Technology - SULFACID^®
July 2, 2015

Introduction

The SULFACID^® process involves the adsorption of SO₂ by activated carbon and the subsequent reaction with oxygen and water to form sulphuric acid.  The SULFACID^® process has been developed to remove SO₂ from waste gases generated by chemical and metallurgical processes.  SO₂ is recovered in the form of dilute sulfuric acid only (i.e. < 20% H2SO4).   The process lends itself particularly well to applications where the dilute sulfuric acid can be directly reused, as for example in titanium dioxide production according to the sulfate process.

The features of the SULFACID^® process are:

• Simple reaction control
• Minimum maintenance requirements
• Minimum operator attendance
• Low specific energy costs
• Simple equipment

The process is designed to handle weak gas containing less than 1% volume (dry basis) SO₂ and minimum 7% volume (dry basis) O₂.   The Temperature must be a minimum of 30°C and the gas cannot contain more than 30 mg/Nm³ of dust.  The feed gas should also have a defined relative humidity prior to being admitted to the SULFACID^® reactor.  Humidification of the feed gas can be done using water, steam or weak acid.

When the feed gas enters the reactor it travels up through the activated carbon bed where the sulfur dioxide is converted to sulfuric acid by wet catalysis in the presence of oxygen and water.  The conversion of sulfur dioxide to sulfuric acid on the catalyst proceeds according to the following reaction equation:

SO2 + ½ O2 + n H2O ð H2SO4 (n-1) H2O + 3.02 kJ

The clean, water-saturated gas leaving the reactor is discharged to atmosphere via a stack. The sulfuric acid formed collects in the pores and on the surface of the catalyst is intermittently washed out by spraying water over the catalyst.  Sulfuric acid in a concentration range of 10 to 20 wt.% flows off into a collecting tank. 

The first SULFACID^® plant was started-up in 1968 with 14 commercial-scale systems now in operation.  When testing in the pilot scale is required, a mobile pilot plant is available to verify the suitability of the SULFACID^® process directly on site and allow optimal scale-up to commercial operation.