Sulfur in gasoline

Keyworth, D. A., Reid, T., Asim, M., and Gilman, R., Offsetting the Cost of Lower Sulfur in Gasoline, presented at NPRA Annual Meeting. New Orleans, La., March 22-24, 1992. 

Sulfur in gasoline contributes to the SO air quality problem and deactivates the catalyst in the catalytic converter. Emissions from a poisoned converter contain higher levels of VOC, NO, and CO. As stated earlier, VCR2 and NOj are catalyzed by sunlight to form smog. 

For the U.S., the new EPA rules will limit sulfur in gasoline to 30 ppm, phased between 2004 and 2006. The automobile industry has made a strong case for lower sulfur because of its effect on the catalytic converter. The converter has the same catalyst as the refinery reformer and it is poisoned just as easily by sulfur. 

Gasoline normally contains 0.04% by weight of sulfur, which is oxidized into sulfur dioxide in the engine. Automobiles contribute about 2% of manmade sources of sulfur in the air. It has been reported recently that oxidation catalysts may accelerate the oxidation of sulfur dioxide to sulfates, which is a more serious respiratory hazard than sulfur dioxide. It may be necessary to reduce the sulfur in gasoline. 

FCC units, and in particular the catalyst regenerating section, may give rise to significant pollution. Sulfur in the coke oxidizes to SO2 and SO3, while the combustion also generates NOx compounds. In addition, the flue gas from the regenerator contains particulate matter from the catalyst. The FCC process is also the major source of sulfur in gasoline. Of all the sulfur in the feed, approximately 50% ends up as H2S in the light gas-LPG fraction, 43% in the liquid products and 7% in the coke on the spent catalysts. 

Mercaptan Sulfur in Gasoline, Kerosene, Aviation Turbine, and Distillate Fuels (Potentiometric Method)... 

An old procedure for the determination of sulfur in gasoline involves the precipitation of BaS04 as the final chemical step and specifies that no more than 1 xg of sulfur be permitted to remain behind in solution. If the precipitation is made from 400 mL, what must the concentration of excess barium ion be KSp for BaS04 is 1.1 x 10-10. 

In addition to this comprehensive scheme, other determinations may be carried out by utilizing specific properties of the sulfur compound types (54, 72). Sulfur may be determined by removal with elemental mercury 51, 70), or by reaction with a mercaptan. In the latter case the sulfur determination is made by measurement of the excess mercaptan after the sample has been treated with litharge, sodium hydroxide, and a known excess of butyl mercaptan 78,81). A qualitative method of detecting elemental sulfur in gasoline is by the addition of sodium hydroxide to a pyridine solution of the gasoline which turns blue if sulfur is present 67). Free sulfur can also be determined polarographically 60). 

With the advent of stricter pollution laws concerning sulfur in gasoline and diesel oil, an outburst of research on the hydrodesulfurization (HDS) process is currently pervading chemical laboratories worldwide. In the HDS process (Eq. 1), sulfur is removed from fossil materials upon treatment with a higher pressure of H2 (35-170 bar) in the presence of heterogeneous catalysts at high temperature (300-425°C) [1],... 

Because sulfur in gasoline inhibited the octane-enhancing effect of the alkyl lead, there was a restriction on the sulfur content of thermally cracked refinery streams for gasoline. By the 1930s, it was determined that larger hydrocarbon molecules had major adverse effects on the octane number of the gasoline, and specifications consistent with the desired properties were developed. 

Monochromatic WDXRF Traditional wavelength dispersive XRF instrument uses polychromatic excitation. This new technology uses monochromatic focused excitation. Preliminary work has shown a reproducibility of about 2 mg/kg at a level of 10 mg/kg of sulfur in gasolines and diesel fuels. Earlier this year this method was issued as ASTM D 7039. 

Sulfur levels in gasoline and diesel fuels have been decreasing steely over the last several years, primarily in response to government regulations both in the U.S. and in Western Europe. For example, U.S. Environmental Protection Agency s (EPA) Tier 2 emission standards mandate sulfur level reduction from current 330 and 550 mg/kg sulfur in gasoline and diesel, respectively, to 30 and 15 mg/kg by 2006 and near zero by 2010 and later years [1-3]. Regulations in California are even more restrictive. Similarly, EN 590 European diesel specification mandates sulfur content of diesels from 350 mg/kg maximum in 2000 to 10 mg/kg maximum by January 1, 2005 in European Union countries. 

Figure 6 demonstrates analyzer response for sulfur in gasoline samples using the HSS analyzer when switching from 225 mg/kg to 15 mg/kg sulfur levels. The arrow points to data from the first injection after the sample was switched from high to low concentration. Injection rates were at one-minute intervals. 

Nadkami, R. A. and Ely, K. J., An Interlaboratory Study for the Evaluation of Test Method Capabilities for the Determination of Low Levels of Sulfur in Gasoline and Diesel, ASTM RR-D02-1547, ASTM International, West Conshohocken, PA, 2003. 

Numerous techniques and instrumental methods can be used to measure sulfur in gasoline and diesel fuels [3]. It is beyond the scope of this paper to cover any of the standard techniques in detail. Unfortunately, many of the traditionally used techniques are out of consideration for analyzing fuels at low levels because of inadequate sensitivity or lack of precision at those levels. For instance, a study group comprised of 69 industry participants has recommended that Energy Dispersive X-ray Fluorescence (EDXRF) and some other older technologies be dropped fi-om consideration for analyzing fuels at the 30 ppm level [3],... 

Special session to address reactive sulfur in gasoline, ASTM D2 Meeting, June 2004, Salt Lake City, UT. 

Similar to atomic emission spectroscopy, equally widely used technique for elemental analysis in the oil industry is X-ray fluorescence (XRF). There are four papers in this book using this technique, three of which deal with the determination of sulfur in gasoline and diesel. 

Nadkarni (Symposium Chairman) reviewed the alternate methods available for sulfur determination in fuels. Out of about 20 ASTM standard test methods available, only about five (D 2622 WDXRF, D 3120 microcoulometry, D 5453 UV-fluorescence, D 6920 pyro-electrochemical, D 7039 MWDXRF) are appropriate for ultratrace amounts of sulfur in gasoline or diesel. However, in their actual industrial use only D 2622 and D 5453 predominate. 

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