Gérald Martines
Derived from the alchemy between sand and fire, glass bottle manufacturing requires high energy quantities. The environmental footprint is considerable, in particular in terms of CO2 emissions. Highly energy-consuming, the production of a single 100-ml bottle typically composed of 200 grammes of glass in a standard gas furnace (they are the most widely used) results in 180 grammes of CO2 emitted [1]. As part of the transition towards more sustainable luxury glassmaking, various eco-design techniques already contribute to reducing the energetic content of bottles. On the industrial level, several projects are under study, or being tested.
Ecodesigned bottles
Since the carbon footprint is roughly proportional to the glass weight, the first approach consists in lightening the bottles. According to Gérald Martines, a bottle half-lightened in terms of glass weight emits twice less CO2 during production. Recently, several major brands have chosen this solution, which proves one can get free from the usual image of luxury associated with a heavy object.
Another approach consists in using post-consumer recycled glass during the manufacturing phase. “The carbon footprint is reduced by 2.5% for every 10% of PCR,” says Gérald Martines. Several initiatives already involve this strategy, like Girl by Rochas, which contains 40% of PCR, or the limited edition of Chanel N°5, based on 15% of recycled glass. Beyond 40% of PCR, glass loses a bit of crystalline transparency, without losing its functional qualities. “Why not imagine that this cultural point, which is subjective, can change, and that slightly less ‘crystalline’ glass can become the modern symbol of responsible luxury?” asks Gérald Martines.
Lastly, “and it is by far the most efficient strategy,” he adds, giving consumers the possibility to keep their own bottles and refill them could reduce the CO2 footprint of a bottle by 50% at the first refill, and up to 90% at the ninth. “To be perfectly accurate, one should take into account the impact of refills, which does reduce the benefit, since it varies according to the refill methods chosen by brands,” explains Gérald Martines.
Of course, all these options can be combined to further optimize the environmental impact.
Targeting the manufacturing process
Another way to make considerable progress towards low-carbon glass consists in improving the production parameters, emphasizes Gérald Martines.
Today, the heating systems used for glassmaking furnaces are usually based on natural gas combustion. This process represents emissions of about 270 kg of CO2 per tonne of glass, i.e. about 5,000 bottles of 100 ml, and also results in emissions of nitrogen oxides, nitrogen being a secondary greenhouse gas.
Electric furnaces offer an alternative to gas furnaces. By default, they are powered with the standard energy mix of the national network. Therefore, the carbon impact varies from one country to another, depending on how they produce electric energy. In France, where nuclear power prevails, the impact is of 143 kg of CO2 per tonne of glass, i.e. 47% less than gas furnaces. On the contrary, in Germany, coal remains the main source of electricity production, so it is more environmentally friendly to choose the gas solution.
For those willing to pay more, there is also electricity derived from renewable energies (hydraulic, photovoltaic, wind-generated electricity…). German glassmaker Heinz Glas chose this option to power one of their furnaces. They obtained CO2 savings of 56% compared to a gas furnace (the calculation takes into account the energetic ‘extra cost’ to store electricity, which cannot be avoided given the sporadic nature of renewable energies).
Oxi-fuel combustion is another possibility consisting in, with a gas furnace, using oxygen as comburent [2] rather than air (the latter contains 80% of nitrogen, which is useless in this process). This alternative saves 15% of CO2 and reduces the emissions of nitrogen oxides by 83%. This experimental model is currently used to produce flat glass.
What’s more, the use of green hydrogen as fuel is a solution put forward and tested by Slovenian glassmaker Steklarna Hrastnik since 2021. Based on renewable energies, hydrogen reduces carbon emissions by 26% to 40%, according to Gérald Martines’s estimations. The balance is impacted by the need to store the electricity used to make hydrogen.
Lastly, 20 European glass packaging manufacturers united as part of the "Furnace of the future" project to design and develop a large-capacity hybrid furnace. This project set up by the FEVE (Federation of European manufacturers of glass) combines different options, since it will be based on 20% of gas, with an oxy-fuel combustion process, and 80% of green electricity. According to the FEVE, this model will help reduce CO2 emissions by 50% to 60%, compared to standard gas furnaces. A prototype should be presented in 2023. “This solution offers better efficiency, plus it is safe in terms of energy supply,” highlights Gérald Martines.
Given the results of the benchmark carried out by the expert, for now the most environmentally friendly manufacturing solution remains the electric furnace powered with renewable energies for a 56% reduction of CO2 emissions.
“Right now, it is the best solution, but all possibilities are interesting and complementary, because they are more or less easy and quick to implement. In the long run, the European project will represent the best alternative given the current state of the art, but this technology of the future will only be operational in five or ten years, because it requires a specific furnace. Bearing in mind that a furnace has a service life of about 20 years and represents a huge investment, the transformation process will move forward as the furnaces currently used are renewed,” concludes Gérald Martines.
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