Feb-2008

Increasing refinery 
biofuels production

The benefits of producing bio-ethers with catalytic distillation compared to blending bio-ethanol are addressed

Kerry L Rock and Maurice Korpelshoek, CDTech

Article Summary

The European Union has set challenging targets for European refiners by increasing the minimum biofuel content in fuels to 5.75% by 2010. As a result, refiners are investing in process units to produce biofuels such as bio-ETBE (ethyl tertiary butyl ether), which is produced by the etherification of bio-ethanol and isobutylene.

In general, the investment cost to produce bio-ETBE is very low because existing MTBE units can be revamped to produce ETBE. The use of bio-ETBE is preferred, because the blending of bio-ethanol into gasoline can lead to water separation and an unwanted increase in gasoline vapour pressure. Bio-ETBE is now a stable and reliable biofuel component.

To meet a 5.75% biofuel content by 2010, the contribution of bio-ETBE will be too small, even if all available isobutylenes are converted to bio-ETBE. Refiners recognise the advantage of using bio-ethers as a stable biofuel component, so other technologies are required to maximise the production of bio-ethers. The first logical step is to utilise the same time-proven process for the etherification of C5 iso-olefins, which is a very cost-effective option for bio-ether production, since C5 iso-olefins are available in sufficient quantities in most refineries. The added advantage is that C5 components that have a high vapour pressure are converted to higher-octane bio-ethers with a low vapour pressure.

The second step is to use skeletal isomerisation technology to convert normal butenes and pentenes to reactive iso-olefins. With this technology, iso-olefin production is increased by 50–100%, which results in a similar increase in bio-ether production.

Refiners who have previously invested in the production of bio-ethers are aware of their benefits and are now considering a further increase in production, either through the production of bio-TAEE or through skeletal isomerisation, or a combination of both.

For gasoline blending, European refiners have a choice of blending bio-ethanol or bio-ethers produced from bio-ethanol and refinery iso-olefins. Several European refiners have already opted to produce bio-ethers because it offers significant advantages over the blending of ethanol.

EU directive
The EU maintains broad objectives towards improving the security of energy supply, reducing greenhouse gas emissions and creating new opportunities for sustainable, rural development. To meet these objectives, it promotes the use of biofuels, which would replace diesel or gasoline for transport purposes. Directive 2003/30/EC has been established to oblige EU member states to use a certain amount of biofuels, while directive 2003/96/EC provides an opportunity for EU member states to allow an excise duty reduction, thereby promoting the use of biofuels.

The former directive calls for a minimum of 2% biofuels relative to the amount of gasoline and diesel sold in 2005, growing to 5.75% in 2010. The percentages indicated are based on energy content. For bio-ethanol, an energy content of 5.75% biofuels corresponds to approximately 8.5 wt% ethanol in gasoline for ETBE, to approximately 14 wt% ETBE in gasoline.

Excise tax incentives
Under normal circumstances, the cost of bio-ethers production is higher than the price of comparable fossil fuels like gasoline. In most European countries, excise tax is a significant portion of the gasoline price, so governments have the option to promote the use of biofuels via tax incentives. Austria, France, Germany, Italy, Spain, Sweden and the UK have implemented the directives efficiently and offer either full tax exemption 
or partial tax exemption on the use 
of biofuels.

With the EU directive in place, some countries offered attractive tax incentives, which resulted in initiatives by refiners and others to produce biofuels. Specifically for the production of bio-ethers, several refiners who operated an MTBE unit opted to revamp their units to produce ETBE. Often, the change from MTBE to ETBE required very few modifications to the MTBE unit. Most refiners opted to modify the unit with minimum changes  and accept a lower conversion and/or a lower throughput. Regardless, the change from MTBE to ETBE production resulted in a significant amount of bio-ether production.

Since the production of biofuels is not mandated in Europe, refiners still use the flexibility of these etherification units to return to MTBE production, especially when MTBE prices are high. Presently, some 63% of the etherification units in Europe have or are producing bio-ethers. The majority of these are located in Germany, France and Spain.

The cost of revamping an existing MTBE unit to produce ETBE is very low. The majority of bio-ether capacity is produced by units that previously produced MTBE. Another option for the production of bio-ethers is to build a grassroots etherification unit. The investment cost of a grassroots unit is obviously higher than that of a revamped MTBE unit, but still moderate because these units operate at low pressure and have few pieces of equipment. In Europe, with its attractive tax incentives, three new etherification units have been constructed in the last five years.

Most unconverted MTBE units are located in Eastern Europe and Italy. Although the production of biofuels is not yet strictly required or promoted in these countries, several refiners in Eastern Europe are already considering a revamp of their existing MTBE units to produce ETBE. For future growth in bio-ether capacity, it is likely that the non-converted MTBE units will eventually be revamped. Further growth in bio-ether capacity will depend on the availability of iso-olefins.

Iso-olefin availability
Bio-ethers are produced by the reaction of reactive iso-olefins (eg, iso-butylene) with bio-ethanol. The reactive iso-olefins are available mainly from fluid catalytic cracking (FCC) units and steam crackers. In addition, iso-butylene is produced by the dehydration of tertiary butyl alcohol (TBA), a byproduct from propylene oxide/tertiary butanol manufacturing.