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INNOBITE Feature: Extraction of Silica from wheat straw

23/08/2013

Wheat is by far the most abundant crop in Europe. Millions of tonnes of residual wheat straw are thus generated every year. The inorganic fraction of wheat straw (mainly silica) accounts up to 10% of the total weight and currently represents a vastly underused resource.

INNOBITE project is developing methods for the extraction of silica from wheat straw.

What is silica?

Silicon Dioxide, often referred to as silica, is a chemical compound most commonly found in sand or quartz. Industrially, silica is a universal filler and thickening additive and is extensively used as reinforcing filler for plastic composites. The European fillers market alone was estimated at more than 5 million tonnes per year, (6% corresponding to silica) with a value of €2.3 billion in 2007.

In recent decades, the use of nanoscale silica in materials has become more prominent. The nanoscale particles in nanoscale silica have extremely high surface areas, which make them ideal fillers in high-performance composites, providing exceptional properties at very low dosages. In 2001, the market of this type of silica surpassed 200,000 tons in Europe and has increased substantially since then.

What are the current methods for production?

Currently, the silica industry is associated with energy-intensive production. Silica flour is produced by grinding high-purity quartz to finer than 74μm.Two methods are mainly used in preparing nanoscale silica: the gas-phase (or the dry method) and the deposition preparation (or the wet method). In the former, which gives rise to smaller particles (~20 nm), the temperature inside the furnace reaches 1000–1200ºC. The second method requires promoting of aggregation of the nanoparticles with a depositing reagent such as ammonia or amine

wheat strawWhy extract silica from wheat straw?

Wheat is by far the most abundant crop in Europe (more than 22million hectares in 2010) and extraction of the inorganic matter (mainly silica) would add significant value since the currently unused silica accounts for up to 10% of total weight of the wheat straw. Using wheat straw would reduce the pressure on primary raw materials, preserving the environment and fostering the use of secondary raw materials from residues.

Further to this, it is expected that bio-based silica will have better properties than standard silica providing unique properties to composites, especially increased surface hardness.

How are the proposed INNOBITE extraction method advantageous?

The two new extraction processes are alternative solutions to current technologies applied to obtain MFC and silica. Several physio-chemical operations, such as mild thermal pre-treatments of wheat straw or extraction with water/alcohol mixtures from the residual product, are being investigated. It is expected, that a controlled extraction of silica from wheat straw will allow small sized silica particles (<1μm) to be obtained, avoiding at the same time the consumption of high-quality quartz and environmentally aggressive and the energy-intensive treatments.

The method follows an eco-friendly approach, for which it will necessarily avoid using high temperatures (e.g. calcination) or strong acids and takes into account the current biorefinery fractionation process as it is applied at INNOBITE's partner CIMV, in order to avoid diminishing the efficiency of the rest of the fractions.

What is the expected impact of the technological developments?

Designing of an environmentally friendly process for the isolation of the inorganic fraction of herbaceous plants will complete the biorefinery process, allowing a more thorough separation of all relevant fractions and thus, adding value to the whole process. It is expected INNOBITE production technology will put into the market 60,000 ton (5 years after project conclusion) of bio-based high value silica.

Tags: wheat straw, silica, plastic composites, performance composites, quartz, raw materials from residues, INNOBITE extraction method, biorefinery process, high value silica

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