First published in Cleantech magazine, Issue 1 2012.
Bioethanol is currently the most widely used biofuel, with the US and Brazil accounting for 88% of world production. In 2010 the US produced around 50 billion litres from corn, while Brazil produced about 26 billion litres from sustainable sugarcane (Renewables 2011 Global Status Report; UNICA). Brazil has been heavily involved in ethanol production since 1975, when the Proalcohol era saw production incentivised by the Brazilian Government in response to soaring global oil prices. More recently, transport and energy security have been the driving forces behind the expansion of production in Brazil, and growth in the US. First generation bioethanol is derived from sugar and starch-based crops (such as cane, corn and wheat), but the transition to second generation bioethanol, derived from sugars created by the breakdown of the cellulose part of the plants, is gathering pace.
The likely next stage in the commercial development of bioethanol is the entry of the oil majors, and there has been notable merger and acquisition activity in Brazil, driven by UK-based companies Shell and BP and Total of France – as well as by the domestic oil company, Petrobras.
Globally, a significant and growing demand for bioethanol is forecast, and output is set to double by 2020. This demand is most likely to be met by plants ranging from mass production down to small scale production plants (e.g. the US cellulosic and African decentralised plants).
The first stage in the production of bioethanol from first and second generation feedstocks is crushing and fermenting the feedstock to generate a ‘beer’ with an ethanol content of around 8-10%. This is followed by distillation, which removes most of the water, but reaches a physical purity limit of 95-96% due to the formation of a low-boiling water-ethanol azeotrope. Even when an azeotrope is boiled, the resulting vapour has the same ratio of constituents as the original mixture, i.e. the ethanol percentage cannot be further concentrated by standard distillation. This mixture is called hydrous ethanol and can be used as a fuel alone, but it cannot be mixed with gasoline (e.g. in an E85 fuel), so a dehydration process is required to remove the water and generate anhydrous ethanol, which can be used with gasoline in combustion engines.
There are two principal ethanol dehydration techniques. The process used in early plants, and which is still used in about 85% of Brazil’s plants, is called extractive distillation, which involves the addition of cyclohexane or benzene and further heating. This is an energy intensive process that involves the disposal of costly, hazardous chemicals. An alternative method in use in the US, Europe and the more recent plants in Brazil is molecular sieve technology (or MSUs). In this process the ethanol/water mixture is passed as a vapour under pressure through a bed of porous ceramic (zeolite) beads, with the pores of the beads absorbing water molecules but not ethanol. However, the beads soon saturate and the bed has to be regenerated. This is a batch process and requires two or more beds to be used to try and achieve a continuous production process.
While MSUs are less energy intensive than extractive distillation, the ethanol industry and regulators are seeking effective ways to further reduce the water and energy consumption of ethanol production as well as to improve the purity of ethanol.
A membrane approach has distinct advantages. Membranes are the most efficient method of molecular separation and can therefore dehydrate ethanol in a more energy/water efficient way. In the early 1990s Dr Stephan Blum (then member of the membrane technology team at Henkel, Germany) was using membrane technology for the production of high quality pharmaceutical grade ethanol. He was inspired to begin using a capillary membrane geometry (a tubular format rather than a plate/stack system) to develop membrane-based processes for ethanol production. In 1998 he began to develop the technology together with Robert Heggemann, which culminated in the establishment of Whitefox Technologies in 2000. In addition to their use in the production of biofuels, membranes are highly suited for the production of ultra dry ethanol for the pharmaceuticals/industrial/potable markets.
Produce more and waste less
Whitefox Technologies was set up to exploit this highly efficient membrane technology. The company has since gained a decade of experience in biofuel production, with one of its early plants in Germany having operated successfully since 2002. In the US the technology has been shown to be capable of scaling up to large production – producing more than 400 million litres per year.
Whitefox membrane technology has the appropriate geometry for scalability, and a patented cartridge concept allows the technology to be used modularly. The company is headquartered in the UK and has subsidiaries in Canada and the US.
Whitefox technology is equally suited to new-build plants, as well as for retrofitting existing plants, as it can work alongside the current technology. Given the impact of the global economy on plans for greenfield projects, retrofits offer good potential opportunities. For example, retrofitting Whitefox technology to the average Brazilian plant reduces the consumption of steam required from 5 kg/litre of ethanol to approximately 2.5 kg/litre – a significant saving in energy and water consumption for Brazil. With further changes to the process it is possible to reduce this even more to 1.4kg steam/litre. It is likely that, owing to the use of hazardous and pollutant chemicals and high energy consumption, Brazil will begin to phase out cyclohexane technology. Given that there are over 380 plants using this technology in Brazil, a viable solution is required in the short term.
In more modern bioethanol plants, MSUs need to recycle a portion of the anhydrous product back into the beds to remove the adsorbed water, thus producing a hydrous regenerate stream which is further recycled back to the distillation tower. Typically, the regenerate recycle represents 15-25% of the total output. Dehydrating the regenerate stream through a membrane would eliminate the recycle, potentially increasing the output of the plant and reducing energy consumption.
Another feature of current production processes is the need to remove the fusel oils (higher order alcohols) from the distillation tower. Large amounts of water are added to the fusel oil draw to achieve phase separation (decantation). The fusel oils are normally then added back into the fuel mixture at the end of the process or sold off separately. As membranes are tolerant to fusel oils this decantation process can be avoided. With an existing facility it is possible to treat the fusel oil stream and efficiently dehydrate it to final product – again saving water and energy. This represents a promising application for Whitefox technology.
“I am encouraged by the signals we receive from ethanol producers,” says Dr Blum, Whitefox’s founder and chief technology officer. “There is a growing understanding that membrane technology can really improve the efficiency of ethanol production, making ethanol a sustainable and economically viable part of the energy mix”.
Whitefox will partner with locally-based engineering companies to roll out the technology. For example, Whitefox has been working with Brazilian engineering company PROENG (Projetos e Desenvolvimento de Equipamentos S/S Ltda) from 2008. Whitefox and PROENG have adapted Whitefox’s membrane-based process to sugarcane, where the significant reductions in steam, electricity and water requirements lead to considerable increases in the output of green electricity to be sold to the grid from waste biomass (bagasse).
Ethanol is the first major application of Whitefox technology, but the technology has a number of further potential uses. Whitefox is currently developing high performance membranes with significant advantages over traditional fuel cell membranes. The membrane technology is ’tuneable’, so gas separation and water treatment are two future potential applications.
Meanwhile, Whitefox is winning recognition. The company was named best in class at Clean Energy Monaco 2011 by an independent panel of judges, and won the prestigious award for Excellence in the Field of Environmental Technology Commercialisation. In December 2011, the Carbon Trust selected Whitefox to participate in the Entrepreneurs Fast Track service.
For more information, visit the Whitefox Technologies website.