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AM-97-27 COST EFFECTIVE SOLUTIONS FOR REDUCTION OF BENZENE IN GASOLINE

Kerry L. Rock; CDTECH Houston, Texas

Format:
Electronic (digital download/no shipping)

Associate Member, International Member, Petrochemical Member, Refining Member - $0.00
Government, NonMember - $35.00

Description:

The requirement to limit the benzene content of gasoline was established by the Clean Air Act Amendment (CAAA) of 1990 when’benzene was about 1.5 volume percent of the gasoline pool. The need to limit benzene is due to its classification as a toxic compound. The restriction applies to gasoline sold in areas in the U. S. which are classified as non-attainment for ozone. The initial application of the limit was 1 % maximum in Reformulated Gasoline (RFG) as mandated in the Simple Model which went into effect January 1, 1995. The same limit was applied to California gasoline by the California Air Resources Board (CARB) effective March 1, 1996. The combination of CAAA and CARB .RFG amounted to about 25% of the U. S. gasoline pool in 1996. The result of reducing benzene from 1.5 % to 1 % in 25% of the gasoline meant that only about 8% of the benzene had to be removed on a global basis. For most refiners, this was easily accomplished using existing options. Many refiners simply adjusted the C6 content of the naphtha feed to their reformer by prefractionation and produced a reformate with reduced benzene content. Refiners with integrated chemical operations were able to send their light reformate to extraction facilities and move benzene into the petrochemical market. Others were also able to take advantage of this option by exporting the light reformate fraction over the fence for outside processing. Only two refineries installed facilities for hydrogenation of benzene. The removal of benzene from the gasoline pool represents the loss of one of the highest octane components. However, both CAAA and CARB RFG programs required the addition of 2.0 weight percent oxygen. This requirement has been met primarily through the use of MTBE and with lesser amounts of ethanol and TAME. All of these oxygenates are high octane components which more than offset the loss of octane due to the removal of benzene. As a result, the benzene/octane issue is not a significant factor in Phase 1 RFG. Complex Model Im P acts Relative Sensitivity to nputs In 1998, the Complex Model will become effective in the CWA RFG program. This model provides more flexibility for the refiner to meet the required automotive emissions reductions in Phase 1 of the program. The model is used to predict 100 emissions of Volatile Organic Carbon (VOC), Toxics (TOX) and Nitrogen Oxides (NOX) based on gasoline composition 60 variables including RVP, benzene, aromatics, sulfur, olefins and percent gasoline evaporated at 200°F and 300°F. The 60 relative sensitivities of emissions to these variables are illustrated in Figure 1 for 1990 average gasoline. In 2000, the 4o CAAA RFG program enters Phase 2 where reduced emission 2o limits will be applied to VOC, TOX and NOX. At this point virtually all C4s and some C5s will be removed from gasoline to 0 reduce RVP and control VOC. Reduction of sulfur in FCC =:-..-, voc TOX NOX gasoline will be necessary to achieve NOX reductions. Since r1gu12 I RVP and Sulfur have very minor impact on TOX, the refiner will look to benzene and aromatics to reduce TOX. Sensitivity studies using the Complex Model have shown that the TOX reduction achievable by removing 1 gallon of benzene from the pool is equivalent to removing as much as 28 gallons of aromatics. With much smaller impact of benzene on gasoline volume the refiner is more likely to consider further reductions in benzene rather than reducing aromatics. Meanwhile, pressure is being applied by various environmental groups including OTAG, NESCAUM, STAPPAALLAPCO and Sierra Club to expand the benefits of RFG to other areas of the U. S. not currently required to participate. In addition, the automotive industry is being required to achieve further improvements in fuel efficiency while maintaining low emissions and driveablilty. The automotive industry maintains that it must have more consistent gasoline composition with narrower ranges of composition in order to achieve these goals. This gasoline would be specified for all states except California since CARB RFG would be acceptable. CAAA RFG has been ‘proposed as the,“49 State Gasoline” for this purpose. Some opponents of oxygenates have supported a version of RFG without oxygenates for this purpose. Such moves to increase the volume of RFG and reduce TOX could require benzene reductions to about 50% of the 1990 pool average or about 0.75%. This is clearly a much larger quantity to deal with and refiners may be forced to make more substantial changes in refinery operations to achieve these levels. For many refiners, prefractionation of the reformer feed will not provide a sufficient benzene reduction. The high capital cost of benzene extraction expansions or new facilities will also not provide an attractive answer. Assuming hydrogen availability is not a problem, benzene hydrogenation may provide the answer. Even if hydrogen supply is a problem, it may well have to be addressed by the need to remove sulfur from FCC gasoline as well as other refinery products, as increased pressure to reduce sulfur emissions comes into play in the near future. The refinerwho is looking down the road and making plans probably has a hydrogen plant increasing in priority. To the extent oxygenates are precluded from the expanded RFG market, then the octane loss associated with benzene reduction ihrill become a more significant issue. Refiners will be looking for ways to replace the octane lost from benzene removal or hydrogenation. Since increased reformate severity or volume is unlikely due to its high aromatics content, other sources such as alkylate and isomerate will be of interest. Reduction of benzene is not only of interest in the U. S. Canada is presently firming its plans to limit benzene in gasoline to less than 1% by 2000. Although there isn’t yet a consensus in Europe, Germany and Sweden feel strongly about a 1% limit and others want to reduce the current 2.5% average to 1.6%. Japan and India are also looking at benzene limits in the near future. Many others recognize the need to deal with this issue.

Product Details:

Product ID: AM-97-27
Publication Year: 1997