Electrolytic Industries

7/22/2019 Electrolytic Industries

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Mindanao State UniversityIligan institute of Technology

College of Engineering

Department of Chemical Engineering and Technology

ELETROLYTIC INDUSTRIES

Submitted by:

Ruel B. Cedeo

BSChE - IV

Submitted to:

Engr. Rodel D.Guerrero

Instructor

2014


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BRIEF HISTORY

The word electrolysis comes from theGreek[ lektron]meaning "amber" and[lsis] "dissolution". The

discovery of electrolysis began in 1785 when Martinus van Marum's electrostatic generator was used to

reducetin,zinc,andantimony from their salts using direct current.

In 1800, William Nicolson and Johan ritter was able to decompose water into hydrogen and oxygen insuch process.

In 1807, potassium, sodium, barium, calcium, and magnesium were discovered by Sir Humphry Davy

using electrolysis. Decades later, Paul Emile Locoq de Boisbaudran discovered gallium in 1875 using similar

procedure. In 1886, Fluorine was discovered by Henri Moissan by applying the same principle. In 1886, the Hall-

Heroult process was developed for making aluminum which is still widely used today. Eventually, Castner-

Kellner process was developed for making sodium hydroxide in 1890.

ELECTROLYTIC INDUSTRIES

I. ALUMINUM INDUSTRYA. USES
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B. RAW MATERIALSThe raw materials needed to produce 1 kg of aluminum, the following relative amounts of raw materials are

necessary: 4 kg bauxite, 0.415 kg carbon, 20 g aluminum fluoride, 2 g cryolite, and a supply of 13460 kWh of

electrical energy.

C. PROCESSESStep 1: Bayer Process. It is the process of production of alumina (Al2O3) from bauxite (raw material)


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Bauxite contains 40 to 60 mass% alumina combined with smaller amounts of silica, titania and iron

oxide. Bayer process dissolves the aluminum component of bauxite ore in sodium hydroxide (caustic soda);

removes impurities from the solution according to the reaction which occurs in the digester

2NaOH + Al2O3.xH2O 2NaAlO2 + (x+1)H2O

The resulting sodium aluminate is then acidified to precipitate aluminum hydroxide in the precipitatorwith this reaction

NaAlO2(aq)+ HCl(aq)Al(OH)3 (s) + NaCl (aq)

Aluminum hydroxide that precipitate out is heated in the rotary kiln to produce alumina according to this

reaction

Al(OH)31/2 Al2O3+ 3/2 H2O

Step 2: Hall-Heroult process. This is the process of producing aluminum from electrolysis of Alumina. Aluminum

cannot be produced by the electrolysis of an aqueous aluminum salt because hydronium ions

readily oxidize elemental aluminum. Although a molten aluminum salt could be used instead, aluminum

oxide has a melting point of over 2,000 C (3,630 F) so electrolyzing it is impractical. In the HallHroult

process alumina, Al2O3, is dissolved in molten cryolite, Na3AlF6 and electrolyzed. Thus, liquid aluminum is

produced by the electrolytic reduction of alumina (Al2 O3) dissolved in an electrolyte (bath) mainly containing

Cryolite (Na3AlF6). The overall chemical reaction can be written as:

2 Al2O3 (dissolved) +3C (s)4 Al (l) +3 CO2 (g)

Pure cryolite has a melting point of 1,012 C (1,854 F). With a small percentage of alumina dissolved in

it, its melting point drops to about 1,000 C (1,830 F).Aluminum fluoride,and calcium fluoride are added to the

mixture to further reduce the melting point.
http://en.wikipedia.org/wiki/Aqueous_solutionhttp://en.wikipedia.org/wiki/Hydroniumhttp://en.wikipedia.org/wiki/Redoxhttp://en.wikipedia.org/wiki/Molten_salthttp://en.wikipedia.org/wiki/Aluminium_oxidehttp://en.wikipedia.org/wiki/Aluminium_oxidehttp://en.wikipedia.org/wiki/Aluminahttp://en.wikipedia.org/wiki/Cryolitehttp://en.wikipedia.org/wiki/Aluminium_fluoridehttp://en.wikipedia.org/wiki/Aluminium_fluoridehttp://en.wikipedia.org/wiki/Cryolitehttp://en.wikipedia.org/wiki/Aluminahttp://en.wikipedia.org/wiki/Aluminium_oxidehttp://en.wikipedia.org/wiki/Aluminium_oxidehttp://en.wikipedia.org/wiki/Molten_salthttp://en.wikipedia.org/wiki/Redoxhttp://en.wikipedia.org/wiki/Hydroniumhttp://en.wikipedia.org/wiki/Aqueous_solution


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Anode Reactions: During the electrolysis reaction gaseous CO2evolved. The carbon is provided by the

anode material, the oxygen is transported to the anode in the form of AL-O-F complex anions. At high

alumina concentrations the species Al2O2F42-and Al2O2F64- may be discharged as suggested by the

reactions:

Al2O2F42-+ 4 F-+ CCO2+ 4e-+ 2 AlF4-

Al2O2F64-+ 2F-+ CCO2+ 4e-+ 2AlF4-

Cathode Reactions- The only cation present in cryolite-alumina melts is Na+. Despite Na+ being themain current carrier, it has been showed that formation of aluminum is favored over sodium in the

electrolyte compositions used industrially, since the reversible EMF is favorable. That is aluminum is the

thermodynamically preferred product. As there is no evidence that Al3+ ions are present, all of the

aluminum in the melt is bound in different anionic complexes. Al-O-F takes part in the anode reactions

so the most probable cathode reactions involve the remaining aluminumcontaining ions AlF63- and

AlF4-. The overall reaction can be written as

AlF63-+ 3e-Al + 6F-

AlF4-+ 3e-Al + 4F-

OVERALL

2 Al2O3+ 3C4 Al + 3 CO2

Anode: 6 O2-+ 3C3CO2+ 12 e-

Cathode: 4 Al3+ + 12 e-4 Al


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Example 1.

The industrial production of aluminum uses a current of 25 000 amps. Calculate the number of hours required

to produce 10 kg of aluminum from the electrolysis of molten aluminum oxide. ( 1 mole e-= 96500 A s )

Solution

Al3++ 3e-Al

10 kg Al ( 1 kmol Al / 27kg )(3 kmol e-/1 kmol Al)(96500 A s/1 mol e -)(1/25000 A)(10000)(1 hr/3600s) = 1.19 hr

II. SODIUM INDUSTRYSodium is a very reactive metal first discovered by Sir Humphry Davy in 1807. This element is extracted by

electrolysing molten sodium chloride in the Down's cell.

A. USESSodium is used for the production of sodium borohydride, sodium azide, indigo,

and triphenylphosphine. Furthermore, it can be utilized as alloying metal, an anti-scaling agent, and as a

reducing agent for metals when other materials are ineffective.Sodium vapor lamps are often used for street

lighting in cities and give colours ranging from yellow-orange to peach as the pressure increases. It is also used

as adesiccant;it gives an intense blue colouration withbenzophenone when the desiccate is dry. It also play an

important role in organic synthesis since it is widely used in various organic reactions such as theBirch reduction,

and the sodium fusion test which is conducted to qualitatively analyze compounds. In a more advanced

technology, it is used to create artificiallaser guide stars thatassist in theadaptive optics for land-based visible

light telescopes.

B. PROCESSES
http://en.wikipedia.org/wiki/Sodium_borohydridehttp://en.wikipedia.org/wiki/Sodium_azidehttp://en.wikipedia.org/wiki/Indigo_dyehttp://en.wikipedia.org/wiki/Triphenylphosphinehttp://en.wikipedia.org/wiki/Anti-scaling_agenthttp://en.wikipedia.org/wiki/Sodium_vapor_lamphttp://en.wikipedia.org/wiki/Desiccanthttp://en.wikipedia.org/wiki/Benzophenonehttp://en.wikipedia.org/wiki/Birch_reductionhttp://en.wikipedia.org/wiki/Sodium_fusion_testhttp://en.wikipedia.org/wiki/Laser_guide_starhttp://en.wikipedia.org/wiki/FASOR_(laser_physics)http://en.wikipedia.org/wiki/Adaptive_opticshttp://en.wikipedia.org/wiki/Adaptive_opticshttp://en.wikipedia.org/wiki/FASOR_(laser_physics)http://en.wikipedia.org/wiki/Laser_guide_starhttp://en.wikipedia.org/wiki/Sodium_fusion_testhttp://en.wikipedia.org/wiki/Birch_reductionhttp://en.wikipedia.org/wiki/Benzophenonehttp://en.wikipedia.org/wiki/Desiccanthttp://en.wikipedia.org/wiki/Sodium_vapor_lamphttp://en.wikipedia.org/wiki/Anti-scaling_agenthttp://en.wikipedia.org/wiki/Triphenylphosphinehttp://en.wikipedia.org/wiki/Indigo_dyehttp://en.wikipedia.org/wiki/Sodium_azidehttp://en.wikipedia.org/wiki/Sodium_borohydride


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The production of metallic sodium begins when the molten sodium chloride is sent to the down cell.

The chloride ions are attracted to the anode, where they lose electrons and form chlorine gas according to the

following reaction

2Cl(l)Cl2(g) + 2e

The positive sodium ions are attracted to the cathode. They gain electrons to form molten sodium metal.

Na+ (l) + eNa (l)

The overall reaction which takes place in the cell is:

2 NaCl (l)2 Na (l) + Cl2 (g)

The cathode is a circle of steel around the graphite anode. At 600C sodium and chlorine would react

violently together to reform sodium chloride. To pre-vent this from happening, the Down's cell contains a steel

gauze around the graphite anode to keep it and the cathode apart. The molten sodium floats on the electrolyte

and is run off for storage.

A problem arises, however, in that calcium ions are also attracted to the cathode, where they form calcium

metal. Therefore, the sodium which is run off contains a significant proportion of calcium. Fortunately, the

calcium crystallises out when the mixture cools and relatively pure sodium metal remains.

III. MAGNESIUM INDUSTRYA. USESMagnesium has a variety of usage which includes flash photography, flares, pyrotechnics, fireworks and

sparklers. It is also used in organic reactions as reducing agents as well as an additive agent in conventional

propellants.

B. RAW MATERIALSThe main sources of magnesium compounds are: seawater (magnesium chloride, MgCl2) and minerals such as

dolomite (CaCO3MgCO3), magnesite (MgCO3), carnallite (KClMgCl26H2O).


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C. PRODUCTION

Dolomite rock is crushed and heated in the kiln which will then undergo precipitation upon addition of

NaOH according to the reaction

MgCO3+ 2 NaOHMg(OH)2+ Na2CO3 and MgCl2 + NaOHMg(OH)2+ NaCl

The precipitate passes through filters where impurities are removed and it is then reacted with HCl in the

neutralizer according to the equation

Mg(OH)2 + 2 HClMgCl2+ 2 H2O

The resulting magnesium chloride is dried and dehydrated from 35% to 73% MgCl2. It will then proceed to the

electrolytic cells which will produce the net following reaction

The major chemical reactions in the process are the following

MgCl2Mg + Cl2


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IV. CHLORATES AND PERCHLORATES INDUSTRYA. USES

Chlorates and Perchlorates are used to treat thyroid disorders, additive in pyrotechnics industry, and

also as a component of solid rocket fuel.

B. RAW MATERIALSSodium chloride

C. PRODUCTION


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Aqueous solution of sodium chloride (brine) or seawater is sent to the settling tank where the

suspended impurities are allowed to settle at the bottom which will be filtered later on. The purified

NaCl is then sent to the electrolytic cells where it undergoes the following reaction

NaCl + 3H2ONaClO3+ 3H2

ClO3(aq) + H2O(l) ClO4(aq) + H2(g)

The by-product hydrogen gas is processed and stored to a secure container. The liquid chlorate and

perchlorate can then be directly supplied to the clients. Alternatively, if solid form is desired, the

aqueous sodium chlorate is sent to a chiller where it is cooled down and then to the settling tank where

it undergoes filtration or any method of separation. The product is dried which can then be supplied to

the market.

V. ELECTROCHEMICAL CELLS

Primary Cells are not rechargeable and are discarded after they run down when all the chemicals are used up ieno more chemical potential energy available. Secondary Cells can be recharged after they have run down ie the

discharge reactions producing the electricity are reversed to built up the store of chemical potential energy

A. Primary CellsGalvanic cells in which the reactants are sealed in when manufactured and ready for immediate use i.e. the

chemicals are capable of spontaneously reacting and the redox changes released energy as an electron

flow (rather than heat energy). They cannot be recharged, and when they run down, that is the chemical

reactants are completely depleted, they stop working and are discarded. The common ones such as the zinc

carbon batteries are used in torches, radios, cameras, flashlights, cameras etc.

Example of a primary cell is the Dry cell zinc-carbon battery.


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In this cell, the anode discharging reaction is

Zn(s) + 4NH3(aq) ==> [Zn(NH3)4]2+(aq) + 2e

While the cathode discharging reaction is as follows

MnO2(s) + NH4+(aq) + e==> MnO(OH)(s) + NH3(aq)

Hence, the overall working cell reaction is given by

Zn(s) + 4NH3(aq) + 2MnO2(s) + 2NH4+(aq)

B. Secondary cells are galvanic cells that must be charged before they can be used and rechargeable manytimes.In the charging process, the spontaneousfeasible cell reaction that produces electrical energy is

reversed, so building up the chemical potential of the cell system. Example of this is the Car battery

In the anode, the discharging reaction is

Pb(s) + HSO4(aq) ==> PbSO4(s) + H+(aq) + 2e

While in cathode, the reaction is given by

PbO2(s) + 3H+(aq) + HSO4(aq) + 2e==> PbSO4(s) + 2H2O(l)

Thus, the working cell reaction can be written as

PbO2(s)+ 2H+(aq) + 2HSO4

(aq) + Pb(s) ==> 2PbSO4(s) + 2H2O(l)

Its advantages are as follows: Inexpensive, high power density (can car starter motor as well as lights),

long shelf life, readily recharges, so has a long working life of many years. However, Lead needs to be recycled

to avoid environmental contamination, sometimes generates hydrogen gas at the cathode when charging(explosive in air + spark)though batteries seem to be made of a high standard these days in completely sealed

units that last many years.

Another example is the Lithium-ion Battery which is a member of a family ofrechargeable battery types

in whichlithium ions move from theanode to thecathode during discharge and back when charging. Li-ion

batteries use anintercalated lithiumcompound as theelectrode material,
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The positive electrodehalf-reaction is:

LiCoO2Li1-nCoO2+ nLi++ ne-

The negative electrode half-reaction is:

nLi++ ne-+ CLinC

The overall reaction has its limits. Overdischarge supersaturateslithium cobalt oxide,leading to the production

oflithium oxide,possibly by the following irreversible reaction:

Li++ e- + LiCoO2Li2O + CoO

Part III - LATEST ADVANCEMENTS

SPE and HTE Water Electrolysis

(Source: ENERGY CARRIERS AND CONVERSION SYSTEMSVol. I - Isao Abe, March 3, 2013)

New technologies of water electrolysis which are under development have more possibilities ofimprovement. These technologies are PEM ( polymer electrolyte membrane) water electrolysis and HTE (high

temperature steam electrolysis).

A. High Temperature Steam Electrolysis (HTE)High temperature electrolysis is more efficient economically than traditional room temperature electrolysis

because some of the energy is supplied as heat is cheaper than electricity, and because the electrolysis is more

efficient at higher temperatures. In fact, at 2500C, electrical input is unnecessary because water breaks down

to hydrogen and oxygen through thermolysis. Such temperatures are impractical; proposed HTE systems

operate between 100C and 850C.

The efficiency improvement of high-temperature electrolysis is best appreciated by assuming the electricityused comes from aheat engine,and then considering the amount of heat energy necessary to produce one kg

hydrogen (141.86 megajoules), both in the HTE process itself and also in producing the electricity used. At 100C,

350 megajoules of thermal energy are required (41% efficient). At 850C, 225 megajoules are required (64%

efficient).

B. Solid Polymer Electrolyte Membrane ElectrolysisOne of the largest advantages to PEM electrolysis is its ability to operate at high current densities. This can

in result in reduced operational costs, especially for systems coupled with very dynamic energy sources such as

wind and solar, where sudden spikes in energy input would otherwise result in uncaptured energy. The polymer

electrolyte allows the PEM electrolyzer to operate with a very thin membrane (~100-200m) while still allowing

high pressures, resulting in low ohmic losses, primarily caused by the conduction of protons across the

membrane (0.1 S/cm) and a compressed hydrogen output.

The polymer electrolyte membrane, due to its solid structure, exhibits a low gas crossover rate resulting in

very high product gas purity. Maintaining a high gas purity is important for storage safety and for the direct

usage in a fuel cell. The safety limits for H2in O2are at standard conditions 4 mol-% H2in O.
http://en.wikipedia.org/wiki/Half-reactionhttp://en.wikipedia.org/wiki/Lithium_cobalt_oxidehttp://en.wikipedia.org/wiki/Lithium_oxidehttp://en.wikipedia.org/wiki/Thermolysishttp://en.wikipedia.org/wiki/Heat_enginehttp://en.wikipedia.org/wiki/Heat_enginehttp://en.wikipedia.org/wiki/Thermolysishttp://en.wikipedia.org/wiki/Lithium_oxidehttp://en.wikipedia.org/wiki/Lithium_cobalt_oxidehttp://en.wikipedia.org/wiki/Half-reaction


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REFERENCES

Austin G. and Shreve R. (1984) Shreves Chemical Process Industries. McGraw Hill Publishing Co.

Brooks G, Trang S, Witt P, Khan, MNH, Nagle M (2006) The Carbothermic Route to Magnesium. TheJournal of Minerals, Metals & Materials Society (JOM): 51-55.

Bushnell S. and Purkis P. (1984). Solid polymer electrolyte systems for electrolytic hydrogen production.

Chemistry and Industry 16 January, pp. 6168. [This is the explanation of SPE water electrolysis system

developed by CJB, an engineering company in the UK, and also a good paper to get the general idea of

SPE water electrolysis.]

Donitz W. and Erdle E. (1984). High temperature electrolysis of water vaporstatus of development and

perspective for application. Hydrogen Energy Progress V (Proceedings of the WHEC 5), 767775. [This

describes the electrolytic cell of HTE.]

Masakalick N. High temperature electrolysis cell performance characterization. Hydrogen Energy

Progress V (Proceedings of the WHEC 5), 801811. [This describes the result of cell module testing of

HTE in detail.]

CSIRO (2006a)http://www.csiro.au/csiro/conte nt/standard/ps18r.html

http://en.wikipedia.com/Aluminum

http://en.wikipedia.com/Magnesium
http://www.csiro.au/csiro/conte%20nt/standard/ps18r.htmlhttp://en.wikipedia.com/Aluminumhttp://en.wikipedia.com/Magnesiumhttp://en.wikipedia.com/Magnesiumhttp://en.wikipedia.com/Aluminumhttp://www.csiro.au/csiro/conte%20nt/standard/ps18r.html

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Electrolytic Industries