Clean Technology : Bio-based & renewable chemicals


Enzymatic Depolymerization of Lignin

UW–Madison researchers provide the first demonstration of an in vitro enzymatic system that can recycle NAD+ and GSH while releasing aromatic monomers from natural and engineered lignin oligomers, as well as model compounds composed of similar chemical building blocks. Nearly 10 percent of beta-ether units were cleaved when the system was tested on actual lignin samples.

The relevant enzymes include dehydrogenases, β-etherases and glutathione lyases. In an exemplary version, the system uses the known LigD, LigN, LigE and LigF enzymes from Sphingobium sp. strain SYK-6. A newly discovered heterodimeric β-aryl etherase (BaeA) can be used in addition to or instead of LigE.

High Yield Method to Produce HMF from Fructose

UW–Madison researchers have discovered that a solvent system comprising water and a polar aprotic solvent (e.g., acetone) is ideally suited for converting C6 carbohydrates into HMF at reasonably low temperatures (such as 120°C), low acid concentration and at very high yields and efficiencies.

The C6 carbohydrate used in the method can be derived from any source including biomass (processed or unprocessed), cellulose and lignocellulosic sources, etc. The nature of the C6 carbohydrate is not critical to the method, although fructose is preferred.

‘Green’ Tylenol: Synthesizing Acetaminophen from Renewable Biomass

UW–Madison researchers have developed a two-step process to synthesize paracetamol (acetaminophen) from p-hydroxybenzamide, from a compound easily isolated from lignin sourced from a number of biomass species including poplar, aspen, willow and palm. P-hydroxybenzamide is produced when such biomass is treated with ammonia in the ammonia fiber expansion process (AFEX) or the extractive ammonia process (EA), or may be easily obtained from the free acid, p-hydroxybenzoic acid, from saponification.

Compared to the current industrial process, which requires the nitration and reduction of a petrochemical derivative, phenol (itself requiring a three-step process from benzene), the new method utilizes a low-cost Hofmann-type reaction to achieve this conversion. The method will work using p-hydroxybenzamide obtained from any source but biomass is preferred.

Recombinant High-Lipid Microbe for Bioproduct & Biofuel Production

By combining genetic and bioreactor engineering, the researchers have developed R. sphaeroides strains capable of producing and secreting lipids at levels found in oleaginous microbes. In the process they isolated and characterized 10 different high-lipid strains.

Following a single genetic alteration, the best performing strain produced 1.3 g/L fatty acids, corresponding to 33 percent of DCW. The researchers are not aware of any previous examples of a microbe accumulating more than 20 percent of its biomass as phospholipid (triacylglycerol or wax esters are typical).

The novel properties of these high-lipid mutants suggest that similar changes in cell envelope structure could be used to increase production of lipids and associated bioproducts from other microbes.

Industrial Streptomyces with Capability to Grow on Cheap and Abundant Cellulose

Building on their work, the researchers have developed an optimized set of enzymes useful to create Streptomyces with the capability to grow on cellulosic polysaccharide substrates. The method enables industrially relevant strains to grow on cellulose as the sole carbon source.

Using an engineered plasmid expression system derived from the ActE strain, the researchers transformed two commercial species (S. lividans and S. venezuelae) and showed that they were able to grow on filter paper as the sole carbon source. Other suitable host stains include S. coelicolor, S. griseus, S. clavuligerus, S. hygroscopicus, S. viridochromogenes and S. avermitilis.

Modified Cyanobacteria for Competitive Sugar Production

UW–Madison researchers have developed strains of Synechococcus sp. Strain PCC 7002 with the highest reported glycogen or starch production rate of any cyanobacteria or algae. The strains are genetically modified to overexpress a glucose-1-phosphate adenylyltransferase.

Electrochemical Reductive Amination of Furfural

UW–Madison researchers have developed an electrochemical method for the reductive amination of furfural-based molecules including HMF and its derivatives. Using the new method, furfural-based molecules can be converted into amines via conversion of their formyl groups into amine groups. The use of water as the hydrogen source at ambient temperatures without requiring chemical reducing agents will decrease the cost and environmental concerns of the process.

“Green” Catalytic Systems for Solvent-Free Alcohol Oxidations

Research from the University of Wisconsin-La Crosse has led to the discovery and development of a novel suite of catalytic systems for industrially-relevant green oxidations including the oxidative conversion of primary and secondary alcohols to value-added aldehydes and ketones. Similar systems have been developed for the oxidation of olefins to produce important epoxides, and for the oxidation of alkanes to produce alcohols. Specifically the team has developed a series of iron-based catalysts known as ‘helmet’ phthalocyaninaoto complexes of iron(III). Preliminary studies have focused on the use of what is commonly referred to as the ‘diiPc’ iron(III) system. Notably, the team has shown that this system is capable of catalytically oxidizing a diverse array of substrates including five non-benzylic alcohols (1-pentanol, 2-pentanol and cyclohexanol as well as 2,4-dimethyl-3-pentanol and 5-hydroxymethylfurfural) in the absence of added organic solvent. The presence of water as the monodentate axial ligand in the diiPc complex allows for markedly increased solubility in non-aromatic alcohols, making it an ideal catalyst for use with a much wider and more diverse range of substrates under solvent free conditions. It is envisaged that modification of the diiPc and related ligands will be undertaken to impart further enhancements to catalyst solubility in substrates or water, and/or superior stability in substrate alcohols. In addition to the diiPc system, the team have also developed a means of forming derivatized catalysts utilizing what is commonly referred to as a “helmet naphthalocyaninato” iron(III) complex. Specifically, a sulfonated version has been produced that possesses excellent solubility in water due to the added hydrophilic groups. To date, the sulfonated helmet naphthalocyaninato complex has been shown to provide for efficient formation of acetone from isopropanol as well as conversion of 2-pentanol to 2-pentanone using hydrogen peroxide as the primary oxidant. As such we anticipate that the same system would also be effective in the oxidation of 2-butanol to produce methyl ethyl ketone (MEK), an important commodity scale industrial chemical, and in many other commercially important transformations. Furthermore, preliminary studies have shown this molecule can be immobilized on various solid supports including anion-exchange resins, thereby resulting in a heterogeneous catalyst that can be utilized in the development of catalytic transformations that occur under flow conditions. Additionally, we now know that the sulfonated catalyst efficiently catalyzes the oxidation of phenol with hydrogen peroxide to produce para-benzoquinone. This transformation, along with other related reactions, is very important in the treatment of wastewater.

Green Method for Producing 1,5-Pentanediol Slashes Catalyst Cost 10,000-fold

Seeking a commercially viable alternative, UW–Madison researchers have developed a new route for producing 1,5-PD from biomass-derived THFA. Their three-step process is orders of magnitude cheaper than competing methods, green and exceeds 90 percent overall yields.

More specifically the new method includes hydration of THFA to dihydropyran, conversion to 2-hydroxy-tetrahydropyran (no need for a mineral acid catalyst) and subsequent production of 1,5-PD. The entire method can be conducted entirely in the absence of noble metal catalysts.

Improved Biomass Conversion with GVL Co-Solvent

Building on their work, the researchers have now developed a process that utilizes an inexpensive co-solvent to replace a fraction of the GVL and also facilitates the separation of the organic solvents from the hydrolysate. Furthermore, the separated aqueous solution, rich in carbohydrates, contains a negligible amount of dissolved lignin.

The new method uses a relatively inexpensive solvent mixture, which also minimizes the separation cost. This improves the economic potential and additionally provides a valuable feedstock for production of aromatics (from lignin). This new improvement offers the opportunity to develop an economically viable process that combines catalytic lignin upgrading and carbohydrate production from biomass. The co-solvent mixture can be tailored for the production of C5 and C6 carbohydrates or degradation products such as furfural.

Solar Cells for Reducing HMF to Valuable Platform Chemicals

UW–Madison researchers have developed a high yield method for reducing HMF to valuable furan alcohols including BHMF.

The new method uses electrochemical cells (ECs) or solar-powered photoelectrochemical cells (PECs) to drive the reduction reaction. The cells feature cost-effective catalytic electrodes made of silver film on copper. The reaction takes place at ambient temperature and pressure using water as the hydrogen source.

The process also can be used to produce linear ketones such as 5-MF (5-methylfurfural) using a zinc catalyst.

Solar Cells Turn HMF to Valuable Platform Molecules

UW–Madison researchers have developed a new method using solar cells to electrochemically oxidize HMF to highly prized furan compounds, specifically FDCA (2,5-furandicarboxylic acid) and DFF (2,5-diformylfuran). These important compounds are used to produce polymer materials, pharmaceuticals, antifungal agents, organic conductors and much more.

The reaction takes place at ambient temperature and pressure using a TEMPO mediator. Unlike previous methods, the process does not require a precious metal catalyst.

High Yield Method to Produce LGO from Biomass

UW–Madison researchers have developed a new method to produce LGO from cellulosic biomass under mild reaction conditions. The biomass material is reacted in a mixture comprising a polar aprotic solvent (e.g., tetrahydrofuran or THF) and an acid in the absence of water. The LGO can be separated out by routine downstream processes such as distillation and evaporation.

Glucose, levoglucosan, furfural and 5-hydroxymethylfurfural also are produced in small quantities.

Preparing HMF from Biomass in Polar Aprotic Solvents

UW–Madison researchers have developed a method to prepare HMF from biomass under mild reaction conditions without the presence of water. The reaction can use any polar aprotic solvent (e.g., tetrahydrofuran). Yields are on par with those obtained using ionic liquids.

The reaction requires mild mineral acids and moderate temperatures (about 200 degrees C). In the process, cellulose decomposes to levoglucosan, which is then dehydrated to HMF. Glucose, levulinic acid and formic acid also are produced as a result of side reactions. HMF and the byproducts can be separated from the solvent using conventional methods like distillation and evaporation.

Concentrated C5 and C6 Sugars from Biomass

UW–Madison researchers have developed a process for producing C5 and C6 sugars from biomass at high yields (70 to 90 percent) in a solvent mixture of water, dilute acid and GVL (gamma-valerolactone). GVL is attractive because it is effective and derived from biomass.

The biomass and solvent system may be reacted at a temperature between 50 and 250oC for less than 24 hours.

The method yields liquid and solid fractions enriched in C5 and C6 sugar, respectively. The fractions are easily separated for post-treatment upgrading. This strategy is well-suited for catalytic upgrading to furans or fermentative upgrading to ethanol at near-theoretical yield.

Producing Linear Alpha Olefins from Biomass

UW–Madison researchers have developed a method for producing LAOs cheaply from biomass. In the process, an inexpensive solid acid catalyst is used in a reaction that converts the carboxylic acids and lactones present in the feedstock. The catalyst features Lewis acid catalytic sites and no precious metal components.

Selective Conversion of Lignin into Simple Aromatic Compounds

UW–Madison researchers have developed a metal-free, aerobic oxidation method that selectively transforms the benzylic alcohol in lignin to the corresponding ketone. The process uses a nitric acid (HNO3) catalyst combined with another Brønsted acid. The reaction leaves unchanged at least a portion of unprotected primary aliphatic alcohols in the lignin or lignin subunit.

The reaction may be carried out in any suitable polar solvent and in the presence of additional reagents including TEMPO and derivatives.

Improved Method for Converting Biomass into Levulinic Acid for Renewable Fuel Sources

A UW–Madison researcher has developed an improved method of producing levulinic acid from biomass. The method comprises a two-stage, acid-catalyzed treatment. First, at least a portion of the pentoses present in the biomass feedstock are separated from the hexose sugars under mild acidic conditions to result in a biphasic sugar mixture consisting of a pentose-rich liquor and a hexose-rich solid. Then the pentose-reduced, hexose-rich biomass fraction is treated to yield levulinic acid. Utilizing this two-stage process, a maximum levulinic acid molar yield of about 66 percent based on the hexose content was obtained under optimized conditions. The method also may comprise separating the first aqueous acidic solution from hexose-rich solid so the pentoses in the solution can be converted into furfural or other compounds.

More Efficient Production of Polymer Chemical from Biomass Glucose

UW–Madison researchers have developed a method to produce HMF from biomass-derived glucose in a two-phase reaction system using Lewis acid and Brønsted-Lowry acid catalysts.

Conducted in a two-phase reaction vessel, the method isomerizes the glucose feedstock material, chemically transforming it into fructose while simultaneously converting that fructose via dehydration into HMF. The aqueous component of the medium comprises the glucose and both types of homogenous acid catalysts. The solution may be saturated with sodium chloride. The organic extraction layer preferably contains one alkylphenol, and into this layer the HMF spontaneously separates.

The two sugar reactions—isomerization and dehydration into HMF—occur in tandem, result in high yields, increase separation efficiency and react in a system that can be conducted continuously or in batch fashion.

Cheaper Process Converts Biomass into Furan Derivatives like Furfural & HMF

UW–Madison researchers have developed a novel, cost-effective method for producing furan derivatives such as HMF, furfural, levulinic acid or gamma-valerolactone from biomass using alkylphenols as solvents. The overall strategy involves converting lignocellulosic biomass into value-added fuels and chemicals by partially removing oxygen to yield reactive intermediates such as HMF, furfural and levulinic acid. These platform molecules are valuable commercial products and can be converted into desirable final products, including liquid transportation fuels.

The acid-catalyzed process for converting biomass into furan derivatives uses a biphasic reactor containing a reactive aqueous phase and an organic extracting phase, which includes an alkylphenol. Alkylphenols are chemically distinct from previously reported extracting solvents. They offer efficient extraction of furan derivatives like levulinic acid and unique options for recovery and processing. For example, the researchers found that no butylphenol is transferred into the aqueous phase, minimizing solvent loss and contamination of the aqueous stream. Additionally, alkylphenols are inert under conditions relevant to levulinic acid processing, including distillation and selective hydrogenation in the presence of butylphenol to yield gamma-valerolactone.

Method to Produce Sorbic Acid and Pentadiene from Renewable Biostock

UW–Madison researchers have developed a method of making 2,4-hexadienoic acid (i.e., sorbic acid) and 1,3-pentadiene (i.e., piperylene) via an acid-catalyzed ring-opening of 6-methyl-5,6-dihydro-2-pyrone (i.e., parasorbic acid). The parasorbic acid can be made from a renewable precursor, 4-hydroxy-6-methyl-2-pyrone (HMP).

The method comprises converting a renewable feedstock, HMP, into parasorbic acid (PSA), and then opening the ring of the PSA by contacting the PSA with a solid acid catalyst. This can be performed with acid-catalyzed ring-opening to yield sorbic acid or with decarboxylation of the opened ring to yield pentadiene. The conversion of HMP to PSA is accomplished by hydrogenating the HMP in the presence of a catalyst comprising one or more noble metals. The conversion takes place in a solvent selected from the group of C1- to C6-alcohols and C1- to C6-carboxylic acids, and the ring-opening reactions take place in a polar, aprotic solvent or a mixed solvent of water and a polar, aprotic solvent.

A more specific, three-step approach begins by hydrogenating 4-hydroxy-6-methyl-2-pyrone (HMP) to yield 4-hydroxy-6-methyltetrahydro-2-pyrone (4-HMTHP). Then, the 4-HMTHP is dehydrated by contacting it with a solid acid catalyst to yield parasorbic acid. Finally, the ring of the PSA is opened by contacting the PSA with a solid acid catalyst to yield sorbic acid or pentadiene.