Chao Liu

Studies on pyrolysis mechanism of syringol as lignin model compound by quantum chemistry

Abstract The pyrolysis of syringol as lignin model compound was investigated using density functional theory methods at B3LYP/6-31G++ (d, p) level. Three possible pyrolytic pathways were proposed and the equilibrium geometries of the reactants, transition states, intermediate and products were fully optimized. The standard kinetic parameters in each reaction pathway were calculated and the formation and evolution mechanism of main pyrolysis products were analyzed. Bond dissociation energies calculation results show that the bond dissociation energy of CH 3 -O of syringol is the lowest and the order of all kinds of bond dissociation energy is CH 3 -O 3 O-C aromatic 2 -H aromatic aromatic -H. In reaction pathway (1) and (2), the main pyrolysis product is 3-methoxycatechol and 2-methoxy-6-methylphenol, respectively. The total energy barrier is 366.6 and 474.8 kJ/mol in pathway (1) and (2), respectively. For reaction pathway (3), the total energy barrier of o-methoxyphenol formation is as low as 21.4 kJ/mol, which shows that addition of hydrogen to the carbon atom connected with methoxyl can effectively lower the reaction energy barrier of demethoxy reaction of lignin model syringol.

Theoretical studies on pyrolysis mechanism of O-acetyl-xylopyranose

Abstract In order to understand the pyrolysis mechanism of hemicellulose and to identify the formation pathways of key products during pyrolysis, the pyrolysis processes of O-acetyl-xylopyranose are investigated by using density functional theory methods at B3LYP/6–31 G ++ (d, p) level. In the pyrolysis, O-acetyl-xylopyranose firstly decomposes to form acetic acid and IM1 with an energy barrier of 269.4 kJ/mol, and then IM 1 is converted to acyclic carbonyl isomer IM2 with a low energy barrier of 181.8 kJ/mol. IM2 further decomposes to form all sorts of small molecules through four possible pyrolytic reaction pathways. The equilibrium geometries of the reactants, transition states, intermediate and products were fully optimized, and the standard thermodynamic and kinetic parameters of every reaction pathway were calculated. The calculation results show that reaction pathways (2) and (4) are the major reaction channels in pyrolysis of O-acetyl-xylopyranose and the major products are low molecular products such as acetic acid, acetaldehyde, glycolaldehyde, acetone, CO, CO2 and CH4, which is according with related analysis of experimental results.

The net power output of ideal supercritical organic Rankine cycle with different flow arrangement evaporators

The theoretical models of net power output for ideal supercritical ORC (organic Rankine cycle) with the evaporator of counter flow, parallel flow, and cross flow are, respectively, proposed. The effects of the ratio of heat capacity rates of heat source and working fluid, the number of heat transfer unit, and the ratio of the cycle high and low temperatures on the net power output of ideal supercritical ORC are addressed. The numerical simulation results of ideal supercritical ORC elucidate that the larger rate difference between the heat capacity of working fluids and heat source will help to improve the net power output. The net power output will be kept constant when the number of heat transfer unit reaches a certain value. In addition, supercritical ORC with counter flow evaporator exhibits the largest net power output while one with parallel flow evaporator does the lowest.

Band gap and oxygen vacancy diffusion of anatase (101) surface: the effect of strain

The effects of strain on the band gap and oxygen vacancy diffusion are investigated for the anatase (101) surface through density functional theory calculations. The results show that biaxial strain can effectively shift the band edge of the surface; for example, tensile strain gently reduces the band gap. With respect to the subsurface-to-surface diffusion of oxygen vacancy, energy barrier has a significant dependence on strain. As strain increases, it facilitates O-vacancy diffusion at the clean surface but hinders this migration for the reduced surface in the presence of water. Analysis based on the water adsorption energy indicates that the interplay between O-vacancy and water is weakened with increasing strain.

Density functional theory study on bond dissociation enthalpies for lignin dimer model compounds

In order to enhance understanding of the mechanism of lignin pyrolysis, homolytic bond dissociation enthalpies (BDEs) in ten lignin dimer model compounds were calculated by using density functional theory methods at B3LYP/6-31G++(d,p) level and B3P86/6-31G++(d,p) level. The BDE values calculated at B3LYP/6-31G(d,p) level are about 20 kJ/mol lower than that at B3P86/6-31G(d,p) level, but the variation trends of BDE values at two levels are the same and the B3P86 functional was found to yield accurate BDEs. The calculation results show that the order of the BDE values for the β-O-4 type of linkage is as follows: Cβ-O < Cα-Cβ < C4-O < C1-Cα, and the substituents (methoxyl, carbonyl, and hydroxyl) on both the aromatic and alkyl groups in model compounds 1 have an important effect on the BDEs. It is found that the BDEs of Caromatic(1,4,5)-C(or O) in lignin model compounds are higher, but the BDEs of Calkyl(α, β)-Calkyl(α, β)(or O) are lower. Therefore, the initial step in pyrolysis of lignin is the homolytic cleavage of the Calkyl(α, β)-Calkyl(α, β)(or O) bond. The possible formation pathways of major products in the pyrolysis process of model compounds have been analysed.

Molecular Dynamics Simulation of the Influence Factors of Particle Depositing on Surface during Cold Spray

Using molecular dynamics simulation, the influence factors of deposition process, such as cluster incident velocity, material hardness and so on, were studied. The cluster incident velocity influences the combination strength between the substrate and cluster greatly. The higher the cluster velocity is, the stronger the combination strength is, and the faster the cluster forms the crystalline structure like the substrate. Higher temperature of the substrate and the cluster will improve the combination strength. The size of the cluster influences the effect of combination as well. The larger the cluster is, the stronger the combination strength is. If a soft cluster impacts on a hard substrate, because of lack of enough deformation at the interface of the substrate, it is difficult to form the effective combination. If a hard cluster impacts on a soft substrate, the lattice defects occur and the cluster takes a longer time to form crystalline structure.

The Emergence of Eco-Design in China in the ICT Sector

This article presents the preliminary results of empirical research on the emerging practices of EcoDesign in the sector of Information Technology and Communication (ICT) in China. We show that the structuring of the organizational field of EcoDesign is under the constraint of external actor-networks, mainly European regulatory constraints. The central government, relayed by major exporting companies in the sector, has had to build an eco-system of EcoDesign that combines economic efficiency and incentive regulation both in order to achieve strategic goals and to meet the global environmentalist demand.

Experimental Study of the First Pyrolysis of Cellulose

Flash pyrolysis of cellulose is done on the laser pyrolysis experiment device, from which some water-loving yellow substances are collected, which is confirmed as active cellulose. HPLC analysis shows that the chief constituent of this yellow substances are glucose, fructose and oligosaccharide, and whose yield are determined. The research indicates that: at high-radiation power, glucose is not the only production decomposing from oligosaccharide, and there is another production decomposing from oligosaccharide which will compete against glucose. At last, the mechanism of the first pyrolysis of cellulose is analysed.