Pyrolysis temperature optimization

A report on the continuous flash pyrolysis of biomass at atmospheric pressure to produce Hquids iadicates that pyrolysis temperatures must be optimized to maximize Hquid yields (36). It has been found that a sharp maximum ia the Hquid yields vs temperature curves exist and that the yields drop off sharply on both sides of this maximum. Pure ceUulose has been found to have an optimum temperature for Hquids at 500°C, while the wheat straw and wood species tested have optimum temperatures at 600°C and 500°C, respectively. Organic Hquid yields were of the order of 65 wt % of the dry biomass fed, but contained relatively large quantities of organic acids. 

Iliev I., Gamburzev S., Kaisheva A., Optimization of the pyrolysis temperature of active carbon-CoTMPP catalyst for air electrodes in alkaline media, J.Power Sources, 1986 17 345 352. 

The types of macrocycles most studied in which the active metal center is believed to be retained include Co, Fe, Ru porphyrins and related macrocycles. In these studies the optimal pyrolysis temperature is often reported to be between 400-800 °C. Above these temperatures, the active site begins to be destroyed, and activity decreases.49 An array of characterization techniques have been used to support these claims. XPS analysis has demonstrated that at the highest activity of samples, the surface composition of metal and nitrogen is also at its highest.78,96 Above the optimal treatment temperature, nitrogen and metal begin to disappear from the surface. Furthermore, Mossbauer spectroscopy and XAS have been used to... 

The pyrolysis temperature and the rate of addition are chosen such that about 50% of the acid chloride is recovered as 2-toluic acid after hydrolysis. Under these conditions only a small amount of benzyl chloride and polymeric material is formed in addition to benzocyclobutenone. The percentage of reactant conversion depends not only on the pyrolysis temperature, but also on the pressure in the reactor and on the rate of reactant addition. It is advisable, therefore, to optimize the pyrolysis temperature in trial runs keeping the other variables constant. 

Apart from multi-element analysis employed for large scale studies, single element analysis (e.g., especially of toxic elements such as Cd, Hg, Tl or Pb) is performed in environmental science for special applications. For example, Hg and Tl have been determined in environmental samples by slurry sampling using electrothermal vaporization (ETV) ICP-MS. If potassium permanganate is employed as a modifier in ETV at optimized pyrolysis temperatures of 300 °C for Hg and 500 °C for Tl, detection limits of 0.18p,gg 1 (Hg) and 0.07p,gg 1 (Tl) are obtained.58... 

Laboratory pyrolysis of HDPE was first carried out using the batch mode reactor (Eigure 13.2). After flushing the system with an inert gas, the reactor was lowered into the floor furnace. The furnace was heated from room temperature to the pyrolysis temperature in 15-20 min and held at that temperature for 1 h before cooling back to room temperature. There was complete conversion of the HDPE in all runs and the reactor was clean at the end of the run. Several runs were carried out to optimize the temperature and pressure conditions. 

The parameters of the pyrolysis experiments are shown in Table 24.4. In the experiments, the pyrolysis temperature was 450°C which was found in previous experiment with pure PMMA to be the optimal temperature. Total mass balances are calculated to the organic content even for the filled PMMA to allow a comparison. The losses (1-2%) calculated to 100% were determined on all product fractions proportionately. The following results should be noted. 

The concentration of arsenic, which was calculated based on the initial weight of arsenic in wood charcoal, increased linearly up to 400 C and then leveled off A longer pyrolysis gave a higher concentration of arsenic at 350 C. On the other hand, there was no difference at 450 °C between 80 and 200 s. The lower the arsenic content in the bio-oil, the lower the yield of bio-oil. These are thought to be the optimal conditions for the application of the bio-oil. This can be obtained between pyrolysis temperature of 450 and 500 X (Fig.4). 

In order to obtain reproducible results and characteristic pyrograms, one must define the optimal experimental parameters, which must then be strictly standardized, as the thermal degradation of a polymer is often sensitive to even minor changes in the pyrolysis conditions. Apart from the cell type, the determining experimental parameters are (1) the pyrolysis temperature and time, (2) the sample size and shape, (3) the nature and velocity of the carrier gas and (4) the chromatographic separation conditions. Let us now consider in greater detail the effect of the above factors on the yield of pyrolysis products and the specificity of pyrolysis. 

The optimal pyrolysis temperature is determined by the analytical task, the nature of the polymer being investigated and the design of the pyrolytic cell. The optimal pyrolysis temperature is normally considered to be the temperature at which the composition of the characteristic products ensures maximum accuracy of determination or is most specific. By the characteristic pyrolysis products are meant compounds whose peaks are used in quantitative measurements or in a qualitative evaluation of the pyrograms using the parameters of characteristic peaks permits more clearly defined specific relationships of the type in eqn. 1 to be obtained. 

Since the temperature of pyrolysis is a function of the Curie-point wire alloy composition, the wire, and consequently the sample, may be heated to that temperature only. If it is desired to evaluate several different pyrolysis temperatures, or to study the behavior of a sample material at different temperatures, it is necessary to use a different Curie-point wire for each run. Therefore, it is not possible with a Curie-point system to optimize the pyrolysis temperature of a sample by placing the material into the instrument and increasing the temperature in a stepwise fashion. 

Some recent results have revealed that the optimal activity for N4-chelate catalysts is normally obtained at a heat-treatment temperature range of 500-700 °C [30-32], However, it has also been discovered that a higher pyrolysis temperature (> 800 °C) is necessary in order to achieve stable performance in a PEM fuel cell enviromnent. A deleterious effect on electrode performance was observed at temperatures higher than 1100 °C [33], Even for some carbon-supported Fe- and Co-phthalocyanines, stability can also be considerably improved. For example, an almost 50 times greater enhancement in electrocatalytic activity was achieved at an electrode potential of 700 mV (vs. NHE) when carbon-supported Co-phthalocyanine was heat-treated in an environment of N2 or Ar at 700-800 °C [34]. Furthermore, in experiments with carbon-supported Ru-phthalocyanine, heat treatment at 650 °C could increase the catalytic activity by 20 times at 800 mV (vs. NHE). Unfortunately, there was no insignificant improvement in catalyst stability. Not all heat-treated carbon-supported metal phthalocyanines gave positive results. For example, the activities and stabilities of Zn- and Mn-phthalocyanines were not affected by heat treatment [34]. The duration of heat treatment for these complexes is usually around 0.3 5 hrs. 

The first step of a method development in GF AAS is usually an optimization of the pyrolysis and atomization temperatures by establishing pyrolysis and atomization curves using a matrix-free calibration solution as well as at least one representative sample or reference material. The pyrolysis curve exhibits the integrated absorbance signal obtained at a fixed atomization temperature as a function of the pyrolysis temperature, as shown schematically in Figure 8.13. 

Instead of the PA precursors, Hayashi et al. deposited a polyimide film on the outer surface of a porous alumina tube by dip-coating three times. After imidization and pyrolyzation at 973-1073 K, the carbon membranes were fabricated on porous alumina tube. The enhancement of the volume of micropores accessible to smaller molecules has been observed. Hayashi et al. obtained an optimal pyrolysis temperature of 973 K and maximum permeance was achieved. In order to improve selectivity, a carbon layer was further deposited on the resultant supported carbon membrane by chemical vapor deposition (CVD) of propylene at 923 K.The CVD process favors the deposition of carbon in micropores, which explains the increase of the selectivity of CO2/N2 from 47 to 73. 

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