This document discusses the production of hydrochloric acid (HCl) from a HCl-water system. It begins with an introduction to HCl, including its physical and chemical properties. It then discusses how HCl is produced, focusing on its production from the HCl-water system. Key points include: - HCl and water form an azeotropic mixture at 20.2% HCl that boils at 108.5°C. - Above the azeotropic point, distillation cannot be used to further separate HCl and water due to the formation of the constant-boiling azeotrope. - Various industrial processes can be used to separate the a

1. CreditHours System Cairo University
CHEN104-PhysicalChemistry 2 Faculty of Engineering
Final Research
Production of HCL
(HCL-Water System)
Submitted to
Dr. Amira Khaled Anwar
Submitted by
Abdulrahim Adel Mohsin
Ahmed Khaled
Zeiad Mohamed
Mamdooh Hatem

2. 2
Abstract
We see and use many chemical compounds in our lives some of them are
organic, while the other some is inorganic. According to kinetics, you can’t study
kinetics on inorganic substances especially for liquids and gases because the
reaction is very rapid and doesn’t take must time. Our chemical compound that
we will study and have discussions of its production is the Hydrochloric acid
(HCl), but first we will introduce what is Hydrochloric acid in general terms and
its use. We will further study its chemical reaction properties its advantages and
disadvantages. However, our main focus will not be only in the production of
(HCl) but also will be in the production of HCl-water system in phase
Equilibrium. Also, we will discuss in detail the system in two cases the
Isothermal and Isobaric cases of the system. Additionally, we will define the
term azeotropic and why it is a problem for the industry and how to separate it
from the industrial processes in both cases.

3. 3
Table of Contents
Abstract.........................................................................................................................2
Table of Contents.........................................................................................................3
Table of Figures...........................................................................................................4
Introduction..................................................................................................................5
Physical properties......................................................................................................6
Chemical properties:...................................................................................................6
Chemical reactions producing HCl............................................................................7
Advantages of HCL......................................................................................................7
Disadvantages of HCL.................................................................................................7
Phase Equilibrium........................................................................................................8
Solubility at fixed temperatures.................................................................................9
HCl-Water System Isothermal Phase Diagram.......................................................10
Azeotropic mixture and point...................................................................................11
Distillation Process................................................................................................11
Boiling Point and Iso-baric Phase diagram............................................................13
Azeotropic Mixture and Separation.........................................................................14
Separation of Azeotropic Mixture and Concentrations Above the Azeotropic
Point ............................................................................................................................14
Extractive Refraction.............................................................................................14
Dual Pressure Technology....................................................................................16
Conclusion..................................................................................................................18
References..................................................................................................................19

4. 4
Table of Figures
Figure 1: Proccess flow diagram of concentration and cleaning of HCL.............8
Figure 2: HCl solubility in liquid and vapor phases. ...............................................9
Figure 3: Graph showing negative deviation from Raoult's Law......................... 10
Figure 4: Isobaric liquid-vapor phase diagram of binary HCl water mixture ..... 13
Figure 5: Process flow diagram of the Extractive Rectification process............ 15
Figure 6: Process flow diagram of dual-pressure technology............................. 16

5. 5
Introduction
HCl is a flexible chemical compound that has various industrial uses, such
as hydrometallurgical processes (results in the formation of titanium dioxide
and/or alumina), chlorine dioxide synthesis, activation of petroleum wells,
hydrogen production, and miscellaneous cleaning/etching operation including
metal cleaning. Also known as muriatic acid, HCl is used by masons to clean
up finalized brick work. Hydrochloric acid is also a known ingredient in many
different reactions and is the preferred acid for catalyzing or speeding up
organic processes. For instance, the carbohydrate reaction is promoted by
hydrochloric acid, similar to those in digestive tract of mammals. (U.S.
ENVIRONMENTAL PROTECTION AGENCY, 1993)
Hydrochloric acid may be produced by several different processes;
however, over 90 % of the HCl produced in the U.S. is a waste product of the
chlorination reaction. For instance, chlorination reactions are the production of
dichloromethane, trichloroethylene, Perchloroethylene, and vinyl chloride.
Chlorine and hydrochloric acid works are taken together because chlorine is
often generated as an intermediate in the production of hydrochloric acid. The
classis mercury cell electrolysis produces both chlorine and hydrogen and
these are then mixed and burnt to form hydrochloric acid gas, hydrochloric acid
gas can also be manufactured by the use of chlorides in chemical processes,
specifically when a chloride and an acid react together. Consistently, the
hydrochloric acid gas is absorbed in water to form liquid hydrochloric with an
acid strength of 33-35 percent. Air pollution problems can also arise when
chlorine or hydrochloric acid are used in other different processes.
Hydrochloric acid works are defined as “works where hydrogen chloride gas
is evolved either during the preparation of liquid hydrochloric acid, or for use in
any manufacturing process, or as the result of the use of chlorides in a chemical
process.” (Environment, Health and Safety division, UAE, 2010) (The Alkali, &
c. Works Order, 1991)
We will discuss in this article what are the properties of HCl and its uses and
how to produce it industrially, and the relationship between phase equilibrium
and diagrams with the production process.

6. 6
Physicalproperties
Although the physical properties of HCL depend on its concentration in
aqueous solution, there are some general physical properties. First of all , its
physical state is liquid, colorless, light yellow. Its odor is pungent (strong). Then
comes its PH level. Concentrated HCl (aq) has a pH level of 0 . However, HCl
(aq) found in the stomach has a pH level of 1 to 2. Then comes its boiling point
and melting point. Boiling Point: 108.58 C @ 760 mm Hg (for 20.22% HCl in
water) 83 C @ 760 mm Hg (for 31% HCl in water) 50.5 C (for 37% HCl in water).
Melting Point: -62.25°C (-80°F) (20.69% HCl in water) -46.2 C (31.24% HCl in
water) -25.4 C (39.17% HCl in water). Then comes its solubility. Soluble in cold
water, hot water, diethyl ether. Finally comes its conductivity to electricity is a
good conductor of electricity. (Physical & Chemical Properties - Hydrochloric
acid)
Chemicalproperties:
Hydrochloric acid, HCl (aq) is a strong acid, meaning that when it is dissolved
in water, all the molecules ionize to form hydrogen ions, H+(aq), and chloride
ions, Cl - (aq). When it comes to stability measurements, HCl is stable. HCL is
highly reactive with metals ,oxidizing agents, organic materials, alkalis, and
water. When it comes to corrosiveness , HCL is extremely corrosive in the
presence of aluminum, copper, or stainless steel while it’s noncorrosive in the
presence of glass.

7. 7
Chemicalreactionsproducing HCl
Hydrochloric acid is a chemical compound that can be produced by a various
way. These ways are classified into five ways that gives us HCl
1. Synthesis from elements:
H2+Cl2  2HCl
2. Reaction of metallic chlorides, particularly sodium chloride (NaCl), with
sulfuric acid (H2SO4) or a hydrogen sulfate:
NaCl+H2SO4  NaHSO4+HCl
NaCl+NaHSO4  Na2SO4+HCl
2NaCl+H2SO4  Na2SO4 +2HCl
3. As a byproduct of chlorination, e. g., in the production of
dichloromethane, trichloroethylene, perchloroethylene, or vinyl chloride:
C2H4+Cl2  C2H4Cl2
C2H4+Cl2  C2H3Cl+HCl
4. 4. By thermal decomposition of the hydrated heavy-metal chlorides from
spent pickle liquor in metal treatment:
2FeCl3+6H2O Fe2O3 +3H2O+ 6HCl
5. From incineration of chlorinated organic waste:
C4H6Cl2+5O2  4CO2 +2H2O+ 2HCl
(U.S. ENVIRONMENTAL PROTECTION AGENCY, 1993)
Advantages of HCL
Hydrochloric acid is used to make a lot of chemicals and as a disinfectant
and slimicide, a chemical that prevents the growth of slime in paper stock.
Other significant uses for hydrochloric acid include household cleaners, pool
maintenance, and food manufacturing.
Disadvantages of HCL
The disadvantages of HCL is that it’s very corrosive. Also, when the acid is
concentrated and it contacted any part of the body, it can lead to dangerous
and severe cases

8. 8
Phase Equilibrium
Phase equilibrium is defined as a state of thermodynamic in which different
phases share common boundary surfaces that does not change quantitatively.
Also Phase equilibrium can be defined as the study of the conditions of solid,
liquid, and vapor phases during equilibrium where the chemical potential of the
components is at steady state when there is no change during time.
Why we study phase equilibrium? We study phase equilibrium because it is
important especially in our industrial work. For instance, phase equilibrium and
its relationship with mass transfer that is used for distillation columns,
absorbers, leaching, and crystallization. Also phase equilibrium used in
manufacturing of steels and cast iron during metallurgic processes. In addition,
phase equilibrium plays an important role in ceramics in refractories.
Phase equilibrium is classified into various component systems which is one
component system, two component system, and three component system.
When we study these systems ,we use phase rule which depend on three
factors number of components, number of restrictions , and number of different
phases to get the degree of freedom to get the information needed to get phase
equilibrium and to know the substance is in which phase depending on the
given information and number of degrees of freedom. (Abuelatta)
Figure 1: Process flow diagram of concentration and cleaning of HCL
In fact, HCl water system is a two-component system that will be discussed
in details further in this research. Two component system is depending on
three factors pressure, temperature, and composition. So, to calculate phase

9. 9
equilibrium is difficult when the three factors are not constant. So, we
classified the graphs of two component systems phase equilibrium into two
groups liquid vapor isobaric system and liquid vapor isothermal system. We
classify these systems into ideal and nonideal systems.
Solubility at fixed temperatures
HCl gas is swiftly absorbed by water. The solubility of it in water at one atm.
is 42% by mass at room temperature. Let us say that x= the concentration of
HCl in water. Until x=0.1 the vapor pressure of HCl is extremely low and from
that point it increases rapidly with the increase in (x) until x reaches ~0.2. At
around x=0.21 the concentrations in the vapor phase as well as the liquid
phase are identical; this suggests this is the azeotropic point of this system.
A concentration of diluted HCl (x<0.2) above the azeotropic point cannot be
measured with simple fractional distillation. At x=~0.4, HCl in the vapor phase
consists predominantly of HCl, meaning that the maximum concentration of
HCl in water is at atmospheric pressure.
After x reaches 0.9 in the vapor phase, the vapor pressure remains to
increase but at much slower rate. (Die Dietrich Process Systems)
The following figure further explains its' solubility at the previously mentioned
conditions.
Figure 2: HCl solubility in liquid and vapor phases.

10. 10
HCl-Water System IsothermalPhase Diagram
This system is considered to be a non-ideal solution, since all the
conditions of ideal solutions are not satisfied; the components do not have the
same chemical composition, they are not completely soluble (around 42% at
20 oC), and there is a tendency of chemical reaction between the components
of the system.
It has been observed that the behavior of this system follows Raoult's law at
high concentrations (x~1) and follows Heney's law at low concentrations (x~0)
but when calculating the pressure in the ideal case it gives a bigger value than
the actual, thus suggesting a negative deviation, and it would make sense
because for HCl, the value of Henry's law constant (HHCl) is lower than its' vapor
pressure (P0HC l). (Ideal and Non-ideal Solutions |Topper)
P0HC l = 603 psia (31184.1 mmHg) (The Chlorine Institute)
HHCl There is a disagreement between scientists about the exact value of
HHCl but according to Pandis and Seinfeld (1989) its' value is 7.2 mol/m3.Pa
(Sander, 2015)
The following graph helps illustrate the behavior of the system
Figure 3: Graph showing negative deviation from Raoult's Law

11. 11
Azeotropic mixtureand point
Azeotropic mixtures are two-component systems that have same
composition in liquid and vapor phase and they boil at constant temperature.
Azeotropic mixture of HCl and water contains 20.2% HCl. These solutions cannot
be separated by simple fractional distillation.
Hydrochloric acid and water form an azeotropic point mixture at atmospheric
pressure the mixture boils at 108.5 °C and has a composition of 20.222 wt %
HCl. As the pressure increases, the boiling point increases and the azeotropic
composition decreases At HCl concentrations below the azeotropic
concentration, the vapor has a higher water concentration than the solution with
which it is in equilibrium. At concentrations higher than the azeotropic
concentration, the vapor is enriched in HCl relative to the liquid. Above 35 wt %
HCl, the vapor has very little water content. (US. Environmental Protection
Agency)
Distillation Process
As described earlier, simple fractional distillation method will not work
efficiently in separating hydrochloric acid from water.
The most common technology to overcome the azeotropic point is the
extractive rectification. This technology overwhelms the azeotropic point and
increases the volatility of hydrochloric acid. This is achieved by the addition of
a third component, an extractive agent, that has strong hygroscopic properties.
In the column, the extraction agent captures the water of the feed and leaves
the column at the bottom. Hydrochloric acid of high concentration or even HCl
gas can then be produced at the head of the extractive rectification column.
Subsequently, the extractive agent is freed from water in an evaporator and
recycled into the extractive rectification process. (Die Dietrich Process
Systems)

12. 12
The process begins as a mixture of hydrochloric acid , water and the
extractive agent all mixed together in a mixing container. The process is then
heated and mixed in order for the chlorides to bond with the secondary acid
solution. Due to the inefficiency of the reaction, excess amounts of HCl have to
be added to the mixing container in order to ensure the chemical reaction is
driven to completion.
Once the reaction time is reached, the mixed acid solution is pumped into
the first distillation still. This first still is operated at temperatures up to108.5 oC
(azeotropic point temperature). Due to the aggressive nature of the mixed acid
all equipment had to be chemical resistant. This particular application used
glass lined pipe and vessels, tantalum heat exchangers, graphite gaskets,
ceramic valves, and Teflon and tantalum
The vapor driven off in the first still is cooled by passing it through a heat
exchanger that produces a liquid which is 32% by weight hydrochloric acid. This
acid is stored in a vessel and eventually blended back into the chemical mix
tank in order to make the original acid mixture blend. Reclaiming the HCl at a
high concentration reduces the amount of new HCl required to create the initial
chemical reaction, resulting in a large economic savings.
The next step in the process is to concentrate the remaining liquid in the first
still into a crystalline matter. The problem with this that it does not satisfy
the demanded quantity of hydrochloric acid.
To solve the cooking issue, a second distillation system is installed to retrieve
the concentrate from the first still and bring the concentration of the it from 30%
up to 70% before heading to the heaters. This process requires the second still
to operate at temperatures in excess of 149 oC. The product
in this second still was at 70% before being introduced to the heaters,
significantly reducing the time and energy required to produce the final material
at the necessary production rate. The acid vapor produced in the second still
was 29%. (Mech-Chem Associates, Inc., 2017)

13. 13
Boiling Point and Iso-baric Phase diagram
A mixture of HCL gas and water forms a non-ideal solution, having a high
boiling point azeotrope (negative azeotrope) at 20.2 wt% and 108° C. Boiling
points tend to decrease with higher concertation of HCL above the azeotropic
point, decreasing quickly to 90° at 30wt%. Between 30% and 38% boiling points
decrease rapidly to 48° C. While higher concertation is attainable chemically
38% is the highest industrially viable concentration as higher and at that point
it is considered fuming hydrochloric acid. At higher concentrations the boiling
point decreases more and the evaporation rate is so high that it will require
special precautions such as cooling and pressurizing so it will be less
economically viable. (Eccles, 2018)
Figure 4: Isobaric liquid-vapor phase diagram of binary HCl water mixture

14. 14
Azeotropic Mixtureand Separation
An azeotrope also called constant boiling point mixture is a mixture of two or
more liquids whose proportions cannot be altered or changed by simple
distillation. (Moore, 1962)
A mixture of HCL and water forms an azeotrope at atmospheric pressure at
about 108°C with an HCl concentration of 20.2wt% at constant atmospheric
pressure. Boiling weaker or stronger solutions will result in loss of either water
or HCL until the azeotropic point is reached. (O'Neil, Heckelman, & Smith,
1996)
Attempting to get a mixture with a higher concertation of acid requires special
procedures. (De Dietrich Process Systems)
Separation of Azeotropic Mixture and ConcentrationsAbove
the Azeotropic Point
It is difficult to separate an aqueous hydrogen chloride solution into
constituent components, hydrogen chloride and water, solely by simple
distillation because of formation of an azeotropic mixture of the components.
Separation of Azeotropic mixture is done by two methods:
 Extractive Refraction
It is the most common technology for overcoming the azeotropic mixture.
This technology increases the relative volatility of HCl by the addition of a third
ingredient a strong electrolyte such as sulfuric acid, calcium chloride
Magnesium chloride to an aqueous hydrogen chloride solution to change
azeotropic condition. (Mech-Chem Associates, Inc., 2017)
The azeotropic mixture is combined with the extractive agent. The process
is then heated and mixed in order for the chlorides to bond with extractive agent.
Excess amounts of HCl have to be added to the mixing container in order to
ensure the chemical reaction is completed.
The lower the water content in the feed for the extractive rectification is the
smaller is the amount of extractive agent to be added and the lower is energy
consumption and investment for the sulfuric acid recycling step. Therefore, a
pre-concentration of the feed can be advantageous if installed before the
extractive rectification.
Once the reaction time is reached, the mixed acid solution is pumped into
the first distillation column. The first column is operated at azeotropic point
temperature (108.5°C).

15. 15
The vapor output at the top of distillation column is cooled off to produce a
liquid that is 32wt Hydrochloric Acid. This acid is eventually blended back into
original chemical mix in order to make the original acid mixture blend better and
ensure the chemical reaction is completed.
Figure 5: Process flow diagram of the Extractive Rectification process
However, this method has problems that expensive apparatus materials are
necessary. For example, in the case of use of sulfuric acid as a third
component, though it is desirable that the concentration of sulfuric acid added
in the hydrogen chloride recovery process is at least 80% by weight or more so
that sufficient effect to change azeotropic condition is obtained. It is difficult to
use a cheap material such as resin-impregnated carbon frequently used in
distillation of an aqueous hydrogen chloride solutions since when sulfuric acid
having such concentration is added, hydrogen chloride, water and sulfuric acid
are present simultaneously in distillation in the. Due to the aggressive nature of
the mixed acid all equipment had to be made from expensive materials that are
chemically resistant. This particular application used glass lined pipe and
vessels, tantalum heat exchangers, graphite gaskets, ceramic valves, and
Teflon and tantalum coated instrumentation.

16. 16
 Dual Pressure Technology
An alternative to the extractive rectification is the dual pressure technology
taking advantage of the fact that the composition of the azeotropic HCl and
water-mixture depends on the pressure. Therefore, it is possible to overcome
the azeotropic point by combining 2 rectification steps at two different
pressures.
Figure 6: Process flow diagram of dual-pressure technology
The process begins by providing a hydrogen chloride distillation column and
a dehydration column then operating the hydrogen chloride distillation column
under a pressure of a top of the hydrogen chloride distillation column higher
than a pressure of a top of the dehydration column.
An aqueous hydrogen chloride solution having a composition richer in
hydrogen chloride than an azeotropic composition of hydrogen chloride and
water under the pressure of the hydrogen chloride distillation column is fed to
hydrogen chloride distillation column and distilled.
Hydrogen chloride is recovered from the top of the hydrogen chloride
distillation column, and a part or all of the bottom liquid of the distillation column
is fed to a dehydration column.
The dehydration column is operated under a pressure lower than the
pressure of the distillation column. An aqueous hydrogen chloride solution
having a composition richer in water than the azeotropic mixture is fed to the
dehydration column, and distilled. Water is recovered from the top of the
dehydration column, and a part or all of the bottom liquid of the dehydration
column is fed to the distillation column.
When the aqueous hydrogen chloride solution discharged from the bottom
of the dehydration column has a composition richer in water than the azeotropic

17. 17
mixture under the pressure of the dehydration column, solution is fed to the
dehydration column as it is.
When solution discharged from the bottom of the dehydration column has a
composition richer in hydrogen chloride than the azeotropic mixture, this acid is
mixed with a chloride solution having a composition richer in water than the
azeotropic mixture so that the resulted acid solution is an aqueous hydrogen
chloride solution having a composition richer in water than an azeotropic
composition of hydrogen chloride and water under the pressure of the
dehydration column, and the resulted acid solution is fed to the dehydration
column.
Hydrogen chloride gas recovered from the hydrogen chloride distillation
column can be fed to the oxidation reactor of hydrogen chloride easily without
using a more expensive compressor as compared with a pump for liquid.
This type of system allows for wider range, and relatively cheaper
construction materials such as a glass lined metal. (Europe Patent No.
EP1099666A1, 2001)

18. 18
Conclusion
To sum up, HCl has many significant uses in industry. It can also be used as
a catalyst in organic processes. Its physical properties depend on its
concentration. Its chemical properties categorized the compound as a strong
acid that one has to take the safety precautions while dealing with it in order to
avoid any harm to the body. In addition, HCl can be produced by a various of
different chemical reactions. Also, it has some advantages and disadvantages.
Advantages consist of its various uses in industry, while its disadvantages are
that the compound can be dangerous and corrosive.
HCl as a substance have different behaviors at different temperatures,
concentrations, and pressures. At atmospheric pressure and temperature of
108.5° C creates an azeotropic mixture when mixed with water. This mixture is
a non-ideal solution with a negative deviation from Raoult's law and the HCl
content in it is 20.2%. Its boiling point tends to decrease as the concentration
HCl increases after the azeotropic point. After the azeotropic point, it becomes
hard to separate the HCl content from the water, and simple fractional
distillation will not work.
Separation can be done by two methods. The most popular one is extractive
refraction method, which separates them by adding a strong third ingredient,
but has to use expensive components because of the aggressive nature of HCl.
The second method is the dual pressure technology method, which is an
alternative to the latter process and has two extra steps of rectification but at 2
different pressures to help overcome the azeotropic point.

19. 19
References
 Abuelatta, A. K. (2020). Lecture on PHASE EQUILIBRIA. Faculty of
Enginerring, Cairo University.
 De Dietrich Process Systems. (n.d.). Concentration of HCl acid above
the azeotropic point. Retrieved from
https://www.dedietrich.com/en/solutions-and-products/mineral-acid-
treatment/hydrochloric-acid-treatment/concentration-hcl-acid
 Die Dietrich Process Systems. (n.d.). HCl Treatment. Retrieved 5 23,
2020, from dpsinc.com: https://www.ddpsinc.com/hcl-treatment
 Eccles, A. (2018). Hydrochloric Acid Storage Tanks & HCl
Specifications. Retrieved from Pro Tank:
https://www.protank.com/hydrochloric-acid
 Environment, Health and Safety division, UAE. (2010). Chlorine And
Hydrochloric Acid Works. Dubai.
 Ideal and Non-ideal Solutions |Topper. (n.d.). Retrieved from Toppr:
https://www.toppr.com/guides/chemistry/solutions/ideal-and-non-ideal-
solutions/
 Iwanaga, K., & Suzuta, T. (2001). Europe Patent No. EP1099666A1.
 Mech-Chem Associates, Inc. (2017). Distillation and Recovery of
Hydrochloric Acid. Retrieved from acidrecovery.com:
https://www.acidrecovery.com/news/distillation-and-recovery-of-
hydrochloric-acid
 Moore, W. J. (1962). Physical Chemistry. Retrieved from
https://www.collinsdictionary.com/dictionary/english/azeotrope
 O'Neil, M., Heckelman, P. E., & Smith, A. (Eds.). (1996). Merck Index:
An Encyclopedia of Drugs, Chemicals and Biologicals (12th ed.). New
Jersey: Merck & Co. Inc.
 Physical & Chemical Properties - Hydrochloric acid. (n.d.). Retrieved
from Weebly.com: https://psa-hydrochloric-acid.weebly.com/physical--
chemical-properties.html
 Sajid, M. (n.d.). Hydrochloric Acid (HCl). Department of Chemical
Engineering, University of Gujrat, Pakistan.
 Sander, R. (2015). Compilation of Henry’s law constants (version 4.0)
for water as solvent. Atmos. Chem. Phys., 15, 4399–4981.
doi:10.5194/acp-15-4399-2015, 2015
 The Alkali, & c. Works Order. (1991). Northern Ireland.
 The Chlorine Institute. (2020). Hydrogen Chloride. Retrieved from

20. 20
https://www.chlorineinstitute.org/stewardship/hydrogen-chloride/
 U.S. ENVIRONMENTAL PROTECTION AGENCY. (1993).
HYDROCHLORIC ACID PRODUCTION. AP 42 Compilation of Air
Pollutant Emission Factors.
 US. Environmental Protection Agency. (n.d.). Properties of
Hydrochloric Acid. Retrieved from
https://ofmpub.epa.gov/apex/guideme_ext/f?p=guideme:gd:::::gd:hcl_3