Feedstocks for the Future - American Chemical Society

Chapter 20 The Biofine Technology: A "Bio-Refinery" Concept Based on Thermochemical Conversion of Cellulosic Biomass

Downloaded by UNIV OF ARIZONA on August 6, 2012 | http://pubs.acs.org Publication Date: January 12, 2006 | doi: 10.1021/bk-2006-0921.ch020

Stephen W. Fitzpatrick Biofine Technologies LLC, 300 Bear Hill Road, Waltham, MA 02451

The Biofine process is a high temperature, dilute acidcatalyzed rapid hydrolysis of lignocellulosic biomass. The process refines the biomass feed into four products: Levulinic acid, a versatile platform chemical, formic acid and furfural, commodity chemicals and a carbonaceous powder that can be burned or gasified to produce steam and electric power. The process is carried out in a reactor system that enhances the yield of the major products making it commercially viable. The process is flexible enough to utilize a wide range of lignocellulose. Derivative products of interest include automotive fuels, monomers, herbicides and general chemicals. A commercial scale process is now under construction. The process could potentially allow biomass to displace crude oil as the primary source of fuels and chemicals.

Introduction In the light of unstable crude oil supplies and increasing environmental constraints, the use of abundant renewable cellulosic resources for energy, transportation and materials would appear to be an obvious strategy for industry to pursue. Provided that an efficient means of conversion and high volume markets for derivatives can be developed, use of plant-derived raw materials to

© 2006 American Chemical Society

In Feedstocks for the Future; Bozell, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2006.

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272 fulfill markets presently based on crude oil holds the promise of a highly profitable, sustainable industrial enterprise. (7,26) In addition to this primary financial driver the use of renewable natural resources to displace crude oil as the main source of commodities has been receiving much attention due to a number of secondary benefits including: • Domestic energy security - The use of domestically produced renewable resources could significantly reduce U.S. and European dependence on crude oil imports from an increasingly uncertain global supply system. Even a partial displacement of imports would have the beneficial effect of buffering the market against increases in crude oil price; (22,23) • Reduction in global warming - The use of renewable resources based on plant-derived matter is carbon dioxide neutral and would consequently eliminate increases in net greenhouse gas emissions due to fossil fuel use (32, 34, 35). • Stimulation of the rural economy - The increased demand for crops grown specifically to supply energy would provide a renewed profit potential for the farming industry (22); • Environmental quality - The derivative chemicals from cellulose are for the most part oxygenated and biodegradable. This generally leads to cleaner burning fuels and more environmentally friendly materials (6); • Stimulation of the recycling economy - The cellulosic component is the largest fraction of municipal solid waste. It is also the most difficult to recycle due to contamination from other co-mingled wastes. A n efficient cellulose conversion process capable of using non-recyclable paper and cardboard would be key to improving the economics of the recycling business (36). • Ecological risk reduction - The use of domestically produced renewable resources will reduce or eliminate the ecological damage caused by drilling, transportation and refining of crude oil (13). The following chapter describes a novel process developed by Biofine based on thermochemical conversion of cellulosic biomass to value-added fuels and chemicals. The technology has the potential to be economically competitive with existing crude oil based refining. Its commercial application offers the prospect of an economically viable fuels and chemicals industry based on domestically grown raw materials. Cellulose is the most abundant polymer on the surface of the earth. It is the largest (non-aqueous) fraction of plant biomass. Annually, through photosynthesis, the solar energy equivalent to many times the world's annual use of energy is stored in plants. It is generated from atmospheric carbon dioxide using solar power. It therefore represents stored solar energy and it is the only renewable source of carbon. Cellulose is also the largest component of solid wastes produced by society comprising municipal, industrial and agricultural residuals (7, 25).



273 With the appropriate conversion technology, plant-derived biomass could become the primary source of energy, chemicals and materials over the next century. It is estimated that by dedicating a third of current forest and marginally arable land to production of short-rotation hybrid species or grassy energy crops it would be feasible to supply all transportation needs and a large fraction of petrochemical needs from biomass sources (2,7). The Biofine process allows the conversion of cellulosic biomass to welldefined primary chemical products that can, in turn be converted to a wide range of derivative chemical products used in many sectors of the present day petrochemical-based industry. The process can utilize cellulosic from almost any source ranging from wood, and agricultural residues to paper sludge and municipal wastes. A refining process using crude biomass to produce a range of value-added chemical and fuel products could justifiably be termed, in concept, a "Biorefinery" (Figure 1) (37). The Biofine technology provides the initial key cracking step unlocking the potential that biomass holds as a renewable, domestic source of industrial chemicals and fuels (3,9). The process works by "cracking" biomass under the influence of dilute mineral acid and moderate temperature. The cellulose fraction, consisting of hexosan (C-6 sugar polymers) is broken down to form a key intermediate chemical, levulinic acid in high yield and a co-product formic acid. Hemicellulose, consisting of pentosan (C5 sugar polymers), if present in the feed, is cracked to furfural. Lignin present in the feed goes through the process

Figure 1. The "Biorefinery" (blockdiagram)

essentially unchanged although some depolymerization may occur. Both cellulose and hemicellulose degradation reactions produce and a carbon-rich


274

char byproduct that with the lignin, is obtained as a dry solid mixture ("ligneous char"). These primary products become the platform chemicals from which other chemical products are produced.


The Primary Chemical Products As mentioned in the previous section, the primary chemical products resulting from the hydrolysis process are levulinic acid, formic acid, furfural and a carbon-rich ligneous char. Levulinic acid has been known as a versatile chemical for over fifty years but its high price ($5.00 per pound) has inhibited its large scale use. The levulinic acid molecule is a C-5 gamma keto acid. It has two functional groups which result in a wide spectrum of chemical reactivity (Figure 2). The Biofine process can produce levulinic acid for a cost in the range that allows it to be an economic starting material for production of fuel substitutes, monomers, novel pesticides and a wide range of commodity chemicals (8, 33, 45, 46, 47).

Figure 2. Structure of Levulinic Acid Formic acid is a well-known commodity chemical with existing large volume uses in the manufacture of rubber, plasticizers, pharmaceuticals and textiles. The estimated world market for formic acid is presently over 450,000 tons per year (44). It is also used in large volume for agricultural silage in Europe and there are several very large volume uses such as formaldehyde and road de-icing agents that will become economically feasible with formic acid available at lower cost (17). A potentially very large future market for formic acid is in the domestic catalyst market. Formic acid is used in the manufacture of nickel, aluminum and other catalysts. It is also used in the regeneration of catalyst metals poisoned with sulfur. As exhaust emission limits for sulfur are tightened there will be increased demand for ultra-low sulfur fuels requiring increased use of metal catalysts used in their production. Esters of formic acid such as methyl and ethyl formate have also shown promise as automobile fuel components and as platform chemicals. Formic acid can also be gasified or biotreated to recover its energy value in the event that there is no available market outlet. Furfural is a commodity chemical with a present-day world market of over 250,000 tons per year. It is used primarily in the manufacture of furan resins, lubricating oils and textiles for leisure wear (30, 42). Furfural can be converted to the main product, levulinic acid, via hydrogénation to furfuryl alcohol in a



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well-known chemical conversion that has been carried out commercially for many years (17,42). Conversion of hemicellulose-derived furfural in this way, significantly increases the overall levulinic acid yield from the process. The carbon rich ligneous char material is produced in the process as a dry powder. It is a mixture of lignin and char from the hydrolysis reactions and is composed of over 60% carbon. It has an energy content of around 27,000 KJ/Kg. It is potentially a suitable feedstock for carbon production or for a gasification reactor for conversion to a high energy "synthesis gas" that can either be used as a source of chemicals via a Fischer Tropsch conversion process or burned as fuel gas in a boiler or gas turbine for energy. Sufficient energy is concentrated in the char to provide both the steam and electric power needs of the process and, at larger scale (300 dry tons per day and over) has the potential to produce excess electric power for sale. This material is also being tested as a potential soil conditioner. The yields of primary products obtained in the process are shown in Table I. Table I. Primary Products from the Biofine Hydrolysis Process Primary product Levulinic acid Formic acid Furfural

Yield 50% 20% 50%

Carbon-rich ligneous char (byproduct char from cellulose and hemicellulose with lignin)

30% 50% 100%

Based on: Cellulose content Cellulose content Hemicellulose content Cellulose Hemicellulose Lignin

Derivative Products The derivatives that can be produced by conversion of the primary products apply to almost every sector of the industrial chemicals, fuels and energy market (Figure 3). By far the largest potential market for levulinic acid is in the production of oxygenated fuels for both transportation (gasoline and diesel) and energy generation (heating oil and gas turbine fuels). Levulinic acid can be directly converted by hydrogénation into the oxygenated gasoline fuel additive, methyltetrahydrofuran (MTHF) (38). M T H F has several attractive properties as a gasoline fuel additive: It has reasonable anti-knock properties (antiknock index (R+M)/2 = 80) and energy density and it has a relatively low volatility (R.V.P = 5.7 psi) (30). It also has the interesting property that it acts as a co-solvent for ethanol in gasoline mixtures i.e. M T H F significantly reduces the vapor pressure of ethanol when co-blended in gasoline and is now being used as a cosolvent for ethanol in Ρ Series fuel (a mixture of ethanol, light hydrocarbons and M T H F )


276 recently approved by the U.S. Department of Energy as an alternative gasoline, meeting the requirements of the Energy Policy Act for automobile fleet usage (5,6, J8). M T H F is also an excellent general solvent being superior to tetrahydrofuran (THF) in many regards. Selected physical properties are shown in Table II (28).

LIGNOCELLULOSE


BIOREFINERY

LEVULINIC ACID KETALS

TELRAPYRROLES LIGNJNS

FORMIC ACID

DIPHENOLIC ACID

DALA

CMA

MTHF

HEATING FUELS

NMP

POLYCARBONATE

HALOGENATED

(ROAD SALT)

TURBINE F U E L S

PYRIDINE

EPOMES

DALA

FURFURAL

GVL

DIPHENOLIC ACID

ETHYL LEVUUNATE

(HERBICIDE)

METHYL LEVUUNATE

ELECTRIC POWER

SODIUM

FUEL E S T E R S

FORMIC ACID

ETHYL FORMATE

BUTANEOIOL

GBL

THF

PENTANEDIOL

SUCCINIC ACID

SUCCINIC ACID

THF

FURANS

(LUBE OIL)

UGN1NS

SUCCINIC ACID

GASIFŒR FUELS

LEVUUNATE

CARBON

Figure 3. Range of Chemical and Fuel Productsfromthe Biofine Biorefinery Table II. Selected Properties of M T H F Boiling pt. (102 mm Hg) Deg. C. Boiling pt. (Attn.) Deg. C. Flash pt. (TCC) Deg. C. R V P psi L H V KJ/Kg Specific gravity Octane rating (R+M)/2

20 80 -11

5.7 32,000 0.813 80

Esters of levulinic acid produced from either methanol or ethanol are under active development as blend components in diesel formulations. These esters are similar to the biodiesel fatty acid methyl esters (FAME) now used in European low emission diesel formulations. F A M E has certain disadvantages as automotive fuel components in diesel due to cold flow properties (24) and gum



277 formation. Addition of ethyl or methyl levulinate to F A M E would be expected to alleviate both of these drawbacks. Levulinate esters also contribute greatly to the lubricity of the diesel mixture. Biofine has shown, in sponsored research, that the addition of 20% E L to a standard No. 2 base fuel was found to improve the lubricity from 410 to 275 using the H F R R index (43). This will be a very significant advantage in low sulfur diesels that have been subjected to high degrees of hydrodesufurization that reduces sulfur levels but also reduces fuel lubricity. Levulinate esters have also the potential to replace kerosene as home heating oil and as fuel for direct firing of gas turbines for electrical generation. (19). Production of levulinic acid esters has the added advantage that there is no co-production of glycerol for commercial disposal. Selected physical properties are shown in Table III. A second very large potential market for levulinic acid is in the production of the photodynamic pesticide delta aminolevulinic acid ( D A L A ) . D A L A is the active ingredient in a range of environmentally benign broad-spectrum herbicides and insecticides under development at the University of Illinois, Urbana Champaign (14). Biofine, in conjunction with the National Renewable Energy Laboratory (NREL), Golden, CO has developed and patented a process for conversion of levulinic acid to D A L A in reasonable yield (75). Table III. Selected Properties of Ethyl Levulinate Boiling pt. (18 mm Hg) Deg. C. Boiling pt. (atm) Deg C. Flash pt. Deg C. (closed cup) R V P psi L H V KJ/Kg Specific gravity Cetane Number (IQT) Lubricity (HFRR microns)

93 206.2 195

Feedstocks for the Future - American Chemical Society

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