Phosphoric acid design

A widely used type of pump—mixer—settler, developed by IsraeH Mining Industries (IMI) (115), is shown in Figure 13a. A unit having capacity 8.3 m /min (2000 gal /min) has been used in phosphoric acid plants (116). The unique feature of this design is that the pumping device is not required to act as the mixer, and the two phases are dispersed by a separate impeller mounted on a shaft miming coaxially with the drive to the pump. 

Uranium is present in small (50—200 ppm) amounts in phosphate rock and it can be economically feasible to separate the uranium as a by-product from the cmde black acid (30% phosphoric acid) obtained from the leaching of phosphate for fertilizers (qv). The development and design of processes to produce 500 t U Og per year at Ereeport, Louisiana have been detailed (272). 

Figure 2 illustrates the three-step MIBK process employed by Hibernia Scholven (83). This process is designed to permit the intermediate recovery of refined diacetone alcohol and mesityl oxide. In the first step acetone and dilute sodium hydroxide are fed continuously to a reactor at low temperature and with a reactor residence time of approximately one hour. The product is then stabilized with phosphoric acid and stripped of unreacted acetone to yield a cmde diacetone alcohol stream. More phosphoric acid is then added, and the diacetone alcohol dehydrated to mesityl oxide in a distillation column. Mesityl oxide is recovered overhead in this column and fed to a further distillation column where residual acetone is removed and recycled to yield a tails stream containing 98—99% mesityl oxide. The mesityl oxide is then hydrogenated to MIBK in a reactive distillation conducted at atmospheric pressure and 110°C. Simultaneous hydrogenation and rectification are achieved in a column fitted with a palladium catalyst bed, and yields of mesityl oxide to MIBK exceeding 96% are obtained. 

Activated alumina and phosphoric acid on a suitable support have become the choices for an iadustrial process. Ziac oxide with alumina has also been claimed to be a good catalyst. The actual mechanism of dehydration is not known. In iadustrial production, the ethylene yield is 94 to 99% of the theoretical value depending on the processiag scheme. Traces of aldehyde, acids, higher hydrocarbons, and carbon oxides, as well as water, have to be removed. Fixed-bed processes developed at the beginning of this century have been commercialized in many countries, and small-scale industries are still in operation in Brazil and India. New fluid-bed processes have been developed to reduce the plant investment and operating costs (102,103). Commercially available processes include the Lummus processes (fixed and fluidized-bed processes), Halcon/Scientific Design process, NIKK/JGC process, and the Petrobras process. In all these processes, typical ethylene yield is between 94 and 99%. 

Chemical Designations - Synonyms-. APO Phosphoric acid triethileneimide Triethylenephosphor-amide Tris (1-aziridinyl) phosphin oxide Chemical Formula-. (CH2CHiN)3PO or C HjjNjPO. Observable Characteristics - Physical State (as normally shipped)-. Solid Color. > ite Odor. Data not available. 

Because of this extreme sensitivity, attention shifted to an acidic system, the phosphoric acid fuel cell (PAFC), for other applications. Although it is tolerant to CO, the need for liquid water to be present to facilitate proton migration adds complexity to the system. It is now a relatively mature technology, having been developed extensively for stationary power usage, and 200 kW units (designed for co-generation) are currently for sale and have demonstrated 40,000 hours of operation. An 11 MW model has also been tested. 

This input to design refers to the long-term stability of the raw material sources for the plant. It is only of importance where the raw materials can or do contain impurities which can have profound effects on the corrosivity of the process. Just as the design should cater not only for the norm of operation but for the extremes, so it is pertinent to question the assumptions made about raw material purity. Crude oil (where HjS, mercaptan sulphur and napthenic acid contents determine the corrosivity of the distillation process) and phosphate rock (chloride, silica and fluoride determine the corrosivity of phosphoric acid) are very pertinent examples. Thus, crude-oil units intended to process low-sulphur crudes , and therefore designed on a basis of carbon-steel equipment, experience serious corrosion problems when only higher sulphur crudes are economically available and must be processed. 

In 2006, Yamamoto and Nakashima picked np on this and designed a chiral A -triflyl phosphoramide as a stronger Brpnsted acid catalyst than the phosphoric acids based on this concept. In their seminal report, they disclosed the preparation of new chiral BINOL-derived A -triflyl phosphoramides and their application to the asymmetric Diels-Alder (DA) reaction of a,p-unsaturated ketones with sily-loxydienes [83], As depicted in Scheme 59, chiral A-triflyl phosphoramides of the general type 4 are readily synthesized from the corresponding optically active 3,3 -substituted BINOL derivatives 142 through a phosphorylation/amidation route. 

Chiral phosphoric acids mediate the enantioselective formation of C-C, C-H, C-0, C-N, and C-P bonds. A variety of 1,2-additions and cycloadditions to imines have been reported. Furthermore, the concept of the electrophilic activation of imines by means of phosphates has been extended to other compounds, though only a few examples are known. The scope of phosphoric acid catalysis is broad, but limited to reactive substrates. In contrast, chiral A-triflyl phosphoramides are more acidic and were designed to activate less reactive substrates. Asymmetric formations of C-C, C-H, C-0, as well as C-N bonds have been established. a,P-Unsaturated carbonyl compounds undergo 1,4-additions or cycloadditions in the presence of A-triflyl phosphoramides. Moreover, isolated examples of other substrates can be electrophil-ically activated for a nucleophilic attack. Chiral dicarboxylic acids have also found utility as specific acid catalysts of selected asymmetric transformations. 

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