Valorising chemical by-products by purifying HCl

The industrial production of liquid chemicals (both organic and inorganic) often involves one or more separation and purification steps to reach demanding technical specifications. DESOTEC has more than 30 years of experience in the purification of liquid chemicals such as hydrochloric acid (HCl), sulphuric acid (H₂SO₄), amino acids, mineral oils, brines and many different types of solvents. This case study demonstrates how our sustainable mobile activated carbon filtration solutions are helping customers purify HCI, developing new income streams and opening up markets.

The Problem

At a European chemical plant, hydrochloric acid is produced by the chlor-alkali process, which involves scrubbing the waste gases that result from the dechlorination of other chemicals.

This results in two separate liquid flows of 32-37% HCl solution, with a production rate of 4 000 kg/h, a temperature of up to 40°C, and an operating pressure of up to 4 bar.

One of the flows contains up to 20-50 ppm of free chlorine (Cl₂), while the other has up to 500 ppm of chloro-paraffins.

The customer’s goal was to purify these streams to the highest level possible.

Industrial chemical producers have a choice of several technologies to purify their chemical streams. These range from common methods such as distillation and molecular sieving up to more advanced treatments.

Activated carbon is a simple technology that is proven to remove a wide range of molecules efficiently. Therefore, the customer contacted DESOTEC for a solution.

The Solution

DESOTEC has installed two Mobicon 1000 liquid filters in series on each flow (a total of four filters). These are filled with high grade, extremely pure granulated activated carbon to obtain a high purification efficiency.

One particular challenge posed by chemical purification is that certain substances may corrode or degrade the vessels used in the process. DESOTEC’s standard Mobicon 1000-HDPE and Mobicon G5 filter units are designed for such corrosive applications, and we can also construct dedicated mobile activated carbon filter systems for use with specific chemicals under given operating conditions.

The Results

The free chlorine in the HCl stream is now reduced to below detection limits, and the chloro-paraffins are heavily reduced to a satisfactory level.

By using DESOTEC’s activated carbon filtration technology, the customer is able to purify its HCl by-product to a grade fit for food applications. This has opened up a new market for them.

DESOTEC is continually researching and developing new filter set-ups to meet customers’ needs. Our Mobicon 2000 G5 and Mobicon 2000 PE units, for example, were designed to handle smaller corrosive liquid flows.

As part of our full-service solution, we organise the exchange of filters once the carbon is saturated. We collect the used filters and replace them with new, prefilled filter units, always in optimal condition. The used filters are transported to DESOTEC’s facilities, so no carbon is handled at customers’ sites and there is no risk of contamination.

In our state-of-the-art facilities, all adsorbed molecules are destroyed in line with national and European legislation. The installation and its emissions are continuously monitored, so only harmless water vapour exits the chimney. Wherever possible, the carbon is reactivated: this circular model drives down costs and boosts sustainability.