Example Ammonia Process

In this example, you will take an input stream to the process (at 80°F and 300 psia) of nitrogen, 100 lb mol/h hydrogen, 300 lb mol/h ammonia, 0 and carbon dioxide, 1 lb mol/h. 

Now that the process is fully specified, you can solve it. Because there is a recycle stream, begin the calculations with the first unit, the compressor. The output from that unit is combined with the recycle stream, which initially is zero. Follow the stream through the rest of the process until it computes the recycle stream. This recycle stream is now different from its previous value. Thus, the program does another iteration, and 

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Exchange of ionizable materials, primarily dissolved iron. Here the preferred media/process is resin bead deep-bed polishers. Resins may be operated in different cycle modes and where, for example ammonia, morpholine, or AVT programs are employed, specific operating conditions are necessary to avoid adverse effects of the ammonia anion cycle. 

PAMAM dendrimers are synthesized in a multistep process. Starting from a multifunctional amine (for example ammonia, ethylenediamine, or tris(2-amino-ethyl)amine) repeated Michael addition of methylacrylate and reaction of the product with ethylenediamine leads to dendrimers of different generation numbers [1,9]. Two methylacrylate monomers are added to each bifunctional ethylenediamine generating a branch at each cycle. Unreacted ethylenediamine has to be completely removed at each step to prevent the initiation of additional dendrimers of lower generation number. Excess methylacrylate has also to be removed. Bridging between two branches of the same or of two different dendrimers by ethylenediamine can also be a problem, and has to be avoided by choosing appropriate reaction conditions. 

Three well known examples of processes employing fluidised-bed operations are the oxidations of naphthalene and xylene to phthalic anhydride using a supported V2O5 catalyst and ammoxidation of propylene utilising a mixed oxide composition containing bismuth molybdate. Typically, this latter reaction is executed by passing a mixture of ammonia, air and propylene to a fluidised bed operating at about 0.2 MPa pressure, 400—500°C and a few seconds contact time between gas and fluidised catalyst peirticles. 

Steam turbines. In modern plants the centrifugal synthesis gas compressors, including recycle, are almost exclusively driven by a steam turbines. These are generally extraction turbines with a condensing section. Steam is extracted at suitable pressure levels (e.g. 45-55 bar) to provide, for example, the process steam in steam reforming plants, and for other drivers, e.g., air compressor, ammonia compressor, boiler feed water pumps, and blowers. 

The term p is the absolute pressure, V is the volume, n is the number of moles, R is the gas constant, and T is the absolute temperature. The units of R have to be appropriate for the units chosen for the other variables. This equation is quite adequate when the pressure is low (such as one atmosphere). However, many chemical processes take place at very high pressure. For example, ammonia is made at pressures of 220 atmospheres or more. Under these conditions, the ideal gas equation of state may not be a valid representation of reality. 

Aspen Plus has the capability of optimizing a function that you define. An example is given here that is very simple, but it illustrates the process. Take a single unit, the reactor in the ammonia process. The reactor RGibbs is used and the production of ammonia is maximized with respect to the reactor pressure. In this example, the reactor is unit BI, with input stream 1 and output stream 2. 

Murphy (91) has also described a converter that will generate condensation nuclei from a reactant that would normally not be detected by TPA. For example, ammonia can be detected by passing it through a flask containing a small amount of hydrochloric acid. The gaseous HCl above the solution reacts with the ammonia to form condensation nuclei of ammonium chloride. Other gases and the conversion processes employed are shown in Table... 

For the ammonia process in Example 5.3, consider operation of the reactor at 932°F and 400 atm. Use a simulator to show how the product, recycle, and purge flow rates, and the mole fractions of argon and methane, vary with the purge-to-recyclc ratio. How do the power requirements for compression vary, assuming 3 atm pressure drop in the reactor and I atm pressure drop in the heat exchanger. 

Indeed, acids and bases react with one another by proton transfer. Scheme 8.13 shows by way of example the process occurring between NH3, which is a base, and the acid HCl. Using the curved arrow method (see Retouches section 8.R.5), we can see what we saw before the lone pair of ammonia makes a bond with the H-end of the acid and causes thereby breakage of the H—Cl bond and departure of Cl . In fact, what we formed is the ionic material NH4 C1 , which we constructed before. 

Many types of reactors are needed in the processing industries to cope with the wide variation in production rates and the extensive range of reactions. These include gas-phase reactions in the presence of solid catalysts (for example, ammonia synthesis and oxidation of SO2 to SO3) and gas-phase reactions in the absence of catalysts. Examples of these homogeneous reactions are certain chlorinations (such as ethene with chlorine), sulphonation of olefins and the oxidation of nitric oxide. 

As we saw in the ammonia process, the reactor is usually the key unit. The reactor will often dictate whether a chemical process is possible. Separators are secondary only to the reactor in most processes the performance of the separator(s) will often determine if a process is profitable. Examples of separators include dryers, filters, absorbers, adsorbers, and centrifuges. The method used to separate a mixture - distillation, condensation, or filtering - is usually indicated by a specific symbol on the flowsheet. We will introduce these specific units later, as needed. 

Cracking of admiralty metal (C 44300) heat-exchanger tubes has been a recurring problem in a number of refining units and petrochemical process units. For example, ammonia is often used to neutralize acidic constituents, such as hydrogen chloride or sulfur dioxide, in overhead systems of crude distillation or alkylation units, respectively. Stripped sour water containing residual ammonia is used as desalter water at some crude distillation units. This practice causes ammonia contamination of the overhead system even if no ammonia is added intentionally. 

By the action of concentrate aqueous ammonia solution upon esters. This process is spoken of as ammonolysls of the ester, by analogy with hydrolysis applied to a similar reaction with water. If the amide is soluble in water, e.g., acetamide, it may be isolated by distillation, for example ... 

Alkylthiazoles can be oxidized to nitriles in the presence of ammonia and a catalyst. For example, 4-cyanothiazole was prepared from 4-methylthiazole by a one-step vapor-phase process (94) involving reaction with a mixture of air, oxygen, and ammonia at 380 to 460°C. The catalyst was M0O3 and V Oj or M0O3, VjOj, and CoO on an alumina support. 

Urea Process. In a further modification of the fundamental Raschig process, urea (qv) can be used in place of ammonia as the nitrogen source (114—116). This process has been operated commercially. Its principal advantage is low investment because the equipment is relatively simple. For low production levels, this process could be the most economical one. With the rapid growth in hydrazine production and increasing plant size, the urea process has lost importance, although it is reportedly being used, for example, in the People s RepubHc of China (PRC). 

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