Chlorine shifts from mercury to membrane

03 September 2010 00:00  [Source: ICB]

European chlorine producers are pushing ahead to move in the direction of cleaner production technologies

European chlorine manufacturers have hit a significant milestone in their efforts to move towards cleaner production processes.

For the first time, more than half of European production now uses membrane technology. Less than one-third is made using the older mercury-based process - which is due to be phased out completely by 2020.

At its annual review this week, chlor-alkali industry association Euro Chlor plans to tell members that chlorine production using membrane technology has risen to 52% (up from 49% in 2009). At the same time, production from mercury-based plants fell to 31% (down from 34%).

"Membrane technology consumes around 30% less energy than mercury technology," says Jean-Pol Debelle, technical director at Euro Chlor. "However, the conversion costs are very high."

The conversion process is restricted mainly to Europe, which has historically relied on mercury technology. Other regions, such as North America, China, India and Russia, tend to use diaphragm technology. This accounts for around 14% of European production.

"A few diaphragm plants in Europe have converted to membrane technology, but there's no pressure to do this," says Debelle.

The shift from mercury to membrane has been taking place for a decade. It began as a voluntary commitment, under which the industry promised to convert or close all mercury-based production by 2020. Now though, many authorities have introduced specific legislation that brings this date forward. "Local authorities give 'permits' to producers. Many of them demand that plants convert or close much earlier than 2020," he says.

Initially, Debelle was worried that many producers would wait until very late before converting. But he is confident that many will convert in the next few years, guided in part by local legislation, and partly by rising maintenance costs for outdated mercury plants.

Yet some producers continue to run both types of plant: "Companies like [Dutch group] AkzoNobel have several plants in Europe: some were converted a decade ago, but others still use mercury - because they can control their emissions and keep maintenance costs down," he says.

The high cost of conversion means that some chlorine plants are running behind in the process. An example is in the Czech Republic, where epoxy resin producer Spolchemie has just negotiated an extension to the terms of its permit.

The firm, which began commissioning a membrane plant back in 2006, ran into financial difficulties in late 2009. It asked for an extension from 2012 to 2015 - but was granted one until 2013 by the local authorities.

"The project to move to membrane technology was postponed," says Lubos Knechtl, technical and investment director at Spolchemie. "Our idea is now to finalize the work by mid-2013, and start at the end of that year."

The company makes chlorine in order to make epichlorohydrin (ECH) - the main feedstock for its core business of epoxy resins. The firm's process to make ECH is a key to its success: it recently sold two licenses for ECH production - one to Taiwanese producer Formosa Plastics Corp. and one to Bila Group of India.

The membrane conversion will help it to save 20-30% in electricity costs, and boost output by more than 30%. After switching to membrane technology, it expects chlorine production to reach 73,000 tonnes/year - while its other main specialist product, potassium hydroxide (KOH), could reach 40,000 tonnes/year. Knechtl says that it will be the largest European membrane production site for KOH. "For making chlorine and hydroxide, the best available technology is membrane technology - that's why we decided to convert," he says.

There is a potential downside to the process, other than its cost: the "other side" of the process - to make caustic soda - is not immediately geared to industry needs. Instead of producing caustic at 50% concentration, it makes 32% concentration. Most customers demand 50% (mainly because it is cheaper to transport). This means the caustic produced by membrane technology must be heated to drive off water - cutting into the energy savings.

There is debate as to whether this makes a difference to the overall cost of the process: for Debelle, this removes the energy advantage, and means the conversion must be made on the basis of its environmental advantage.

"The financial aspects alone are not enough to justify the investment," says Debelle.

But Knechtl says the energy advantage remains, despite the need to produce steam and evaporate excess water. And he says that some processes will use caustic at 32%.

"In this case, it's even more of an advantage," says Knechtl.

Like Spolchemie, German polyvinyl chloride (PVC) giant Vinnolit makes chlorine for its own purposes. It makes vinyl chloride monomer (VCM), which it then converts into PVC. The firm - owned by private equity company Advent International - invested €100m ($127m) to upgrade its two chlorine production plants to membrane technology. It makes 180,000 tonnes/year of chlorine in Gendorf and 250,000 tonnes/year in Knapsack. This represents a total increase of around 10%.

The company estimates that the new technology saves 20-22% in energy (around 330,000MWh per year). While Vinnolit's motivation was economic, it went beyond just energy saving. "The main reason was to close the chlorine gap at our Gendorf site - which we previously filled with imports," says managing director Ralph Ottlinger.

Ethylene dichloride (EDC), a VCM intermediate, had been delivered from Knapsack to Gendorf. Now it is made on site, saving huge transport costs.

And while €100m sounds like a fortune, Ottlinger says it was a tight budget for this type of plant conversion: a new chlorine plant might cost €1m for every 2,000 tonnes of capacity - suggesting that this option would have been twice the cost. "We wanted to stay within the budget by reusing as much equipment as possible," he says.

As well as being more energy efficient, the new technology is more compact - occupying about 20% of the space of mercury technology. Vinnolit boosted production four-fold in Gendorf, with the electrolysis cells taking up just one-third of the previous space.

At the end of the day, the energy savings will probably be a bigger incentive than legislation in forcing firms to convert their plants. "Energy prices in Germany are very high - and as they rise, the new process will become more of an advantage," says Ottlinger.

Most chemists know that chlorine gas is green. Now producers are trying to make it greener still.

Euro Chlor's list of techniques for making chlorine includes a column labeled 'other' - into which a new method from German chemical company Bayer MaterialScience might fit.

The company says that its technique, using an oxygen depolarized cathode, consumes around 30% less energy than standard membrane technology because feeding in gaseous oxygen helps electrolysis to take place at a lower voltage.

The company developed the technology with German plant engineering company Uhde, and three German universities.

The process can make chlorine from common salt. Bayer is due to start a 20,000 tonne/year unit at its Chempark Krefeld-Uerdingen plant early next year. It has already used the technique to electrolyze hydrochloric acid, at facilities in China and Germany.

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Author: Lou Reade

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