Published July 2003
The ConocoPhillips S Zorb process desulfurizes diesel fuel by sorption on a proprietary sorbent. Sulfur-containing molecules are adsorbed, including sterically hindered molecules like 4,6 dimethyldibenzothiophene, and the sulfur atom is split from the molecule. The sulfur is retained on the adsorbent while the hydrocarbon desorbs. Sulfur is typically removed to about 5 ppm from feedstock of 500 ppm sulfur (but greater than 2000 ppm sulfur feedstocks are possible). The process responds well to feed sulfur changes. Depending upon the feedstock, the process operates at very mild conditions: 275 to 500 psig about 700 to 800°F (371 to 427°C). H2S is not released. Critical diesel fuel properties are unchanged. Due to very low hydrogen consumption, the process potentially produces relatively lower CO2 and NOx refinery emissions.
The fluid bed design of the S Zorb process enables long run lengths that can match the refinery run length. Diesel fuel has grown faster globally than the growth in total transportation fuels, a trend that is likely to continue. In Europe and Japan, the number of diesel powered cars increased in the last two decades faster than the growth of all cars.
Currently the most common on road diesel fuel sulfur specification is 500 ppm (350 ppm in Europe) with higher limits in some countries. The European Commission adopted a 10 ppm sulfur specification for on road diesel fuel beginning in 2005 with full conversion by 2010. An U.S. EPA rule phases in 15 ppm sulfur highway diesel fuel starting June 1, 2006. In Japan, 10 ppm sulfur fuel is proposed for 2008. Furthermore, the U.S. EPA recently proposed sulfur in off road diesel fuel be limited to 15 ppm in 2010.
The capital investment needed by the refining industry to meet the new diesel fuel specifications is anticipated to be substantial (estimates range from $3 to 13 billion for the U.S. industry). The S Zorb process can be added to a refinery to further process diesel stock from existing hydrotreaters and other units, enabling prior investments to continue to be utilized.
A 6,000 BPSD gasoline unit has operated at ConocoPhillips Borger refinery since April 2001. Overall, S Zorb technology is licensed to 42 sites. ConocoPhillips is reviewing locations for the first diesel unit and expects to soon begin design work.
We review the S Zorb diesel process. Economics for a 30,000 B/CD unit desulfurizing 500 ppm sulfur diesel to 5 ppm are estimated.