Other Common Processes

The feedstock in hydrodealkylation units is heated to 1,200° F (650°C) in a preheat furnace before entering the reactor. Above 1,100°F (590°C), metal dusting or catastrophic carburization occurs on ail alloys that are otherwise suitable for the temperature conditions. The attack is very rapid and takes the form of round bottom pits. The surface of the remaining metal is heavily carburized. A small quantity of sulfur (0.05 to 0.5 wt%) in the form of hydrogen sulfide or mercaptan added to the feed will prevent attack. Aluminizing has also been used to prevent attack. 

Polymerization units use phosphoric acid as a catalyst in the reactor. Because solid phosphoric acid catalysts do not cause corrosion, carbon steel can be used. However, liquid phosphoric acid is very corrosive to carbon steel, so corrosion resistant materials are required. At a phosphoric acid concentration of 100%, type 304L SS is satisfactory up to 120 F (50 C), and type 316L SS is required from 120 to 225°F (50 to 107°C). 

Phenol is produced by the oxidization of cumene And is followed by cleavage of the oxidation product of phenol and acetone. Type 304L SS (clad) is required to resist corrosion in the oxidation vessel, and alloy 20 (clad) is often used in the cleavage vessel. 

Hydrogen, Methanol, Ammonia, Gas Treating, Hydrodealkylation, Polymerization, Phenol, and Solvent Treating 

Steels were manufactured in Germany and tested in pilot plants at the I.G. Farbenindustrie Ammonia Werke, Merseburg.3 

---

Regeneration involves the removal of the adsorbed contaminants from carbon by means of processes that destroy neither the contaminants nor the carbon. A common process is pressure swing adsoiption, where low pressure is applied to remove the contaminants from the solid phase. Other common processes involve the use of steam (volatilization of adsorbed contaminants) or the use of a hot inert gas, such as nitrogen. The contaminants are recovered as liquid after a condensation step. 

Aluminum can now be produced from clay, but the process is not economically feasible at present. Aluminum is the most abundant metal to be found in the earth s crust (8.1%), but is never found free in nature. In addition to the minerals mentioned above, it is found in granite and in many other common minerals. 

Lead is obtained chiefly from galena (PbS) by a roasting process. Anglesite, cerussite, and minim are other common lead minerals. 

In general, acryUc ester monomers copolymerize readily with each other or with most other types of vinyl monomers by free-radical processes. The relative ease of copolymerization for 1 1 mixtures of acrylate monomers with other common monomers is presented in Table 7. Values above 25 indicate that good copolymerization is expected. Low values can often be offset by a suitable adjustment in the proportion of comonomers or in the method of their introduction into the polymerization reaction (86). 

Small loads are commonly processed in a box furnace. The product is placed on the furnace hearth through a door. Box furnaces may be single-ended or double-ended. A single-ended box furnace is usually used in an air atmosphere appHcation where the product can be removed hot from the furnace for cooling. A double-ended box furnace is usually used in a controlled atmosphere appHcation. In this case a water cooler is attached to one end. The product can be placed on the hearth (in the heat chamber) through the front door, then after the product reaches temperature, it is manually transferred into the water cooler for cooling before it is manually removed out the exit door on the other end of the water cooler. 

Other common radical-initiated polymer processes include curing of resins, eg, unsaturated polyester—styrene blends curing of mbber grafting of vinyl monomers onto polymer backbones and telomerizations. 

Flexo and gravure inks are both known as Hquid inks because of their low viscosity. The inks for both systems have basic components in common with inks for other printing processes. Vehicles disperse and carry the pigment, and also contribute most to the end use properties. Colorants provide color. Solvents dissolve resins in the vehicle and determine drying rate. Additives modify ink properties to overcome deficiencies. 

Slurry Viscosity. Viscosities of magnesium hydroxide slurries are determined by the Brookfield Viscometer in which viscosity is measured using various combinations of spindles and spindle speeds, or other common methods of viscometry. Viscosity decreases with increasing rate of shear. Fluids, such as magnesium hydroxide slurry, that exhibit this type of rheological behavior are termed pseudoplastic. The viscosities obtained can be correlated with product or process parameters. Details of viscosity deterrnination for slurries are well covered in the Hterature (85,86). 

Some alkylphenols in commercial production have low vapor pressures and/or low thermal decomposition temperatures. Eor these products, the economics of distillation are poor and other recovery processes are used. Crystallisation from a solvent is the most common nondistUlation method for the purification of these alkylphenols. 

As with any other fabrication process, masks are needed to define the features to be etched. It is common that the etch used for the semiconductor also etches the masking material. For this reason many different masks are used in etching, including photoresist, dielectric films, and metals. Masking can be a complex issue, especially when very deep etches (>5 fim) are performed with high aspect ratios (148). 

Liquid Injection. Liquid injection units are the most common type of incinerator today for the destmction of Hquid hazardous wastes such as solvents. Atomizers break the Hquid into fine droplets (100—150 microns) which allows the residence time to be extremely short (0.5—2.5 s). The viscosity of the waste is very important the waste must be both pumpable and capable of being atomized into fine droplets. Both gases and Hquids can be incinerated in Hquid injection units. Gases include organic streams from process vents and those from other thermal processes in the latter case, the Hquid injection incinerator operates as an afterburner. Aqueous wastes containing less than 75% water can be incinerated in Hquid injection units. 

To allow flexibility, the database manager must also perform point addition or deletion. However, the abihty to create a point type or to add or delete attributes of a point type is not normally required because, unlike other data processing systems, a process control system normally involves a fixed number of point types and related attributes. For example, analog and binary input and output types are required for process I/O points. Related attributes for these point types include tag names, values, and hardware addresses. Different system manufacturers may define different point types using different data structures. We will discuss other commonly used point types and attributes as they appear. 

Crystalhzation is important as an industrial process because of the number of materials that are and can be marketed in the form of crystals. Its wide use is probably due to the highly purified and attractive form of a chemical solid which can be obtained from relatively impure solutions in a single processing step. In terms of energy requirements, crystallization requires much less energy for separation than do distillation and other commonly used methods of purification. In addition, it can be performed at relatively low temperatures and on a scale which varies from a few grams up to thousands of tons per day. 

The success of these two processes, one requiring refrigeration at -300°F, and the other at -125°F, poses the questions What are the preferred applications for turboexpanders Why not use them in air conditioners or other commonly used refrigeration systems ... 

The setting of these materials after shaping occurs via a chemical process, that of cross-linking. The most common process is moulding but some extrusion, sintering and other miscellaneous processes are also used. A typical compression moulding process is illustrated in Figure 8.12. 

---