Autoclave temperature development

This section describes some of the tools available for intelligent development of process cycles, such as the time-temperature cycles used in curing composites. Current industrial practice is typically limited to the use of cure cycles. The cycles are based on a series of autoclave temperature and pressure states so that traditional linear, regulatory process control methods can be used. These recipes may not be the ideal method for process control of batch processes because they do not ... 

Figure 15.3 The temperature lag between autoclave (AIRTC) and composite part (PARTTC) is large, so a supervisory controller is used to drive the autoclave setpoint up and achieve the desired cure cycle in the composite. Because this cure cycle was developed for the autoclave temperature, however, the resin gels before compaction is complete...

With respect to thermosetting, it has been well documented that crude Ca-based SSL can be used as a particleboard adhesive (46). This application has been evaluated on a mill-scale basis in Denmark, Finland, and Switzerland, but has not been adopted on a commercial scale. This is because resin curing required both high press and autoclave temperatures as well as long heating times. While this development was a technical success, it was - according to Nimz (36) - never commercialized due to the frequency of fires experienced during mill-scale trials. 

Hydro(solvo)thermal synthesis is a heterogeneous reaction in aqueous or non-aqueous media with temperatures above the boiling point of the solvent and pressures higher than 1 bar. Hydrothermal synthesis is believed to have been first introduced by Schafhautl in 1845 with water as the reacting media, and the device in the modern form of hydro(solvo)thermal synthesis, a sealed glass ampoule in an autoclave, was developed by de Senarmont in 1851 [11]. 

High Pressure in the Chemical Industry. The use of high pressure in industry may be traced to early efforts to Hquefy the so-called permanent gases using a combination of pressure and low temperature. At about the same time the chemical industry was becoming involved in high pressure processes. The discovery of mauveine in 1856 led to the development of the synthetic dye industry which was well estabUshed, particularly in Germany, by the end of the century. Some of the intermediate compounds required for the production of dyes were produced, in autoclaves, at pressures of 5-8 MPa (725-1160 psi). 

An independent development of a high pressure polymerization technology has led to the use of molten polymer as a medium for catalytic ethylene polymerization. Some reactors previously used for free-radical ethylene polymerization at a high pressure (see Olefin polymers, low density polyethylene) have been converted to accommodate catalytic polymerization, both stirred-tank and tubular autoclaves operating at 30—200 MPa (4,500—30,000 psig) and 170—350°C (57,83,84). CdF Chimie uses a three-zone high pressure autoclave at zone temperatures of 215, 250, and 260°C (85). Residence times in all these reactors are short, typically less than one minute. 

Scale-Up Fermenters ranging from about two to over 100 hters (0.07-3.5 fP) have been used for research and development, but the smaller sizes provide too httle volume for sampling and are difficult to replicate, whue large vessels are expensive and use too much medium. Autoclavable small fermenters that are placed in a water bath for temperature control are less expensive than vessels with jackets or coils, but much labor is required for handling them. Pressure vessels that... 

With autoclave syntheses a high yield of clusters is achieved, and it is possible for researchers to follow the reaction path in solution by gradually changing (from experiment to experiment) the working parameters of the synthesis (temperature, pressure, exposure at working temperatures, etc). All these advantages of the autoclave technique have resulted in an abundance of new forms of technetium clusters (particularly, polynuclear ones) because it has been possible to develop and improve the method of obtaining these compounds. 

A review is presented of the nitrogen autoclave process for the manufacture of crosslinked polyolefin foams. Process and product developments over the last few years are summarised and future possibilities are described. Process developments include use of higher temperatures and pressures to produce foams having densities as low as 10 kg/cub.m. Product developments include foams based on HDPE/LDPE blends, propylene copolymers and metallocene-catalysed ethylene copolymers. The structure and properties of these foams are compared with those of foams produced by alternative processes. 5 refs. 

In recent work we have developed a modified autoclave which solves these difficulties by allowing the starting components, aminoalcohol and aqueous NaOH containing the catalyst, to be preheated separately to reaction temperature before mixing (10). Here we have made use of this modified reactor to determine rate constants for a range of alcohols with different structures. 

Several viscosity and kinetic models, and experimental procedures for developing these models, are available for a number of commercially available resin systems [1-5]. These models allow insight into autoclave process decisions based on changes in resin viscosity and kinetic behavior and can be used to determine hold temperatures and durations that allow sufficient resin flow and cross-linking to avoid over bleeding, exotherms, and void formation. 

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