Separation of Hydrogen and Nitrogen

In this application hydrogen is separated as a permeate at the lower pressure side of the membrane. Consequently, it must be recompiessed to the pressure of the reactor. 

Membrane material (pore dia. in nm) Temp 0 0 TMP (bar) S.F. P (baner) Reference Note 

AI2O3 (10-20) 20 3.7 2.5x105 Toyo Soda [1985] anodic oxide 

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Table 4 summarizes commercial and precommercial gas separation appHcations (86,87). The first large-scale commercial appHcation of gas separation was the separation of hydrogen from nitrogen ia ammonia purge gas streams. This process, launched ia 1980 by Monsanto, was followed by a number of similar appHcations, such as hydrogen—methane separation ia refinery off-gases and hydrogen—carbon monoxide adjustment ia oxo-chemical synthetic plants. 

In gas separation with membranes, a gas mixture at an elevated pressure is passed across the surface of a membrane that is selectively permeable to one component of the mixture. The basic process is illustrated in Figure 16.4. Major current applications of gas separation membranes include the separation of hydrogen from nitrogen, argon and methane in ammonia plants the production of nitrogen from ah and the separation of carbon dioxide from methane in natural gas operations. Membrane gas separation is an area of considerable research interest and the number of applications is expanding rapidly. 

Example 7.2 Separation by thermal diffusion Consider two vessels connected by a thermally insulated conduit. The system is filled with a solution of hydrogen and nitrogen. The hydrogen mass fraction is wu = 0.2. Estimate the difference between the mass fraction of the components in the two vessels at stationary state when one of the vessels is at 200 K and the other at 370 K. 

Haber focused on the scientific question at the heart of the problem, the willingness of hydrogen and nitrogen atoms to combine into ammonia, rather than maintain their separate fives. In the language of chemistry, he was trying to find the point of balance, or equilibrium, between the reaction that created ammonia and the opposite one, in which ammonia broke down into free nitrogen and hydrogen. 

For analytical purposes low-temperature distillation has now to some extent been superseded by gas chromatography (chap. 5.1.2). If, however, the object is to prepare a considerable quantity of a pure gas or to effect a comparison with a large-scale installation, low-temperature distillation is still the best method. This applies especially to industrial waste gases without hydrogen concentrations and, more recently, to natural gas. For example, the separation of helium and nitrogen from natural gas is still a difficult problem. The separation of fission rare gases from the used air of... 

The basic synthetic process is the Haher-Bosch method. As presented in Fig. 32.2, ammonia is produced by the reversible reaction of hydrogen with nitrogen. The reactants mixture, often called the synthesis gas, consists of hydrogen and nitrogen in roughly 3 1 molar ratio and impurities such as argon, methane, carbon dioxide, carbon monoxide, and water vapor. Nitrogen is separated from the air. 

Molecular Sieve 13X Separation of hydrogen, oxygen, nitrogen, methane, and CO. 

Figure 1.1. A schematic design of the circulation system used to obtain ammonia continuously from the stoichiometric mixture of hydrogen and nitrogen (A) is the compressor, (B) the reactor, (C) the separator, and (D) the circulation pump.

The iodine compound is more stable and separates as so-called nitrogen trHodide monoammoniate [14014-86-9], NI NH, an insoluble brownish-black soHd, which decomposes when exposed to light in the presence of ammonia. In reactions of the halogens with the respective ammonium salts, however, the action is different. Chlorine replaces hydrogen and nitrogen chloride [10025-85-1], NCl, separates as oily, yeUow droplets capable of spontaneous explosive decomposition. 

Ammonium nitrate is manufactured by reacting ammonia with nitric acid. Consider the process shown by Fig. 9.19. First, namral gas is reformed and converted into hydrogen, nitrogen and carbon dioxide. Hydrogen and nitrogen are separated an fed to the ammonia synthesis plant. A fraction of the produced ammonia is employed in nitric acid formation. Ammonia is first oxidized with compressed air then absorbed in water to form nitric acid. Finally nitric acid is reacted with anunonia to oduce ammonium nitrate. 

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