Flow-sheeting PROCESS

Fig. 1. (a) Process flow sheet for human insulin production, recovery, and purification (12) (b) corresponding steps in recovery of biosynthetic human... 

At this time over 95% of all new urea plants are Hcensed by Snamprogetti, Stamicarbon, or Toyo Engineering. SNAM utilizes thermal stripping while STAC (Stamicarbon) and Toyo use CO2 stripping. Only these three processes are, therefore, covered in detail. Process flow sheets are included for others at the end of this section. 

Other Processes. Flow sheets for typical partial-recycle process and typical once-through urea process are given in Figures 9 and 10, respectively. 

Oxidation Step. A review of mechanistic studies of partial oxidation of propylene has appeared (58). The oxidation process flow sheet (Fig. 2) shows equipment and typical operating conditions. The reactors are of the fixed-bed shell-and-tube type (about 3—5 mlong and 2.5 cm in diameter) with a molten salt coolant on the shell side. The tubes are packed with catalyst, a small amount of inert material at the top serving as a preheater section for the feed gases. Vaporized propylene is mixed with steam and ak and fed to the first-stage reactor. The feed composition is typically 5—7% propylene, 10—30%... 

Acrylic Acid Recovery. The process flow sheet (Fig. 3) shows equipment and conditions for the separations step. The acryUc acid is extracted from the absorber effluent with a solvent, such as butyl acetate, xylene, diisobutyl ketone, or mixtures, chosen for high selectivity for acryUc acid and low solubihty for water and by-products. The extraction is performed using 5—10 theoretical stages in a tower or centrifiigal extractor (46,61—65). 

Esterifica.tlon. The process flow sheet (Fig. 4) outlines the process and equipment of the esterification step in the manufacture of the lower acryflc esters (methyl, ethyl, or butyl). For typical art, see References 69—74. The part of the flow sheet containing the dotted lines is appropriate only for butyl acrylate, since the lower alcohols, methanol and ethanol, are removed in the wash column. Since the butanol is not removed by a water or dilute caustic wash, it is removed in the a2eotrope column as the butyl acrylate a2eotrope this material is recycled to the reactor. 

An extraction plant should operate at steady state in accordance with the flow-sheet design for the process. However, fluctuation in feed streams can cause changes in product quaUty unless a sophisticated system of feed-forward control is used (103). Upsets of operation caused by flooding in the column always force shutdowns. Therefore, interface control could be of utmost importance. The plant design should be based on (/) process control (qv) decisions made by trained technical personnel, (2) off-line analysis or limited on-line automatic analysis, and (J) control panels equipped with manual and automatic control for motor speed, flow, interface level, pressure, temperature, etc. 

A flow sheet of the basic TVA process for granular diammonium phosphate is given in Figure 12. The raw materials are wet-process phosphoric acid and anhydrous ammonia. Feed acid concentration of at least 40% P2 5 required to give a satisfactory water balance. This average concentration usually is provided by two separate feed streams, one of 54% P2 5 concentration and one of about 30% P2 5 arrangement shown, the 54% acid is... 

Process Design and Machinery. Following the field work of geologists and mining engineers and analyses (assays) to estabhsh the grades (concentrations) of values in ores, a mineral concentration flow sheet is estabhshed on the basis of a number of preliminary tests. These include studies of... 

Fig. 2. Process flow sheet of (a) Sasol One and (b) the Sasol synfuel process for Sasol Two and Three (36). LPG is Hquefied petroleum gas other terms are...

The first step is to have a complete and detailed description of the system, process, or procedure under consideration. This must include physical properties of the materials, operating temperatures and pressures, detailed flow sheets, instmment diagrams of the process, materials of constmction, other detailed design specifications, and so forth. The more detailed and up-to-date this information is, the better the result of the analysis. 

The first step in the procedure is to define the purpose, objectives, and scope of the study. The more precisely this is done, the more focused and relevant the committee discussions can be. The next step is to collect all relevant information on the process under consideration. This includes flow diagrams, process equipment specifications, nominal flows, etc. The procedure is highly dependent on the reflabiUty of this information. Efforts expended here are worthwhile. Many committees use the flow sheet as the central stmcture to organize thek discussions. 

Peroxide-Ketazine Process. Elf Atochem in France operates a process patented by Produits Chimiques Ugine Kuhhnaim (PCUK). Hydrogen peroxide (qv), rather than chlorine or hypochlorite, is used to oxidize ammonia. The reaction is carried out in the presence of methyl ethyl ketone (MEK) at atmospheric pressure and 50°C. The ratio of H202 MEK NH2 used is 1 2 4. Hydrogen peroxide is activated by acetamide and disodium hydrogen phosphate (117). Eigure 6 is a simplified flow sheet of this process. The overall reaction results in the formation of methyl ethyl ketazine [5921-54-0] (39) and water ... 

Fig. 6. Peroxide—ketazine process flow sheet. MEK = ethyl ketone.

MIDREX Process. The primary components of a MID REX process plant include the shaft furnace, reformer, and heat recuperator. These components are supported by ancillary systems for handling iron ore, gas, water, and direct reduced iron. A flow sheet is shown in Figure 1. 

The dehydrogenation of 2-butanol is conducted in a multitube vapor-phase reactor over a zinc oxide (20—23), copper (24—27), or brass (28) catalyst, at temperatures of 250—400°C, and pressures slightly above atmospheric. The reaction is endothermic and heat is suppHed from a heat-transfer fluid on the shell side of the reactor. A typical process flow sheet is shown in Figure 1 (29). Catalyst life is three to five years operating in three to six month cycles between oxidative reactivations (30). Catalyst life is impaired by exposure to water, butene oligomers, and di-j -butyl ether (27). 

Soda. Process. Use of a soda smelting process for treating copper drosses in the reverberatory furnace increases the copper to lead ratios in the matte and speiss, and aUows lower operating temperatures. A flow sheet describing this process is shown in Figure 11. 

Fig. 4. Process flow sheets for (a) the silicothermic reduction and (b) the MOR process. See text.

Production of a metal is usually achieved by a sequence of chemical processes represented as a flow sheet. A limited number of unit processes are commonly used in extractive metallurgy. The combination of these steps and the precise conditions of operations vary significantly from metal to metal, and even for the same metal these steps vary with the type of ore or raw material. The technology of extraction processes was developed in an empirical way, and technical innovations often preceded scientific understanding of the processes. 

The essential operations of an extractive metallurgy flow sheet are the decomposition of a metallic compound to yield the metal followed by the physical separation of the reduced metal from the residue. This is usually achieved by a simple reduction or by controlled oxidation of the nonmetal and simultaneous reduction of the metal. This may be accompHshed by the matte smelting and converting processes. 

Fig. 4. Flow sheet for the processing of titanium ore by chlorination followed by reduction with magnesium.

Hydrometallurgical Flow Sheets. The various hydrometallurgy operations can be combined in many ways to design processes appropriate for specific metals. 

Fig. 5. Flow sheet foi Sheiiitt-Goidon process for production of nickel and cobalt metals from sulfide ore.

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