed to form levoglucosenone, while the low content of IL (50%) effectively prevented formation of char, leading to a yield near 20% even at 250 °C. The thermally stable IL could be fully recovered from the mixture pyrolyzed up to 300 °C and reutilized for pyrolysis.

Molecular Size Determination of Coal-Derived Asphaltene by Fluorescence Correlation Spectroscopy

The molecular properties of asphaltenes have been the subject of uncertainty in the literature; in particular the molecular architecture is still a matter of debate. Some literature reports provide evidence that the contrast of petroleum asphaltenes versus coal-derived asphaltenes is useful for understanding the governing principles of asphaltene identity. Here, we employ fluorescence correlation spectroscopy to measure the diffusion constants of asphaltenes obtained from the distillation resid from coal liquefaction fluids. Concentrations employed herein are ∼10−8 molar, precluding asphaltene aggregation. These are compared with the same measurements on petroleum asphaltenes. These results confirm that the molecular sizes of these coal-derived asphaltenes are much smaller than virgin petroleum asphaltenes. Coal-derived asphaltenes are simpler than petroleum asphaltenes and provide correspondingly tighter constraints for understanding asphaltene molecular architecture. The small size, small alkane fraction, and large PAH of coal-derived asphaltenes are consistent with an “island” molecular architecture.

Theoretical Study on Reaction Pathways Leading to CO and CO2 in the Pyrolysis of Resorcinol

Possible pathways for the pyrolysis of resorcinol with the formation of CO and CO2 as final products were proposed and evaluated using ab initio calculations. Our experimental study revealed that large quantities of CO2 are generated in the pyrolysis of 1,3-dihydroxybenzene (resorcinol), while the pyrolysis of the dihydroxybenzene isomers 1,2-dihydroxybenzene (catechol) and 1,4-dihydroxybenzene (hydroquinone) produces little CO2. The fate of oxygen atoms in catechol and hydroquinone was essentially the formation of CO. In the proposed pathways, the triplet ground state m-benzoquinone was generated initially from simultaneous cleavage of the two O-H bonds in resorcinol. Subsequently, the direct cleavage of a C-C bond of the m-benzoquinone diradical yields 2-oxidanylcyclopenta-2,4-dien-1-yl-methanone, which can be converted via two channels: release of CO from the aldehyde radical group and combination of the ketone radical and carbon atom in the aldehyde radical group to form the 6-oxabicyclo[3.2.0]hepta-2,4-dien-7-one, resulting in the release of CO2. Potential energy surfaces along the proposed reaction pathways were calculated employing the CBS-QB3 method, and the rate constants at the high-pressure limit were also evaluated based on transition-state theory to assess the feasibility of the proposed reaction pathways.

Nano-sized nickel catalyst for deep hydrogenation of lignin monomers and first-principles insight into the catalyst preparation

This paper reports, for the first time, complete arene hydrogenation of phenolic compounds as lignin monomers over a non-noble metal catalyst supported by a general material. A type of nano-sized Ni catalyst was prepared in ethanol and in situ supported by ZSM-5 zeolite through general borohydride reduction of Ni2+ to Ni0, but with application of a simple ligand, pyridine. This catalyst showed an activity so high as to completely or near completely hydrogenate the aromatic rings of phenol and its twelve derivatives as potential lignin monomers at 180 °C. The activity was clearly higher than that of another type of conventional Ni catalyst prepared in the absence of pyridine. Analyses of the catalysts by TEM/EDS, XPS, XAFS and others demonstrated that pyridine had crucial roles in selective formation of nano-sized Ni and maintenance of its activity by appropriate interaction with the support. This paper also shows our theoretical approach to the mechanism of the borohydride reduction. First-principles calculations based on density functional theory (DFT) revealed the reaction pathway from Ni2+ to Ni0 and the role of pyridine, which was validated by some experimental facts. The DFT calculations also explain the variety of reactivities of the lignin monomers, which are strongly influenced by their molecular electrostatic and steric nature.

A reduced mechanism for primary reactions of coal volatiles in a plug flow reactor

In the present paper, the authors study the primary reactions of coal volatiles and a detailed mechanism has been made for three different environments: thermal decomposition (pyrolysis), partial oxidation (O2) and O2/CO2 gasification in a plug flow reactor to analyze the combustion component. The computed results have similar trend for three different environments with the experimental data. A systematically reduced mechanism for O2/CO2 gasification has also been derived by examination of Rate of Production (ROP) analysis from the detailed mechanism (255 species and 1095 reactions). The reduced mechanism shows similar result and has been validated by comparing the calculated concentrations of H2, CH4, H2O, CO, CO2 and polycyclic aromatic hydrocarbon (PAH) with those of the detailed mechanism in a wide range of operating conditions. The authors also predicted the concentration profiles of H2, CO, CO2 and PAH at high temperature and high pressure.

Theoretical Study on Elementary Reaction Steps in Thermal Decomposition Processes of Syringol-Type Monolignol Compounds

This paper theoretically investigated a large number of reaction pathways and kinetics to describe the vapor-phase pyrolytic behavior of several syringol-type monolignol compounds that are derived from the primary pyrolysis of lignin: 1-(4-hydroxy-3,5-dimethoxyphenyl)prop-2-en-1-one (HDPP), sinapyl alcohol, 3-hydroxy-1-(4-hydroxy-3,5-dimethoxyphenyl)propan-1-one (HHDPP), 1-(4-hydroxy-3,5-dimethoxyphenyl)propane-1,3-diol (HDPPD), and syringol. The possible pyrolytic pathways involving unimolecular decomposition, addition, and abstraction reactions were investigated by comparing the energy barriers calculated at the B3LYP/6-311++G(d,p) level. In the proposed pathways, all syringol-type monolignols containing a side chain undergo its cleavage to form syringol through the formation of syringaldehyde or 4-vinylsyringol. Syringol is then converted into two products: (a) pyrogallol via the homolysis of the O-CH3 bond and hydrogenation or (b) guaiacol via addition of an H atom with a carbon bearing methoxyl group in syrignol and the subsequent demethoxylation. The pyrolytic pathways of pyrogallol are classified into two processes: (a) the concerted dehydrogenation of the two hydroxyl H atoms and the unimolecular decomposition to produce acetylene (C2H2), ethynol (C2HOH), and CO or (b) the displacement of an OH with H to produce catechol and resorcinol. Additionally, HDPP undergoes O-CH3 bond cleavage to form but-1-en-3-yne. The high-pressure limit rate constants for all the proposed elementary reaction steps were evaluated on the basis of transition state theory.

Theoretical Study on the Kinetics of Thermal Decomposition of Guaiacol and Catechol

The theoretical aspects of the development of a chemical kinetic model for guaiacol and catechol pyrolysis are presented to describe the pyrolysis behaviors of the individual lignin-derived components. The possible pyrolysis pathways involving both unimolecular and bimolecular decomposition were investigated by the potential energy surfaces (PES) calculated at CBS-QB3 level. The high-pressure limiting rate constants of each elementary reaction step were evaluated based on the transition state theory (TST) to determine the dominant pyrolysis pathways. The kinetic analysis results predicted the most favorable catechol unimolecular decomposition pathways, where catechol isomerization to 2-hydroxycyclohexa-2,4-dien-1-one occurred via migration of the hydroxyl H atom, followed by decomposition into 1,3-cyclobutadiene, acetylene, and CO. In the case of the bimolecular reaction of catechol, a hydrogen radical is coupled to the carbon atom in the benzene ring, leading to the formation of phenol and a hydroxyl radical through dehydroxylation. On the other hand, guaiacol is likely to form catechol and phenol via the O-CH3 homolysis and coupling of a hydrogen radical to the carbon atom with the methoxyl group, respectively.