Mechanism of Hydrogen Formation in Solar Parabolic Trough Receivers Page: 4 of 8
This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
2008 14th Biennial CSP SolarPACES (Solar Power and Chemical Energy Systems) Symposium, 4-7 March 2008, Las Vegas, Nevada (CD-ROM) (NREL/CD-550-42709)
0 -
-0 0\ /0 +
H' 0
+
*0 -
Figure 4. Cleavage reactions of DPO
2.2 Thermal decomposition of DPO/biphenyl mixtures
Considering the multitude of reactions that the radical species can engage in, the product slate generated from a
mixture of DPO and biphenyl can be expected to be even more complex. We found only one report that
describes a study of the thermal degradation of Dowtherm A in a temperature range of 400-4250C, and that
provides some insight into the overall kinetics as well as the products formed during the fluid breakdown." It
was found that under static conditions the fluid viscosity increased by 17% at 4250C after 120 h, and this
empirical approach suggested that the thermal breakdown of this aromatic mixture involved a polymerization
process. The presence of heavier degradation products was confirmed through the use of gel permeation
chromatography (GPC). Moreover, a linear correlation was found between the quantitative GPC analysis of
these heavy products and the viscosity of the fluid after heating at 4000C, 412.50C, and 4250C, respectively.
Using a first-order kinetic approach, an activation energy of 72 kcal/mol was calculated that fit well with the
thermochemical data mentioned earlier for biphenyl. When Dowtherm A was heated at 4250C for 120 h, about
8% of the fluid had degraded to form a mixture of a) gaseous products consisting of hydrogen gas (44% of the
total gas volume) and small hydrocarbons, and b) a fraction containing the aromatic compounds shown in Figure
5.0
OH
/ OH
n
a -_1
, ~00Figure 5. Aromatic compounds formed during thermal breakdown of Dowtherm A
Much heavier aromatics were detected during the GPC analysis, but their structures were not determined.
Nevertheless, this work led to the formulation of a plausible mechanistic scheme that explains the formation of
hydrogen gas as a significant by-product, as well as the observed aromatic products (Fig. 6).
Upcoming Pages
Here’s what’s next.
Search Inside
This article can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Article.
Moens, L. & Blake, D. M. Mechanism of Hydrogen Formation in Solar Parabolic Trough Receivers, article, March 1, 2008; Golden, Colorado. (https://digital.library.unt.edu/ark:/67531/metadc902848/m1/4/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.