Refining residual oils, biodiesel, acid water and emissions reduction

Estación depuradora de aguas residuales - Wikipedia, la enciclopedia libre

The trend in the manufacture of biofuels is the elimination in the medium term of traditional crops. By means of the sustainability directives, taking into account the indirect change in land use, the objective is to eliminate from the catalogue of raw materials all those that compete in the animal or human food markets, as well as in land use.

The generation of acidic water increases the cost of biodiesel production, the consumption of chemical products and energy, and consequently the emissions associated with this treatment, so that the final product may have a higher or lower level of emissions depending on its generation of sewage water. At the same time, they can be a vector of contamination of the subsoil if there are spills or the best available techniques for their treatment are not used.

The water treatment has its value assigned within the default values ​​detailed by the certification bodies. What is evident is that a reduction or elimination of the wastewater generated, as well as its pollution load, will result in the manufactured product having lower emissions in the process, and therefore our product is more competitive.

Most of the biodiesel plants that I have had the pleasure of visiting had the same Achilles heel, the wastewater. All of them generated a much higher quantity of water than they were designed for, and with a characterization of wastewater that completely exceeded the treatment capacity. The main reason was that plants that had been designed to work with first-use vegetable oils had been transformed / adapted to work with recovered oils and other residues. This generated more and worse waters for the following reasons.

  • Chemical refining

To refine vegetable oils such as soy or rapeseed, the most common practice is to use a chemical refiner. These oils have acidities in crude between 0.5% and 1.5%. Chemical refining generates approximately 2% waste for each acid point, which is removed as soapstocks.

When working with residual oils, this acidity can be up to 7 or 8%, which generates a waste of oil that makes the business totally unviable.

The economic solution is to recover the fat from the soapstocks. This is done through an acid shock with a strong acid, which separates two phases, olein that can be reincorporated in the process via esterification, and acidic waters that must be treated.

  • Esterification

The olein mentioned above usually have acidities between 40 and 60%. The acid esterification process is usually used where the reaction of olein plus methanol, using an acid as a catalyst, results in methyl ester and water.

In this process, an acidity of over 1-2% is usually reached, which allows the resulting product to be incorporated into the head of the process.

But it has generated acidic waters with the catalyst. In this case, apart from the problem of their treatment, we find serious corrosion problems in the equipment.

  • Biodiesel wash

Plants designed for vegetable oils have settings to work with first-use oil, that is, dosages of water and the acid that is used to wash.

Residual oils largely carry compounds such as high molecular weight polymers, polar compounds, and others, which have an impact on a poorer quality of biodiesel, specifically in the total contamination parameter.

This means that, to be able to enter the norm, more water is dosed, and also more acid, which leads to an increase in acidic wastewater.

With the technology available today, water can be reduced in all three processes, and even reach a zero-effluent level.

A quantification and characterization of wastewater is essential when deciding which is the best solution to reduce wastewater, and consequently costs and emissions.

From CMB Italy we can offer you the engineering and technology necessary to reduce your wastewater emissions, and became your product more competitive.

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