We have studied the blue-shifted and the red-shifted bands formed in mixed Langmuir–Blodgett films of the merocyanine dye (MS)-arachidic acid (C20)-n-octadecane (AL18) ternary system with the molar mixing ratio [MS]:[C20]:[AL18]=1:2:x(0.5≦x≦5.0). The formation of the blue-shifted and the red-shifted bands depends on the AL18 content, and shows that the aggregation state can be modulated by changing the AL18 content. The observed overlapping spectra of the blue-shifted and the red-shifted bands are deconvoluted into two original bands. The extended dipole model has been applied to examine the aggregation state of MS referring to the deconvoluted spectra. Thus the estimated minimum aggregation number Nmin and the slip angle α between the long axis of the aggregate and the transition dipole moment are Nmin=40 and α=30° and Nmin=40 and α=50° for fully-developed J- and H-aggregates, respectively, seen for x≦1.5, and Nmin tends to decrease with increasing x.
The purpose of this research was to investigate biomass pyrolysis process focusing on intra-particle heat transfer. Thermal decomposition characteristics of wood cylinder with a diameter of 8mm were studied experimentally and numerically. In an experiment, a thermobalance reactor was used to investigate weight loss of wood cylinder during the pyrolysis. Three K-type thermocouples with a diameter of 0.5 mm were placed in the sample to measure the intra-particle temperature. Wood cylinders were heated by infrared furnace under inert gas at 1 Ks−1 and 30 Ks−1. In a calculation, unsteady two-dimensional heat and mass transfer equations were discretized by using Finite Volume Method with first order implicit scheme. The reaction kinetics of biomass pyrolysis were modeled by using a multi-step kinetic scheme. To investigate the effect of intra-particle heat transfer, calculations with considering temperature gradient and with uniform temperature were carried out. As a result, the calculation results with considering intra-particle heat transfer were in good agreement with experimental ones, while calculation results without considering temperature gradient were quite different from experimental ones at high heating rate. Intra-particle heat transfer mechanism at low heating rate was quite different from that at high heating rate. Both numerical and experimental results showed that there was a distinct peak of intra-particle temperature due to strong exothermic reaction at low heating rate. Meanwhile, endothermic reactions were dominant at high heating rate, and there was no temperature peak. Moreover, an increase in the slope of temperature history observed at high heating rate. It was difficult to explain the slope increase by only weak exothermic reactions. This was because that heat capacity was decreased significantly during pyrolysis. When the heating rate was high, the yield of volatile matter whose heat capacity was quite less than that of char or wood was increased. It was shown that volatile and char formation characteristics were strongly related with intra-particle heat transfer characteristics.
This paper reports on the pyrolysis process of various biomass materials in a thermobalance. In particular, the primary yields of total volatiles, tar and non-condensable gases, together with the composition of non-condensable gases, are measured as a function of temperature. The use of a high-intensity infrared heating source, in conjunction with a non-absorbing carrier gas (viz. argon), is reported to reduce the significance of secondary gas-phase pyrolysis reactions. The results indicate that the pyrolysis process of wood and grass biomass (tar and gas evolution process) is greatly affected by the main composition (cellulose, hemicellulose and lignin) and the linear trends with atomic H/C ratio are observed in the tar yield, total volatile yield CO, CO2 and CH4 yields. The volatile yields of wood and grass biomass are predicted based only on the values of ultimate analysis of the biomass.
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