Recycle ammonia

Fig. 38. Caustic purification system a, 50% caustic feed tank b, 50% caustic feed pumps c, caustic feed preheater d, amonia feed pumps e, ammonia feed preheater f, extractor g, trim heater h, ammonia subcooler i, stripper condenser j, anhydrous ammonia storage tank k, primary flash tank 1, evaporator reboiler m, evaporator n, caustic product transfer pumps o, purified caustic product cooler p, purified caustic storage tank q, ammonia stripper r, purified caustic transfer pumps t, overheads condenser u, evaporator v, evaporator vacuum pump w, aqueous storage ammonia tank x, ammonia scmbber y, scmbber condenser 2, ammonia recirculating pump aa, ammonia recycle pump. CW stands for chilled water.

Fig. 1. Andrussow process plant with ammonia recycle.

The second reaction represents the decomposition of the carbamate. The reaction conditions are 200°C and 30 atmospheres. Decomposition in presence of excess ammonia limits corrosion problems and inhibits the decomposition of the carbamate to ammonia and carbon dioxide. The urea solution leaving the carbamate decomposer is expanded by heating at low pressures and ammonia recycled. The resultant solution is further concentrated to a melt, which is then prilled by passing it through special sprays in an air stream. Figure 5-3 shows the Snamprogetti process for urea production. ... 

The Heat Recycle Urea Process (HRUP) was developed by Urea Technologies in the 1970 s and is now offered by Monsanto Enviro-Chem. This process is shown in Figure 11.5. In this process ammonia, recycled carbamate and about 60% of the make-up CO2 feed are charged to the top of an open-ended reactor coil at 3200 psig (220 bar). Ammonium carbamate is formed within the coil, exits the coil at the bottom and flows up and around it. The exothermic heat of carbamate formation in the coil drives the endothermic dehydration of carbamate to urea on the outside of the coil. This isothermal reactor design allows the conversion rate to reach 77%. The reactor has a uniform temperature profile that eliminates corrosion in the bottom of the reactor112. 

Figure 19.1. Andrussow HCN Process with Ammonia Recycle. (This material is used by permission of John Wiley and Sons, Inc.)...

Singh, R., Khwaja, A., Gupta, B., and Tandon, S. (1999) Extraction and separation of nickel(II) using bis(2,4,4-trimethylpentyl) dithiophosphinic acid (Cyanex 301) and its recovery from spent catalyst and electroplating bath residue. Solv. Extraction Ion Exch., 17 (2), 367-390. Malinowska, B., Rakib, M., and Durand, G. (2001) Ammonia recycling and cadmium confinement in chemical bath deposition of CdS thin layers. Prog. Photovoltaics, 9 (5), 389—404. 

The difficult elimination is accomplished by making it an ammonia transfer reaction rather than an elimination of ammonia. Recycling the enzyme does eventually require elimination of ammonia... 

Fig. 22.29. Andrussow HCN process with ammonia recycle.129 (Copyright by John Wiley Sons, Inc. and reproduced by permission of copyright owner.)...

Description Anhydrous liquid ammonia, recycled amines and methanol are continuously vaporized (1), superheated (3) and fed to a catalyst-packed converter (2). The converter utilizing a high-activity, low-byproduct amination catalyst simultaneously produces MMA, DMA and TMA. Product ratios can be varied to maximize MMA, DMA, or TMA production. The correct selection of the N/C ratio and recycling of amines produces the desired product mix. Most of the exothermic reaction heat is recovered in feed preheating (3). 

The urea solution from synthesis section is sent to MP decomposer at 17 bar and LP decomposer at 2.5 bar for further purification. No pure ammonia recycle is required due to the high separation efficiency in the stripper. 

Description Anhydrous liquid ammonia, recycled amines and methanol are continuously vaporized (1), superheated (3) and fed to a catalyst-packed converter (2). The converter utilizing a high activity, low byproduct amination catalyst simultaneously produces MMA,... 

Calculates mo from the known value of the nitric acid feed rate, the current value of the ammonia recycle rate (mi), and the specified value of 5% excess ammonia in the reactor feed. 

Raw biomass is extremely persistent to enzymatic degradation. Therefore, methods of thermochemical pretreatment have been developed to improve the digestibility of biomass (18). For example, ammonia explosion, aqueous ammonia recycle, controlled pH, dilute acid, flow through, and hme treatment were applied to prepare com stover, i.e., the leaves and stalks of maize, for a subsequent conversion to sugars. 

Iyer PV, Wu ZW, Kim SB, Lee YY. (1996). Ammonia recycled percolation process for pretreatment of herbaceous biomass. Appl Biochem Biotechnol, 57-58, 121-132. 

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