Materials Turning
Materials Turning biomass into bioplastics and carbon fibers Conceptually, to be able to use naturally synthesized biopolymers from plant biomass, one needs to devise a ‘sorting mechanism’ that separates at high yield and high purity the products of interest. This, however, is not an easy task since plants are a natural composite material, where the components making it are organized in a highly intricate way. This challenge of devising an efficient extraction process for carbohydrates from cellulosic polymers and lignin polymers is well met by the CASE TM process of Virdia. In this process, the biomass is first pre-treated to extract by chemical means much of the hemi cellulose sugars along with a great deal of the extractives and the ash components present in the feedstock; the sugars are then refined and concentrated from this stream. The remaining ‘clean’ (preextracted) wood is then hydrolyzed in high concentration HCl at low temperatures, where all the remaining cellulose is hydrolyzed to saccharides while lignin is collected as solid. Both sugars and lignin are then refined to high purity in sequential processes. All chemicals including the acid are recycled effectively in these processes to minimize environmental effects and to reduce costs. As implied by the process name - CASE stands for Concentrated Acid Solvent Extraction, it utilizes HCl at 42- 43% to fully hydrolyze the cellulose including the cellulose crystalline fraction, thus enabling the harvest of ca. 95% of the theoretical carbohydrates in the biomass. Typically the overall cellulose and hemi cellulose fractions consist about 65% of the dry biomass weight. Hydrolysis of the crystalline fraction, that can constitute up to 63% of the cellulose in biomass, is not possible in enzyme based saccharification, and is typically not attained neither in sulfuric based hydrolysis nor in organosolv technologies. Another factor that contributes to achieving high yield of sugars is the low operation temperature of the process of 10-15°C in the concentrated acid solution, in contrast to other processes which require high temperatures (~200°C). Consequently only a small fraction of the hydrolyzed sugars degrade despite the high acidity of the solution. This is an old-new approach to the challenge of producing from biomass. A similar hydrolysis process was utilized in industrial scale in Germany in the 1930’s to 1940’s, only the acid was diluted with water, which made recycling complex and too costly. Virdia’s technology relies on recycling of the acid through solvent extraction. One more essential element is the quality of the product: to support use of cellulosic sugars in fermentation processes other than ethanol production, high purity of the sugar syrup is an absolute must, as many of the fermenting microbe species, particularly engineered ones as envisioned for the production of new plastic materials, are highly sensitive to impurities that are typically found in biomass hydrolysate such as furfurals, soluble lignin fractions, ash elements and organic acids. Virdia sugars are compatible with the best of corn sugars (DEX95 standard). This is achieved by removing as much as possible extractive and ash upfront in the pretreatment stage, by working at low temperature and hence minimizing degradation of sugars, and by designing purification steps in the final stages of the process. The Virdia team enjoys many years of experience in sugar production of its leading engineers, who earlier spent a lifetime career in the sugar industry giants of the world. The quality of the sugars has been repeatedly demonstrated by partnering companies that fermented the sugars or applied them in chemically catalyzed processes to produce amino acids, citric acid, yeast, plastic monomers and polymers, jet fuel, as well as ethanol and butanol. Similarly, the quality of the lignin was designed to meet the requirements of high end applications. Lignin makes some 20-30% of the dry weight in most biomass. Current use of lignin for any purpose other than burning it for its energy is very minimal. Nonetheless, sustainable development of a biobased value chain necessitates that high value applications of 22 bioplastics MAGAZINE [06/12] Vol. 7
Materials by Noa Lapidot, EVP R&D and Eran Baniel, General Manager & VP Business Development Virdia Danville, Virginia, USA and Herzlia, Israel Figure 2: Potential applications: carbon fibers for automotive applications (iStockphoto/BrooksElliott) lignin be developed and commercialized. The poor volume of lignin use in the world is not for lack of wanting; much efforts have been and still are being directed to the development of such applications. In many cases a major obstacle to utilizing lignin as raw material was the high percent of impurities present in available lignin streams, particularly high levels of sulfur compounds and ash. Carbon fibres from lignin Through the CASE process, lignin remains as solid and is washed to recover acid and sugars which are held by its sponge-like form. The purity of this lignin is high (~93-95%), but still insufficient for high end applications such as the manufacturing carbon fibers from this lignin or using it as raw material for catalytic cracking. To that end, a further refining process was designed whereby residues of acid, carbohydrates and ash are removed to obtain lignin which is 99% pure. Recently, Oak Ridge National Laboratories (ORNL) Oak Ridge, Tennessee, USA successfully prepared carbon fiber prototypes from high purity pine lignin prepared this way. According to ORNL, the lignin sample performed well in spinning and stabilization/carbonization trials and shows promise of being a commercial carbon fiber precursor. Virdia continues its collaboration with ORNL to develop lignin as a source for low cost carbon fibers, to be incorporated in common vehicles for weight reduction. Cellulosic sugars, from plant-derived biomass, can be a game changer for the sugar market, with the potential to reach quantities able to supply much of the bioproduct industries as well as meet up to a third of global liquid fuel demand. Cellulosic sugars can be made from a variety of easily available and interchangeable sources of biomass, such as wood and wood waste, agricultural products and agricultural waste, and municipal and green waste, and can easily endure market fluctuations that plague traditional sugar production. The conditions for making this possible simply require a cost-effective solution to turn biomass into sugars, and the know-how to cheaply refine the sugars and remove all impurities. All this Virdia has compiled under one roof, with the proposal for an additional critical condition – creation of a high-value co-product solid lignin stream. Current economic evaluation of lignin price is done according to its energy value: 0.07-0.13 €/kg (0.04-0.08 US$/lb). Any higher price that can be obtained from other lignin products will contribute dramatically to the value proposition of the technology. Several directions seem to be a good valorizing opportunity for lignin, including the above mentioned use as source for carbon fiber, but also cracking lignin to small molecules (phenols, BTXs (= benzene, toluene and xylene isomers)) or using lignin as polymer, to substitute petroleum derived polymers and as flame retardant, anti oxidant and UV absorber. Cellulosic sugar and lignin as a commodity A crucial aspect in the establishment of this emerging technology is the cost aspect. Cellulosic sugars have to compete in price with traditional sugars. Sugar prices, whether sourced from cane, beet or corn sugars, have fluctuated from 0.35 €/kg (0.20 US$/lb) to 0.70 €/kg (0.40 US$/lb) over the past five years on US and World commodity exchanges. This high volatility has been a result both of environmental impacts of changing weather conditions, as well as from quickly growing end-user markets for bioproducts and ethanol. bioplastics MAGAZINE [06/12] Vol. 7 23
