Carbon Black’s history can be traced back as far as ancient Egypt, where is was used as a pigment in early inks. Today, two carbon black manufacturing processes are in widespread use (furnace black and thermal black) and produce nearly all of the global production of around 8.1 million tonnes of the material per year. Traditionally, as oil prices and, in turn, feedstock prices have fallen, so have the costs for carbon black producers.
However, in an interview with Asia Rubber, Bart Kalkstein, senior vice president and President, Reinforcement Materials Segment, Cabot Corporation, one of the world’s largest carbon black suppliers said that while oil process are currently low, the actual costs of carbon black feedstocks relative to fuel oil indices have been rising.
“This widening difference between the indices and actual costs has persisted since early 2015, and is forecasted to continue into the future putting pressure on our business and causing us to raise our prices in many places simply to keep up with feedstock costs,” he said.
With around 2-2.5kg of oil used to make 1kg of carbon black some 20 million tonnes of petroleum products are being burned globally each year in its production. Rising feedstock costs could prove to be a significant factor in the move to a more circular use for end-of-life tyres and other rubber products.
For years there have been efforts to deliver a commercially viable closed loop recycling process for tyres, but until recently the challenge has proved to be a bridge too far. For the most part tyre waste has been either used for granulate in low value applications, sent for energy recovery, or simply buried. However, there are now a handful of companies getting ready to role out large scale closed loop recycling facilities for rubber materials. One of those, Dutch firm Black Bear Carbon, is already operating its first commercial scale plant.
“Over the past decades there have been tens or even hundreds of projects which have used pyrolysis to recover raw materials from tyres, but they mostly recover oil. Over the past 10 years there have been a number of projects to recover carbon black so that it can be used again. But up till now we are the only one, or one of very few, that can extract carbon black at such a high quality that it can be used in high value applications,” says Rik Leunissen, commercial and business manager at Black Bear Carbon.
Technology
The company was founded at the end of 2010 by three partners including a waste management entrepreneur who had never found a good solution to disposing of tyres, a chemical engineer with significant knowledge of pyrolysis processes, and a rubber industry expert with decades of experience with carbon black. The pyrolysis process they developed uses end-of-life tyres as a feedstock and is claimed to produce consistent, high quality carbon blacks.
Speaking with WMW Leunissen explains: “We have developed our technology to extract the carbon black from the tyres at such a high quality that you can reuse it again in high quality applications like new tyres. That really allows us to close the loop on a significant portion of the carbon black cycle. What we have is a pyrolysis based system with a couple of other added elements.”
Prior to arriving at Black Bear’s facility the steel is removed from the tyres and sent for recycling. The resultant crumbs then undergo a carbonisation process. Here the rubber is heated in the absence of oxygen and broken down into gaseous molecules. A solid carbonaceous char is left behind is valuable because it contains all of the high value 'furnace' carbon blacks that were used, but the process of recovering them is far from complete.
“After the pyrolysis step what you’re left with is char,” explains Leunissen. “It’s globs of carbon black stuck together. It looks like something you might find in your fireplace. It’s actually a useless product because of the form. Depending on how you do the pyrolysis even the carbon black particles that are in there might not be useful.”
The next stage in producing high value carbon black is a de-agglomeration process. Here the char is broken down into smaller particles, or aggregates. The process controls the ‘particle size distribution’ (PSD) of the final product. PSD is a key product performance property as it relates to carbon black’s reinforcing effect in rubber compounds.
“We’re really talking nanometre size,” says Leunissen. “It’s not entirely separate particles, but almost. The primary particle size is around 30 NM. Depending on the application we then pelletise it. This makes small granules out of it, like instant coffee. The don’t dust very much but they do break down very easily. This is what they typically use in the tyre industry, but we can also pack it as a powder.”
To achieve the correct consistency in the pelletising process the company uses small amounts of water and binding agents in a pelletiser mixer. Large volumes of air are removed from the carbon black powder and pellets. Once pelletisation is complete the water that was used is evaporated under controlled conditions in a drying stage. A very small amount of binding agent remains behind and ensures that the dried pellets hold together.
Purity
Different parts of a tyre require different physical characteristics. To achieve this there are six to eight different types of carbon black used in a typical tyre. Currently Black Bear’s facility is recovering a mix of those different types of carbon black, which has both advantages and disadvantages and offers a mix of mechanical reinforcement and dynamic performance.
“Because it’s a mix of different types of carbon black it’s never a full one to one replacement,” says Leunissen. “The performance impact will always be slightly different to the pure form that the customer was using before. It can very often give performance improvements, but it is something to be aware of and something that we educate and support our customers with in terms of understanding what the impact will be.”
However, in the future Leunissen sees the potential to recover the various types of carbon black more specifically than is currently possible by adding additional pretreatment steps to sort the various parts of the tyres prior to the pyrolysis process.
“The more specific you can be in separating the different rubber compounds of a tyre before processing, the more specific the type of carbon black you can recover,” says Leunissen. “We need to separate the sidewall from the tread. At the moment we process the whole tyre with the steel removed. We are working on automating separation of the tyre because the margins are too low to have people doing it manually and it will be fairly easy to automate.”
Carbon Negative
While the recycling of carbon black is the company’s primary objective, the facility also produces other valuable products from the process.
“In the Netherlands we have our first industrial scale factory which has a capacity of 15,000 tonnes, or 1.5 to 2 million tyres per year,” explains Leunissen. “The output from that is 5000 tonnes of carbon black, 4000 tonnes of oil, and 3000 tonnes of gas. We use the gas for energy generation on site.”
The plant generates around 95% of its energy needs using a combined heat and power gas engine. To do this it first has to scrub the gas to remove the sulphur. The electricity generated is fed into the national grid rather than being used directly on-site as that setup provides a more stable supply.
According to the company an independent Life Cycle Assessment to validate its environmental impact found that the process is net ‘negative’ - meaning it takes more CO₂ out of the atmosphere than it consumes. Key driver of this is the production of energy in the process, which otherwise would have to be produced using fossil fuels. The process produces around 1.6 MWe and approximately 1 tonne of oil per tonne carbon black.
The Future
Leunissen sees a bright future for the technology: “We’re now at a stage where we have proven the technology at industrial scale. We’re now starting to actively engage with the bigger tyre collectors in the world to partner with them to provide a higher value way of recycling those tyres. Because of the logistical costs of transporting waste tyres it will likely be a technology which will provide a local solution.”
In terms of the business model the firm pays for its rubber granulate feedstock and does not need a gate fee to be commercially viable.
“Of course life becomes much easier if there’s a gate fee,” concludes Leunissen. “It also becomes easier if the oil price is twice as high because the carbon black price is linked to oil.”
Deepening on the markets and direction EPR regulations take that could well happen. Even there is little change in those regards, it’s good to see a commercially viable solution which retains the valuable of fossil based materials and keeps them in circulation.
