“Lignin is nature’s plastic and any organism that wants to get to the sugars in a plant has to be able to get past this protective barrier,” professor Ming Tien of Penn State.

There’s lignin, lignin everywhere. Next to cellulose, it is the second most abundant organic material on Earth, representing 24-35 percent of softwood weight and 17-25 percent of hardwoods. That’s around 135 billion tons of lignin

Generally, when we use lignin at all, we use it for burning., By and large, it has similar moisture and BTU values as coal (in the 11-12,000 Btu/lb range) with a low ash content. With Central Appalachian coal in the $65/ton range, it’s a low value product at around 3 cents per pound.

Not only is there a lot of low-value lignin in biomass, it surrounds and protects the cellulosic sugars in biomass, making them difficult and expensive to access.

So there have been two basic approaches to the science of lignin: get plants to make less of it, or find ways to get around it.

But new science in the use of lignin is prompting some reassessment. It may be that the optimal approach is not to find a way to limit or work around lignin, but to find better uses for it. Other processes are focused less on finding new uses, but new low-cost ways to isolate lignin from cellulose, converting cellulose into higher-value products while converting lignin into pellets that are optimized as biomass for power generation.

Here’s a Digest recap of some of the most important work being done commercially and in the lab to unlock the value of lignin.

Lignin pellet technologies

Inbicon
Symbiosis between ethanol refinery, power plant with lignin as a key element

Last November, Prince Joachim of Denmark inaugurated the 1.4 Mgy, demonstration-scale Inbicon cellulosic ethanol plant in Kalundborg, which is utilizing wheat straw as its initial feedstock. The plant became the largest cellulosic ethanol facility in Europe.Inbicon and its parent company DONG Energy, the state oil, power and gas firm, confirmed that Inbicon will license its technology for use outside of Denmark, while DONG CEO Alders Eldrup said that the company expects to “construct a few factories also in Denmark.

A unique feature of the technology is symbiotic relationship with power production — utilizing waste heat from power gen to eliminate the use of natural gas and costly heating infrastructure in a free standing ethanol plant, which also reduces greenhouse gas emissions associated with production. In addition, the company has pioneered a proprietary pretreatment process and proprietary designs on its first-stage hydrolysis units, where enzymes are first introduced to capture sugars from the lignin and cellulose – both innovations are designed to reduce the energy intensity of the process, thereby reducing emissions and cost.

The remaining lignin is converted into pellets and supplied back to the power plant where it is co-fired with coal, or completely replaces coal as a power-generation feedstock.

KL Energy
Cellulosic ethanol process produces pellets, and optimizes pretreatment for higher yields

Last October, KL Energy and Fair Energy announced a long term cellulosic ethanol off take agreement for the US and European markets. Under the agreement, KL will supply cellulosic ethanol from the first  first commercial demonstration cellulosic ethanol plant, based in Upton, to the Swiss and US-based energy trading firm.KL’s commercial demonstration facility produces cellulosic ethanol and lignin pellets from wood waste, using a proprietary thermo-mechanical pretreatment and an enzymatic hydrolysis process.

Mascoma
Consolidated bioprocessing venture partners with Chevron for lignin offtakeIn New Hampshire, Mascoma announced that it has entered into a feedstock processing and lignin supply agreement with Chevron Technology Ventures.  Under terms of the agreement, CTV will provide various sources of lignocellulosic feedstock to Mascoma.

Mascoma will then convert the feedstock to cellulosic ethanol through its proprietary process, which produces lignin as a by-product.  Mascoma will provide this lignin to CTV for evaluation.“This is an important moment for us at Mascoma,” said Dr. Jim Flatt, President of Mascoma. “The upgrading of our byproduct lignin to high value transportation fuels is an important step in our effort to prove the effectiveness of integrated biorefineries. It has been our goal all along to make our process as integrated and sustainable as possible.”Lignin is a complex chemical compound derived from woody biomass.

After biomass has been converted through Mascoma’s proprietary Consolidated Bio Processing method, which breaks down the sugars in the cellulose and turns it into ethanol, energy-rich lignin is left over.Michael Kannelos at Greentech Media commented, “The lignin angle is interesting. Ligning keeps microbes from gobbling up plants. It is why we have coal: the lignin outlasted the microbes and the cellulosic material fossilized into coal over millions of years.”It’s a high-energy material. Some ethanol companies plan to burn lignin to run their own plants. Others transform it thermochemically and add the byproducts back into the ethanol mix.

Gasification

Chemrec
Gasifiying lignin trapped in pulp mill black liquor, for biofuels

Gasification has long been used to convert coal, oil and natural gas into syngas containing the building blocks of valuable fuels and chemicals. Black liquor is a byproduct of the kraft pulp production process and also an excellent gasification feedstock for syngas production. Black liquor consists of dissolved wood substance, mostly lignin, and spent pulping chemicals. It is traditionally burned by pulp mills in a Tomlinson-type recovery boiler to produce steam to drive the pulp mill processes and to recover the spent pulping chemicals. A gasification-based biofuels unit added to an existing pulp mill includes the patented Chemrec process and other technology extensively used in the petrochemicals industry.

Mild pyrolysis: Torrefaction

Torrefacation can generally be defined as a process that uses  “mild pyrolysis” to separate water, VOCs and hemicellulose from the cellulose and lignin contained in  woody biomass. The VOCs and hemicellulose fractions are combusted to generate process heat, leaving only the cellulose and lignin to produce TW, a charcoal like solid. And depending on the process time, the TW yield is quite high. varying between 66% and 75%.>The mild pyrolysis process  is lucidly described  in an article written by Robert Flanagan, titled “Torrefied Wood vs. Charcoal”.

As Flanagan explained, in mild pyrolysis, green woody biomass with 50% moisture is subjected to temperatures in the 250oC to 300oC range in a closed torrefaction unit in which little or no oxygen is added. And depending on the process dwell time (i.e., residence time), the woody biomass is reduced to a char, with only 25% to 33% of the amount of input material used, being driven off as a gas.

The torrefaction units that are available differ primarily in how the woody biomass is fed into the torrefaction unit, how it moves through the unit and how ash is removed. All units need a backup heat source such as a natural gas burner to ignite the process and help control the process temperatures, but process heat is primarily provided by the synthetic gases produced from the woody biomass being torrefied. Although torrefaction is a sophisticated process it is not nearly as complex or as costly as processes used in biorefining.

New Science

Purdue
Researchers suppress gene, reduce lignin precursor phenylalanine by 80 percent in petunias>

In April, Purdue researchers have identified, in an article published in the Plant Cell online journal, a gene linked to potential increases in cellulosic ethanol process efficiency. The gene is responsible for phenylalanine production, and by suppressing the gene’s expression, the research team reduced 80 percent of phenylalanine content in petunias. Lignin is synthesized from phenylalanine.

ArborGen
Testing low-lignin eucalyptus

In Washington, the USDA approved a permit for ArborGen to field trial 200,000 genetically modified trees on 28 sites, in seven states, involving 300 acres of land. The purpose of the test: the eucalyptus has new genes inserted to make them freeze-tolerant, making it possible to plant eucalyptus throughout the Southern timber areas as a fast-growing timber source. The trees have also had their lignin modified to make it possible to more easily convert wood into ethanol.

Chevron
Holds two patents for converting lignin to hydrocarbon fuel components

In February 2008, Chevron filed applications for two patents on refinery-based processes for converting lignin to hydrocarbon fuel components. In one embodiment, the lignin is first separated from the black liquor at a paper mill and then the lignin is transported from the paper mill to the refinery for hydroprocessing. In an alternative embodiment, the entire black liquor solution may be transported from the paper mill to the refinery for hydroprocessing. The Mascoma agreement opens up the potential for an alternative source of lignin.

Beijing University
Researchers develop process to convert lignin to gasoline, diesel precursors

In 2008, researchers at Beijing University identified a means to convert lignin, the primary component of plant matter and wood, into 8-18 carbon alkanes that can be refined into gasoline or diesel. The scientists reported that they have developed catalysts that breakdown carbon-oxygen-carbon bonds using hydrogen, and “near-critical” (250-300 degrees Celsius) water at pressures of 7000 kilopascals (about 70 atmospheres of pressure).  The researchers say that the process produces 8-9 carbon alkanes that are precursors for gasoline, 12-18 carbon alkanes for diesel, and methanol.

Penn State
Inserting protein between lignin molecules to make breakdown easier to achieve

Researchers at Penn State University said that they have developed a technique to genetically modify the connections in lignin to make it a more efficient feedstock for biofuels. The technique focuses on inserting a protein between lignin molecules. The protein does not affect plant rigidity or health, but makes it possible to use enzymes that attack proteins, rather than lignins, to break open the lignin polymer and facilitate glucose conversion and ethanol production.

Iowa State
Testing lignin as a roadbed building material

The Grow Iowa Values Fund, Iowa Highway Research Board, Grain Processing Corp. of Muscatine and Iowa State University’s Office of Biorenewables Programs have jointly funded and resourced a $93,775 project to study the use of lignin, a byproduct of corn ethanol production, in Iowa road construction. Natural Iowa roadbeds are less stable than desired and lignin’s properties as a roadbed binding agent are the subject of the research.