Purification of hydrochloric acid (HCl) with mobile activated carbon filters

Desotec Mobicon G5

The industrial production of liquid chemicals (both organic and inorganic) often involves one or more separation and purification steps in order to obtain a chemical product meeting a set of technical specifications. Numerous different technologies are used on an industrial scale, ranging from common distillation and molecular sieves to more advanced technologies. Also activated carbon has been proven to be able to efficiently remove certain types of impurities.

Over the past 26 years DESOTEC has gained extensive experience in the purification of liquid chemicals like hydrochloric acid (HCl), sulphuric acid (H2SO4), amino acids, mineral oils, brines and many different types of solvents, using granular activated carbon in its mobile activated carbon filter systems. The treatment of chemicals obviously poses a challenge in terms of corrosion and chemical degradation of the used filter vessel materials. A commonly used mobile activated carbon filter type in this application are the standard DESOTEC filters MOBICON®1000-HDPE and MOBICON®G5, but DESOTEC also has the ability to construct dedicated mobile activated carbon filter systems compatible with the customers liquid chemicals under given operating conditions.

DESOTEC purifies hydrochloric acid on several chemical plants across Europe. The hydrochloric acid is produced for example by the chlor-alkali process or during scrubbing of the waste gases from the production of chemicals involving a dechlorination step. As an example we will briefly discuss the purification of two separate hydrochloric acid flows produced on a chlor-alkali plant.

Both flows are 32-37 % hydrochloric acid solutions at a production rate of 4 000 kg/h, a temperature of max. 40°C and an operating pressure of max 4 barg. One of the flows contains up to 20-50 ppm of free chlorine (Cl2) as an impurity and the other flow contains up to 500 ppm of chloroparafins. The goal of the customer was to reduce these impurities to the ‘lowest level possible’. To treat both flows DESOTEC installed two MOBICON®1000 filters in series (4 filters in total). The filters were filled with high grade, extremely pure activated carbon products to obtain a high purification efficiency and avoid secondary contamination. The free chlorine was reduced to below detection limit and the chloroparafins were strongly reduced to a satisfactory level.

Using DESOTEC’s activated carbon based purification technology for hydrochloric acid, the customer was able to obtain a hydrochloric acid grade fit for food applications, thus opening a new market for them. Using DESOTEC’s mobile activated carbon filter service, the customer doesn’t have to bother about the activated carbon bed replacements. When the filters are saturated DESOTEC organises the pickup of the saturated filters and the immediate replacement with new, identical, prefilled filters always in mint condition. There is no manipulation of activated carbon (waste) on site. This is a clean, safe and fast way of dealing with a saturated activated carbon filter. DESOTEC takes care of the transport and waste treatment/recycling in its modern reactivation/recycling factories.