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Apr-2010

When MTBE outscores ETBE for 
bioenergy content

If MTBE is produced from biomethanol, its bioenergy content as a fuel additive will be counted twice, according to EU biofuels regulations

Eelco Dekker
BioMCN

Viewed : 3050


Article Summary

Despite improvements in engine technology and fuel efficiency, total CO2 emissions from road transport fuels continue to grow every year. We must reduce our global dependency on the use of fossil energy.

Over the past decade, we have seen an increase in the use of biodiesel as an alternative to diesel, with ethanol being used as a biocomponent in gasoline, either in ethyl tert-butyl ether (ETBE) or through splash blending. Although these biofuels are made from renewable resources, the past few years have seen increasing concern over sustainability issues, such as deforestation, indirect land use change and competition with food. These issues are driving legislators to insist on the use of “better” biofuels made from more sustainable feedstocks. For biodiesel, alternative oil feedstocks include algae, jatropha and used cooking oils. Much effort is similarly going into the research and development of cellulosic ethanol. But there are other solutions. One such alternative sustainable fuel, biomethanol, is already commercially available in large volumes.

Biofuel generations

The development towards more sustainable biofuels has been described by some as second-generation biofuels to distinguish between traditional biofuels and those with more environmentally friendly attributes. In the EU’s Renewable Energy Directive (RED), however, there is no mention of the term. And to make matters more confusing, some of the latest developments are now described as third- or fourth-generation biofuels.

Even though there is no clear definition of these different generations, a number of specific characteristics are typically mentioned in reference to second-generation biofuels: feedstock sustainability; innovative technology; similar fuel properties; and reduction in GHG emissions. These help to distinguish between different biofuels and demonstrate that biomethanol does, indeed, qualify as a “better” biofuel.

What makes a second-generation biofuel?
Feedstock sustainability

Biofuels were introduced as an important part of the solution to reducing the use of fossil energy sources and limiting the effects of global warming. But with growing volumes of ethanol and biodiesel being blended in the fuel pool, there also came concern over the potential negative effects some biofuels themselves might have on the environment.

Although many factors have an impact on the agricultural sector, when food prices shot up in 2008 many analysts were quick to blame biofuels as the main cause. Deforestation, change in land use and child labour are but a few of the other negative trends blamed on biofuels. As a result of 
these concerns, there is increasing pressure on biofuel producers to start using more sustainable feedstocks.

Article 17 of the RED lists sustainability criteria that biofuels need to fulfill to be taken into account for:
• Measuring compliance with the requirements of the RED concerning national targets
• Measuring compliance with renewable energy obligations
• Eligibility for financial support for the consumption of biofuels and bioliquids.

An exception is made for biofuels made from waste and residues. These only need to comply with the sustainability criteria described in paragraph 2 of the same article, which deals with GHG emissions.

One such feedstock is crude glycerine, the raw material for producing biomethanol. Crude glycerine is a processing residue from biodiesel production and the oleochemical industry, and is recognised as such in Annex V.C.18 of the RED:
“Wastes, agricultural crop residues...and residues from processing, including crude glycerine (glycerine that is not refined), shall be considered to have zero life-cycle greenhouse gas emissions up to the process of collection of those materials.”

Innovative technology
Another common denominator in discussions about “better” biofuels is the use of innovative production technologies to convert sustainable feedstocks into biofuels. Typical examples include Fischer-Tropsch, hydrogenation processes and biomass gasification.

Biomethanol production is based on the original methanol production process, which converts natural gas (CH4, methane) into methanol. Here, three stages — steam reforming, synthesis and distillation — produce 99.85% pure methanol.

After purification, natural gas is cracked in a steam reformer. Steam reforming mixes the methane with large amounts of steam. The 
methane/steam mixture flows through pipes over a catalyst and is heated to 500–850°C. After the steam reformer, the methane is split into syngas: a mixture of carbon monoxide (CO), carbon dioxide (CO2) and hydrogen (H2). The syngas is cooled to an ambient temperature and compressed to close to 100 bar before it is fed to the synthesis reactor. In this reactor, the syngas components react to form methanol. This methanol contains about 17% water, which is removed by distillation. In the distillation process, water, light alkanes and the heavy ends (denser fractions) are removed from the main stream. The outcome is 99.85% pure methanol.

The production process for biomethanol is no different to the production of regular methanol. What is different is the origin of the gas stream going into the methanol reformer. Instead of natural gas, the feedstock is glycerine. It is not possible to feed liquid glycerine to the reformer directly. It first has to be converted to the gas phase. The glycerine is purified and evaporated in a process patented by BioMCN.

The crude glycerine contains several impurities, mainly water, sodium and potassium salts, and a certain amount of undefined organic components. These have to be removed, since the glycerine feedstock to the evaporation unit has to have a high purity level with a low chloride and sulphur content.


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