SUPUESTOS DE DECLARACION DE RUINA Y DEMOLICION DE LAS EDIFICACIONES

Below are thermograms of the four test fuels and their corresponding stressed versions. In the case of EN590 diesel and RME20, thermograms are provided for both stressed layers.

Figure 6.4: Thermograms of stressed (red) and unstressed (blue) commercial diesel. Experiments were conducted under nitrogen at a heating rate of 10oC/min. Solid lines – mass loss curves; dashed lines – derivatives

Figure 6.4 shows that the decomposition/evaporation temperature of stressed diesel has shifted to higher temperatures. The peak maximum has shifted by 34o_{C. This is likely due to} the presence of higher molecular weight species which were formed during thermo-oxidative stressing of the fuel. Because of their higher molecular weight, such species will have higher boiling points. Alternatively such species could contain oxygen moieties which if hydrogen

0 0.2 0.4 0.6 0.8 1 1.2 1.4 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0 50 100 150 200 250 300 350 400 D er iv at iv e m as s (% / oC) Ma ss (% ) Temperature (o_C)

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bonded would also have higher boiling points. It should be note that the extent of stressing (15h) was chosen to exaggerate the extent of deposition so that further analysis, e.g. ESI-MS, could be performed. Interestingly a shift was observed, despite very little deposit being observed in the QCM. A very small shoulder can be observed above 275oC in the DTG curve. The near Gaussian shape of the derivative suggests a Gaussian boiling point distribution.

Figure 6.5: Thermograms of the two layers of stressed (red (bottom) and green (top)) and unstressed (blue) EN590 diesel. Experiments were conducted under nitrogen at a heating rate of 10o_{C/min. Solid lines – mass loss curves; dashed lines – derivatives}

Figure 6.5 presents thermograms of stressed and unstressed E590 diesel. It is apparent that, as with the commercial diesel, stressed and unstressed EN590 diesels have different volatilities; with stressed EN590 diesel displaying lower volatility (shifting of thermogram to the right). Furthermore the shift is greater for the bottom layer (peak shift of 29oC for the bottom layer and 12o_{C for the top layer). This suggests that the bottom layer contained higher molecular} weight species which had precipitated from the bulk fuel. This is consistent with the darker colour of this layer. Furthermore this layer has a much longer tail than the top layer. No tail can be seen in the neat EN590 diesel which has a sharp end point. Note that the neat EN590 diesel was blended from three petroleum streams which explains the non-Gaussian nature of the derivative curve.

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The top layer had a residue of 0.1% at 600o_{C but the residue for the bottom layer was a} noticeable 0.9% . This may be the result of the presence of carbonaceous materials but may also be the result of charring that occurs when these high molecular weight species are pyrolysed under nitrogen. Not only is there a shift in the peak maximum of the derivative for top and bottom layers but a shoulder can be seen to develop at higher temperatures.

Figure 6.6: Thermograms of the two layers of stressed (red (bottom) and blue (top)) and unstressed (green) RME20, compared with unstressed RME20. Experiments were conducted under nitrogen at a heating rate of 10o_C/min

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Figure 6.6 clearly indicates that stressed and unstressed RME20 have very different thermal behaviour under an inert atmosphere. A number of interesting features can be seen. Firstly the maximum in the derivative peak for RME20 has shifted to 210oC. RME20 if a 4:1 EN590 diesel:RME blend. RME is less volatile than EN590 which explain the shift. In both the top and bottom layer a larger shoulder from 225-350oC can be observed. This shoulder can be seen to form, but not to the same extent, when the neat RME20 is heated. It is ascribed to pyrolysis reactions [99]. Such a shoulder in the heating of FAME has been noted by other authors [84, 100].

The size of this shoulder is greater for the bottom layer and for both is greater than the shoulder that develops in EN590 diesel when stressed. It is suggested that the bulk of the compounds that are volatile at the temperatures, associated with the shoulder, are FAME- derived. Interestingly the maximum in the derivative actually drops. Furthermore if one looks closely at the top layer one sees that the early part of the mass loss curve is very similar to the neat fuel. These two results would suggest that in combination with EN590 diesel, it is the FAME components that are more likely to be oxidised.

Figure 6.7: Thermograms of unstressed (green) and stressed (red) SME20. Experiments were conducted under nitrogen at a heating rate of 10oC/min

0 0.2 0.4 0.6 0.8 1 1.2 1.4 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0 50 100 150 200 250 300 350 400 D er iv at iv e m as s (% / oC) Ma ss (% ) Temperature (o_C)

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According to Figure 6.7, stressed SME20 has similar features to the bottom layer of RME20. However, these features were more pronounced, i.e. the size of the shoulder was larger. A 4% residue remained at 600oC. The mass remaining at the onset of the shoulder was approximately 40% which would suggest that at least part of the stressed compounds is EN590 diesel derived. Nonetheless, if one looks at the neat fuel one sees that even in nitrogen some degradation takes place.

If one compares this neat fuel to the previous neat fuels one sees that the mass does not immediately reach zero after the bulk of the fuel has evaporated. The shoulder that forms on heating the SME20 is larger than that that forms when RME20 was heated. Focke et al. performed similar studies on neat sunflower, soybean and canola FAME and found the residual mass to be in the order sunflower > soybean > canola [84]. Since canola is edible rapeseed, this result is consistent with what was seen in this study. The extent of pyrolysis increases with increasing unsaturation. SME has a much higher degree of unsaturation and importantly bis-allylic structures. These are capable of cross-linking and are the likely pre- cursors of higher molecular weight species, formed on heating.