Glycerine, a clear, odourless viscous liquid, is used in a variety of industrial applications such as food and beverages, pharmaceutical, cosmetics, tobacco, antifreeze, paints and coatings.
Glycerine, also known as glycerol, is generally obtained from natural glycerides present in fats and oils, or manufactured synthetically from propylene. Natural glycerine is a by-product from a number of different industrial processes, including fatty acid manufacturing, soap production and fatty acid ester production.
The decolourisation of glycerine (right to left) using increasing quantities of granular activated carbon.
In recent years, there has been a significant surge in glycerine production. This also promoted the attractiveness to use glycerine in biodiesel market. Glycerine is a key-by-product in biodiesel production, which is a formed from the transesterification of vegetable oils and animal fats.
The purification of glycerine process can sometimes be relatively complex, depending on its starting purity and treatment objective. The traditional transesterification process leads to a mixture of glycerine in aqueous solution together with salts and other bodies.
As major applications involve food/cosmetic/pharmaceutical industry end users, the removal of colour and odour is vital to ensure glycerine products meets the required industry standards, including the Food Chemical Codex and other various regional pharmacopeia protocols.
The recent use of solid catalysts to produce biodiesel has changed the nature of the glycerine generated as a by-product. Its exceptional purity simplifies its further treatment to an acceptable quality to suit a wide range of applications. A single activated carbon filtration step on a selected, unique, high purity, high activity carbon could help manufacturers to achieve a high standard of decolourisation and deodourisation.
Activated carbons can be used either in granular form, in fixed-bed adsorbers /filters, or dosed as a powder in a batch type process.
When purifying glycerine with activated carbon, both colour and odour are removed, leaving the glycerine water-white and colourless.
Granular Activated Carbon
In a fixed–bed filtration system using granular activated carbon, odour is typically first breakthrough, for example, it is the first contaminant to appear in the liquid flowing from the adsorber. This is because the molecules responsible for colour contamination are generally better retained in the adsorption pores of the activated carbon.
Ideally, an activated carbon that has more capacity for odour, while retaining its capacity for colour removal, should be selected. With a higher capacity for odour, the granular carbon filtration bed will last longer, reducing the specific use rate of activated carbon in kilogram per ton of glycerine produced.
When a granular activated carbon is spent, the adsorption capacity is exhausted or the treatment objective of the purification process is reached, it could be recycled by thermal reactivation. This involves removing the spent carbon from the customer’s site and returning to it to a reactivation facility capable of handling food grade materials.
Activated carbons can possess a good balance of odour and colour adsorption capacities. One by Calgon Carbon for example, is a low dust and agglomerated coal-based granular activated carbon that has these qualities.
Reactivation involves treating the spent carbon in a high temperature furnace, reaching up to 950 deg C. In a carefully controlled process, the undesired organic impurities of carbon are thermally destroyed and carbon is return to an activity level suitable for it to be returned to the customer and re-used in its operation.
Advantages Of GAC (Granular Activated Carbon)
Granular Activated Carbon (GAC)
In summary, activated carbons have a long history of use in the glycerine industry for the decolourisation and deodourisation of the product. Both granular and powdered grades could be used, depending on the process requirements and preferences, but the use of granular activated carbon (GAC) offers key advantages over powdered activated carbon (PAC).
- • Has more buffer capacity to deal with upstream feed quality fluctuation compared to PAC where dosage ratio is fixed. The product quality will be more consistent regardless of upstream quality fluctuation or process upset.
- • Has no waste disposal issue to deal compared to PAC
- • GAC with reactivation will have less overall operation cost compared to PAC
- • Can be reactivated at a suitable food grade reactivation facility