Special Focus on Chlorine

The Indian Chlor-Alkaii Industry: A Review

IntroductionTHE global chlor-alkali industry is a very important eco-nomic contributor to the global economy. The industry di-rectly provides jobs for tens of thousands of people all overthe world. Estimates show that the production of chlorineand caustic soda alone generated worldwide sales rev-enues of US$16-bn in the year 2004.

The global demand for chlorine in 2005 was estimated tobe over 50-mt. Globally, production increased by 6% in2004. The industry is currently operating at around 90% ofcapacity. However, demand is expected to grow manifold. InIndia alone, demand by 2010 Is expected to exceed 4.5-mt,driven primarily by growth in demand for polyvinyl chloride(PVC).

With global economy continuing to improve, returns tothe global chlor-alkali industry have improved despite higherenergy and raw material prices. As the economy strength-ens, chlcr-alkali demand and pricing are set to changefavourably.

Global overviewThe chlor alkali industry comprises the following prod-

ucts: caustic soda (also known as sodium hydroxide), chlo-rine and soda ash (sodium carbonate). The industry is highlyenergy intensive, with electricity and other utilities account-ing for 40-50% of production costs. The top ten producers ofchlor-alkali products account for about 40% of global capac-ity. Some of the leading players are Dow Chemicals, FormosaPlastics, Occidental, PPG industries, Bayer, Solvay, Olin,Akzo Nobel, Atofina and Tosoh Corp.

Demand-supply dynamics

The world demand for chlorine is projected to grow at anannual rate of 2% through the year 2011. Capacity will growto 54-mtpa from 45-mtpa in 2001. Low cost energy regions,such as Middle East, are projected to have higher annualgrowth rates of 3.0-3.5%.

The global chlor-alkali industry has generally been facingmaturing demand, a problem made even more challengingby any weakness in the economy. The distinguishing fea-ture of the industry, as compared to other segments of thechemical industry, is the unique co-product relationshipbetween chlorine and caustic soda.

Chlorine markets follow the economy closely. Some ofthe most significant end-products for chlorine, such as PVC,used in the housing and automotive industries, and ethylenedichloride (EDC) - the raw material for PVC - tend to seeweak demand in an economic downturn. As a result, chlo-rine prices come under additional pressure from failing PVCand EDC prices, impacting the margins of chlor-alkali pro-ducers.

The imbalance between supply and demand for chlorineand caustic soda, generally leads to production cut backsand increased prices for either chlorine or caustic soda.

Business outlook

Globally, few new chlor-alkali projects are coming onstream in the next few years, except in China. A studyrecently conducted by US-based Consulting ResourcesCorporation on the outlook for key chlor-alkali chemicals,indicates relatively stable market ahead for chlorine, causticsoda and soda ash.

Longer-term, the outlook for the chtoralkali industry issomewhat predictable. As in the past, the industry is ex-pected to follow the lead of the economy as a whole. As theglobal economy strengthens, chlor-alkali demand and pric-ing will also change favourably.

Manufacturing processThe chlor-alkali industry is one of the largest electro-

chemical technologies in the worid. It is the second largestconsumer of electricity (2,400-bn kWh) among electrolyticindustries. Chlorine is produced electrolyticaily using threetypes of electrolytic cells. In 1998, about 63 per cent of the

CHEMICAL BUSINESS • OCTOBER 2007 41

Membrane

18%

Mercury-16%

total world chlorine capacity ofabout 43.4-mt was producedelectrolytically using diaphragmand membrane cells, whileabout 35 per cent was madeusing mercury cells (Figure 1).

Chlorine is produced by theelectrolysis of sodium chloridesolution, called 'brine' Whensodium chloride is dissolved inwater, it dissociates Into sodiumcations and chloride anions. Thechloride ions are oxidised at theanode to form chlorine gas andwater molecules are reduced atthe cathode to form hydroxylanions and hydrogen gas. The sodium ions in the solutionand the hydroxyl ions produced at the cathode constitute thecomponents of sodium hydroxide.

The main difference in three chlorine process technolo-gies lies in the manner by which the chlorine gas and thesodium hydroxide are prevented from mixing with eachother to ensure generation of pure products. Thus, indiaphragm cells, brine from the anode compartmentflows through the separator to the cathode compart-ment, the separator material being either asbestos orpolymer-modified asbestos composite deposited on aperforated cathode.

Fig. 1: Chlorine manufacturingtechnologies

feed and exit streams with a flexible rubberor rubber-coated steel cover. Adjustable metalanodes hang from the top, and mercury (whichforms the cathode of the cell) flows on theinclined bottom. The current flows from thesteel bottom to the flowing mercury.

Some cells are designed with chlorineand anolyte outlets from the end box, whichare separated in the depleted brine tank. Themercury from the decomposer is pumpedback to the cell.

Diaphragm cells

The diaphragm cell is a rectangular boxwith metal anodes supported from the bot-tom with copper-base plates, which carries a

positive current. The cathodes are metal screens or punchplates connected from one^nd to the other end of therectangular tank. Asbestos, dispersed as a slurry in a bath,is vacuum deposited onto the cathodes, forming a dia-phragm. Saturated brine enters the anode compartment andthe chlorine gas liberated at the anode during electrolysis,exits from the anode compartment.

Diaphragm62%

In membrane cells, on the other hand, an ion-ex-change membrane is used as a separator. Anolyte-catholyte separation is achieved in the diaphragm andmembrane cells using separators and ion-exchangemembranes, respectively, whereas mercury cells con-tain no diaphragm or membrane and the mercury itselfacts as a separator. The anode in all technologies istitanium metal coated with an electrocatalytic layer ofmixed oxides. All modern cells (since the 1970s) usethese so-called 'dimensionally stable anodes' (DSA).Earlier cells used carbon based anodes. The cathode istypically steel in diaphragm cells, nickel in membranecells, and mercury in mercury cells.

These cell technologies are schematically depicted inFigures 2-4 and are described below.

Mercury cells

The mercury cell has steel bottoms with rubber-coatedsteel sides, as well as end boxes for brine and mercury

MercuryCell

MerciJfy in •

Fig. 2: Schematic of mercury cell

Satutai-acf- Sbdiurr;

^Gfir<';

DiaphragmCeil

Dilute Causlic Sod>a

F]g. 3: Schematic of a diaphragm cell

42 CHEMICAL BUSINESS • OCTOBER 2007

Hydrogen

Saturated Waier

MembraneCell

ConoonltalodCaustic Soda

Fig. 4; Schematic of a membrane cell

Membrane cells

In a membrane cell, an ion-exchange membrane sepa-rates the anode and cathode compartments. The separatoris generally a bi-layer membrane made of perfluorocarboxylicand perfluorosulfonic acid-based films, sandwiched betweenthe anode and the cathode. The saturated brine is fed to theanode compartment where chlorine is liberated at the an-ode, and the sodium ion migrates to the cathode compart-ment.

Thus, all three basic cell technologies generate chlorine

at the anode, and hydrogen along with caustic soda in the

cathode compartment. The distinguishing difference be-

tween the technologies lies in the manner by which the

anolyte and the catholyte streams are prevented from mix-

ing with each other. Separation is achieved in a diaphragm

cell by a separator, and in a membrane cell by an ionexchange

membrane. In mercury cells, the cathode itself acts as a

separator by forming an alloy of sodium and mercury (so-

dium amalgam) which is subsequently reacted with water to

form sodium hydroxide and hydrogen in a separate reactor.

Chlorine processing

The chlorine gas from the anode compartment contains

moisture, by-product oxygen, and some back-migrated hy-

drogen. In addition, if the brine is alkaline, it will contain

carbon dioxide and some oxygen and nitrogen from the air

leakage via the process or pipelines. Chlorine is first cooled

to 60°F {16°C) and passed through demisters to remove the

water droplets and the particulates of salt and sodium

sulphate. The cooled gas goes to sulphuric acid circulating

towers, which are operated in series. Commonly, three

towers are used for the removal of moisture. The dried

chlorine then goes through demisters before it is com-

pressed and liquefied at low temperatures. The non-con-

densed gas, called snift gas, is used for producing hy-

pochlorite or hydrochloric acid, if there is no market for

hydrochloric acid, the snift gas is neutralised with caustic

soda or lime {calcium hydroxide) to fonn hypochlorite. Thehypochlorite is either sold as bleach or decomposed to formsalt and oxygen.

Applications of chlorine

The major application of chlorine is In the manufacture of

EDC. which in turn is used to make vinyl chloride and

subsequently PVC (Figure 5). PVC is a very versatile ther-

moplastic, used in a wide variety of daily products.

Watertreatment 5%

Bleaching 4% / ^

Inorganics 'J13% 1

Fig.

Other11%

Other Organics28%

5: Chlorine end uses

EDC/VCM39%

Chlorine is used in pulp and paper manufacturing opera-

tions for bleaching to produce a high quality whitened

material and in water treatment operations as a disinfectant

The major use of chlorine in the production of inorganicchemicals is for titanium dioxide (a widely used pigment),manufactured from naturally occurring ores (Ilmenite orrutile).

Energy efficiency

There are good reasons for this. Operation with mem-

brane cells is more efficient in terms of energy consumed

per ton of caustic soda produced than the mercury cell

process. Chlor-alkali units that draw their power needs from

the state electricity grids are saddled with power costs that

are high and any improvements in efficiency of energy

usage are welcome. Many units have now resorted to using

captive power (which is almost always cheaper), in a bid to

rein in operating costs and to ensure continuous supply, and

a switchover to membrane cells will certainly add to the

savings. All these switches also come with a small expan-

sion of capacity, which implies that the power cost per unit

of production is even lower.

CHEMICAL BUSINESS • OCTOBER 2007 43

The chlor-alkali industry is energy inten-sive, with electricity and other utilities typi-cally accounting for 40-50% of productioncosts. As the chlor-alkali {and other indus-tries) have been harping for more than adecade, power costs in India are among thehighest in the world. To some extent this hasto do with hydrocarbon (oil, gas and coal)pricing, but to a larger extent due to thecross-subsidy mechanism that makes in-dustrial consumers {especially large ones)pay more in order to serve seemingiy socialneeds of providing "deserving' sections withlow (and sometimes, free) power. Yet an-other cause for the escalation in power arethe inefficiencies in transmission and distri-bution (T&D losses, in power industry jar-gon, but oniy half-jokingly referred to as theft and dacoity, bycynics).

The industry has coped with this state of affairs by settingup captive power stations, using whatever fuel it can lay itshands on. From the exorbitant diesel generating sets, toplants based on coal, fuel oil or natural gas (if the industryis lucky enough to get a linkage to a gas source), the chlor-alkali industry now operates a large portion of its capacity oncaptively generated power. The cost of the power generatedvaries, depending, obviously, on the fuel used, the size ofthe power plants etc. More often than not, however, thispower is cheaper than grid electricity, and comes with areliability the tatter has never been able to ensure.

Not withstanding these developments, it would be kite-flying to imagine a scenario in India akin to the Middle East,where a combination of cheap power and seemingly inex-haustible supply of ethylene is proving to be a winningcombination for a tremendous build-up in capacity along thevinyl chain, starting with caustic soda-chlorine. A number ofworld-scale chlor-alkali plants have been built in the region inthe last few years and more are coming up in Kuwait, Qatar,Iran, for example. While the chlorine is expected to find anoutlet to fuel the EDC/ VCM plants, much of the caustic sodawill be looking for markets outside the region. India, locatedjust a few hours away, will feel some of the heat.

Opportunities for growth

There is, however, considerable scope to grow theutilisation of chlorine in other outlets, as water treatment.The Alkali Manufacturers' Association of India {AMAl) isleading an initiative to get the government prescribe mini-mum standards for treatment of water with chlorine to makeit potable and fit for human consumption. This can take the

Table 1 : Caustic Soda

Caustic Soda

End-use

Pulp & paperAluminaSoaps, detergents.textilesOrganicsInorganicsWater treatmentDyesPharmaceuticalsOthers

Total

India

161128

1085

22

100

and Chlorine Utilisation - India(Percentage of total)

Global

179

12

16155

24

100

Chlorine

End-use

VinylsOrganicsWater treatment

Pulp & paper

and the World

India

773

22Chlorinated intermediates 13Chlorinated paraffin wax 10PesticidesPharmaceuticalsEnd-productsOthers

Total

63

236

100

Global

34

196

472

28

100

form of bulk chlorine usage in large treatment facilities or theuse of chlorine tablets to treat local sources as ponds, wells,etc. Water treatment, still has a long way to go in India: muchof the water consumed for domestic purposes is untreatedin much of rural India and even in urban centres.

Consumption of caustic soda in the paper industry too isset to rise, although the role of chlorine could be limited byenvironmental considerations that are propelling a drive toelemental-chlorine-free (ECF) bleaching, using a combina-tion of enzymes, hydrogen peroxide, ozone and other chlo-rine derivatives.

The fortunes of the industry will ultimately be determinedby the gainful utilisation of the chlorine and the value that itcan generate. Unlike in the rest of the world, very little -about 7% - of the chlorine produced in India ends up in thevinyl chain as PVC (Table 1). Much of it goes into pulp andpaper, and for manufacture of organic/inorganic chemicalsand chlorinated paraffin wax (CPW). Use in the bleaching ofpulp and paper could be throttled by the trend to movetowards elemental chlorine-free bleaching, in the short term,and totally chlorine-free bleaching in the long term, in linewith international trends. While there are presently no legis-lative imperatives in India for paper companies to make theswitch away from chlorine to alternate bleaching and treat-ment systems - as in some more developed countries -these could be in the offing. There is also a question markover the safety of CPW (which is used as a secondaryplasticizer, along with phthalates, when compounding PVC),with some short chain CPWs suspected to have carcino-genic properties in animal studies. While the verdict is stillnot out in this matter, it is an issue that bears watching.

Courtesy : Chemical Weekly •

44 CHEMICAL BUSINESS • OCTOBER 2007