Processing high-temperature

Separation of Fatty Acids. Tall oil is a by-product of the pulp and paper manufacturiag process and contains a spectmm of fatty acids, such as palmitic, stearic, oleic, and linoleic acids, and rosia acids, such as abietic acid. The conventional refining process to recover these fatty acids iavolves iatensive distillation under vacuum. This process does not yield high purity fatty acids, and moreover, a significant degradation of fatty acids occurs because of the high process temperatures. These fatty and rosia acids can be separated usiag a UOP Sorbex process (93—99) (Tables 8 and 9). 

High process temperatures generally not achievable by other means are possible when induction heating of a graphite susceptor is combined with the use of low conductivity high temperature insulation such as flake carbon interposed between the coil and the susceptor. Temperatures of 3000°C are routine for both batch or continuous production. Processes include purification, graphitization, chemical vapor deposition, or carbon vapor deposition to produce components for the aircraft and defense industry. Figure 7 illustrates a furnace suitable for the production of aerospace brake components in a batch operation. 

Cultured buttermilk is that which is produced by the fermentation (qv) of skimmed milk often with some cream added. The principal fermentation organisms used are l ctococcus lactis suhsp. cremoris l ctococcus lactis suhsp. lactis and l euconostoc citrovorum. The effect of the high processing temperature and the lactic acid provide an easily digestible product. 

Chlorendic anhydride is the common name of the Diels-Alder adduct of maleic anhydride and hexachlorocyclopentadiene, 3,4,5,6,7,7-hexachloroendomethylene-l,2,3,6-tetrahydrophthahc anhydride (HET). The resultant resins from HET contribute to the flame retardancy of the alkyd coatings. HET gives a greater reaction rate than phthaUc anhydride, to the extent that at 204—210°C the reaction rate approximates that of phthaUc anhydride at a temperature of 238°C (8). However, the resins tend to develop darker color, particularly at high processing temperature. Tetrachlorophthahc anhydride [117-08-8] made by conventional chlorination of phthaUc anhydride, would also impart flame retardancy to its alkyds. However, it is appreciably less soluble in the usual processing solvents than is phthaUc anhydride, and is reported to be of appreciably lower chemical reactivity (8). 

Polyurethane engineering thermoplastics are also manufactured from MDI and short-chain glycols (49). These polymers were introduced by Upjohn/Dow under the trade name Isoplast. The glycols used are 1,6-hexanediol and cyclohexanedimethanol. 1,4-Butanediol is too volatile at the high processing temperatures used in the reaction extmsion process. Blends of engineering thermoplastics with TPU are also finding uses in many appHcations... 

Esters of thiopropionic acid tend to decompose at high processing temperatures, and their odor makes them unsuitable for some food-packaging apphcations. 

The cooling requirements will be discussed further in Section 8.2.6. What is particularly noteworthy is the considerable difference in heating requirements between polymers. For example, the data in Table 8.1 assume similar melt temperatures for polystyrene and low-density polyethylene, yet the heat requirement per cm is only 295 J for polystyrene but 543 J for LDPE. It is also noteworthy that in spite of their high processing temperatures the heat requirements per unit volume for FEP (see Chapter 13) and polyethersulphone are, on the data supplied, the lowest for the polymers listed. 

Viscous deformations, at a fixed deforming stress, increase rapidly with temperature whereas elastic deformations change much more slowly. For this reason the high elastic deformation component tends to be more important at lower processing temperatures than at high processing temperatures. 

Because of the high processing temperatures there are few pigments suitable for use with PTFE. A number of inorganic pigments, particularly the cadmium compounds, iron oxides and ultramarines, may, however, be used. 

Because polycarbonates are good light absorbers, ultraviolet degradation does not occur beyond a depth of 0.030-0.050 in (0.075-0.125 cm). Whilst this is often not serious with moulded and extruded parts, film may become extremely brittle. Improvements in the resistance of cast film may be made by addition of an ultraviolet absorber but common absorbers cannot be used in moulding compositions because they do not withstand the high processing temperatures. 

The common feature of the p-phenylene group stiffens the polymer backbone so that the polymers have higher TgS than similar polymers which lack the aromatic group. As a consequence the aromatic polymers tend to have high heat deformation temperatures, are rigid at room temperature and frequently require high processing temperatures. 

The steam for process heating is generated in either fire or water-tube boilers, using the most economical fuel available. The process temperatures required usually can be obtained with low pressure steam (tyq ically 25 psig), and steam is distributed at a relatively low pressure (typically 100 psig). Higher steam pressures are needed for high process temperatures. 

Counterclockwise from top (1) Extruded fins offer high performance, reliability, and economy. (2) Hy-Fin extruded-serrated fins represent the state-of-the-art in fin tube construction technology. (3) Imbedded fins are recommended for applications involving high process temperatures. (4) L-base wrap-on fins offer low initial cost for applications involving low process temperatures. 

In addition to the maintenance application described above, this coupling (also referred to as extension or spacer sleeve coupling) is commonly used where equipment is subject to thermal expansion and possible misalignment because of high process temperatures. The purpose of this... 

Maintenance requiring considerable distance between the driver and driven shaft ends. 2) Misalignment results from expansion due to high process temperatures. 

Excessively high processing temperatures can increase the rate of thermal decompo-... 

Shrinkage The transition from room temperature to a high processing temperature may decrease a plastic s density by up to 25 %. Cooling causes possible shrinkage (up to 3 % ) and may cause surface distortions or voiding with internal frozen strains. As discussed in other chapters, this situation can be reduced or eliminated by special techniques, such as controlled cooling under pressure. 

The unusual thermal stability and water uptake properties are due to the formation of a three-dimensional network in polysaccharides at high processing temperatures [12]. 

Why is it sometimes necessary to cool an extruder barrel, even though you need to maintain high processing temperatures ... 

---