Dehydrogenation heat treatment

DHT (Dehydrogenation Heat Treatment) This is a heat treatment procedure used during the fabrication cycle only when welding or preheat is interrupted or stopped. Done at 600 - 650°F (min 570°F). Very common and used in lieu of ISR. It is a bakeout to ensure that trapped hydrogen in the welds has the opportunity to escape to the atmosphere. Used for less restrained welds like main reactor seams. 

Heat Treatment Temperature and Soak Time. A study of Mochida and Marsh (53) indicates, unlike classical kinetics, that time and temperature for mesophase formation are not interdependent. The reason for this is the controlling influence of viscosity (not found for reactions in the gas or solution phase). Maximum size of optical texture and coalescence results if the mesophase is formed under conditions which provide a minimum viscosity as quickly as possible. Probably, rate controlling processes for mesophase growth are not the dehydrogenated polymerization reactions. Therefore, the attainment, relatively quickly, of temperature of 400°C has provided the necessary size of molecule and consequently the resultant mesophase sbbws minimum viscosity because it is at a high temperature ( 400°C). Mesophase formed at lower (relative) temperatures can have a higher viscosity and coalescence behaviour can be restricted. 

The desorption and decomposition of benzene has been studied on Pt(lll) and on Sn-modified Pt(lll) for comparative purposes. On the former surface, only a portion of the chemisorbed benzene desorbs upon heat treatment the remainder is dehydrogenated to form a layer of carbon on the surface. On the Pt(lll)-Sn alloys, only physisorption takes place. 

Transition metal compounds catalyze an infinite number of organic reactions. (For a recent review, see e.g. Ref. Most probably, these compounds will have an effect on the processes going on during the heat treatment of acrylic fibers, in particular on dehydrogenation reactions, provided they can be introduced into the fiber in a way such that they will not be washed out during the spinning process. 

Prolonged heat treatment under oxygen certainly leads to dehydrogenation with concomitant aromatization of the ring structures (Huron and Meybeck So far, however, it has not been established whether a high degree of aromatization is in fact required for effective stabilization. 

C1-C5 hydrocarbons were found among the products. The process of non-oxidizing dehydrogenation is accompanied by coke formation on the catalyst surface. Its amount was controlled by CO+CO2 formation during the heat treatment of the catalyst in an air stream. 

Table 1 presents the properties of vanadium-magnesium oxide catalysts subjected to the heat treatment. The temperature of the heat treatment determines both the textural and the catalytic properties of the catalyst. Similar to the dehydrogenation of ethylbenzene into styrene [10,11], the most active catalysts occurred to be those... 

A V-ZSM-5 sample with a Si/V o 42 was synthetized outgoing from V0(C00)2 and Q-brand sodium silicate using TPA-Br as template. ESR spectroscopy proved that vanadium(IV) ions in the zeolitic framework exhibit a distorted square planar symmetry. Upon heat treatment a part of the framework vanadium ions migrate to extra-framework positions. After dehydration no Bronsted acidity was found. Treatment in oxygen and hydrogen above 570 K revealed the redox character of the V-ZSM-5 sample. In oxidation of n-bu-tane (as catalytic test reaction) the V-ZSM-5 zeolite exhibits selective dehydrogenation and aromatization activity. 

With further heat treatment, the anthracene pitch is transformed to an infusible solid coke at about 500 °C and to a pregraphitic carbon at about 1000 °C. At these stages, the carbonaceous residues behave as intractable and infusible solids and can only be described in terms of average structural parameters. The conversion of anthracene to carbon involves further polymerization with continual loss of hydrogen. The rate of dehydrogenation can... 

The stabilization treatment of thermoplastic precursor fibers for carbon fibers is usually a heat treatment process performed in an oxidizing atmosphere above 470K. For stabilization treatment of PAN fibers, 600K is the highest temperature up to which cyclizjation, dehydrogenation and oxidation processes prevail. 

Carbon black is now mainly manufactured by thermal decomposition, by dehydrogenation, or by partial oxidation of aromatic petroleum hydrocarbons. Graphon (Cabot Corporation) is produced by heat treatment of Spheron 6 carbon at very high temperatures to remove oxygen-containing surface groups and to increase ordering of layers. The major use of carbon black is in the manufacture of rubber for tires. Other uses are in inks and in batteries. 

In the case of Pt-Sn/C bimetallic NPs, Jeyabharti et al. [138] observed that heat treatment and the allopng between Pt and Sn increased the particle size as well as the lattice parameter. The increase in the lattice parameter creates an unfavorable situation for adsorption/dehydrogenation of methanol and hence for the MOR. The ORR activities followed the order Pt-Sn/C (as prepared)>Pt-Sn/C(250°C)>Pt-Sn/C(500 C)>Pt-Sn/C(600 C)>Pt-Sn/C (800°C). The ORR followed first-order kinetics with a Tafel slope of 120mV/decade. 

The spectrophotometric methods described earlier were used to determine the optimum pH for the isoenzymes (Schabort et al., 1971). Cytochrome c [together with a small amount of phenazine methosulfate (PMS) as intermediate electron acceptor] was particularly useful for determinations below pH 6.4, because the absorbance of DCIP at 600 nm decreases rapidly below this value. The five isoenzymes showed the same optimum pH of 6.8 for both the dehydrogenation and the total conversion of jSCA into aCA. The temperature stability of the five isoenzymes was essentially the same. They lost all their activity after heat treatment for 10 min at 75.5°C, but retained 70% of their activity after 10 min at 55" C. 

Majumdar published several aza-Claisen rearrangements of 2-cyclohexenyl-1-anilines 39 (R -R =(CH2)3, Table 2, entries 22-28) [14]. The reaction was carried out upon heating the reactant in EtOH/HCl. The corresponding 2-cy-clohexenylanilines 41 were obtained with 50 to 90% yield. The cyclization to give indole derivatives 42 could be achieved in a separate step treatment of the rearrangement products 41 with Hg(OAc)2 in a suitable alcohol in the presence of acetic acid induced formation of the tetrahydrocarbazole 42. The tricyclic products 42 were synthesized with 70-85% yield. Finally, carbazoles could be obtained after DDQ dehydrogenation. 

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