Enhancing Molten Sulfur Filtration during Sulfuric Acid Manufacturing for Phosphate Fertilizer Production in Morocco with Cellulose-Based Filter Aids

Abstract

The filtration of liquid sulfur is a key operation in the production of sulfuric acid that is used for phosphate fertilizer production in Morocco and elsewhere. The purpose of the filtration process is to remove solid impurities from liquid sulfur, which could clog the sulfur burner spray nozzles, leading to the reduction of the lifetime of the sulfuric acid production unit. The standard life cycle operation for sulfuric acid units is 24 months, while due to clogging, this lifetime can be reduced to less than 18 months, which is obviously a tremendous economic disadvantage. In the liquid sulfur filtration process, a precoat made of diatomaceous earth is usually used. In this work, the performance of a standard diatomaceous earth filter aid was compared to the performance of two commercial, inexpensive, cellulose-based filter aids, namely, FILTER-900 and FILTER-1100, which are distinguished by their respective Dalton numbers (900 Da and 1100 Da). The experiments were realized using an industrial sulfur filtration device, and the results indicated that all three of the filter aids yielded similar performance in terms of the impurity content in the filtered liquid sulfur. The cellulose-based filter aids did, however, show a lower specific filter-aid consumption, accompanied by an increase in operating cycle times from 24 to 72 h. In addition, the use of the cellulose-based filters allowed for the relatively easy removal of the filter cake without damaging the filter cloths (which is often an issue with the diatomaceous earth filter aids). It was further noticed that the filtered liquid sulfur obtained using the cellulose-based filter aids remained uncontaminated by silicate, which is one of the main elements that can result in clogging of the sulfur spray nozzles. The first experimental data presented here are therefore promising, and further industrial tests as well as economic analysis for using cellulose-based filter aids in industrial sulfuric acid production are encouraged.