Valorising by-products in the chemical industry

Many companies are seeking to improve their sustainability by moving towards a circular approach that makes better use of the Earth’s finite natural resources.

Activated carbon can be used to purify chemical by-products, turning waste into valuable raw materials and saving companies hefty disposal costs.

The problem

A multinational chemical company produces intermediates at its site in Italy, which are then used by its sister company in the US.

One by-product is phosphorous acid (H3PO₃), which in its pure form has a wide range of industrial uses. However, this by-product is not pure enough to be used as a raw material: it contains around 2-3 % organic matter and a higher percentage of colour (derived from the organic matter).

Because of the contamination, the client needed to dispose of this by-product. This is a costly and complicated process, and the client was having difficulty finding a waste handling company capable of taking on the task of dealing with the phosphorous acid.

Meanwhile, the client’s American sister company was buying phosphorous acid from a supplier in China to use as a raw material. To improve the acid’s quality, the company was purifying it using coconut-based activated carbon.

The Italian branch realised that although its phosphorous acid was more contaminated than the Chinese product, it might be possible to treat it and sell it to the American site. This would not only make the client money, but also save it disposal costs and boost its sustainability.

The client began looking for solutions, and contacted DESOTEC in December 2019.

The solution

The client needed a system that could handle a flowrate of 1-2 m³/h. The process would be discontinuous, as the client would store the phosphorous acid by-product until it had a batch to treat.

To be accepted by the American branch, the purified phosphorous acid should contain no more than 0,8 % organic matter and 3 % colour.

In early 2020, DESOTEC delivered two MOBICON 2000 filters to be placed in series, later optimising the system by adding a third filter.

In similar applications, coal-based carbon is typically used. However, the client wanted to follow the lead of its American colleagues and use a coconut-based type. This has the advantage of coming from a renewable source and has already proven itself in purification of phosphorous acid at the American plant.

The results

Trials showed perfect results: the filters were effective in reducing impurities in the phosphorous acid to the level required.

The first batch was sent to the US plant, where it was confirmed that it was now pure enough to use as a raw material.

Purification then began in earnest in summer 2020, with three filters in series.

As chemical companies seek ways to boost their circularity and sustainability by reducing their consumption of raw materials, many are looking into the untapped potential of by-products or residuals from reactions. Such companies currently send many products for disposal that might be purified and valorised.

How can DESOTEC help?

At DESOTEC, we have extensive experience of working with chemical manufacturing companies. We can draw on our expertise to guide clients on the best treatment for each chemical, supporting with tests in our lab where necessary. As our filters are modular, we can also optimise systems after installation.

Such processes reduce waste to a considerable degree: in this case, the client purifies 70 tonnes of phosphorous acid with just 1,5 tonnes of carbon. DESOTEC handles this dangerous spent carbon in partnership with an Italian waste disposal company, transporting it safely away from the client’s site in closed filter units.

Contact DESOTEC today

This case study is just one example of DESOTEC’s work in the chemical industry. To discuss how we could support your company, contact our team of engineers today.


At DESOTEC’s facilities, all used carbon is analysed so the right measures can be taken for handling and removing the saturated carbon out of the mobile filters. Used carbon which meets DESOTEC's acception criteria can be reactivated.

This means that all molecules that were adsorbed on the activated carbon at the customers’ site are desorbed inside DESOTEC’s reactivation furnaces. These contaminants are then fully destroyed, in accordance with National and European legislationby an incineration and neutralisation setup. The entire installation and its emissions are under continuous online monitoring, which guarantees that only harmless water vapour is seen exiting the chimney.

In case the saturated carbon does not meet our acceptation criteria, it is being sent for specialized external disposal.