Eurochlor 2017/Chlorine Production The (R)Evolution of Chlorine: Ways into the Post-Mercury Era

Author / Editor: Dominik Stephan* / Dominik Stephan

Europe’s chlorine industry enters the post-mercury era — The shutdown of the last amalgam systems are taken out of service in December 2017, a technological era will come to an end. However, with membrane electrolysis technology underway, it will not mean the extinction of the industry. Plant operators and engineers are moving on on to the next level of the chlorine (r)evolution, balancing sustainability, energy efficiency and safety.

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The origin of species: The membrabe elctrolysis process (right) is the last step in an ongoing process eveolution from mercury cells (left) via the diaphragm processes (middle).
The origin of species: The membrabe elctrolysis process (right) is the last step in an ongoing process eveolution from mercury cells (left) via the diaphragm processes (middle).
(Source: © adrenalinapura/, doethion/, DOC RABE /, [M]-Sahlmüller)

Is this the end for chlorine? The versatile element, valued as a raw material for polymers and pharmaceuticals, yet decried as a toxic element by environmentalists, has gone through challenging times. In March 2017, European chlorine production fell compared with the previous year: 791833 tonnes of chlorine (2016: 802803 tonnes) - a decrease of 1.4%.

To make matters worse, is December the curtain call for the production process with mercury electrodes, also called Castner-Kellner process. This electrolysis process, which utilises a mercury cathode, may be highly selective, but also represents a risk factor for operators, local residents and the environment due to the toxic and environmentally harmful mercury.

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Thus, the EU regulatory authority no longer classifies the mercury process as a "best available technology". The last reprieve for this form of production in the European Union ends on 11th December 2017 – while worldwide mercury plants for chlorine production may operate until 2025 under the umbrella of the Minamata Convention. At the time, about 20% of Europe’s chlorine is produced using mercury, yet these figures are already in strong decline. All experts agree: The clock is ticking!

Nevertheless: There will not be a “chlorine-free” future in the EU. At the 2017 Eurochlor Technology Conference in Berlin, the spectre of plant closures, which had dominated discussions in previous years, played no role anymore. In fact, experts assume that by the end of the year, almost all the remaining 23 mercury systems (as of 2016) will have been converted to diaphragm electrolysis.

Although plant manufacturers and suppliers are hampered by the industry’s reluctance for major investments, there are reasons for cautious optimism. Now, the Eurochlor, the association of the chlorine manufacturers at the European Chemical Industry Association CEFIC, wishes to set the industry on a new course underpinned by three issues: Sustainability, energy supply and security.

Europe's Chlorine Hotspot 2017

At the tenth Eurochlor Conference in Berlin, technology experts, plant operators, engineering specialists and waste managers exchanged views on all aspects of chlorine production, from energy efficiency to the disposal of generated mercury over a total of three days.

360 participants from 34 countries discussed with technology specialists, plant manufacturers, representatives from policy and regulatory authorities and experts in the field of decommissioning and disposal of mercury-containing products. At the adjacent exhibition, over 50 companies presented solutions from fittings, smart process control and equipment and pipes to powerful process pumps.

How can you Make Chlorine More Sustainable?

The good news: There is life after mercury. The Eurochlor is certain that only two sites in Europe are currently threatened by closure. Although a boom of new chlorine sites is highly unlikely, the conversion and demolition of the old mercury plants at least promise full order books of engineering firms and project managers.

For now, the industry has put the topics of security, sustainability and energy on the agenda. "Safety is our license for production", said Ton Manders, Eurochlor’s technical director. And there is still much to be done, the specialist admits self-critically: "Our performance is not good enough."

Safety First!

Although there were fewer accidents per tonne of chlorine produced, the total number of incidents stagnated. The industry thus intends to present a ten-point plan for better safety to the international Chlorine Alkali Conference in September, Manders says.

Even more haunting for the industry is the perennial energy issue: Chlorine electrolysis is an extremely energy-consuming process - and therefore under high cost pressure in Europe. Saving energy is therefore not just at the very top of the list of priorities of plant operators for sustainability reasons. Yet, current figures dampen over-zealous visions: Since 2015, after years of decline, energy consumption for chlorine production has grown slightly, (by 1.2% compared to the previous year).

The current values are still around 3.7% below the level of 2011 (and almost ten percent below the level in 2001), but the trend towards lower consumption values seems to have come to a halt in around 2013. This could be due to the reduced efficiency of the ageing mercury plants, experts suggest.

Can Chlorine Cut its Energy Bill Even Further?

Nevertheless, it should no one should expect chlorine producers to cut their energy bill much further: The amount of energy required for the electrolysis to break-up the sodium chloride molecules is unavoidable. "Chlorine is stored energy", explained Dieter Schnepel, Eurochlor chairman and Vice-Chairman of Dow-Stade – one reason why it is also so reactive.

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Accordingly, the association Eurochlor is campaigning for the recognition of chlorine-alkali chemistry as a secondary emitter in emissions trading with corresponding rights. Companies are already saving hydrogen through the material use of the reaction product, of which 89% is used as a base chemical, for steam generation or for fuel cells. The use of depolarised cathodes, can even, in some cases, prevent the emergence of hydrogen entirely.

Modernize or Tear Down: The Mercury Question

The disposal of residual mercury from old plants is a cause of great concern for plant operators: Experts estimate that up to 6000 tonnes have to be disposed of after 2017. But where to get rid of toxic transition metal? Exporting elemental mercury is prohibited under new EU regulations as the substance is used for gold mining in many countries. This controversial method often causes major environmental damage and health risks for miners and local population alike.

The new rules also prescribe a stabilisation of waste as mercury sulphite, as the material is much less dangerous to man and environment in this state. The stabilised mercury can then, for example, be stored as hazardous waste in underground storage in salt domes, such as the salt mine Herfa-Neurode, Germany, one of Europe’s largest storage areas for highly hazardous substances. In fact, it is the very same salt that is used as a raw material for chlorine production that serves as a repository for toxic waste from the manufacturing process.

What About the Mercury?

However, the capacity for mercury stabilization in the EU is limited - and the substance may be stored on the company premises for no longer than one year before the site is effectively regarded as landfill and must operate according to the appropriate rules and regulations. This period ends after another five years; although a one-off extension for a period of three years is possible in exceptional cases.

In view of the limited capacity for the stabilisation of mercury, experts believe that mercury will trouble the industry long after 2017. Therefore, Eurochlor organised a workshop on the implementation of examples of good practice for association of companies in 2016.

But it is not just mercury causes complain about costs: Current studies indicate that the number of regulations for the chlorine-alkali chemistry has doubled in the last ten years. This has incurred additional costs of approximately 30%, according to the European chemical industry association CEFIC.

Nevertheless, experts are optimistic: With the changeover to membrane electrolysis, the industry in Europe is well positioned. Cefic has a strong partner in emissions trading and the implementation of the REACH regulations.

Evolution or Revolution?

One way or another: The seemingly troubled chlorine chemistry has proven to be more durable than predicted. A revolution in, or even extinction of, the industry is basically out of the question. In fact, the continuous further development of process components at Eurochlor such as membranes, pipes or fittings, has shown the way forward into the future.

This way, Asahi Kasei was able to significantly improve its membrane classic Aciplex: With a new coating and reinforced diaphragm, the Aciplex F700 1X has a thinner layer thickness and thus high selectivity at a lower voltage than predecessor models. The Japanese company emphasises the fact that impurities in the lye have a lower impact on the membrane.

Technologies for a New Era

Thyssen Krupp Uhde’s Chlorine Engineers (UCE) presented a further evolutionary stage of their filter presses technology with the Nx-Bitac, as well as the BM 2.7 membrane electrolysis element which combines zero-gap membrane technology with a single-cell-construction.

And the oxygen depolarised cathode ODC developed in cooperation with Covestro is designed to help chlorine producers reduce energy consumption by up to 25% or increase production with the same energy usage by the same amount.

The concept of Restore to use the electrolysis cells as a flexible energy consumers by Demand Side Management for grid stabilisation, shows the way to a whole new level of evolution. Thanks to intelligent algorithms and fully networked production, the cell performance can adapt to the line voltage within a certain framework to absorb voltage peaks, buffer supply bottlenecks or simply contribute to the stabilisation of the power network with a stable basic consumption.

Together with the operator, Restore is developing concepts as to how the flexible use of energy can not only reduce the electricity bill, but also create additional monetisation opportunities through emissions trading and flexible energy prices - entirely in accordance with the Industry 4.0-concept, but adapted to the needs and specificities of chemistry. Evolution rather than revolution are about to usher in a new age for the chlorine chemistry.