Heat soak

The cmde phthaUc anhydride is subjected to a thermal pretreatment or heat soak at atmospheric pressure to complete dehydration of traces of phthahc acid and to convert color bodies to higher boiling compounds that can be removed by distillation. The addition of chemicals during the heat soak promotes condensation reactions and shortens the time required for them. Use of potassium hydroxide and sodium nitrate, carbonate, bicarbonate, sulfate, or borate has been patented (30). Purification is by continuous vacuum distillation, as shown by two columns in Figure 1. The most troublesome impurity is phthahde (l(3)-isobenzofuranone), which is stmcturaHy similar to phthahc anhydride. Reactor and recovery conditions must be carefully chosen to minimize phthahde contamination (31). Phthahde [87-41-2] is also reduced by adding potassium hydroxide during the heat soak (30). 

Competent ABM manufaeturers heat soak the eomponents and test them for eompatibility and resistanee to eoiTosion. Extensive ehemieal soak tests were performed in the early 1990s and the results did not... 

Singer [22] developed a process for converting 50% of low-cost Ashland 240 isotropic pitch to mesophase by heating the pitch to 400-410°C for approximately 40 hours. During this "heat-soak," mesophase tended to collect at the bottom of the vessel, due to its greater density. The production of highly-oriented, graphitizable... 

Fig. 6. Typical molecule of a heat-soaked mesophase (adapted from [26]).

Residues (petroleum), steam-cracked heat-soaked naphtha... 

OptiCAT-plus A process for regenerating hydrotreating catalysts. It uses a fluidized-bed pretreatment to control the initial exotherms found in regeneration, followed by a moderate heat soak to eliminate sulfur and carbon. Developed in the 1990s by the Criterion Catalyst Company. 

A general summary of temperatures and heat-soak times that are favorable for the formation... 

A variety of techniques have been used to accomplish this. Branching comonomers such as divinylbenzene can be used.The amount needed to branch the polymer adequately is generally so low that the reagent can hardly be detected in the final product. Additives which cause metalation of the polymer chains can be included in the polymerization mixture or added after polymerization to create new growth sites along the polymer chain.12 Or, polymer can be heat soaked by increasing the residence time. 

It has been clearly demonstrated that extensive and irreversible damage to the catalyst can occur during such procedures and they have been largely replaced by the heat soak technique. In this procedure the inlet temperature to the catalyst bed is held at some 15 - 20 C above normal for several hours and it is generally effective in removing intrapore retained sulfur. 

Bopp, A. F. Goff, G. B. Howard, B. H., "Influence of Maximum Temperature and Heat-Soak Times on the Properties of Calcined Coke," Light Metals 1984, pp. 869-882. 

In Figure 1, the classic definition of asphaltenes is illustrated. This definition is an operational one that is, asphaltenes are soluble in benzene and insoluble in pentane. Usually, for virgin petroleum samples, the residuum is completely soluble in benzene. However, with heat-soaked samples or coal-derived liquids, the benzene insolubles can be appreciable. Therefore, further... 

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