CHAPTER 12FEEDSTOCKS: MAXIMUM UTILIZATION OF

RENEWABLE AND BIOLOGICAL MATERIALS

From Green Chemistry and the Ten Commandments of Sustainability, Stanley E. Manahan, ChemChar Research,

Inc., 2006manahans@missouri.edu

12.1. SOURCES OF FEEDSTOCKSFeedstocks are the main ingredients that go into the production of chemical productsReagents act upon feedstocks and often the two are not readily distinguishedFeedstock selection largely dictates the reactions and conditions that will be employed in a chemical synthesisFeedstocks should come from renewable sources rather than depletable resources, if possible• Biomass is renewable • Petroleum is depleting

Feedstocks (Cont.)Most feedstocks now from petroleumPetroleum hydrocarbon molecules are in a highly reduced chemical state and often must be oxidized for feedstocksOxidation of petroleum hydrocarbons• Consumes energy • Often severe and hazardous reagentsChallenge and potential environmental harm in separating feedstock from other materials• Cellulose from wood • Hydrocarbon mixture in petroleumConsider the whole life cycle of materials in evaluating feedstocks

12.2. UTILIZATION OF FEEDSTOCKSIdeal feedstock• Renewable • Poses no hazards• Converted to the desired product using few steps• 100% yield •100% atom economy

Three Major Categories of Reaction Processes by Which Feedstocks are Acted upon by Reagents to Yield Products+Feedstock AFeedstock BAdditionProduct containingall the materialoriginally infeedstocks

FeedstockSubstitutionReagentProductByproducts

FeedstockEliminationReagentProductByproducts

reactionreactionreaction

12.3. BIOLOGICAL FEEDSTOCKSOrganisms have provided a huge share of the materials used by humans throughout their existence.Biomass: Plant material generated by photosynthesis• Leading candidate to replace petroleum as a feedstock for the

organic chemicals industry• Partially oxidized biomass material avoids expensive, sometimes

difficult oxidation steps in oxidizing petroleum

Major Categories of Biomass That Can Be Used for Feedstock

1. Carbohydrate, general formula of approximately CH2O• Glucose sugar from photosynthesis • In cellulose

2. Lignin, a complex biological polymer in wood having few uses3. Lipid oils extracted from seeds, including soybeans, sunflowers,

and corn.4. Hydrocarbon terpenes produced by rubber trees, pine trees, and

some other kinds of plants.5. Proteins, produced in relatively small quantities, but potentially

valuable as nutrients and other uses.

Obtaining Feedstocks from BiomassPathways by which feedstocks can be obtained from biomass• Simple physical separation of biological materials, such as tapping

latex from rubber trees• Extraction of oils by organic solvents• Physical and chemical processes such as separation of cellulose

bound together by lignin “glue” in making paper

Carbohydrate FeedstocksCarbohydrates as feedstocks for chemical processesCarbohydrates in several forms

• Sucrose sugar, C12H22O11, squeezed from sugar cane as sap and extracted from sugar beets and sugar cane with water

• Starch, a polymer of glucose readily isolated from grains, such as corn, or from potatoes and readily broken down adding water to give glucose

• Huge amounts of cellulose, which occurs in woody parts of plants and broken down to glucose with cellulase enzymes

Lipid Oils and TerpenesLipid oils are extracted from the seeds of some plants

• Volatile solvent n-hexane, C6H14, is used to extract oils• Solvents are distilled off from the extract and recirculated through

the process.Hydrocarbon terpenes can be tapped from rubber trees as a latex suspension in tree sapSteam treatment and distillation to extract terpenes from sources such as pine or citrus tree biomass

ProteinsGrain seeds as sources of protein• Generally used for food• Potentially useful as chemical feedstocks for specialty applications• Transgenic plants to make specialty proteins, such as medicinal

agents

12.4. FERMENTATION AND PLANT SOURCES OF CHEMICALS

Two main biological sources of materials to provide specialty and commodity chemicals and feedstocks• Plants • Microorganisms, especially bacteria and yeastsFermentation refers to the action of microorganisms on nutrients under controlled conditions to produce desired products• Anaerobic (anoxic, absence of air)• Aerobic (oxic, presence of air)Fermentation used for thousands of years to produce alcoholic beverages, sauerkraut, vinegar, pickles, cheese, yogurt, other foods and ethanolLactic acid from fermentation

More recently production by fermentation of organic acids, antibiotics, enzymes, and vitamins

Lactic acidH

H

H

C

HO

H

C

O

CHO

Penicillin Starting in the 1940s, Later, Other Antibiotics from Fermentation

Penicillin Fermentation Process

Fermentation Processes (Cont.)Requirements for successful fermentation production processes• The right microorganisms • Proper nutrients• Sterile conditions •Temperature regulation• Oxygen levels •pHTransgenic microorganisms in fermentationMost commonly to make proteins and polypeptides that are used as pharmaceuticals• Human insulinLargest scale production of chemicals by fermentation is ethanolOther large-scale chemicals may be possible in the future

Production of Materials by PlantsPlants generate their own biomass and are very efficient producers of materialsDistinct advantages in plant production and harvesting• No contamination problems such as those in fermentation• Grown by relatively untrained personnel using well known

agricultural practices• Easily harvested in the form of grains, stalks, and leaves

Now transgenic plants can be bred to produce a variety of more pure materials directed by genes transplanted from other kinds of organisms• Example of almost pure cellulose in cottonHybrid plants may generate large amounts of biomass by photosynthesis• Hybrid corn is one of the most productive field crops• Hybrid poplar tree

Advantages of glucose• Produced in abundance by plants• Partially oxidized

12.5. GLUCOSE AS FEEDSTOCK

HO OH

H

OH

H

H

OH

H

CH2OH

H

OC

CC

C CGlucose

• Contains hydroxyl groups (-OH) around the molecule, which act as sites for the attachment of various functionalities

• Metabolized by essentially all organisms, so it serves as an excellent starting point for biosynthesis reactions using enzymes

• Glucose and many of its products are biodegradable, adding to their environmental acceptability

Glucose from several sources• Enzyme-catalyzed processes from other sugars including sucrose

and fructose• Most glucose from enzymatic hydrolysis of cornstarch• Enzymatic hydrolysis of cellulose

Ethanol from GlucoseThe greatest use of glucose for synthesis is by fermentation with yeasts to produce ethanol,

H

H

H

C

H

HC OH

Ethanol

• Gasoline additive • Solvent • Chemical feedstockA byproduct of fermentation to make ethanol is carbon dioxide• Green chemical applications such as for supercritical fluid solventGlucose as a feedstock for the biological synthesis of a number of different biochemical compounds• Ascorbic acid • Citric acid • Lactic acid• Amino acids used as nutritional supplements, including lysine,

phenylalanine, threonine, and tryptophan• The vitamins folic acid, ubiquinone, and enterochelin

Glucose in Chemical ManufactureGlucose feedstock for chemical manufactureGenetically engineered microorganisms that can be made to express genes for the biosynthesis of a number of productsExample of synthesis from glucose of adipic acid required for nylon

The muconic acid is then treated under relatively mild conditions with H2 under 3 atm pressure over a platinum catalyst to give adipic acid.

OH

O

C

H

H

C

H

H

C

H

H

C

H

H

C

O

CHOAdipic acid

Conventional synthesis of adipic acid is not green

• Severe conditions • Dangerous chemicals • Wastes • N2OBiological synthesis using genetically modified Escherichia coli bacteria

(12.5.4)

cis,cis-muconic acid

C

C

C

C C

C

OHO

H H

H H

OHO

E. coli

HO OH

H

OH

H

H

OH

H

CH2OH

H

OC

CC

C C

Catechol from Glucose

• Flavors • Pharmaceuticals • Carbofuran pesticide • Other• About 20 million kilograms catechol per year worldwide

Catechol

• May be made by E. coli bacteria of a genetically modified strain designated AB2834/pKD136/pKD9/069A acting on glucose

Antioxidant 3-Dehydroshikimic acid may be synthesized by action of E. coli on glucose

Catechol

OH

OH

3-Dehydroshikimic acid

C OH

O

HO

H

HO

H

OH

HH

C C

C

CC

C

12.6. CELLULOSESegment of the cellulose molecule in which from 1500 to several thousand anhydroglucose units (glucose molecules less H2O) are bonded together:Cellulose is the most abundant natural material produced by organisms• Annual world production around

500 billion metric tonsBond to remainder of polymer

1500-6000(C6H11O5)

H

OH

H

H

OH

H

CH2OH

H

OC

CC

C CO

CC

C C

C O

H

CH2OH

H

OH

H

H

OH

H

Preparation of Cellulose from Plant SourcesPreparation of cellulose• Separation from matrix of lignocellulose (hemicellulose and

lignin)• Harsh chemical processing required• Cellulose product may require bleaching with potentially

hazardous chemicalsMicrocrystalline cellulose used in foods, pharmaceuticals, and cosmetics

Cellulose Products

Cellulose acetate, an ester in which most of the -OH groups on cellulose are replaced by acetate groups by reaction with acetic anhydride

Chemically modified cellulose• Chemical modification aided by abundance of -OH groups to

which various other groups can be bonded to impart a variety of properties

• Rayon made by treating cellulose with base and carbon disulfide, CS2, then extruding the product through fine holes to make thread

• Similar process extruding through a long narrow slot to make cellophane

HH C

H

H

C

O

O C

O

H

H

CO

O

C

H

H

CH

Acetate group Acetic anhydride reagent

Cellulose NitrateCellulose nitrate in which the -OH groups on cellulose are replaced by -ONO2 groups by treating cellulose with a mixture of nitric acid (HNO3) and sulfuric acid (H2SO4)• Used as explosive• Transparent film used in the early days of moving pictures for

movie film resulting in some disastrous fires giving off highly toxic fumes of NO2 gas

12.7. FEEDSTOCKS FROM CELLULOSE WASTESLarge quantities of cellulose-rich waste biomass as byproducts of crop production• Straw remaining from grain harvest• Bagasse residue from the extraction of sucrose from sugar cane• Other plant residuesRumen bacteria acting on cellulose wastes treated with lime in large fermentors from which oxygen is excludedProduce calcium acetate, calcium propionate, and calcium butyrate that can be acidified to produce corresponding acids

OHC

H

H

C

H

H

C

H

H

CH

O

OHC

H

H

C

H

H

CH

O

OHC

H

H

CH

O

Acetic acid Propionic acid Butyric acid

Feedstocks from Cellulose Wastes (Cont.)Hydrogenation to convert organic acids to alcohols:

Heat treatment of the organic acids at 450˚C to produce ketones

OHH

H

CH

H

CH

H

CH

H

CHOHH

H

CH

H

CH

H

CHOHC

H

HC

H

HH

Ethanol Propanol Butanol

H

H

H

C

H

H

CC

H

H

C

H

H

CH

O

H

H

H

C

H

H

CC

H

H

CH

O

H

H

H

CC

H

H

CH

O

Acetone Methylethyl ketone Diethyl ketone

12.8. LIGNINLignin is a chemically complex biopolymer that is associated with cellulose in plants• Serves to bind cellulose in the plant structure• Ranks second in abundance only to cellulose as a biomass material

produced by plantsLignin is difficult to use because of its inconsistent, widely variable molecular structure, a typical segment of which is shown below:

Bond to the remainder of the polymer

Aromatic (benzene) ringO

HH C

C

H

O

OOH

HO

OCH3

HOH

HH

CC

HC

OCH3

OH

Lignin (Cont.)Lignin’s resistance to biological attack makes it a difficult substrate to use for the enzyme-catalyzed reactions favored in the practice of green chemistrySome current uses of lignin:• Burned for fuel• Binders to hold materials together in coherent masses, fillers, resin

extenders, and dispersants• Some potential as a degradation-resistant structural material, such

as in circuit boards

12.9. DIRECT BIOSYNTHESIS OF POLYMERSCellulose in wood and cottonProtein polymers in wool and silkEnvironmental advantage in that polymers made biologically are also the ones that are most likely to be biodegradableFrom the standpoint of green chemistry, it is ideal to have polymers that are made by organisms in a form that is essentially ready to use• Recent interest has focused on poly(hydroxyalkanoate)

compounds, of which the most common are polymers of 3-hydroxybutyric acid:

H

H

H

C

H

O

C

H

H

CCHO

O

H

3-Hydroxybutyric acid

• Can be engineered to have a variety of properties ranging from rubber-like to hard solid materials

• Biodegradable• Thermoplastic properties, meaning that they melt when heated and

resolidify when cooled

Biosynthesis of Polymers (Cont.)Biological synthesis of a polymer in which 3-hydroxybutyrate groups alternate with 3-hydroxyvalerate groups, where valeric acid has a 5-carbon atom chain using a genetically engineered bacterium called Ralstonia eutropia fed glucose and the sodium salt of propionic acid to make the polymer in fermentation vatsPoly(hydroxyalkanoate) polymers produced by transgenic plants may eventually be possible

12.10. BIOCONVERSION PROCESSES FOR SYNTHETIC CHEMICALS

Advantages of enzymatic processes to make synthetic chemicals• Work well on natural products • Mild conditions

• Safe reagents such as molecular O2 • High specificity• p-Hydroxybenzoic Acid from Toluene

p-Hydroxybenzoic acidOHHO C

O

This compound is an important intermediate used in the synthesis of pharmaceuticals, pesticides, dyes, preservatives, and liquid crystal polymersCurrently p-hydroxybenzoic acid is made by reacting potassium phenolate with carbon dioxide under high pressure at 220˚C:

O-+

K Potassium phenolate

Synthesis of p-Hydroxybenzoic Acid (Cont.) Process for making p-hydroxybenzoic acid from potassium phenolate• Dates back to the early 1860s• Converts slightly less than half of the potassium phenolate• Produces substantial impurities• Requires severe conditions• Produces metal and phenol wastes

• Reactive alumina powder (Al2O3) used to catalyze the process has caused explosions

Biosynthesis of p-Hydroxybenzoic Acid from TolueneBiosynthetic alternative synthesis of p-hydroxybenzoic acid from toluene with genetically engineered Pseudomonas putida bacteria1. Attachment at the para position on toluene of a hydroxyl group by

the action of toluene-4-monooxygenase (T4MO) enzyme system transferred to Pseudomonas putida from Pseudomonas mendocina:

(12.10.1)

p -Cresol

Para position on the aromatic ring

H3C OHT4MO

O2H3C

2. p-Cresol methylhydroxylase (PCMH) enzyme from a strain of Pseudomonas putida to give p-hydroxybenzyl alcohol followed by conversion to p-hydroxybenzaldehyde:

(12.10.2)C OH

O

H

PCMH

H2OC OH

H

H

HOPCMH

H2OH3C OH

p-Hydroxybenzaldehyde

p-Hydroxybenzyl alcohol

Biosynthesis of p-Hydroxybenzoic Acid (Cont.)3. Aromatic aldehyde dehydrogenase enzyme designated PHBZ also

obtained from a strain of Pseudomonas putida to convert the aldehyde to the p-hydroxybenzoic acid product:

(12.10.1)H2O C OH

O

HOC OH

O

H

Biosynthesis of 5-CyanovaleramideProduction of 5-CyanovaleramideCurrently performed chemically with a stoichiometric mixture of adiponitrile with water and a manganese dioxide catalyst under pressure at 130˚C:

(12.10.4)NC

H

H

C

H

H

C

O

H

HN

H

H

C

H

H

C C

NC

H

H

C

H

H

CN

H

H

C

H

H

C C

5-Cyanovaleramide

Amide groupAdiponitrile

MnO2+ H2O

• Isolation of the 5-cyanovaleramide product entails dissolving the hot reaction mixture in toluene solvent, which is then cooled to precipitate the product

• For each kilogram of 5-cyanovaleramide product isolated, approximately 1.25 kg of waste MnO2 requires disposal

Biosynthesis of 5-Cyanovaleramide (Cont.)Biochemical synthesis of 5-cyanovaleramide with microoorganisms that had nitrile hydratase enzymes to convert the CN functional group to the amide group using Pseudomonas chloroaphis B23• Run at 5˚C over cells immobilized in beads of calcium alginate, the

salt of alginic acid isolated from the cell walls of kelp with 97% conversion

• Water-based reaction mixture simply separated mechanically from the calcium alginate beads containing the microorganisms, which are then recycled for the next batch of reactant

• Water then distilled off of the product to leave an oil, from which the 5-cyanovaleramide product was dissolved in methanol, leaving adipamide and other byproducts behind with only 0.006 kg of water-based catalyst waste residue produced per kg of product