Cellulosic ethanol made by sunliquid
Cellulose, the world’s most abundant biopolymer, is getting a lot of attention these days. And that’s not surprising. The polysaccharide’s great potential is obvious after it is broken down into its building blocks – the sugars that serve as a second-generation platform for the production of sustainable cellulosic ethanol and other green chemicals. The last few years have seen increasing success in development and deployment in the field of cellulosic ethanol production. The main challenge so far has remained demonstrating economic feasibility of up-scaling to industrial levels. In the town of Straubing in Lower Bavaria, this will soon become reality; Süd-Chemie has almost finished construction on its sunliquid® demonstration plant. The facility will be Germany’s largest cellulosic ethanol plant, producing up to 1,000 tons of ethanol annually starting at the beginning of next year.
Bioeconomy, green chemistry, sustainability – those buzzwords are associated with the need for a change in thinking in our industrialized society. Petroleum is still the primary resource for industrial production and energy generation, but cheap oil will come to an end eventually, and thus there is an urgent need to find a suitable replacement. Energy independence, climate change and environmental protection are also stark reminders of the need for a switch to a more sustainable and renewable feedstock base.
The sugar platform
Plants containing sugar and starch already serve as feedstocks for a wide range of biobased products, but they have certain limits. Greenhouse-gas emission savings are modest when using first-generation feedstocks, and new sustainability issues like competition for food and feed production – as well as additional land use – need to be taken into consideration. Efforts are therefore pursuing an alternative, second-generation sugar platform.
Lignocellulosic material like that found in agricultural residues is available in large quantities all around the world. Its main components are cellulose and hemicelluloses, sugar polymers that can be broken down into monomers (C5 and C6 sugars) which in turn can be used for fermentation into biofuels or biobased products.
The sunliquid® technology
Over the last five years, Süd-Chemie AG (a member of the Clariant Group) has developed the sunliquid® technology to commercial maturity. Its primary product is cellulosic ethanol, which can be used as biofuel with high greenhouse-gas emission savings – almost 100% compared to the fossil fuel gasoline.
The integrated design of the technology assures a highly efficient and economically competitive process. The enzymes used for saccharification are optimized and highly specific for the applied feedstock and process conditions, thus ensuring the highest sugar yields in short reaction times. They are produced in a process-integrated fashion, with a small portion of the pretreated feedstock serving as a substrate, which cuts overall production costs to a bare minimum and helps maintain independence from external suppliers. Ethanol output is further increased by about 50% by the simultaneous one-pot fermentation of both C5 and C6 sugars through a proprietary yeast strain, compared to other processes that use only C6 sugars for fermentation.
The high greenhouse gas emissions savings that can be achieved by the sunliquid® process can only be obtained by thorough and efficient planning and use of all energy and biomass streams. In combination with a newly developed ethanol separation technology that cuts energy demand in this step by up to 50% compared to standard distillation, the sunliquid® process remains self-sufficient in energy terms. All of the required process energy can be produced through combustion of the residual lignin fraction that cannot be used for fermentation.
The sunliquid® technology platform opens up possibilities for a very wide range of biobased products. Apart from being used as biofuel, cellulosic ethanol can also serve as an intermediate for the production of other substances. It can be converted via standard chemical processes into other C2 building blocks and further chemicals. For example, via conversion into ethylene, cellulosic ethanol can also be used to produce green polyethylene, the world’s most common plastic. Furthermore, sunliquid® creates a second-generation sugar platform. Subsequent fermentation applications can convert these into biobased chemicals like organic acids, solvents, higher alcohols or other bulk or specialty chemicals.
One question that often arises is whether there is enough feedstock to make the switch from an oil-based economy to a bioeconomy. Of course, there are many aspects that have to be taken into consideration, but looking at a few numbers gives an impression of the huge potential represented by lignocellulosic biomass alone.
In the US, annual production of agricultural residues (cereal straw and corn stover) reached almost 384 million tons in 2009. Brazil produced more than 670 million tons of sugar cane in 2009, which yielded more than 100 million tons of bagasse (dry basis). In the European Union, almost 300 million tons of cereal straw are produced annually. Depending on region, climate and soil conditions, about 60% of this straw can be removed from the field without endangering soil quality and humus balance, and is thus available for other uses. It’s estimated that the amount of cellulosic ethanol produced from this feedstock alone would be sufficient to substitute more than 20% of the EU’s gasoline demand with locally-produced biofuel. In fact, those are rather conservative calculations. A recent study by Bloomberg New Energy Finance estimates that by 2020, between 52% and 62% of the EU’s predicted gasoline consumption could be substituted by cellulosic ethanol. This would result in potential greenhouse-gas emission savings of 42%-50%, according to the report.
Engine and automobile technology will also advance continuously, providing even more convincing arguments to the huge potential of this new technology. It opens up a new and renewable energy source that is at hand – one that can be produced domestically by simply utilizing an already existing feedstock for which no additional land or production capacity is required. In the EU, an estimated 1,000 to 2,000 cellulosic ethanol plants would have to be built just to exhaust the existing straw potential. Doing so would result in additional income for the agricultural sector – and the creation of several 100,000 new “green” jobs – and would reduce the EU’s oil dependence by roughly 5%.
From laboratory to market
Süd-Chemie has been successfully operating a sunliquid® pilot plant at its Munich research center since 2009. The demonstration project that will soon begin operating in Straubing is the last step between laboratory and industrial production, confirming the technology at a large scale. First industrial production plants are to be realized together with partners from 2013/2014 onwards.
What is needed now are stable framework conditions to create an investment fostering environment. There are several measures along the whole value chain that can be taken by national and international authorities to create more security for investors. Especially first production plants, so called first-of-its-kind plants, require substantially more investment than later plants due to uncertainties in scale-up and the related typical “start-up” costs. Supporting their construction is therefore crucial. Incentives for the development of feedstock logistics, mandatory blending quotas and tax regulations can provide further start-up aid.
Such measures are necessary to unlock the new technology’s full economic and environmental potential, and enable it to bridge the “Valley of Death” on its way from research to commercialization. Today, innovative solutions are essential to dealing with the challenges of our modern world. A growing population – and thus an ever-increasing demand for food and energy – is forcing us to find sustainable solutions and use the resources at our disposal as efficiently as possible.