Production of Dimethyl Sulfoxide from Lignin

Production of Dimethyl Sulfoxide from Lignin Team Bravo is: Jake Biberstein, Stan Das, Jeff Umbach, Russ Boyer, Krista Sutton, Mike Czepiak Project Lead: Jake Biberstein

Project Goals • Overall: Production of dimethyl sulfoxide (DMSO) from wood • Using lignin, an important component in plant cell walls (biopolymer) • Cleavage of lignin ether bonds with sulfur nucleophile, creating lignosulfates/lignosulfonates • Reduction of lignosulfates/lignosulfonates to dimethyl sulfide (DMS) • Oxidation of DMS to DMSO with NO2

What is DMSO? Dimethyl sulfoxide (DMSO) is a strongly polar aprotic solvent that dissolves organic and inorganic compounds. With excellent solvating power, it is frequently used in reactions involving salts and nucleophilic substitutions. DMSO is a naturally occurring part of the sulfur cycle; dimethyl sulfide (DMS) is produced by marine phytoplankton, which then oxidizes into DMSO in the atmosphere.

Some Uses of DMSO • Stripping of photo-resistant materials in electronics manufacturing. • Skin penetrating solvent for drug delivery. • Cryoprotectant for preservation of organs, tissues, and cell suspensions. • Non-toxic paint stripper. • NMR spectroscopy solvent. • Solvent for pesticide delivery. • Catalyst presulfiding and aromatic extraction. • Polymer cleanup.

Sources of DMSO • While DMSO is naturally occurring in nature, it is present in very low concentrations. • DMSO is commercially produced from lignin, a component of wood. There are two processes that exist to extract lignin from wood: the Kraft (Sulfate) Process and the Sulfite Process.

Lignin Lignin is a major component of the cell walls of plant cells and a few types of algae. Lignin is seen as the “glue” that holds a tree together. “Compression” woods, such as conifers, are very rich in lignin. One quarter to one third of the dry mass of wood is made up of lignin. “A small section of lignin polymer.”

Composition of Common Pulpwood (% mass)

The Kraft (Sulfate) Process • The Kraft Process accounts for approximately 80% of wood pulp production. • It is a cyclical process that is nearly self-sustaining due to recovery and reuse of the inorganic chemicals used and a recovery boiler. • Cellulose is separated from the wood and made into pulp while the lignin is concentrated into a waste product called “black liquor”. • Black liquor is concentrated using a multiple effect evaporator. Rosin soap is skimmed off and used to manufacture Tall Oil. • The inorganic parts of the black liquor are used to regenerate the sodium sulfide and sodium hydroxide that is used for pulping. • The organic parts, including the lignin, are burned in a recovery boiler to provide energy to help run the pulping mill. • Approximately 7 tons of black liquor are produced for every ton of pulp.

The Kraft Process (cont.) “Continuous Kraft Paper Mill”

The Sulfite Process • Sulfite pulping was the dominant process for making wood pulp until it was surpassed by the Kraft process in the 1940s. Now accounts for less than 10% of pulp production. • Process is highly acidic, which can cause problems with equipment degradation and hydrolyzes the cellulose and weakens the fibers. • Produces a higher yield of pulp than the Kraft process (depending on wood source) and the fibers are easier to bleach, however the fibers are not as strong. • Like the Kraft process, the lignin is contained in a red or brown liquor that is concentrated using a multiple effect evaporator. • If sodium based reagents are used then they can be recovered from the liquor in a similar method to that used in the Kraft process. • The liquor is burned in a recovery boiler just like in the Kraft process.

The Sulfite Process (cont.) • The Sulfite process has somewhat lower energy needs than the Kraft process and does not degrade the lignin as much. • Can be used to produce “dissolving pulp”, a raw material of cellulose derivatives such as rayon, cellophane, cellulose acetate, and methylcellulose. • Acid hydrolysis of cellulose during sulfite pulping produces monosaccharides, predominantly mannose, which can be fermented to produce ethanol. • Produces lignosulfonates as a byproduct, which have many uses in the manufacture of construction materials and in the tanning of leather. • DMS and DMSO can also be produced from the lignosulfonates.

Kraft Process Pros Most widely used. Wider range of fiber sources. Stronger pulp produced. Lower sulfur dioxide emissions than Sulfite process. Tax credit for burning the liquor. Sulfite Process Pros Less destructive to lignin, more useful byproducts. Potentially higher pulp yield, easier to bleach fibers for paper making. Liquor can be burnt for fuel or neutralized and the useful byproducts extracted. Lignosulfonates can be used to make DMS and DMSO. Kraft Process versus Sulfite Process • Kraft Process Cons • Black liquor being used a fuel is needed to achieve maximum efficiency. • Black liquor has higher viscosity and more dissolved solids, increasing fouling issues. • Degrades lignin more than Sulfite process. • Sulfite Process Cons • Mostly a specialty process today. • Cellulose fibers are weaker, restricted to fine papers and cellulose derivatives. • Acidic process, presents metallurgy problems in plant design.

Obstacles • We would need to get Kraft mills to part with the black liquor in order to extract the lignin, this would be an obstacle as the recovery boiler is a large part of what makes the Kraft process more profitable than the Sulfite process. • It is possible to remove the lignin from the black liquor and then return it to the Kraft mill for burning in their recovery boiler. This would only be practical if the DMSO plant was built adjacent to the mill. Such a setup is used by Gaylord Chemical Corporation. • The Sulfite process produces more useful byproducts but is not as commonly used anymore. There would be less plants to choose from and the number of remaining sulfite pulping mills continues to decrease. The pulp is also not as useful for most paper production. • Using the lignosulfonates to produce DMSO would lead to less supply for other industries to utilize, however it does cut out a step as the lignin will not need to be reacted with sulfur.

From Lignin to DMSO A process flow diagram based on the Sulfite Process

DMS Safety Facts • Dimethyl sulfide is a water-insoluble flammable liquid that boils at 37°C and has a characteristic disagreeable odor. It is oxidized to produce DMSO. • The odor is present even at extremely low concentrations of 0.02 to 1 ppm. • It is also produced in small quantities as a byproduct in the Kraft process and is usually burned off along with the black liquor in the recovery boiler. • It can be used as a food additive is very small quantities (> 150 ppb) and occurs naturally during the cooking of corn, cabbage, beetroots, and seafood. • DMS is highly flammable with a flash point of -48ºC and auto-ignition temperature of 205ºC. • Piping should be mild or stainless steel and should be designed so that liquid velocities do not exceed 10 feet per second and the entry of DMS into tanks should be at the bottom through a dip tube to avoid static electricity. • DMS is a skin and eye irritant as well as an inhalation hazard. While OSHA has not defined a Permissible Exposure Limit, the ACGIH recommends a Threshold Limit Value of 10 ppm.

DMSO Safety Facts • DMSO is much less toxic than other solvents in its class, such as: • dimethylformamide (DMF) • dimethylacetamide (DMAC) • N-methyl-2-pyrrolidone (NMP) • Hexamethylphosphoramide (HMPA) • DMSO has a no observable effects limit (NOEL) that is 4.4 to 22 times higher than the above chemicals. Neither OSHA or ACGIH have established safe limits due to its low toxicity. Inhalation hazard is less than that of acetic acid. • DMSO is not considered a carcinogen. • DMSO has a boiling point of 189°C and a flashpoint of 89ºC. • Toxicity to aquatic life is very low, the LD50 for Trout and Salmon ranges from 12 to 17 g/kg. • The EPA considers DMSO to be practically non-toxic.

Future Goals • Designing the “back-end” • Conversion of DMS to DMSO • Safety concerns with respect to DMS-containing vessels • Purification/seperation processes • Regeneration of NO2 • Handling of waste • Waste salts • Waste cellulose

In Conclusion

References • Dimethyl Sulfoxide. Wikipedia. • Dimethyl Sulfide. Wikipedia. • Robert Vignes. Dimethyl Sulfoxide (DMSO) - A “New” Clean, Unique, Superior Solvent. American Chemical Society. (2000) • Dimethyl Sulfoxide (DMSO) Health and Safety Information. Gaylord Chemical Corporation. (2007) • Dimethyl Sulfide Overview. Gaylord Chemical Corporation. (2007) • Rafel Simo, et al. Particulate dimethyl sulphoxide in seawater: production by microplankton. (1998) • Robert Summit, Alan Sliker. Handbook of Materials Science, Volume IV: Wood. (1980) • Kraft Process. Wikipedia. • Sulfite Process. Wikipedia. • Understanding the Kraft Process in Paper Production. PaperIndustry.com

Production of Dimethyl Sulfoxide from Lignin