A Wealth of Opportunities for Economy and Environment
Ready To Buy - Biomass as a resource for chemicals and plastics is on the rise. Drivers may differ - while some regions are looking for ways to commercialize their abundant biomass, others are driven by high oil prices or by climate concerns - but the interest is increasing globally.
For instance, China's 12th Five-Year Plan identifies biotechnology as one of seven "Strategic Emerging Industries." Besides a strong focus on biopharmaceuticals, this also includes bio manufacturing. There definitely is a market: According to a survey released by DuPont in December, the acceptance of bio-based products with Chinese consumers is even larger than in North America. In the survey, more than three-quarters of the urban consumers interviewed said they would "definitely or likely buy bio-based products."
Currently, available consumer products include detergents with enzymes and cosmetics ingredients. The capacity for bioplastics production is soaring. But biomass has much more to offer.
Two Distinct Approaches
In principle, there are two approaches toward the production of bio-based chemicals. Many of today's large-scale bio-based products are based on the first approach: To use the high functionality of natural molecules in specific products with only moderate chemical modification. Typical examples include biopharmaceuticals, bio-based polymers and products from fats and oils. The second approach, which takes more effort but might eventually revolutionize the chemical industry, is the concept of integrated biorefineries. Similar to a petrochemical refinery, biorefineries convert biomass to produce a series of chemical raw materials and fuel products. The ultimate goal is to use the whole plant instead of only parts and to obtain a wide range of potential products.
Bioplastics are one of the strongest growing markets for bio-based products. Driven by the continuing demand for plastics in all kinds of applications and due to rising oil prices as well as environmental concerns, the share of bioplastics is expanding slowly but surely.
The first bio-based plastic was the thermoplastic polymer polyhydroxybutyrate (PHB), which is used by bacteria as energy storage. It was placed on the market in the 1990s under the trade name Biopol. In recent years however, the approach has been not to use biopolymers directly. Instead biotechnology or chemical techniques are employed to extract monomers from renewable feedstock to provide a basis for new (functional analogue) or traditional (structural analogue) polymers.
Currently the most popular functional analog bio-based plastic is polylactic acid (PLA). Industrial production of PLA got underway in 1994. Worldwide production capacity exceeded 110,000 mt/year in 2010. Production plants are located in the U.S., the Netherlands and China.
PLA has properties similar to those of conventional mass-produced thermoplastics and can be processed on existing production lines. Because it is compostable, PLA has considerable potential for throwaway packaging such as beverage cups and plastic food packaging trays. Because of a lack in infrastructure, however, it is currently incinerated. One disadvantage of PLA is its low melting point, which makes it unsuitable for items that are exposed to heat.
Biotechnology and chemical techniques are used in combination to make the lactide polyester. Sugar or starch is fermented to make lactic acid, and a chemical dimerization process is then used to produce lactide. Finally, ring-opening polymerization is performed on the lactide monomer.
An entirely different approach is used for the production of bio-based polyethylene (PE). PE is not biodegradable, but established recycling paths exist, at least in Europe. By making the platform chemical ethylene from renewables, the existing value-added chains starting from the production of different plastics and continuing right through to the end-of-life scenarios can be utilized.
The production of bio-based ethanol is well established in China. As China's ethylene production is currently lower than the demand, the conversion of ethanol to PE might be economically feasible.
The higher degree of functionalization (alcohol and acid groups) of bio-based monomers compared with fossil feedstock can be exploited in a variety of plastics applications. To cite some examples, bio-based dicarboxylic acids (succinic acid) and polyols (castor oil, 1,3-propandiol) are used in bio-based polyesters. Polyols are also used in polyurethane. Dehydration of lactic acid produces acrylic acid, a monomer of polyacrylic acid.
Biolubricants are not the same as bio-based lubricants. They include all lubricants that are readily biodegradable regardless of whether they are bio-based, mineral-based, made with recycled oil or synthetic.
In contrast to mineral-based lubricants, bio-based lubricants are generally made from vegetable oil. Depending on requirements, they are used either in their native state (natural ester) or they are chemically modified (synthetic ester). The range of applications for bio-based lubricants covers the entire spectrum of conventional lubricants.
Because of their long service life, low toxicity and fast biodegradability, bio-based lubricants are particularly attractive for environmentally sensitive applications. By nature, bio-based lubricants provide better lubrication than comparable mineral-based products.
In a study, the Fraunhofer Institute for Systems and Innovation Research (ISI), Germany, estimated that the global solvents market is around 19.7 million mt/year. At least 12.5% of the total market volume could be produced from biomass, but the current figure is only 1.5%.
Production of most solvents is based largely on fossil feedstock. Due to sustainability and environmental protection considerations, the spectrum is expected to shift toward bio-based solvents. The list of new bio-based solvents includes things like fatty acid methyl esters, which are also used in biodiesel, and esters of lactic acid with methanol (methyl lactate) or ethanol (ethyl lactate) as well as natural substances such as D-limonene, which is obtained from the rind of citrus fruits.
Another trend is to replace conventional organic solvents with biogenic solvents. Conversion of bio-based succinic acid or furfural (a byproduct of the cellulose industry) to tetrahydrofuran (THF) is one example.
Bio-based surfactants are produced by microbial fermentation or enzyme-catalyzed reactions. Surfactants normally contain both hydrophobic and hydrophilic groups. In the case of bio-based surfactants, at least one of these groups is made from renewable resources.
The bio-based hydrophobic group is usually made from coconut oil or palm kernel oil. A hydrophilic group is normally made from carbohydrates such as sorbitol, sucrose or glucose. The use of animal fat has significantly decreased.
In contrast, the market for bio-based surfactants is expanding. Due to their good biodegradability and low to zero toxicity, they are used in specific applications by the paint, cosmetic, textile, agricultural, food and pharmaceutical industries. The mining and ore processing industry uses them as an emulsifier to facilitate oil production and for biological cleanup of contaminated sites.
The most promising approach for a widespread use of biomass for the production of chemicals is the integrated biorefinery. The Association of German Engineers (VDI) Technology Center has conducted a study to assess the extent to which biomass and its maximum utilization in biorefineries will replace conventional oil-based production techniques. The study provides information on bio-based production methodologies for 26 precursors (platform chemicals). There are strong indications that production is being migrated to bio-based techniques on eleven of these precursors.
Biotransformation of biomass in living cells or biocatalysis using isolated enzymes or enzyme systems is widespread in the white biotech industry. A very wide range of microorganisms is used for biotransformation, the most common ones being yeast, Escherichia coli and Corynebacterium glutamicum. A variety of hexoses (C6 sugar) such as glucose and fructose serves as precursors that can, for example, be isolated from the biomass through hydrolytic pretreatment. A different methodology is needed for lignocellulose, however, to separate the non-fermentable lignin from the sugar.
Currently, lignocellulosic biomass passes through a mechanical or chemical pretreatment process using acids, phenol derivatives or hot steam and, to an increasing extent, hydrolytic-catalytic pretreatment with cellulases. Hemicellulose recovered from the lignocellulose has a high pentose content (C5 sugar), for example xylose, and particular microorganisms are needed to break these substances down.
Technical Hurdles and Solutions for Biomass Processing
To roll out competitive, cost-effective bio-based production on an industrial scale, a number of technical hurdles will have to be overcome.
The challenges begin with handling aspects that are closely related to the very nature of biomass. Large quantities have to be harvested, transported and processed. The sheer volumes are not the only a challenge for industry. Diversity is another issue that needs to be addressed. The term biomass extends beyond dry bulk solids such as corn and wood chips to include high-viscosity liquids like sewage sludge and liquid manure. Given this level of diversity, different techniques are needed to move the biomass to the intended destination.
Logistics is not the only area that calls for special solutions. Biomass has to be stored between delivery and industrial processing. Spontaneous ignition has been a recurring problem with wood chips. Chemical oxidation reactions are the largest exothermic factor in the overall process, but physical processes may also play a role. For example, water adsorption on the surface of relatively dry solids also raises the temperature when adsorption heat is released.
Following conversion, the products are normally highly diluted, often in the form of complex product mixtures that contain constituents that are very similar to each other. The products also contain various residues and waste products. Fermentation solutions, cell cultures and plant extracts are typical examples.
Product purification to meet chemical standards is a big challenge, too. Large amounts of aqueous solution are normally involved, and the product often still has to be isolated from the organism. Extracting the product from a fermentation broth can often account for 80% of production costs, making it a major cost factor in biotech production. The list of additional technological hurdles includes the development of new specific catalysts and biocatalysts.
Product inhibition during fermentation can be another problem if high product concentrations are not conducive to the organisms involved. Innovative approaches such as in-situ product isolation or low-pH process design can provide the answer.
Upscaling from the lab environment can also cause problems. Bio-based processing needs to be combined with conventional chemical techniques. Hybrid chemical production is essential, particularly during the early stages of development. Intensive work is underway in the U.S. and China on polybutylene succinate. The process combines biological fermentation with chemical hydrogenation.
The transformation of the raw material base is a global question. The current hurdles and technological challenges require creativity and ongoing R&D efforts.
This article is based on a trend report developed by international experts and journalists on behalf of Dechema (Society for Chemical Engineering and Biotechnology), Germany, in preparation for AchemAsia 2013, 9th International Exhibition and Conference on Chemical Engineering and Biotechnology, which took place in Beijing May 13-16.