SODA ASH AND BAKING SODA

INDUSTRY

USAMA PERVAIZ

BS CHEMICAL ENGINEER

Department of Chemical Engineering, CIIT Lahore

PRODUCTION OF

SODIUM CARBONATE/BICARBONATE

• Uses and History

• Raw materials

• Process flow diagram

• Steps involved in production

•

Uses of Sodium Carbonate

Use Process Notes

Glass MakingA mixture of Na2CO3, CaCO3 and SiO2(silicon dioxide

sand) is used for window or bottle glass.

Water Softening Agent

CO32- from dissolved Na2CO3 can precipitate Mg2+ and

Ca2+ ions from hard water as the insoluble carbonates,

preventing them from forming a precipitate

with soap resulting in scum.

For this reason, sodium carbonate is also known as

washing soda.

Paper MakingNa2CO3 is used to produce the NaHSO3necessary for

the sulfite method of separating lignin from cellulose.

Baking Soda Production

Baking soda (or sodium hydrogen carbonate or sodium

bicarbonate), NaHCO3, is used in food preparation and

in fire extinguishers.

Sodium Hydroxide Production

for Soaps and Detergents

Na2CO3 is reacted with a Ca(OH)2, slaked lime,

suspension.

RAW MATERIALS

• SALT(SODIUM CHLORIDE)

• LIME STONE

• COAL

• AMMONIA

• DEIONIZED WATER

THE OVERALL

REACTION

NaCl+CaCO3 Na2CO3 +CaCl2

However……..

PROCESS FLOW

DIAGRAM

STEPS INVOLVED IN THE PRODUCTION OF NA2CO3 /NAHCO3 BY SOLVAY

PROCESS

1- Ammonia absorption

Saturation of salt solution with ammonia

bubble and cap absorber

1.Trayed towers (plate columns). 2.Packed columns.

perforated valve cap Bubble cap

SOLVAY PROCESS……….CONTD.

2- Burning of limestone to produce carbon dioxide and

lime

• Combustion of C to CO2 (highly exothermic and produces

96.5 Kcal/mole of C burnt)

• Decomposition of 1 mole of CaCO3 need 43.44 Kcal

Thus mixing lime with coke…….

SOLVAY PROCESS CONTD.

3- The Solvay tower/carbonation of ammoniated brine

SOLVAY PROCESS………..CONTD.

4- Separation of Sodium Bicarbonate

Filtering and washing of precipitated bicarbonate

5- Thermal decomposition of NaHCO3 to Na2CO3

(Calcination)

SOLVAY PROCESS……….CONTD.

6- Production of milk lime (calcium

hydroxide)

SOLVAY PROCESS……….CONTD.

7- Regeneration of ammonia

LIGHT VS HEAVY

SODA ASH

Soda ash can be classified into two forms –

heavy and light.

Product after calcination is called light form is obtained first and some is then converted into the heavy form containing less than 0.5% sodium chloride.

Heavy sodium carbonate is obtained by hydrating light sodium carbonate to the monohydrate (Na2CO3.H2O) and then dehydrating it to give a product with an increased crystal size and density.

The two grades have different uses.

The major uses of heavy sodium carbonate are as a solid, particularly in making glass, where it is used as a flux in the melting of silica (sand).

The uses for light sodium carbonate are traditionally where the chemical is required in solution.

Sodium carbonate, is used

In the manufacture of glass, paper, rayon, soaps, and detergents.

As a water softener

To control pH (carbonate solutions neutralize acids, producing only carbon dioxide and water).

In the chemical industry to synthesize many different sodium compounds, including sodium bicarbonate (baking soda), sodium silicate (used in detergents), sodium tripolyphosphate (a detergent builder), sodium hydroxide (lye), sodium chromate and sodium dichromate (used in chrome plating), sodium aluminate (used in refining aluminum), and sodium cyanide (for electroplating).

Q-1

Why sodium carbonate called as washing soda?

Q-2

Identify the raw materials used in the Solvay process and

name the products

Q-3

Describe the uses of sodium carbonate

Q-4

Identify the sequence of steps used in the Solvay process

and describe the chemistry involved in:

brine purification

hydrogen carbonate formation

formation of sodium carbonate

ammonia recovery.

Q-5

ICI soda ash at khewra, Punjab province, Pakistan, produces

350 000 tons per year of soda ash (sodium carbonate). How

many tons of calcium carbonate are needed to produce

this? Take the overall equation as,

CaCO3(s) +2NaCl(aq)

Na2CO3(aq) +CaCl2(aq)

Q-6

Evaporative basins at Dry Creek near Adelaide produce an

average of 650 000 tons per year of salt. This is purified,

then dissolved to form a saturated brine solution that is

pumped to the Solvay plant.

Ammonia is dissolved in the brine solution and then the

ammoniated brine is reacted with carbon dioxide.

I. Write an equation for this reaction.

II. If 50% of the original salt is sodium chloride, what mass

of ammonia will be needed to react with it?

Olympia chemicals limited (OCL), is the second largest producer

of soda ash in Pakistan. Based on the available evidance,

determine the criteria used to locate a chemical industry using

OCL as an example. The answer should include

Proximity to supply of raw materials

Proximity to market

Availability of raw materials- for raw materials and finished

product

availability of housing, transport, schools & shops for workers &

family

facilities for waste disposal

CO32- from dissolved Na2CO3 can precipitate Mg2+ and

Ca2+ ions from hard water as the insoluble carbonates,

preventing them from forming a precipitate with soap

resulting in scum. For this reason, sodium carbonate is also

known as washing soda.

Brine purification

Salt water (brine) is pumped into shallow ponds, where the water is evaporated by the sun leaving salt. This is a mixture of calcium and magnesium salts as well as sodium chloride. The Ca and Mg ions must be removed.

Calcium salts are precipitated by the addition of sodium carbonate.Ca2+(aq) + CO3

2–(aq) CaCO3(s)

Magnesium salts are precipitated by the addition of sodium hydroxide.Mg2+(aq) + 2OH–(aq) Mg(OH)2(s)

A flocculant is added (this causes suspended particles to clump together and fall out of solution) and the precipitates are skimmed off the brine.

Production of hydrogen carbonate and sodium carbonate

Calcium carbonate is heated in a kiln to form carbon dioxide

& calcium oxide

The calcium oxide is removed, to be used in ammonia

recovery.

Coke is also present in the kiln, producing more carbon

dioxide when heated, as well as providing heat to decompose

the calcium carbonate.

C(s) + O2(g) CO2(g)

Ammonia is dissolved in the purified brine (NaCl) and carbon dioxide is dissolved in this solution.NaCl(aq) + NH3(g) + H2O(l) + CO2(g) NH4Cl(aq) + NaHCO3(aq)

Sodium and chloride ions are spectator ions, so this equation may be written as the following ionic equation:

NH3(g) + H2O(l) + CO2(g) NH4+(aq) + HCO3

–(aq)

This reaction is carried out at a low temperature (0°C) so that sodium hydrogen carbonate, which is relatively insoluble at low temperatures, precipitates out. The mixture is filtered. Sodium hydrogen carbonate is washed, dried and used to make sodium carbonate. The ammonium chloride filtrate is sent to the ammonia recovery plant so that ammonia can be recovered and reused.

Sodium hydrogen carbonate is heated to about 300°C and decomposes into sodium carbonate and carbon dioxide. Sodium carbonate is removed and sold. Carbon dioxide is reused.

Ammonia Recovery

Calcium oxide (from the first step) is dissolved in water to

form calcium hydroxide.CaO(s) + H2O(l) Ca(OH)2(aq)

Ammonium chloride is reacted with this calcium hydroxide

forming calcium chloride and ammonia. The ammonia is

reused, but calcium chloride is waste.

2NH4Cl(aq) + Ca(OH)2(s) 2NH3(g) + CaCl2(aq) + 2H2O(l)

Calculate molesFrom the periodic table, molar mass of Na2CO3 = 2 x 22.99

+ 12.01 + 3 x 16.00 = 105.99 gno mol in 325 000 tonnes = 325 000 x 1 000 000/105.99 =

3066 327 000 mol

From the equation:1 mol Na2CO3 produced from 1 mol CaCO3

3 066 327 000 mol Na2CO3 produced from 3 066 327 000 molCaCO3

Moles to mass1 mol CaCO3 = 40.08 + 12.01 + 3 x 16.00 = 100.09 g3 066 327 000 mol CaCO3 = 100.08 x 3 066 327 000 = 306 878 006 200 g = 306 878 tonnes CaCO3

Q6

NaCl(aq) + NH3(g) + H2O(l) + CO2(g) NH4Cl(aq) + NaHCO3(aq)

50% 650 000 = 325 000 tonnes

Calculate moles1 mol NaCl = 22.99 + 35.45 = 58.44 g325 000 tonnes = 325.000 x 1 000 000/58.44 = 5 561 259 411 mol NaCl

From the equation1 mol NaCl reacts with 1 mol NH3

5 561 259 411 mol NaCl reacts with 5 561259 411 mol NH3

Moles to mass

Moles to mass

1 mol NH3=14+3x1=17g = 17/1000 000 tons

5561259.4 mol= (17x5561259.4)/1000

= 94730.5 tons NH3