Production of bulk raw materials from agro residues one step closer

Agro-industry residues have an important role to play in the new bioeconomy. These residues can potentially be used on a large scale as renewable raw materials for chemicals, fuels and other materials, providing a sustainable alternative to fossil-based raw materials. However, they are currently underused because they are still more costly than the current fossil-based raw materials and they can't easily be traded as commodities.

At present, the chemical industry still uses vast amounts of fossil-based raw materials. Over the next few decades, we will need to transition to renewable raw materials for fuels, energy, chemicals and materials, in line with the objectives of the Paris and Glasgow climate conferences. Biomass will need to play a substantial role in this, though not at the expense of deforestation and food production.

The CAPCOM-NL project brought together a range of businesses and research institutes to develop technology for the processing of agro-industry residues into a raw material suitable for the large-scale production of chemicals (such as bioplastics and fertilisers), soil improvers, fuels and other materials. This was done by developing a process for treating low-value residues and turning them into an intermediate product in the form of a pellet, known as a biocommodity. This well-defined and relatively clean bulk raw material can be used to generate energy and can be fermented to provide building blocks for chemicals and other materials. It also paves the way for raw biomass materials to be traded on the global market, just like fossil-based raw materials.

The researchers carried out trials with a variety of residues that are currently often left to rot on the land, or at best processed as low-value products. These include empty fruit bunches from oil palms, bagasse (fibre residues left over from crushing sugar cane to extract the sugar), and sugar cane trash (leftover sugarcane leaves). Research was also carried out into the potential of miscanthus as a source of bulk raw materials. This crop can be grown on soils that are not suitable for food crops.

Removing contaminants

Contaminants have to be removed from the biomass before it can be used to produce any well-defined and usable commodities. “These contaminants are predominantly chloride and potassium,” explains Koen Meesters, a research associate at Wageningen Food & Biobased Research. “Producers don’t want these components in their raw materials, because they lead to corrosion and fouling of equipment and piping, and in the end to equipment breakdowns.” The removal of these contaminants was achieved through a process of counter current extraction, in which water is used to remove around 90% of the unwanted minerals out of the biomass. The potassium-rich water can then be used to irrigate sugar cane or palm plantations, says Meesters. “Plantations use potassium on a large scale as a fertiliser. Recycling the extraction water delivers substantial cost savings. And it’s good for the environment, because it reduces the need to extract raw materials from potassium mines.”

Production of uniform pellets

Raw materials are often traded and transported in pellet form, a method also used in other products like fertilisers and plastics. Once the contaminants have been extracted, further steps are still needed to enable biomass to be turned into such pellets. The researchers developed a process for this using high-pressure steam and high temperatures. “The idea is to be able to produce a commodity suitable for both energy generation (heat and/or electricity) as well as for fermenting into ethanol as a building block for fuels and materials,” says Meesters. “This does require some modifications to the process for each of the targeted applications. With ethanol, for example, it's important to use moderate temperatures so that afterwards enzymes can properly hydrolyse the material. But if heat and/or electricity is the intended application, higher temperatures are beneficial to ensure better calorific value, moisture resistance, durability and milling properties. However, the major advantage is that the pellets can still be made in the same production system. The settings need to be changed depending on the intended application.”

Base chemicals and materials

So technically, it’s certainly possible to produce bulk raw materials on a large scale from agro-industry residues. Edwin Hamoen, programme manager for biorefinery at Wageningen Food & Biobased Research, confirms this. “The residues we worked with in this project are often left to rot on the land. In this project, we have shown how we can use them as a commodity raw material for the production of a solid fuel and ethanol. The next step is to produce bio-commodities for other base chemicals and materials. The challenge with this is to maximise the use of local residues. In the Netherlands, that might be tomato stems from greenhouse horticulture being processed into a specific commodity.”

The CAPCOM-NL partnership also showed that the process is economically viable: the cost of producing the biobased pellets is comparable to wood pellets and is therefore a viable alternative.

A win-win for the environment

Environmentally, the large-scale transformation of residues from palm oil and sugar cane production into commodities is a win-win situation. “Sustainability analyses (such as Life-cycle Analyses, or LCAs) have shown that this process delivers sharp reductions in greenhouse gas emissions,” says Hamoen. “The savings can be up to 90% compared to using coal for energy production. And if you wanted to power a car with ethanol, you would save 70% compared to the petroleum-based process. This means the process we have developed fully complies with the future RED II objectives, which are the EU’s latest guidelines for sustainable energy.”