PROCESS 2
PRODUCTION OF POTASSIUM NITRATE FROM NITRIC ACID
AND POTASSIUM CHLORIDE
INTRODUCTION
Potassium Nitrate is a transparent, white or colorless, crystalline (sand-like) powder or
solid with a sharp, salty taste. It is used to make explosives, matches, fertilizer, fireworks, glass
and rocket fuel. It mixes well with other materials simplifying processing of granular and nongranular fertilizer and it tends to reduce the hygroscopicity of mixtures, and thus favors
maintenance of good mechanical condition. It has a low salt index and therefore reduces danger
of seeding injury and plant burn.
There are three primary plant nutrients, nitrogen (N), phosphate (P2O5) and potash
(K2O). Plants need all three of these to grow properly. Numerous other elements are also needed
in lesser amounts for satisfactory plant growth. However, the primary nutrients are depleted from
almost all soils by continuous cropping. Then for satisfactory crop growth these nutrients must
be replaced with naturally occurring or chemically produced fertilizer materials. Approximately
93% of the K2O applied as fertilizer in this country is applied as potassium chloride (KCl). With
the exception of specialized crops, one potash fertilizer is as effective as any other as a source of
potash for the plant. Tobacco is one example of a crop sensitive to chlorides; quantities of K20 in
excess of 30 to 40 lb/acre as chloride are harmful to the tobacco burning quality. An alternate
source of potassium is needed for tobacco and other chloride sensitive crops. Two forms of K2O
are immediately brought to mind, potassium sulfate (K2SO4) and potassium nitrate (KNO3).
Potassium sulfate is used to a limited extent while KNO3 has hardly been used at all. The
purpose of this investigation was to develop a KNO3 process.
Early in the work it was decided that KCl and nitric acid (HNO3) would be the reactants
and that the most desirable co-product would be elemental chlorine (CI2). Initially the KCl was
reacted directly with HNO3 on a batch basis. However, the solid product contained too much
KCl. Published solubility curves for KCl and KNO3 in water indicated that a fractional
crystallization process for KNO3 might be possible and a study of the mutual solubility of KNO3
and KCl in aqueous HNO3 solutions tended to confirm this possibility. Following the solubility
study a continuous fractional crystallization process for KNO3 was investigated using glass
equipment.
REACTION MECHANISM
Reaction between Potassium Chloride and Nitric Acid
3KCl + 4HNO3 = 3KNO3 + Cl2 + NOCl + 2H2O
RAW MATERIALS
Potassium Chloride
Potassium chloride, also known as KCl or potassium salt, is a metal halide salt composed
of potassium and chlorine. It is odourless and has a white or colourless vitreous crystal
appearance. The majority of the potassium chloride produced is used for making fertilizer,
called potash, since the growth of many plants is limited by potassium availability. The two main
types of potash are: Muriate of Potash (MOP, Potassium Chloride) and Sulphate of Potash (SOP,
Potassium Sulphate).
Nitric Acid
Nitric acid is a highly corrosive mineral acid. It is widely used for the production
of fertilizers, such as ammonium nitrate, and some polymers. It is a powerful oxidizing agent,
and reacts violently with many non-metallic compounds. By far the principal use of nitric acid
(80%) is in the manufacture of fertilizers. Of this 96% is used to make ammonium nitrate and
calcium ammonium nitrate. A relatively small amount of ammonium nitrate is used to make
explosives.
PROCESS FLOW DIAGRAM FOR THE PRODUCTION OF POTASSIUM NITRATE
FROM POTASSIUM CHLORIDE AND NITRIC ACID
PROCESS DESCRIPTION
The process uses KCl and 60% HNO3 as the starting materials and the intended coproduct is Cl2 and NOCl. From information in the literature it was decided to react the KCl
directly with HNO3 in a continuous stirred-tank reactor. The reactor operates at an absolute
pressure of 349 mmHg and at a temperature of 90°C. The steam flow rate to the reactor jacket
should be controlled in order to maintain the temperature and thereby the concentration constant.
The liquid draw from the reactor should be controlled in order to maintain the liquid level. The
gas flow rate to the gas treatment plant should be controlled in such a manner as to maintain the
reactor pressure constant. The gas evolved from the reactor was Cl2 and NOCl. Solid residue
was found to contain some excess chloride ions. And the liquid product is a mixture of KCl and
KNO3 in HNO3 solutions. The gas withdraw from the reactor will now enter in a packed
column, 2 1/2 in. o.d. by 18 in. long and packed 1 with 1/2 in., between the reactor and the reflux
condenser. This column was added to the equipment to reduce the acid loss to the condensate
from the final condenser. The solubility of KCl, is 27.5% or 0.275 gm/gm of solution at 30° C.
This is greater than any of the values which would be experienced upon cooling to 30° C.
Therefore, no KCl would be crystallized from any of these solutions when they were cooled to
30° C. Also a study of the solubility of KNO3 in solutions of 0.304 gm HNO3 per gm H2O with
controlled amounts of KC1 was carried out at 30° C. These studies showed that the KNO3
solubility in such solutions changed markedly with temperature while the KCl solubility did not
change very much over the range of temperature studied. The gas withdraw from the packed
scrub column entered into a condenser and cooled it at a temperature of 0° C. The water is
withdrawn from the condenser and enter into a condenser tank. The condenser will contain two
products: the one with impurities and water without impurities. The purified water will sent back
to the packed-column to maintain the temperature in the column. The gas withdrawn by the
packed scrub column will contain NOCl and Cl2 gas that will undergo to a gas treatment plant.
The liquid withdraw from the reactor was pumped into a crystallizer operating at 30° C. The
crystallizer product is a mixture of KCl and KNO3 in HNO3 solutions. And will pumped into a
centrifuge machine and was added by a wash water. Two products were withdrawn from the
centrifuge: the mother liquor (the wet KCl) and the wet KNO3. The wet KNO3 will be subjected
to drying to evaporate all the water in KNO3. And the mother liquor will be returned to the
reactor.
To demonstrate the final process, equipment was set up to continuously react KCl and
HNO3, withdraw liquid from the reactor, and pumped into a crystallizer, then subject to
centrifugation to separate KCl and KNO3 and continuously remove the gaseous products. This
procedure produced solid KNO3 which contained no solid KCl. The mother liquor is returned to
the reactor. The reaction was found to proceed more rapidly as the temperature or the
concentration of the reactants was increased.
I. SUSTAINABILITY
Availability of Raw Materials
Potassium Chloride
Growth of the potassium chloride market is gaining traction by the surge in demand for
potash fertilizers owing to its properties which supports the improvement in flavors, color, and
texture to crops used as food. Additionally, the fertilizers industry is witnessing positive growth
owing to higher demand from the developed and developing countries which are focusing on the
improvement in agricultural sectors. The countries such as India and China are fuelling adoption
of fertilizers and which is likely to boost the growth of the global potassium chloride market. The
worldwide market for Potassium Chloride is expected to grow at a CAGR of roughly 0.8% over
the next five years, will reach 13200 million US$ in 2024, from 12600 million US$ in 2019,
according to a new Research Report. In Philippines, the supply of potassium nitrate is increasing
as shown in the table.
Nitric Acid
Nitric acid market is majorly driven by fertilizer industry. The global nitric acid market is
expected to reach USD 23.31 billion by 2025, owing to its high consumption in fertilizer
production. The nitric acid market is expected to increase at a 2.0% CAGR during the forecast
period. In Asia, the top main supplier of this chemical is China and India. Out of the total
demand for nitric acid in Asia-Pacific, China held more than 60% of the total revenue share in
2017. Abundant availability of precursors and high presence of downstream industries are
driving the product demand in the country. Moreover, the Indian nitric acid industry is also
expected to witness a rapid boost attributed to the increasing growth of fertilizers and chemical
manufacturing industries in the country. And in the Philippines, there are many companies that
supply this type of chemical; 1. Labsmoni SSD Solution, 2. Nextlube, 3. Jadis Enterprise 4. TNC
Chemicals Philippines 5. Emerald Chemicals Incorporated 6. Neco Philippines Incorporated.
When in comes to the supply of nitric acid in the Philippines, there’s no need to import this
chemical from other countries because the supply is still increasing every year.
Cost of Raw Materials
The following table shows the estimated prices of each raw material that will be used for
the production of potassium nitrate from nitric acid and potassium chloride. Costs are based on
the available quotations of standard weights (ton) of the raw materials.
Table 2.1 Cost of Raw Materials (source: alibaba.com)
Raw Material
Price per ton (Php)
Potassium Chloride
30,591.00
Nitric Acid
15,295.50
TOTAL
45,886.50
II. MANUFACTURABILTY
Table 2.1 Equipment that will be utilized for the Production of Potassium Nitrate from Nitric
Acid and Potassium Chloride
1
2
3
4
EQUIPMENT
Continuous Stirred-Tank Reactor
Packed Scrub Column
Condenser
Condensate Tank
5
6
7
Crystallizer
Centrifuge
Dryer
Process Usage in the Industry
The corrosive nature of aqua regia is well known. Very similar conditions will occur in a reactor
built to react KCl with HNO3 and corrosion difficulties may develop throughout a plant built to
produce KNO3. Many corrosion problems are inherent in Solvay Process Company's sodium
nitrate process. A study of possible materials of construction is necessary. A corrosion study to
find materials of construction suitable for the various pieces of equipment is recommended. A
proper study is important especially the material of construction of the equipment because nitric
acid and potassium chloride is highly reactive with each other.
III. SAFETY
Toxicological Rating
Toxicity level of raw materials was analysed based on the corresponding health hazards
that it may cause to humans. The basis for attaining the level of toxicity was in Table 2.2 which
elaborates the health hazards of the raw materials. The basis is obtained from the Material Safety
Data Sheet of each raw material used in the process. Health hazard rating from Table 2.33 was
used to evaluate the level of toxicity of raw materials.
Table 2.2 Basis for attaining Toxicity of Raw Materials
Raw Materials
Criteria
The severity of Immediate Effects
Sensitization Level
Potassium Chloride
Nitric Acid
Skin and eye contact may
cause mild irritation.
No data available.
Skin and eye contact may
cause irritation.
Carcinogenicity Level
Not classified as
carcinogen.
Reproductive Toxicity Level
No data available.
The severity of Chronic Effects
No data available
No data available.
No substance in this
material has been
considered carcinogen.
No data available.
Extremely corrosive and
destructive to tissues.
Table 2.3 Health Hazard Rating
Level
0
1
2
3
4
Health Hazard Rating
For minimal hazard or no significant risk for health
For slight hazard or minor reversible injury possible
For moderate hazard, a temporary or minor inquiry may occur
For serious hazard, a major inquiry likely unless prompt action is taken and medical
treatment is given
For severe hazard, life-threatening, major or permanent damage may result from
single or repeated exposures
Table 2.4 Toxicity Rating of Raw Materials
Criteria
The severity of Immediate Effects
Sensitization Level
Carcinogenicity Level
Reproduce Toxicity Level
The severity of Chronic Effects
Weighted Score
Average
TOTAL
Raw Materials
Levels of
Importance Potassium Chloride
Nitric Acid
3
1
1
3
0
0
5
0
0
4
0
0
5
0
2
3
13
0.15
0.65
0.8
IV. ENVIRONMENTAL ASPECT
Environmental hazard level of raw materials was analysed based on the corresponding
hazards that it may cause to the environment. The basis for attaining the level of environmental
hazards was in Table 2.5 which is explained in details. The basis is obtained from the Material
Safety Data Sheet of each raw material used in the process. Environmental hazard rating from
Table 2.6 was used to evaluate the raw materials.
Table 2.5 Basis for attaining Environmental hazard level of Raw Materials
Criteria
Aquatic Toxicity
Raw Materials
Potassium Chloride
Nitric Acid
Toxic to some aquatic
May be harmful to aquatic
organisms due to shift of pH.
invertebrates.
Toxicity on Plants and
Animals
Toxicity of Immediate
Degradation
Long-term Degradation
Effects
No data available.
No data available.
No data available.
No data available.
No data available.
No data available.
Table 2.6 Environmental Hazard Rating
Level
0
1
2
3
4
Environmental Hazard Rating
For minimal hazard or no significant risk to environment
For slight hazard or minor reversible damage possible
For moderate hazard, a temporary or minor damage may occur
For serious hazard, a major damage to environment unless prompt action is taken
For severe hazard, major or permanent damage may result
Table 2.7 Environmental Rating of Raw Materials
Criteria
Aquatic Toxicity
Toxicity on Plants and Animals
Toxicity of Immediate Degradation
Long-term Degradation Effects
Subtotal
Average
TOTAL
Level of
Importance
3
3
4
5
15
Raw Materials
Potassium Chloride Nitric Acid
1
1
0
0
0
0
0
0
3
3
0.2
0.2
0.4
REFERENCES
Joshi, Chirag S.; Shukla, Krunel Patel; Joshi, Jigar S.; “Environmentally and Economically
Feasibility Manufacturing Process of Potassium Nitrate for Small Scale Industries: A Review”
(2014).
Gabrielson, James Earl; “Potassium nitrate form nitric acid and potassium chloride” (1964).
Retrospective Theses and Dissertations. 2664
https://lib.dr.iastate.edu/rtd/2664