Pyrolysis increment

Figure 2. Pyrolysis increments in each centigrade step, expressed in mass of volatiles per mass of original wood.

Pyrolysis Increment x Heat of Pyrolysis = Heat Release... 

Figure 1 applies to pyrolysis in which the wood temperature is raised from 100 C in about 10 h to various final temperatures. The weight losses, depicted as volatiles, and solid residues have been determined after the trials, and originate mainly from Klason, v. Heidenstam, and Norlin (4), under consideration of data published by Goos (18) and Stamm (19). Measurements on small samples by Beall and Eickner (20), LeVan and Schaffer (21), and Elder (22) have been compared. Up to about 275 or 300 C — the temperature range in which cellulose rapidly disintegrates — increased final trial temperatures cause increased increments of volatiles beyond 300 C the increments steadily diminish. 

The slope of the volatile = f(final temperature) curve in Figure 1 amounts to volatile increments at particular temperature steps, and is a measure of the pyrolysis rate. The slopes have been obtained by differentiating the volatile curve of Figure 1 for drafting Figure 2. For example, volatiles at 200"C equal 4.6%, and 7.7% at 220"C that is a 3.1% increment in the 20"C step and amounts to a... 

Figure 2 gives rates of pyrolysis in trials with gradually increasing temperatures. In the case of wood heated to 500 C for example, the volatile increments increase from temperature step to temperature step up to 300 C, dropping off in further steps. The sum of the increments reaches 75% at 500 C, as they should according to Figure 1. The area under the curve corresponds to that sum. One can estimate the sum for each final temperature from the areas. For example, in the case of heating to 250 C, the increments average 0.1%, and the sum of the increments becomes 0.1 x (250 - 100) = 0.1 x 150 = 15%, or 0.15 g/g (compare Figure 1).

Finally, because of the small yields and scale relative to even many specialty petrochemicals, one should not automatically assume that the recovery "production" costs of chemicals from biomass pyrolysis are necessarily competitive with the actual production costs from petrochemicals there is usually a large mark-up over costs, because the markets are small, the number of producers is small and there are technical barriers to entry, sales and application development. It would be wise to codevelop recovery with a current manufacturer, just to assure distribution channels. If recovery costs are lower than conventional production, and the market is growing, there will likely be interest, because expansion capital costs can be avoided, and incremental additional production becomes feasible. 

To understand the chemical effects of the various process variables, we need a definition or two. First "severity , which is, subjectively, how hard we crack to get a desired product mix. A typical qualitative definition is the following (3) "Severity is the summary effect of the increments of residence times through a pyrolysis reactor at their corresponding temperatures." Making the concept quantitative is difficult. Various expedients are used to obtain measures of severity - some based on actual times and temperatures, others on internal analytical criteria. Some of these measures are shown in Table I. 

The monomer mass spectra were similar to those produced by pyrolysis GC/MS (Fig. 21). The MS detector was calibrated for the amount of butyl acrylate present and was used to determine the amount of this monomer present in unknown polymers. Linear relationships were observed between ion intensity/concentration and ions characteristic of both methyl methacrylate (m/z = 100) and butyl acrylate (w/z = 127). The peak compositions in Fig. 21 range from methyl methacryate homopolymer, A, to butyl acrylate homopolymer, F, in 20% butyl acrylate increments. 

The thermal soak time can be different depending on the final pyrolysis temperature [24]. This parameter may be used to fine-tune the transport properties of a ear-bon membrane using a particular final pyrolysis temperature [91], Previous studies showed [41,87, 89, 91,92] that increments in thermal soak time would inerease the selectivity of carbon membranes. It is beheved that only mierostmctural rearrangement occurs during the thermal soak time, thus affeeting the pore size distribution and average porosity of carbon membranes [34]. 

It is assumed that, at least initially, the transmission of heat through the laminate from layer 1, (which includes the surface, s), to layer n, (the insulated base of the laminate), is by conduction, since it is assiuned that the laminate, (prior to pyrolysis and the internal evolution of gaseous volatiles), is principally solid with minimal porosity. In this circumstance it is possible to represent a temperature increment between two successive layers within the laminate i and i+7, respectively, as a function of the instantaneous heat flow of conduction, and the specific heat capacity and density of the laminate, (14.4) ... 

Distribution of the particle size was studied in order to examine the uniformity or disparity in the dimensions of the solid powder obtained by different processes. The results are presented in figure 5 where the curves for pyrolysis process at 450"C and 750"C are compared to the curve acquired for thermal shock process. It is possible to observe the similarity in the three evnves even when the two procedures are different especially in the burning time inside the furnace. Curves initiate with an exponential increment for small sizes fi om 0 to about 180 qm then a maximum appears at about 210 and 250 qm. Finally the curves go down towards stabilization at about 600 jtm and continue to low levels of bigger particles. Invariably the particle sizes in any process are identical this could be attributed to the manual pulverization with a pestle and mortar by using the same conditions such as pressure force and time for powdering the solids obtained. This is the result of irregular thickness as no special technique was followed in the preparation of the sample other than mere pulverisation of the pellets. 

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