Reactors, crystallization

Process equipment function changes with different steps in process sequence (e.g., same vessel used as feed tank, reactor, crystallizer pump... 

Process equipment function changes with different steps in process sequence (e.g., same vessel used as feed tank, reactor, crystallizer pump used to pump in/out). Instrumentation and controls not kept in phase with the current process step (e.g., control set points, interlocks etc.). 

Figure 9.9 Adipic acid reactor-crystallizer-separation system optimization Chang and Ng, 1998)...

Generally, in MPPs one centrifuge or pressure/vacuum filter, one drier, and one fractionation system of reasonable capacity are installed for every two or three reactors/crystallizers. On average, about 2 to 5 m solvent storage capacity and the same amount for intermediates are needed per 1 m of reactor capacity. 

Generally water is used, in a nickel sulfate plant for process reaction, cooling of reactor, crystallization, plant washdown of spills, pump leaks and general cleanup. The water used in the process reaction is for preliminary preparation of the spent plating solution. In other units, especially where impure nickel raw material is used, the wastewater is often recycled. Wastewaters from this plant contain contact and noncontact water, which predominantly contain nickel as a major impurity. 

Many effective control schemes have been established over the years for individual chemical units (Shinskey, 1988), For example, a tubular reactor usually requires control of inlet temperature. High-temperature endothermic reactions typically have a control system to adjust the fuel flowrate to a furnace supplying energy to the reactor. Crystallizers require manipulation of refrigeration load to control temperatui e. Oxygen concentration in the stack gas from a furnace is controlled to prevent excess fuel usage. Liquid solvent feed flow to an absorber is controlled as some ratio to the gas feed. We deal with the control of various unit operations in Chaps. 4 through 7. 

In this monograph, a number of notations, units, and abbreviations will be used, and they are summarized in Appendix A. It contains lists of notations for crystal orientations, process parameters for CVD, analytical techniques, CVD reactors, crystal growth, and carbon materials in addition to a description of standard diamond film characterizations, i.e. Raman spectroscopy and cathodoluminescence (CL). The readers are recommended to just quickly read through Appendix A at this point. 

Figure 9.18 General purpose glass-lined batch reactor/crystallizer.

Table 25.1 lists several combinations of reaction and separation. The sequencing of the two in the nomenclature of the different combinations clearly reveals their orientations. This chapter is primarily concerned with reactive extraction (also termed dissociation-extraction), extractive reaction, reactive distillation (or dissociation-extractive-distillation), and distillative reaction (or distillation column reactors). Crystallization is almost always used for separation and seldom for enhancing a reaction. A notable exception is when one of the reactants is a sparingly dissolving solid and the size of the crystallizing solid is less than the thickness of the film surrounding the reactant. Then the crystallizing microphase enhances the rate of dissolution and hence the rate of reaction, a situation that was considered in Chapter 23. 

Feeders are devices that introduce a variety of materials into dryers at a controlled, specified rate. Usually, the feeder is located at the interface stage between material-handling equipment or upstream process and the dryer. The materialhandling equipment may be a hopper or a bin whereas the upstream process may be a reactor, crystallizer, filter, hydrocyclone, centrifuge, etc. 

The underflow solvent stream from the reactor/crystallizer contains both dissolved and precipitated. sulfur plus the water formed in the reaction between H2S and S02- After flashing to remove part of the residual dissolved H2S and some of the hydrocarbons, the liquid is cooled to 10°C, and sent to a sulfur settler. The flow to the settler is adjusted to keep the water content of the solvent from exceeding S% with the flow rate typically at about 10% of the total flow of solvent through the primary absorber. The sulfur settler is a dual-purpose ves.sel. Its primary function is to separate and recover the precipitated sulfur particles. Its secondary role is to serve as a solvent surge tank. 

Pu (86 years) is formed from Np. Pu is separated by selective oxidation and solvent extraction. The metal is formed by reduction of PuF with calcium there are six crystal forms. Pu is used in nuclear weapons and reactors Pu is used as a nuclear power source (e.g. in space exploration). The ionizing radiation of plutonium can be a health hazard if the material is inhaled. 

Fig. 3. Typical nitric acid oxidation process. A, reactor B, optional cleanup reactor C, bleacher D, NO absorber E, concentrating stUl F, crude crystallizer G, centrifuge or filter H, refined crystallizer I, centrifuge or filter , dryer K, purge evaporator L, purge crystallizer M, centrifuge or filter N,...

A typical flow diagram for pentaerythritol production is shown in Figure 2. The main concern in mixing is to avoid loss of temperature control in this exothermic reaction, which can lead to excessive by-product formation and/or reduced yields of pentaerythritol (55,58,59). The reaction time depends on the reaction temperature and may vary from about 0.5 to 4 h at final temperatures of about 65 and 35°C, respectively. The reactor product, neutralized with acetic or formic acid, is then stripped of excess formaldehyde and water to produce a highly concentrated solution of pentaerythritol reaction products. This is then cooled under carefully controlled crystallization conditions so that the crystals can be readily separated from the Hquors by subsequent filtration. 

Sodium fluoride is normally manufactured by the reaction of hydrofluoric acid and soda ash (sodium carbonate), or caustic soda (sodium hydroxide). Control of pH is essential and proper agitation necessary to obtain the desired crystal size. The crystals are centrifuged, dried, sized, and packaged. Reactors are usually constmcted of carbon brick and lead-lined steel, with process lines of stainless, plastic or plastic-lined steel diaphragm, plug cock, or butterfly valves are preferred. 

The same reactants are used for manufacture as for sodium fluoride. An excess of acid is required to crystallize the bifluoride. The crystals are dewatered, dried, sized, and packaged. Cooling of the reaction is necessary to avoid over-heating and decomposition. Reactors and auxiUary equipment are the same as for sodium fluoride. 

The reactor effluent, containing 1—2% hydrazine, ammonia, sodium chloride, and water, is preheated and sent to the ammonia recovery system, which consists of two columns. In the first column, ammonia goes overhead under pressure and recycles to the anhydrous ammonia storage tank. In the second column, some water and final traces of ammonia are removed overhead. The bottoms from this column, consisting of water, sodium chloride, and hydrazine, are sent to an evaporating crystallizer where sodium chloride (and the slight excess of sodium hydroxide) is removed from the system as a soHd. Vapors from the crystallizer flow to the hydrate column where water is removed overhead. The bottom stream from this column is close to the hydrazine—water azeotrope composition. Standard materials of constmction may be used for handling chlorine, caustic, and sodium hypochlorite. For all surfaces in contact with hydrazine, however, the preferred material of constmction is 304 L stainless steel. 

For the production of tartar emetic (antimony potassium tartrate [28300-74-5]), potassium bitartrate [868-14 ] and antimony oxide, Sb202, are added simultaneously to water in a stainless-steel reactor. The reaction mixture is diluted, filtered, and collected in jacketed granulators where crystallization takes place after cooling. Centrihiging, washing, and drying complete the process. 

Up to 0.4 g/L of the iodine stays in solution and the rest precipitates as crystallized iodine, which is removed by flotation (qv). This operation does not require a flotation agent, owing to the hydrophobic character of the crystallized element. From the flotation cell a heavy pulp, which is water-washed and submitted to a second flotation step, is obtained. The washed pulp is introduced into a heat exchanger where it is heated under pressure up to 120°C to melt the iodine that flows into a first reactor for decantation. From there the melt flows into a second reactor for sulfuric acid drying. The refined iodine is either flaked or prilled, and packed in 50- and 25-kg plastic-lined fiber dmms. 

The softened seawater is fed with dry or slaked lime (dolime) to a reactor. After precipitation in the reactor, a flocculating agent is added and the slurry is pumped to a thickener where the precipitate settles. The spent seawater overflows the thickener and is returned to the sea. A portion of the thickener underflow is recirculated to the reactor to seed crystal growth and improve settling and filtering characteristics of the precipitate. The remainder of the thickener underflow is pumped to a countercurrent washing system. In this system the slurry is washed with freshwater to remove the soluble salts. The washed slurry is vacuum-filtered to produce a filter cake that contains about 50% Mg(OH)2. Typical dimensions for equipment used in the seawater process may be found in the Hterature (75). 

Spain, Tmbia nea Oviedo 1972 spray chamber as primary roaster, plate reactor as secondary stage continuous electrolysis of filtered electrolyte, continuous crystallization 2,000 112... 

Ammonia, hydrochloric acid, and sodium perchlorate are mixed and the reaction mixture crystallised in a vacuum-cooled crystalliser. Ammonium perchlorate crystals are centrifuged, reslurried, recentrifuged, and then dried and blended for shipment. Mother Hquor is evaporated to precipitate sodium chloride and the depleted mother Hquor is recycled to the reactor. The AP product made by this method is 99% pure and meets the specifications for propeUant-grade ammonium perchlorate. The impurities are ammonium chloride, sodium perchlorate, ammonium chlorate, and water insolubles. 

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