Potassium Industries

Potassium, K

Potassium occurs in nature only in the form of its compounds. It is one of the ten most common
elements in the earth’s crust. Potassium compounds are obtained almost entirely by the mining of salt
deposits. The more important salt minerals are halite, anhydrite, sylvanite, sylvite, carnallite, and
kieserite that were obtained from USA, Canada, Russia and Germany.

In 1807, potassium metal was first isolated using an electrolysis apparatus. When potassium metal
reacts with oxygen in dry air, it produces a powerful oxidizing agent, potassium superoxide (K 2O).
With moisture air, potassium hydroxide is produced.

Manufacturing Processes. Potash ores are treated today by three basic processes:
1. Leaching-crystallization (originally cooked in open vessels, an oldest process; vacuum
cooling was introduced in 1918 in the United States)
2. Flotation (introduced in 1935 in the United States)
3. Electrostatic treatment (first used on a large scale in the German potash industry in 1974)

Fine KCl
Carnallite Leach Tank Deslimator Hydroseparator

Coarse KCl

Brine Crushed Carnallite Amine/Starch

Separator

Treating Chamber
K
salts
Flotation Cells
Figure 1. Flow Chart of K salts production from carnallite

Importance and Uses. The most important function of potassium is the activation of more than 80
enzymes. It is also integral to a number of other plant processes, translocation of carbohydrates, and
protein synthesis. As a result, potassium deficiencies cause numerous problems from decreasing rates
of photosynthesis to the weakening of straw in grain crops. In addition it has important effects on
quality factors of plants.

Economics. The world potash production is amounted to 25.8 x 106 t K2O in 2001. However,
potassium chloride is not a versatile potassium source. The more favourable potassium sources for
the production of multi-component fertilizers are potassium sulfate and potassium nitrate.

Compounds of Potassium

Potassium Chloride, KCl

It occurs in many salt deposits mixed with halite and other salt minerals. It is also occurred in natural
sylvite, which is usually opalescent or milky white. When this compound is mixed with magnesium
chloride, they formed the double salt carnallite (KCl•MgCl2•6H2O), which is also commonly found
in salt deposits.

Manufacturing and Production. Hot Leaching Process – An oldest industrial process used to produce
potassium chloride from potash ore (1860). Two different processes are used, depending on the
composition of the ore:
 1. Sylvinite Hot Leaching (the other salts present in addition to KCl and NaCl play only a
minor role in the process solutions)
2. Hard Salt Leaching (solutions contain appreciable amounts of MgCl2 and MgSO4)

Process:
1. Potash ore, ground to a fineness of <4–<5 mm, is stirred in a continuous dissolver with
leaching brine heated to just below its boiling point.
2. Coarse fraction is removed from
the dissolver and debrined.
1 2
3. Fine fraction (fine residue/ slime)
is removed from the dissolver
along with the crude solution,
which is clarified with the aid of
clarifying agents. 3
4. Slime that separates is filtered off 4
and then recycled to the
recirculating brine. Clarification
includes washing the residues with 9 5
water to remove the adhering crude H2O
solution.
5. Hot, clarified crude solution is 6
cooled by evaporation in vacuum 7
equipment. 8
6. Potassium chloride and sodium
chloride crystallize as the water is
removed.
Figure 2. Overall Systematic: Hot Leaching Process
7. The crystals formed are separated from the
mother liquor and processed further.
8. Mother liquor is heated.
9. Mother liquor is recycled to the dissolver as leaching brine.

Economics. More than 90% of the potassium chloride produced is used in single-nutrient or multi-
nutrient fertilizers, either directly or after conversion to potassium sulfate.

Importance and Uses. As a chemical feedstock, it is used for the manufacture of potassium
hydroxide and potassium metal. It is also used in medicine, in scientific applications, in food
processing, and as a sodium-free substitute for table salt (sodium chloride). Potassium chloride is
used as the third of a three-drug combination in lethal injection. Additionally, it is used (rarely) in
fetal intracardiac injections in second- and third-trimester induced abortions. Potassium chloride was
once used as a fire extinguishing agent.

Potassium Carbonate, K2CO3

Potassium carbonate was produced in antiquity and used for many purposes. Anhydrous potassium
carbonate is a white, hygroscopic, powdery material that deliquesces in moist air.

Manufacture and Production. The currently industrially most important process of potassium
carbonate is the carbonation of electrolytically produced potassium hydroxide. Fifty percent
potassium hydroxide is saturated with carbon dioxide; the solution partially evaporated and the
potassium carbonate hydrate (K2CO3•1.5H2O), which precipitates out and is separated. After drying,
the product is either marketed as potash hydrate or is calcined in a rotary tube furnace at temperature
of 250°C to 350°C to anhydrous potassium carbonate.

From Caustic Potash and Carbon Dioxide. KOH reacted with carbon dioxide or CO2-
containing off-gases (flue gas, lime kiln gas):
 2KOH + CO2 → K2CO3 + H2O

7
3
6 5
9
8 4

Figure 3. Preparation of potassium carbonate with continuous crystallization.

a) Carbonization; b) Crude liquor filter; c) Fresh liquor tank; d) Mixed liquor tank;
e1,2) Preliminary evaporation; f) Vacuum/ cooling crystallization (Chemietechnik Messo system);
g) Preheater; h) Vapor condenser; i) Vacuum pump; j) Hydrocyclone;k) Centrifuge; l) Centrifuge

Steps:
1. Solid potassium carbonate is then obtained by crystallization (under vacuum and with
cooling) from liquors or in the fluidized-bed process.
2. Until the hydrate K2CO3•1.5H2O finally precipitates in the crystallizer after cooling
under vacuum.
3. The mother liquor is separated from the crystal suspension in hydrocyclones.
4. Mother liquor centrifuges.
5. Mother liquor is then filtered.
6. Mother liquor that is separated is fed back to the process.
7. The crystals are dried at ca. 110°C–120°C. Impurities such as soda, sulfate, silicic acid,
and iron that concentrate in the mother liquors can be partially removed by removing a
partial stream of the mother liquor or by drying process.
8. Crystals are calcined at 200°C–350°C to give 98%–100% K2CO3.
9. The resulting potassium carbonate is very pure and meets the requirements if the process
is operated in appropriate manner.

Steps:
1. Aqueous potassium
1 hydroxide solution is
4
sprayed into a fluidized-
bed reactor from above
3 and exposed to a
countercurrent of CO2-
2 containing hot gas.
Carbonization and
calcinations take place in
the same reactor.
2. Hard, spherical potassium
5 carbonate prills are formed
 having a high packing density.
3. The prills are discharged and sieved.
Figure 4. Production of potassium carbonate by the fluidized-bed process
4. The coarse grains are ground and returned to the
reactor together with the very fine grains, where
they act as crystallization seeds.
5. The salable, dust-free, medium grains are cooled and packed. Because no mother liquor is
formed, the quality of the potassium carbonate depends on that of the raw materials.

Other processes of manufacturing potassium carbonate were included, yet these processes are
uneconomical today because of high energy consumption and poor product quality, and are no
longer used:
1. Amine Process
2. Nepheline Decomposition Process
 The mineral nepheline is decomposed with limestone by sintering at 1300°C:

(Na, K)2•Al2O3•2SiO2 + 4CaCO3 → (Na, K)2O•Al2O3 + 2(2CaO•SiO2) + 4CO2

The sinter product is leached with a Na2CO3–NaOH solution. After filtration, a filter cake
is obtained that is processed to give portland cement and an aluminate solution containing
silicic acid. After precipitation of the silicic acid as alkaline aluminum silicate the purified
aluminate solution is reacted with carbon dioxide:

2(Na, K)AlO2 + CO2 + 3H2O → 2Al(OH)3 + (Na, K)2CO3

3. The magnesia process (Engel – Precht process; limited interest):

3(MgCO3•3H2O) + 2KCl + CO2 → 2(MgCO3•KHCO3•4H2O) + MgCl2

In hot water the double salt (MgCO3·KHCO3·4H2O) decomposes under pressure into
magnesium carbonate and dissolved potassium carbonate.

4. Le Blanc process:

K2SO4 + CaCO3 + 2C → CaS +K2CO3 + 2CO2

5. Formate process:

K2SO4 + Ca(OH)2 + 2CO → 2HCOOK + CaSO4

HCOOK + KOH+ 1.5O2 → K2CO3 + H2O

6. Piesteritz process :

K2SO4 + 2CaCN2 + 2H2O → 2KHCN2 + CaSO4 + Ca(OH)2

2KHCN2 + 5H2O → K2CO3 + 4NH3 + CO2

7. Ion-Exchange Process

Economics. About 4% to 5% of potash production is used in industrial applications. In 1996, the

world supply of industrial grade potash was close to 1.35Mt K2O. This industrial material is 98%-
99% pure, compared with the agricultural potash specification of 60% K2O minimum (equivalent to
95% KCl). Industrial potash should contain at least 62% K2O and have very low levels of Na. Mg,
Ca, SO4 and Br.

Uses. Since 1860, potash salts have replaced wood as a raw material for the manufacture of
potassium carbonate. Potassium carbonate is used for fertilizer, for production of commercial soap,
as a compound found in gunpowder and for making glass. Large amounts are also required for
potassium silicate manufacture; used for many organic syntheses; electrical industry, the dye
industry, the printing trade, the textile industry, the leather goods industry, and the ceramic industry.
The food industry uses potassium carbonate as a leavening agent in baked goods, as a debitterizing
agent for cocoa beans, and as an additive for drying raisins.

Potassium Sulfate (sulfate of potash), K2SO4

It occasionally occurs in nature in the pure state in salt deposits but is more widely found in the form
of mineral double salts in combination with sulfates of calcium, magnesium, and sodium. Its mineral
name is arcanite. It is refined from naturally occurring mineral salt deposits or by chemical synthesis.

Manufacture and Production. Industrial synthesis of potassium sulfate is a two-step process:

1. ionic separation of mined potassium chloride and another sulfate-bearing salt via electrolysis
2. joining of potassium ion and sulfate ion in controlled lab-setting at temperatures up to 120°C.

From Potassium Chloride and Sulfuric Acid (Mannheim Process). The reaction of sulfuric acid with
potassium chloride takes place in two
stages:

1. KCl +H2SO4 → KHSO4 + HCl

2. KCl +KHSO4 → K2SO4 + HCl

The first reaction step is exothermic and

proceeds at relatively low temperature. The
second is endothermic and must be carried
out at higher temperature.
Process: Furnace, closed dish-shaped
chamber with diameter up to 6 m, is heated
externally. Potassium chloride and sulfuric
acid are fed into the chamber in the
Figure 5. Schematic diagram of a Mannheim furnace
required ratio at an overhead central point. The
mixture reacts with evolution of heat and is mixed by a slowly moving stirrer fitted with stirring
arms with scrapers. Potassium sulfate leaves the reaction chamber at this point and is neutralized and
cooled. It normally contains 50 – 52% K2O and 1.5 – 2% Chloride. Hydrogen chloride gas formed
when absorbed in water will form hydrochloric acid.

From Potassium Chloride and

Magnesium Sulfate. The sulfate required
is provided by kieserite, MgSO4•H2O.
The reaction can be represented by the
following overall equation:

1. 2KCl +MgSO4 → K2SO4 + MgCl2

Kieserite reacts very slowly and must be

ground finely before reaction.
Alternatively, it can first be Figure 6. Flow diagram of the two-stage production of
recrystallized to give epsomite, MgSO4•7H2O. potassium sulfate from potassium chloride and
magnesium sulfate

Figure 6. Solid epsomite or finely ground kieserite with potassium chloride and presence of a
definite quantity of water are mixed in conversion chamber with the sulfate mother liquor which
is recycled from the second stage to form schoenite, K2SO4•MgSO4•6H2O or leonite,
K2SO4•MgSO4•4H2O. Potash – magnesia liquor/brine is also formed. The schoenite is reacted
with additional potassium chloride to form potassium sulfate and sulfate mother liquor and
sulfate mother liquor is stirred with potassium chloride solution:
 1. 2KCl + 2MgSO4 + xH2O → K2SO4•MgSO4•6H2O+ MgCl2 (aq)
2. 2KCl +K2SO4•MgSO4•6H2O+ xH2O → 2K2SO4 + MgCl2 (aq)

From Potassium Chloride and Kainite. Kainite, KCl•MgSO4 •2.75H2O, is obtained from a potash ore
by flotation.
Steps:
1. Kainite, KCl•MgSO4•2.75H2O is obtained from a grinned potash ore by flotation.
2. Kainite is converted into schoenite at 25°C with mother liquor containing the sulfates of
potassium and magnesium.
3. Schoenite is filtered off and decomposed with water at 48°C.
4. Most of the potassium sulfate to crystallize.
5. Sulfate mother liquor is recycled to the kainite– Figure 7. Flow diagram of the production of
schoenite conversion stage. potassium sulfate from kainite
6. Contains 30% of the 1
potassium used, is
treated with gypsum,
2
CaSO4•2H2O causing 6
sparingly soluble
syngenite,
K2SO4•CaSO4•H2O, to
precipitate.
7. Syngenite is 7
3
decomposed with 5 8 9
water at 5°C, which
dissolves potassium 4
sulfate and
reprecipitates gypsum.
8. Potassium sulfate
solution is recycled to
the schoenite decomposition stage.
9. Gypsum is reused to precipitate syngenite.

From Potassium Chloride and Sodium Sulfate. The production of potassium sulfate from
potassium chloride and sodium sulfate takes place in two stages, with glaserite, Na 2SO4•3K2SO4,
as an intermediate, according to the following equations:

1. 4Na2SO4 + 6KCl → Na2SO4•3K2SO4 + 6NaCl

2. Na2SO4•3K2SO4 + 2KCl → 4K2SO4 + 2NaCl

Potassium chloride and sodium sulfate are reacted at 20°C–50°C in water and recycled
process brines to form glaserite, which is filtered and then reacted with more potassium
chloride and water to form potassium sulfate. Because the mother liquor from the glaserite
stage has a high potassium and sulfate content, the maximum potassium yield is 73%, and the
maximum sulfate yield is 78%. The yield can be increased considerably by cooling the
mother liquor to produce more crystals and by including a final evaporation stage.

Other processes of manufacturing potassium sulfate include:

1. From Potassium Chloride and Calcium Sulfate (processes based on gypsum,

CaSO4•2H2O)
2. From Alunite, K2SO4•Al2(SO4)3•4Al(OH)3
3. Single-Stage Process from Sodium Sulphate:
For the sake of thermodynamics constraints, the process of potassium sulfate production
from the sodium sulfate proceeds in two steps:
 1. 6KCl + 4Na2SO4 → 2K3Na(SO4)2 + 6NaCl
2. 2KCl + 2K3Na(SO4)2 → 4K2SO4 + 2NaCl

4. From Potassium Chloride and Langbeinite:

K2SO4•2MgSO4 + 4KCl → 3K2SO4 + 2MgCl2

Economics. Worldwide, almost all technical grade potassium sulfate production, >99%, is used in
agriculture. Moreover, sulfate of potash production since the mid-80’s has been characterized by an
up and down cycle. The latest upward trend ended in 1998 due to development of new sulfate of
potash sources that outpaced demand, and a massive destruction of tobacco cropping acreage in the
US and China. (According to industry representatives, the sulfate of potash market is characterized
by major over-capacities in production with further increase expected.)

Importance and Uses. Potassium sulfate is, after potassium chloride, the most important potassium-
containing fertilizer, being used mainly for special crops. Potassium sulfate constitutes 5% of the
world demand for potash fertilizer and used in a wide range of industrial uses, for manufacturing
potassium alum, for manufacturing potassium carbonate and for manufacturing glass.

Potassium Hydroxide, KOH

Commonly called caustic potash. It is a caustic compound of strong alkaline chemical dissolving
readily in water, giving off much heat and forming a caustic solution.

Manufacture and Production. Today, potassium hydroxide is manufactured almost exclusively by

potassium chloride electrolysis. There are three different processes:
1. Diaphragm process (KCl-containing, 8%–10 % potassium hydroxide solution is initially
formed, whose salt content can be reduced to 1.0%–1.5% KCl by evaporation to a 50%
liquor)
2. Mercury process [very pure KCl brine must be utilized, because even traces (ppb range) of
heavy metals such as chromium, tungsten, molybdenum, and vanadium, as well as small
amounts (ppm range) of calcium or magnesium; very pure potassium hydroxide solution
running off the decomposers is cooled, freed from small amounts of mercury in precoated
filters]
3. Membrane process [cell liquor has a low chloride content (10–50 ppm); the KOH
concentration is 32%; before dispatch, it is concentrated to 45%–50% by evaporation]

Economics. World production is estimated at 700–800 10 3 t/a. Main producers are the United States,
Germany, Japan, and France.

Uses. Pure-quality potassium hydroxide is used as a raw material for the chemical and
pharmaceutical industry, in dye synthesis, for photography as a developer alkali, and as an electrolyte
in batteries and in the electrolysis of water; raw material in the detergent and soap industry; as a
starting material for inorganic and organic potassium compounds and salts; for the manufacture of
cosmetics, glass, and textiles; for desulfurizing crude oil; as a drying agent; and as an absorbent for
carbon dioxide and nitrogen oxides from gases.

Potassium Dichromate, K2Cr2O7

Potassium dichromate is a major patent chromium chemical of commerce. In 1880, Germany

introduced Na2CO3 as a substitute for K2CO3 in manufacturing, since then sodium dichromate
gradually replaced K2Cr2O7.

Manufacture and Production. Potassium dichromate process starts:

1. Reaction of potassium hydroxide and chromium trioxide in a reactor creating a mother liquor:
 CrO + 2KOH → K2Cr2O7 + H2O

2. The mother liqour is filtered and the resultant filter solids are sent off-site for disposal to a
facility.
3. The mother liquor is then sent to a crystallizer to precipitate crystalline K 2Cr2O7, which is
recovered by centrifuging.
4. The resulting mother liquor from the product centrifuge is returned to the reactor.
2 mother liquor
Filtration 3 Crystallizer
CrO3 1 mother liquor Resultant solids
facilit *centrifuging
4
Reactor

Figure 8. Flow diagram of the production of

KOH potassium dichromate crystals

It is also prepared from chromite ore (FeCr2O4). Chromite ore is finely powdered and is heated with
sodium carbonate in the presence of air in a reverberatory furnace. The reaction produces sodium
chromate:

4FeCr2O4 + 8Na2CO3 + 7O2 → 8Na2CrO4 +2Fe2O3 + 8CO2

Na2CrO4 + H2SO4 → Na2Cr2O7 + Na2SO4 + H2O
Na2Cr2O7 + KCl → K2Cr2O7 + 2NaCl

Uses. Wide variety of uses in leather tanning, dyeing, painting, porcelain decorating, printing,
photography, pigment-prints, staining wood, pyrotechnics, safety matches, and for blending palm oil,
wax and sponges; for water-proofing fabrics, as an oxidizer in the manufacture of organic
compounds, in electrical batteries, and as a corrosion inhibitor, and in oil refining.

Potassium Nitrate, KNO3

It was first known by Hasan al-Rammah (Arab, 1270). Into the 20th century, niter-beds were
prepared by mixing manure with mortar or wood ashes. It usually under a cover from the rain, kept
moist with urine, turned often to accelerate the decomposition and leached with water after
approximately one year. The product was ammonia from the decomposition of urea and other
nitrogenous materials would undergo bacterial oxidation to produce various nitrates.

From 1903, fertilizer was produced on an industrial scale from nitric acid produced via the
Birkeland–Eyde process. Haber process (1913) was combined with the Ostwald process after 1915,
allowing Germany to produce nitric acid for the war.

Manufacture and Production. Almost all potassium nitrate, now used only as a fine chemical, is
produced from basic potassium salts and nitric acid. Potassium nitrate can be made by combining
ammonium nitrate and potassium hydroxide:

NH4NO3 (aq) + KOH (aq) → NH3 (g) + KNO3 (aq) + H2O (l)

without a by-product ammonia:

NH4NO3 (aq) + KCl (aq) → NH4Cl (aq) + KNO3 (aq)

from neutralization and the reaction is highly exothermic:

 KOH (aq) + HNO3 → KNO3 (aq) + H2O (l)

Uses. Potassium nitrate fertilizer is the most widely used application of the compound. It contains all
the macro nutrients needed for growth of plant species. It has potassium that is vital for growth of
plants. Nitrogen helps the crops to fully mature, rather than delaying their growth. Used as food
preservatives during the Middle Ages; used in many processes like curing meat, production of brine
and making corned beef. Seventy five percent potassium nitrate is found in the "Chinese Snow" or "
Devil's Distillate", a black power that is now commonly known as gunpowder and also frequently
used ingredient in cigarettes.

Nitrogen Industries

Nitrogen, N

The nitrogen cycle represents one of the

most important nutrient cycles found in
terrestrial ecosystems. Nitrogen is used
by living organisms to produce a
number of complex organic molecules.
The store of nitrogen found in the
atmosphere, where it exists as a gas
(N2), plays an important role for life.
Despite its abundance in the
atmosphere, nitrogen is often the most
limiting nutrient for plant growth. This
problem occurs because most plants can
only take up nitrogen in two solid
forms: ammonium ion (NH4+) and the
Figure 8. Nitrogen Cycle or nitrification
ion nitrate (NO3-).

Manufacture and Production. Nitrogen in the form of ammonium can be absorbed onto the surfaces
of clay particles in the soil. The ion of ammonium has a positive molecular charge is normally held
by soil colloids. This process is sometimes called micelle fixation. Ammonium is released from the
colloids by way of cation exchange. When released, most of the ammonium is often chemically
altered by a specific type of autotrophic bacteria (genus Nitrosomonas) into nitrite (NO2-);
modification by another type of bacteria (genus Nitrobacter) converts the nitrite to nitrate (NO 3-).
Both of these processes involve chemical oxidation and are known as nitrification.

Economics. Scientists estimate that biological fixation globally adds approximately 140 million
metric tons of nitrogen to ecosystems every year.

Importance and Uses. Almost all of the nitrogen found in any terrestrial ecosystem originally came
from the atmosphere. Significant amounts enter the soil in rainfall or through the effects of lightning.
The majority, however, is biochemically fixed within the soil by specialized micro-organisms like
bacteria, actinomycetes, and cyanobacteria. Members of the bean family (legumes) and some other
kinds of plants form mutualistic symbiotic relationships with nitrogen fixing bacteria. In exchange
for some nitrogen, the bacteria receive from the plants carbohydrates and special structures (nodules)
in roots where they can exist in a moist environment.

Compounds of Nitrogen
Nitric Acid, HNO3

Nitric Acid is a strong, highly corrosive and toxic mineral acid and one of the most important
inorganic acids. It is one of the few substances capable of dissolving gold and platinum, which were
known as the royal or noble metals. Pure Nitric Acid is a colourless liquid but older samples may
take on a yellowish colour due to the accumulation of oxides of Nitrogen.

Manufacture and Production. Nitric Acid is produced in two methods:

1. Weak Nitric Acid (yields 30%-90%; oxidation, condensation, and absorption)
2. High-strength Nitric Acid (yields 90%; dehydrating, bleaching, condensing, and absorption)

Weak Nitric Acid. Manufactured by the high-temperature catalytic oxidation of ammonia.

Processes include:
1. Ammonia oxidation
2. Nitric oxide oxidation
3. Absorption
Processes:
1. A 1:9 ammonia/air mixture is oxidized at a temperature of 1380°F to 1470°F as it
passes through a catalytic convertor:

4NH3 + 5O2 → 4NO + 6H2O; exothermic reaction

2. Under these conditions the oxidation of

ammonia to nitric oxide (NO) EMMISION
POINT

proceeds a range of 93 to 98 percent AIR

yield.
TAIL Oxidation temperatures
GAS
can vary from 1380°F to 14

1650°F. Higher catalyst

EFFLUENT
temperatures increase 1 TANK 2

reaction selectivity toward AMMONIA

NO production. Lower COMPRESSSOR

VAPOR
AMMONIA
OXIDIZER

catalyst temperatures EXPANDER NOX EMISSIONS

tend to be more 13
CONTROL

selective toward less useful FUEL

CATALYTIC
1 2
11

products: nitrogen (N2) and 10

nitrous oxide (N2O). 3

AIR
PREHEATER
ENTRAINED
NITRIC OXIDE GAS
3. The nitrogen dioxide/dimer 7
MIST
SEPARATOR

mixture then passes through WATER 8 a

waste heat boiler and a WASTE
STEAM
HEAT AIR
platinum filter. 4 NITROGEN
12

4. The process stream is passed DIOXIDE

ABSORPTION
TOWER
through a cooler/condenser PLATINUM 6
COOLING
WATER
FILTER
and cooled to 100°F or less at
pressures up to 116 psia. The SECONDARY AIR
nitric oxide reacts 5 PRODUCT:
30%-70%
noncatalytically with HNO 3

residual oxygen to form COOLER/CONDENSER 9

nitrogen dioxide (NO2) and Figure 9. Flow diagram of typical nitric acid
its
liquid dimer, nitrogen plant; weak nitric acid production
tetroxide:

2NO + O2 → 2NO2 ↔ N2O4

A secondary air stream is introduced into the column to re-oxidize the NO that is
formed in step 8. This air also removes NO2 from step 4.
 5. The final step introduces the nitrogen dioxide/dimer mixture into an absorption
process after being cooled. The mixture is pumped into the bottom of the absorption
tower.
6. Air with liquid dinitrogen tetroxide is added at a higher point.
7. Deionized process water enters the top of the column.
8. The absorption trays are usually sieve or bubble cap trays. The exothermic reaction
occurs as follows:

3NO2 + H2O → 2HNO3 + NO

9. An aqueous solution of 55% to 65% (typically) nitric acid is withdrawn from the
bottom of the tower. The acid concentration can vary from 30% to 70% nitric acid.
The acid concentration depends upon the temperature, pressure, number of absorption
stages, and concentration of nitrogen oxides entering the absorber.
10. The absorber tail gas (distillate) is sent to an entrainment separator for acid mist
removal.
11. The tail gas is reheated in the ammonia oxidation heat exchanger to approximately
392°F.
12. The nitric acid formed in the absorber (bottoms) is usually sent to an external bleacher
where air is used to remove (bleach) any dissolved oxides of nitrogen. The bleacher
gases are then compressed and passed through the absorber.
13. The thermal energy produced in this turbine can be used to drive the compressor. Tail
gases from the absorption tower are heated to ignition temperature, mixed with fuel
(natural gas, hydrogen, propane, butane, naphtha, carbon monoxide, or ammonia)
and passed over a catalyst bed.
14. Two seldom-used alternative control devices for absorber tailgas are molecular sieves
and wet scrubbers. In the presence of the catalyst, the fuels are oxidized and the NO x
are reduced to N2.

High-Strength Nitric Acid Production. It can be obtained by concentrating the weak nitric
acid (30% to 70% concentration) using extractive distillation.
Processes:
1. Nitric Acid from the Wweak nitric acid production is mixed with concentrated sulfuric
acid (60%) as a dehydrating agent. The acid mixture flows downward, countercurrent
to ascending vapors.
2. Concentrated nitric acid
O , HNO , NO
leaves the top of the column DEHYDRATING
2 3 2
INERT,
UNREACTED
BLEACHER
as 99 percent vapor, AGENT
AIR
GASES

containing a small amount of COOLING

WATER

NO2 and oxygen (O2)

resulting from dissociation of H SO 2 HNO
4 3 2 O , NO
ABSORPTION
CONDENSER
nitric acid. COLUMN
3. The concentrated acid vapor
leaves the column and goes to
a bleacher and a Figure 10. Flow diagram of high-strength
WEAK
HNO
3

countercurrent condenser nitric acid production from weak nitric acid

system to effect the
condensation of strong nitric acid and the separation of oxygen and oxides of nitrogen
(NOx) byproducts.
4. These byproducts then flow to an absorption column where the nitric oxide mixes
with auxiliary air to form NO2, which is recovered as weak nitric acid. Inert and
unreacted gases are vented to the atmosphere from the top of the absorption column.

Economics. In 1991, there were approximately 65 nitric acid (HNO 3) manufacturing plants in the
U.S. with a total capacity of 11 million tons of HNO 3 per year. The plants range in size from 6,000
tons to 700,000 tons per year. About 70 percent of the nitric acid produced is consumed as an
intermediate in the manufacture of ammonium nitrate (NH4NO3).

Uses. Another 5% to 10% of the nitric acid produced is used for organic oxidation in adipic acid
manufacturing. Nitric acid is also used in organic oxidation to manufacture terephthalic acid and
other organic compounds. Explosive manufacturing utilizes nitric acid for organic nitrations. Nitric
acid nitrations are used in producing nitrobenzene, dinitrotoluenes, and other chemical intermediates.
Other end uses of nitric acid are gold and silver separation, military munitions, steel and brass
pickling, photoengraving, and acidulation of phosphate rock.

Ammonia, NH3 Figure 11. Schematic representations of the

ammonia synthesis process

As the active product of “smelling salts,” the compound can1 quickly revive the faint of heart and
light of head. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by
serving as a precursor to food and 2 Natural gas
fertilizers. Ammonia, either directly or
indirectly, is also a building block
3
for the synthesis of many Desulfuriser
pharmaceuticals. atmosphere
4 flue gases
Steam reformer
Manufacture and Production.
7
Ammonia is produced in a process
Waste heat
known as the Haber process, in Air Air reformer water
boiler
which nitrogen and hydrogen react 8
steam
5

in the presence of an iron catalyst to 9 Waste heat

form ammonia. The hydrogen is water boiler
formed by reacting natural gas and 12
13
6

steam at high temperatures and the 10

nitrogen is supplied from the air. water Shift converter
Other gases (such as water and 14
11

carbon dioxide) are removed from

the gas stream and the nitrogen and saturated UCARSOL CO 2 removal UCARSOL
hydrogen passed over an iron 15
16
catalyst at high temperature and CO 2 stripper Methanation water
pressure to form the ammonia.

Steps: CO 2 Compression and

1. Natural gas may cooling
contained sulfrous
Urea plant NH 3 unreacted gases
element or compound. Mixer
2. All sulfurous compounds
must be removed from
the natural gas to prevent NH 3 converter
catalyst poisoning. These
are removed by heating
cool to 30°C
the gas to 400°C and
reacting it with zinc NH3
impurities
oxide: Decompression NH 3 recovery

NH 3
ZnO + H2S → ZnS +
Ammonia purge gas
H2O

3. Primary reformer where superheated steam is Industryfed Urea plant

with methane. The gas mixture heated with natural gas and purge gas to 770oC in the
presence of a nickel catalyst:
 CH4 + H2O ↔ 3H2 + CO
CH4 + 2H2O ↔ 4H2 + CO2
CO + H2O ↔ H2 + CO2

4. Synthesis gas (cooled to 735°C) flows to the secondary reformer where it is mixed with
calculated air:

CO + H2O ↔ CO2 + H2
O2 + 2CH4 ↔ 2CO + 4H2
O2 + CH4 ↔ CO2 + 2H2
2O2 + CH4 ↔ 2H2O + CO2

5. Carbon monoxide is converted to carbon dioxide (which is used later in the synthesis of
urea):

CO + H2O ↔ CO2 + H2

Achieved in two steps:

1. Gas stream is passed over a Cr/Fe3O4 catalyst at 360°C.
2. Gas stream is passed over a Cu/ZnO/Cr catalyst at 210°C.

6. Water condenses out and is removed from 40°C.

7. Gas with carbon dioxide is passed through a stripper chamber and removal chamber to
remove and to stripped carbon dioxide with UCARSOL. Carbon dioxide in the mixture
dissolves.
8. Saturated UCARSOL from carbon dioxide removal chamber is feed to carbon dioxide
stripper to strip the remaining carbon dioxide for urea manufacturing.
9. Remaining carbon dioxide is passed through the methanation chamber where water is
produced and is removed by condensation at 40°C. Carbon dioxide is converted to
methane using a Ni/Al2O3 catalyst at 325°C:

CO + 3H2 ↔ CH4 + H2O

CO2 + 4H2 ↔ CH4 + 2H2O

10. Gas mixture is cooled and compressed.

11. Gas stream is mixed with the mixture of ammonia and unreacted gases and cooled to 5°C.
12. Ammonia is removed and is passed through decompression with another ammonia.
13. Unreacted gases is heated to 400°C with P = 330 barg and passed over an iron catalyst
and is converted to ammonia.
14. Outlet gas is cooled from 220°C to 30°C. This process condenses more ammonia.
15. Ammonia after cooling is passed through decomposition with the ammonia from the step
11:

N2 + 3H2 ↔ 2NH3; P = 24 barg

16. Impurities such as methane and hydrogen become gases and are sent to the ammonia
recovery unit. Purge gas (used for primary or steam reformer) and recovered ammonia are
removed.

Economics. Annually 105 000 tonnes of pure ammonia (300 T day-1) are produced in Kapuni, and
most of this is converted to urea. Ammonia is produced in large petrochemical plants typically 400
000 tonnes to 800 000 tonnes per year and costing $150m to $250m. Ammonia is produced in about
80 countries and 85 per cent is for nitrogen fertiliser production including about 6 per cent for direct
use in agriculture. Production capacity has grown strongly – doubling from 62 million tonnes in 1974
to 130 million tonnes in 2000.

Importance and Uses. Most of the ammonia is used on site in the production of urea. The remainder
is sold domestically for use in industrial refrigeration systems and other applications that require
anhydrous ammonia. It is an industrial chemical, but its most important use is as the building block
of nitrogen fertilizers urea and ammonia chemicals.

Urea, NH2CONH2

Also called carbamide, is an organic chemical compound which essentially is the waste produced
when the body metabolizes protein. It is a compound not only produced by humans but also by many
other mammals, as well as amphibians and some fish. Urea was the first natural compound to be
synthesized artificially using inorganic compounds— a scientific breakthrough.

Manufacture and Production. Urea is produced from ammonia and carbon dioxide in two
equilibrium reactions:
2NH3 + CO2 ↔ NH2COONH4 (ammonium carbamate)
NH2COONH4 ↔ NH2CONH2 (urea) + H2O

CO2 NH3

Synthesis
urea, excess NH3,
carbamate, H2O

heat Decomposition NH3, CO2 Recovery cooling

urea, H2O

heat Concentration H2O H2O

urea
The urea manufacturing process is designed to
Granulation maximize these reactions while inhibiting biuret
formation:

Urea granule 2NH2CONH2 ↔ NH2CONHCONH2 (biuret) +

NH3

Steps:
1. Carbon dioxide and ammonia is mixed in a reactor to form ammonium carbamate
(exothermic reaction):

2NH3 + CO2 ↔ NH2COONH4 (ammonium carbamate); P = 240 barg

First reactor – achieves 78% conversion of carbon dioxide to urea

 Second reactor – receives the gas from the first reactor and recycle solution from the
decomposition and concentration sections; 60% conversion of carbon dioxide to urea
at P = 50 barg.
2. Water and unconsumed reactants (ammonia, carbon dioxide, ammonium carbamate) are
removed ; pressure is reduced from 240 barg to 17 barg and the solution is heated:

NH2COONH4 ↔ 2NH3 + CO2 (decomposition of ammonium carbamate)

NH2CONH2 + H2O ↔ 2NH3 + CO2 (urea hydrolysis)
2NH2CONH2 ↔ NH2CONHCONH2 + NH3 (biuret formation)

3. Ammonia and carbon dioxide is passed through a recovery chamber. Unconsumed

reactants are passed through the second reactor and purified excess ammonia is passed
through the first reactor.
4. Urea and water from the decomposition of ammonia carbamate is concentrated from 68%
w/w to 80% w/w. Seventy percent of the urea solution is heated at 80°C-110°C under
vacuum, which evaporates off some water. Molten urea is produced at 140°C; remaining
25% of the 68% w/w solution is processed under vacuum at 135°C.
5. Urea that is 80% w/w is processed under granulation. Dry, cool granules classified using
screens. Oversized granules are crushed and combined with undersized ones for use as
seed. The final product is cooled in air, weighed and conveyed to bulk storage ready for
sale.

Economics. Global urea production increased by 3.6% in 2009 to reach 146m tonnes, estimated the
International Fertilizer Industry Association (IFA). Currently 182 000 tonnes of granular urea are
produced annually (530 T day-1), but this is soon expected to increase to 274 000 tonnes. The IFA
forecasted that world urea capacity will increase by 51m tonne/year between 2009 and 2014 to reach
222m tonne/year, a growth rate of 6%/year. Global demand for urea is forecast to grow at 3.8%/year
to around 175m tonnes in 2014. Much of the increase was from fertilizer demand while industrial
applications for urea, accounting for 12% of total consumption, is expected to grow at 7%/year.

Uses. The urea is used as a nitrogen-rich fertilizer, and as such is of great importance in agriculture.
It is also used as a component in the manufacture of resins for timber processing and in yeast
manufacture. Urea is also used in the manufacture of urea-formaldehyde (UF) resins produced by the
condensation reaction between urea and formaldehyde. Urea is also a constituent of cattle feeds, and
is a useful viscosity modifier for casein or starch-based paper coatings. Small quantities are used as
an intermediate in the manufacture of polyurethanes, pharmaceuticals, toothpaste, cosmetics, flame-
proofing agents, sulphamic acid and fabric softeners.

Ammonium Nitrate, NH4NO3

A salt of ammonia and nitric acid, is a colourless, crystalline substance. Ammonium Nitrate reacts
with combustible and reducing materials as it is a strong oxidant. It is prepared commercially by
reaction of nitric acid and ammonia.

Manufacture and Production. Ammonium nitrate (NH4NO3) is produced by neutralizing nitric acid
(HNO3) with ammonia (NH3).
Steps:
1. Ammonia and nitric acid are reacted in a solution formation chamber which is resulted a melt
stream:

HNO3 + NH3 → NH4NO3

2. As the melt stream is feed to a solution concentration chamber, an additive – magnesium

nitrate or magnesium oxide – is injected. Purposes:
1. to raise the crystalline transition temperature of the final solid product;
 2. act as an desiccant, drawing water into the final product to reduce caking;
3. to allow solidification to occur at a low temperature by reducing the freezing
point of molten ammonium nitrate. 2
3. Melt stream from step 2 is passed to solids formation chamber by prilling and 3 by granulating.
4
1
4. Solid NH4NO3 is passed Ammonia to solids finishing chamber by drying and cooling.
5. Dried solids are Nitric Acid processed again for screening. These solids vary in
sizes and must be screened for consistently
5
sized prills or granules.
Offsize prills are dissolved and recycled to the solution concentration
6 process.
6. Screened prills is processed for
coating for bulk shipping and
bagging.

Economics. In 1991, there were 58 U.S.

ammonium nitrate plants located in 22
states producing about 8.2 million
megagrams (Mg; 9 million tons) of
ammonia nitrate.

Uses. Approximately 15% to 20% of this

amount was used for explosives and the
balance for fertilizers. The commercial
grade contains about 34 percent nitrogen,
all of which is in forms utilizable by
plants; it is the most common nitrogenous component of artificial fertilizers. Ammonium nitrate also
is employed to modify the detonation rate of other explosives, such as nitroglycerin in the so-called
ammonia dynamites, or as an oxidizing agent in the ammonals. Ammonium nitrate is also used in the
treatment of titanium ores and in solid-fuel rocket propellants, in pyrotechnics.

Ammonium Sulfate, [NH4]2SO4

Manufacture and Production. About 90% of ammonium sulfate is produced in three different
processes:
1. caprolactam [(CH2)5COHN] by-product 3

2. synthetic manufacture
3. coke-oven by-product 4
9
5

Processes:
1
1. Synthetic ammonium sulfate is produced by combining anhydrous ammonia and6 sulfuric acid 10

in a reactor.
2. Coke-oven by-product ammonium sulfate is produced by reacting the ammonia recovered
2 8
from coke-oven offgas with 7

sulfuric acid.
3. Ammonium sulfate crystals are
formed by circulating the
ammonium sulfate liquor through
a water evaporator, which
thickens the solution.
4. Ammonium sulfate crystals are
separated from the liquor in a
centrifuge.
5. The crystals are fed to either a
fluidized-bed or rotary drum
dryer.
6. Dryers are continuously steam
heated, while the rotary dryers are fired directly.
 7. Rotary vacuum filters may be used in placed of a centrifuge and dryer.
8. Crystal layer is removed as product; not generally screened;carried by conveyors to bulk
storage.
9. Dryer exhaust gases pass through a particulate collection device, wet scrubber.
10. After being dried, the ammonium sulfate crystals are screened into course and fine crystals.

Economics. In 1991, U.S. facilities produced about 2.7 million megagrams (Mg; 3 million tons) of
ammonium sulfate in about 35 plants. Production rates at these plants range from 1.8Mg to 360Mg (2
tons to 400 tons) per year.

Uses. It is commonly used as fertilizer.

Ammonium Phosphate, NH4H2PO4

Manufature and Production. Two basic mixer designs are used by ammoniation-granulation plants:
pugmill ammoniator and rotary drum ammoniator.

Processes:
1. Phosphoric acid is mixed in an acid surge tank with 93% sulfuric acid and with recycled acid
from wet scrubbers.
2. Mixed acids are then partially neutralized with liquid or gaseous anhydrous ammonia in a
brick-lined acid reactor.
3. A slurry of ammonium phosphate and 22% water are produced and sent through steam-traced
lines to the ammoniator-granulator.
4. Ammonia-rich offgases pass through a wet scrubber before exhausting to the atmosphere.
5. Granulation, by agglomeration and by coating particulate with slurry, takes 13place in the
7
rotating drum and is completed1 in the dryer.
4
3
6. Primary scrubbers use raw materials2 mixed with acid.8
10 10
5
7. Secondary scrubbers use raw materials mixed with pond water. 11
12

8. Moist ammonium 6
phosphate granules 9
are transferred to a
12
rotary concurrent
dryer.
9. Then transferred to a
cooler.
10. Before being
exhausted to the
atmosphere, these
offgases pass through
cyclones and wet
scrubbers.
11. Cooled granules pass to a double-deck screen, in which oversize and undersize particles are
separated from product particles.
12. Oversized granules are crushed, mixed with undersized.
13. They recycled back to the ammoniator-granulator.

Economics. Total ammonium phosphate production in the U.S. in 1992 was estimated to b e 7.7
million megagrams (Mg; 8.5 million tons).

Uses. Ammonium phosphate is used as an ingredient in some fertilizers as a high source of elemental
nitrogen. It is also used as a flame retardant in thermoplastic compositions. It is analytically used as
buffer solutions.