What Is the Maximum Mass of Ammonia That Can Be Produced From a Mixture of 1.00

The industry of ammonia is crucial for the world'southward agricultural manufacture for from it all fertilizers that incorporate nitrogen are produced.

Uses of ammonia

The manufacture of fertilizers is by far the nigh important apply of ammonia. These include urea, ammonium salts (ammonium phosphates, ammonium nitrate, calcium ammonium nitrate) and solutions of ammonia.

Figure i The uses of ammonia.

An increasing corporeality of ammonia, although still small-scale compared with other uses, is used equally a concentrated solution in combating the discharge of nitrogen oxides from power stations.

Annual production of ammonia

Ammonia ranks 2nd, to sulfuric acid, as the chemical with the largest tonnage. It is being increasingly made in countries which accept low price sources of natural gas and coal (China and Russia account for ca 40%). The largest plants produce about 3000 tonnes a day and there are plans to build plants that produce 4000-5000 tonnes a solar day, which would mean that the total earth output could exist managed with 100 such units. Current production is:

World	146 1000000 tonnes
China	48 million tonnes
Russia	12 million tonnes
Republic of india	xi meg tonnes
U.South.	ix meg tonnes
Indonesia	5 million tonnes
Trinidad and Tobago	v meg tonnes
Ukraine	4 million tonnes

Data from:
U.S. Geological Survey, Mineral Commodity Summaries, 2016.

The increment in tonnage of ammonia made is only keeping pace with the increasing globe polulation and with its increasing standard of living.  It is expected that the demand for ammonia will increase to nearly 200 million tonnes by 2018¹.
1.  International Fertilizer Association, 2014.

Manufacture of ammonia

The industry of ammonia from nitrogen and hydrogen takes place in two main stages:

a) the manufacture of hydrogen

b) the synthesis of ammonia (the Haber Process)

The manufacture of hydrogen involves several distinct processes. Figure 2 shows their sequence and the location within an ammonia constitute (steps1-v). The converter used to make ammonia from the hydrogen is also shown (step vi). What occurs in each of these steps is described below the figure.

Effigy 2 An ammonia plant in Western Australia: 1 Desulfurisation units 2 Master reformer 3 High temperature and low temperature shift reactors iv Carbon dioxide absorber v Carbon dioxide stripper (recovery of the pure solvent, ethanolamine) 6 Ammonia converter 7 Ammonia storage as liquid 8 Pipeline to the ship for consign By kind permission of Yara International ASA.

(a) The manufacture of hydrogen

Hydrogen is produced from a variety of feedstocks, mostly from natural gas, coal or naphtha. The ways in which hydrogen is obtained from these feedstocks are dealt with separately.

Hydrogen from natural gas (methane)

This involves two stages:

i) the industry of synthesis gas (a mixture of carbon monoxide and hydrogen (steam reforming))

ii) the removal of the carbon monoxide and production of a mixture of hydrogen and nitrogen (the shift reaction)

(i) The industry of synthesis gas

Whichever way the methane is obtained, information technology will contain some organic sulfur compounds and hydrogen sulfide, both of which must be removed. Otherwise, they will poisonous substance the catalyst needed in the manufacture of synthesis gas. In the desulfurisation unit, the organic sulfur compounds are oftentimes first converted into hydrogen sulfide, prior to reaction with zinc oxide. The feedstock is mixed with hydrogen and passed over a catalyst of mixed oxides of cobalt and molybdenum on an inert support (a specially treated alumina) at ca 700 Thou.

Then the gases are passed over zinc oxide at ca 700 K and hydrogen sulfide is removed:

Primary steam reforming converts methyl hydride and steam to synthesis gas, a mixture of carbon monoxide and hydrogen:

High temperatures and low pressures favour the germination of the products (Le Chatelier's Principle). In practice, the reactants are passed over a goad of nickel, finely divided on the surface of a calcium oxide/aluminium oxide support contained in vertical nickel alloy tubes. The tubes, upwards to 350 in parallel, are heated in a furnace above grand Thou and under a pressure of ca xxx atm. This is an instance of a tubular reactor.

Secondary steam reforming reacts oxygen from the air with some of the hydrogen present and the resulting mixture is passed over a nickel goad. The steam and oestrus produced from the combustion reforms most of the residue methane. Among the key reactions are:

The emerging gas from this net exothermic stage is at ca 1200 One thousand and is cooled in heat exchangers. The steam formed from the water used in cooling the gases is used to operate turbines and thus compressors and to preheat reactants.

Some recent designs use waste heat from the secondary reformer directly to provide heat for the primary reformer.
At this stage the gas contains hydrogen, nitrogen, carbon monoxide and carbon dioxide and most 0.25% methyl hydride. Equally air contains 1% argon, this also accumulates in the synthesis gas.

(ii) The shift reaction

This process converts carbon monoxide to carbon dioxide, while generating more hydrogen.

It takes place in ii stages. In the first, the loftier temperature shift reaction, the gas is mixed with steam and passed over an iron/chromium(III) oxide catalyst at ca 700 Thou in a fixed bed reactor. This decreases the carbon monoxide concentration from xi%:

In the second stage, the low temperature shift reaction, the mixture of gases is passed over a copper-zinc catalyst at ca 500 K. The carbon monoxide concentration is further reduced to 0.2%.

The reaction is done in ii stages for several reasons. The reaction is exothermic. However, at high temperature, the exit concentration of carbon monoxide is nonetheless quite loftier, due to equilibrium command. The copper catalyst used in the depression temperature phase is very sensitive to high temperatures, and could not operate effectively in the high temperature stage. Thus, the bulk of the reaction is carried out at high temperature to recover well-nigh of the estrus. The gas is then removed at low temperature, where the equilibrium is much more favourable, on the very active just unstable copper catalyst.

The gas mixture now contains virtually xviii% carbon dioxide which is removed by scrubbing the gas with a solution of a base of operations, using one of several available methods. One that is favoured is an organic base (in the carbon dioxide cushion), a solution of an ethanolamine, often 2,2'-(methylimino)bis-ethanol (N-methyl diethanolamine).

The carbon dioxide is released on heating the solution in the carbon dioxide stripper). Much of it is liquefied and sold, for example, for carbonated drinks, every bit a coolant for nuclear power stations and for promoting the growth of plants in greenhouses.

The concluding traces of oxides of carbon are removed by passing the gases over a nickel goad at 600 K:

This process is known as methanation. A gas is obtained of typical limerick: 74% hydrogen, 25% nitrogen, 1% methane, together with some argon.

Hydrogen from naphtha

If naphtha is used as the feedstock, an extra reforming stage is needed. The naphtha is heated to grade a vapour, mixed with steam and passed through tubes, heated at 750 K and packed with a goad, nickel supported on a mixture of aluminium and magnesium oxides. The main product is methane together with oxides of carbon, and is then candy by steam reforming, every bit if it was natural gas, followed by the shift reaction.

Hydrogen from coal

If coal is used, it is kickoff finely ground and heated in an temper of oxygen and steam. Some of the coal burns very rapidly in oxygen (in less than 0.1 southward) causing the temperature in the furnace to rise and the rest of the coal reacts with the steam:

The gas emitted contains ca 55% carbon monoxide, 30% hydrogen, x% carbon dioxide and minor amounts of methane and other hydrocarbons. This mixture is treated by the shift reaction.

The main problems of using coal includes the large amounts of sulfur dioxide and trioxide generated in burning coal and the significant amounts of other impurities such as arsenic and bromine, all of which are very harmful to the atmosphere and all of which are severe poisons to the catalysts in the process. There is besides a massive problem with disposal of the ash.

Hydrogen from biomass

Synthesis gas gas can be produced from biopmass.  The process is outlined in the unit on biorefineries.

(b) The manufacture of ammonia (The Haber Procedure)

The heart of the procedure is the reaction between hydrogen and nitrogen in a stock-still bed reactor. The gases, in stoichiometric proportions, are heated and passed under force per unit area over a catalyst (Figure 3).

Figure iii A diagram illustrating a conventional synthesis reactor (a converter).

The proportion of ammonia in the equilibrium mixture increases with increasing pressure level and with falling temperature (Le Chatelier's Principle). Quantitative data are given in Tabular array 1. To obtain a reasonable yield and favourable rate, high pressures, moderate temperatures and a catalyst are used.

Pressure/atm	Percentage ammonia present at equilibrium at a range of temperatures
	373 Chiliad	473 K	573 One thousand	673 K	773 K	973 Yard
10	-	50.7	14.7	3.9	one.ii	0.ii
25	91.vii	63.six	27.4	8.vii	2.9	-
50	94.5	74.0	39.5	15.3	5.half-dozen	1.ane
100	96.7	81.vii	52.5	25.2	10.6	2.2
200	98.4	89.0	66.7	38.8	18.3	-
400	99.4	94.half-dozen	79.7	55.4	31.9	-
1000	-	98.3	92.6	79.eight	57.5	12.9

Table i Pct, by book, of ammonia in the equilibrium mixture for the reaction
betwixt nitrogen and hydrogen at a range of temperatures and pressures.

A wide range of conditions are used, depending on the structure of the reactor. Temperatures used vary between 600 and 700 M, and pressures between 100 and 200 atmospheres. Much work is being done to improve the effectiveness of the goad so that pressures every bit depression equally 50 atmospheres tin be used.

As the reaction is exothermic, cool reactants (nitrogen and hydrogen) are added to reduce the temperature of the reactors (Figure three).

The ammonia is ordinarily stored on site (step 7) and pumped to another function of the plant where it is converted into a fertilizer (urea or an ammonium salt). However it is sometimes transported past sea (Figure 4) or by road, to be used in another institute.

Figure 4 In a plant in Western Australia, the ammonia is transferred by pipeline to a nearby harbour (Effigy 2, stride eight) and transported by transport. This one is conveying almost 40 000 tonnes of liquefied ammonia. By kind permission of Yara International ASA.

The original catalyst that Haber used was Atomic number 26₃O₄, which was reduced by the reactant, hydrogen, to iron. Much work was done to improve the catalyst and it was institute that a small amount of potassium hydroxide was effective every bit a promoter.

Recently enquiry has been focussed on finding even more effective catalysts to enable the process to take place at lower pressures and temperatures. Ruthenium on a graphite surface is a promising one.

Effigy five The production of ammonia.

Postscript

The Haber Process is of such importance to our lives that it has figured in 3 Nobel Prizes in chemical science, all to German scientists, over a flow of about ninety years, a remarkable record.

The first was given in 1918, to Fritz Haber, the chemist who adult the process in the laboratory. The second was to Carl Bosch, whose brilliant engineering skills fabricated the process viable on a massive scale, but who waited until 1931 for his award.

In 2007, Gerhard Ertl was awarded the Prize for his piece of work on catalysis of gaseous reactions on solids. Among the wide range of reactions he studied, he gained evidence for the adsorption of nitrogen molecules and hydrogen molecules on the surface atomic number 26 and that these adsorbed molecules dissociate into atoms. These atoms then join up in stages to grade the ammonia molecule. It must be remembered that the weather used in these studies (at less than ten^-10 atm) are very unlike from the conditions used in industry, ca 150 atm.

Summary

The whole procedure of producing ammonia from methane is summarized in Figure five. If coal or naphtha is the feedstock, actress processes are needed. Naphtha is converted into methyl hydride and oxides of carbon earlier going into the principal reformer and thence to the shift reaction. Coal is also converted into hydrogen and carbon oxides and this mixture and then undergoes the shift reaction.

Engagement last amended: 18th October 2016

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Source: https://www.essentialchemicalindustry.org/chemicals/ammonia.html

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