(213e) Analysis of Commercial and Synthesized H2S Scavengers for High Performance, Safe and More Economical Asphalt Roads

In recent years, the product quality and related processing conditions have been challenged by the increasing sulfur levels of crude oil resources. In addition to the recent strict legal regulations on allowable sulfur amounts in the products, those sulfur compounds have tendency to accumulate in the bottom products such as bitumen and fuel oil which makes it harder than ever to reach the required sulfur limits for the heavy bottom products. In addition to the naturally existing sulfur, it can also be artificially added into the bitumen at quite low amounts in order to cope with the bitumen-polymer incompatibilities caused by the properties of crude oil blends being processed in the refinery. Sulfur is known to trigger the cross-linking reactions and thereby improve the compatibility and storage stability of polymer modified bitumen that is used for long lasting and high performance asphalt roads. Since the storage and pavement temperatures of bitumen reaches up to 180 ¢ªC, this may results in the release of poisonous, flammable and colourless gas of hydrogen sulphide (H₂S). It can cause the road workers to die during pavement if above 300 ppm or make them suffer from several illnesses when exposed to concentrations as low as 10 ppm for longer than 8 hours. This study focuses on the H₂S scavenger performances of different commercial and synthesized chemicals by on-line monitoring of the concentrations of H₂S and other sulfur based chemicals. A home-made apparatus was made with a stainless steel column (1 m in long and ¼” in diameter) packed with ceramic beads. One end of the column is connected with Gas Chromatography - Sulfur Chemiluminescence Detector (GC-SCD). The other end is connected with 316 L stainless steel, 0.5  liter bomb reactor having a pressure gauge at the top and containing refinery gas sample with known amount of H₂S concentration and taken from an absorber of a fluid catalytic cracking, FFC, unit. Calibration curves are obtained by using FCC unit gas of high H₂S concentration and commercially available standard gases of low H₂S concentration, details of which are given elsewhere (M. Yasar et al., 2013 “ New Technique for Quantitative Determination of Sulfur Compounds in Refinery Gases by using GC-SCD” American Chemical Society (ACS) 2013 Proceedings, Hydrocarbon Resources, Pub# 500). During the experiments, different H₂S scavengers are loaded into the column in equal amounts at each measurement. Then refinery gas with known amount of H₂S is passed through the column at room temperatures and the scavenging performances are observed by GC-SCD simultaneously. For the next step, scavenging performances of these chemicals in the bitumen is studied. Firstly, thermal stability of these chemicals at high temperatures are analysed by Thermal Gravimetric Analysis (TGA). Later on, 0.5-25 %(wt.) sulfur and 1-5 % (wt) scavenger containing bitumen samples are prepared and analysed at 150 ¢ªC. The results indicated that the third scavenger in a form of supported and pre-determined mixture of metal oxides has the best performance among synthesized ones and has a comparable performance with the commercial ones both in the refinery gas and in the bitumen phase.  Scavenging performances up to 99 % decrease in H₂S concentration at the outlet are observed. As a further study, sulfur and scavenger added bitumen samples are further modified with varying amounts of Styrene-Butadiene-Styrene (SBS) diblock co-polymers addition. Rheological properties of those samples are studied by Dynamic Shear Reometer (DSR) to understand the improved performance and compatibility of prepared modified bitumen samples. Comparable performances together with decreased amount of required polymer have been found indicating that the prepared chemicals are potential bitumen additives for high performance, safe and more economical asphalt roads.