The main chemical use of toluene is to make benzene and xylenes using a number of technologies. In the hydrodealkylation (HDA) process, toluene and hydrogen are reacted to make benzene only. A toluene disproportionation (TDP) plant will convert toluene to benzene and xylenes while there are selective toluene disproportionation (STDP) processes that produce a paraxylene-rich stream. The transalkylation (TA) process takes toluene and C9 aromatics to produce xylenes.
Toluene is also used as a solvent but this application is expected to continue to weaken because of environmental and health regulations restricting solvent emissions. The definition of solvent end use and quality varies around the world. In most industrialised countries, solvent grade toluene is a high quality stream where purity is essential as environmental exposure levels must be quantified.
Toluene is consumed in the manufacture of toluene diisocyanate (TDI) which is used in the manufacture of polyurethane flexible foams used in upholstery, mattresses and automotive seats. Smaller uses for TDI include polyurethane elastomers and coatings.
Other minor chemical uses include the manufacture of phenol, caprolactam, nitrobenzene, benzoic acid and benzyl chloride.
In non-chemical uses, toluene is used in large quantities as an octane booster in gasoline but most of that portion is not removed from refinery streams.
There are three grades of toluene: TDI grade of 99+% purity; nitration grade at 98.5-100%, so called because it was used to make nitrotoluene, but now is used in solvents and TDP and HDA plants; and commercial grade of 96% for gasoline blending and HDA feedstock.
World toluene demand in 2006 was 23m tonnes with Asia surpassing North America as the largest consuming region, according to US-based consultant CMAI. More than 50% of toluene demand is used in the production of benzene and xylenes, around 25% in solvents and 7-8% in the TDI, benzoic acid and caprolactam. Around 15% of demand is accounted for by gasoline.
CMAI points out that downstream demand for toluene is different for each of the regions. In West Europe, the single largest use of toluene at just over 30% is the conversion to benzene in HDA plants. STDP and TDP plants for making benzene and xylenes account for nearly 30%, the remaining chemical demand including solvents is about 25% while gasoline blending accounts for the rest. CMAI expects HDA demand to decline modestly over the next few years.
Demand in Europe has been steady and most HDA units have been operating, supported by a spread between toluene and benzene. US-based consultant DeWitt & Co estimates that demand for toluene in Europe in 2007 was 2.38m tonnes, out of which 1.38m tonnes were converted to benzene and xylenes, and 526,000 tonnes were consumed by solvents.
Toluene demand growth in Europe is expected to be positive but low at a rate less than GDP. Demand will get a fillip in 2009 following the start-up of ExxonMobil’s new TDP unit in Rotterdam, the Netherlands.
Europe has excess capacity and needs to export to keep the region balanced. However, with the build-up of capacity in Asia in 2008-2010, trade flows between Europe and Asia could change.
In North America, the single largest end-use of toluene in 2006 was gasoline followed closely by STDP. These two categories accounted for two-thirds of demand and highlights the strong competition between gasoline and chemicals in the US, notes CMAI. In the US, some of the toluene produced is controlled by the refinery companies and generally not offered to the chemical markets. HDA and conventional TDP accounted for 15% of demand with TDI, solvents and others making up the remaining balance.
Asian demand patterns are completely different to the other two regions. Solvents were the largest end use in 2006 at around 40%. The second largest was toluene transaklyation which uses C9 aromatics as a co-feed to make xylenes. STDP plants consumed 15% of demand with HDA and TDI accounting for around 5% each of toluene demand.
Capacity will be added at a faster rate than growth in demand with most of the additions in Asia, particularly China. CMAI expects most of the surplus will be exported while imports into North America will reach 1m tonnes by 2009.
Updated: March 2008. Sources: ICB Chemical Profile, 3 March 2008; 2007 CMAI World Petrochemical Conference, 21-22 March 2007, Houston, Texas.