CHAPTER 12
FEEDSTOCKS: MAXIMUM UTILIZATION OF RENEWABLE
AND BIOLOGICAL MATERIALS
From Green Chemistry and the Ten Commandments of
Sustainability, Stanley E. Manahan, ChemChar Research,
Inc., 2006
manahans@missouri.edu
12.1. SOURCES OF FEEDSTOCKS
Feedstocks are the main ingredients that go into the production of
chemical products
Reagents act upon feedstocks and often the two are not readily
distinguished
Feedstock selection largely dictates the reactions and conditions that
will be employed in a chemical synthesis
Feedstocks should come from renewable sources rather than
depletable resources, if possible
• Biomass is renewable
• Petroleum is depleting
Feedstocks (Cont.)
Most feedstocks now from petroleum
Petroleum hydrocarbon molecules are in a highly reduced chemical
state and often must be oxidized for feedstocks
Oxidation of petroleum hydrocarbons
• Consumes energy
• Often severe and hazardous reagents
Challenge and potential environmental harm in separating feedstock
from other materials
• Cellulose from wood
• Hydrocarbon mixture in petroleum
Consider the whole life cycle of materials in evaluating feedstocks
12.2. UTILIZATION OF FEEDSTOCKS
Ideal 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 A
Addition
+
reaction
Product containing
all the material
originally in
feedstocks
Feedstock B
Reagent
Byproducts
Substitution
Feedstock
Product
reaction
Byproducts
Reagent
Elimination
Feedstock
reaction
Product
12.3. BIOLOGICAL FEEDSTOCKS
Organisms 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 uses
3. 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 Biomass
Pathways 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 Feedstocks
Carbohydrates as feedstocks for chemical processes
Carbohydrates 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 Terpenes
Lipid 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 sap
Steam treatment and distillation to extract terpenes from sources
such as pine or citrus tree biomass
Proteins
Grain 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 yeasts
Fermentation 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 ethanol
Lactic acid from fermentation
O H H
HO C C C H
HO H Lactic acid
More recently production by fermentation of organic acids,
antibiotics, enzymes, and vitamins
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 •pH
Transgenic microorganisms in fermentation
Most commonly to make proteins and polypeptides that are used as
pharmaceuticals
• Human insulin
Largest scale production of chemicals by fermentation is ethanol
Other large-scale chemicals may be possible in the future
Production of Materials by Plants
Plants generate their own biomass and are very efficient producers
of materials
Distinct 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 cotton
Hybrid plants may generate large amounts of biomass by
photosynthesis
• Hybrid corn is one of the most productive field crops
• Hybrid poplar tree
12.5. GLUCOSE AS FEEDSTOCK
CH2OH
C
O
H H
C OH H
HO C
C
H
OH
H
C
OH
Advantages of glucose
• Produced in abundance by plants
Glucos e
• Partially oxidized
• 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 Glucose
The greatest use of glucose for synthesis is by fermentation with
yeasts to produce ethanol,
H H
H C C OH
Ethanol
H H
• Gasoline additive
• Solvent
• Chemical feedstock
A byproduct of fermentation to make ethanol is carbon dioxide
• Green chemical applications such as for supercritical fluid solvent
Glucose 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 Manufacture
Glucose feedstock for chemical manufacture
Genetically engineered microorganisms that can be made to express
genes for the biosynthesis of a number of products
Example of synthesis from glucose of adipic acid required for nylon
O H H H H O
HO C C C C C C OH
Adipic acid
H H H H
Conventional synthesis of adipic acid is not green
• Severe conditions • Dangerous chemicals • Wastes • N2O
Biological synthesis using genetically modified Escherichia coli
bacteria CH OH
2
H
C
HO
C
H
OH
C
H
O
H
E. coli
C
H
C OH
OH
H
H
C
O
C
C OH
HO C
C
O
(12.5.4)
C
H
cis,cis-muconic acid
H
The muconic acid is then treated under relatively mild conditions
with H2 under 3 atm pressure over a platinum catalyst to give adipic
acid.
Catechol from Glucose
Catechol
OH
OH
Catechol
• Flavors • Pharmaceuticals • Carbofuran pesticide • Other
• About 20 million kilograms catechol per year worldwide
• 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
O
of E. coli on glucose
H
C
O C
C C OH
H C H
H H
3-Dehydroshikimic acid
C
C
OH
HO
12.6. CELLULOSE
Segment of the cellulose molecule
CH2OH
C
O
in which from 1500 to several
H
H
thousand anhydroglucose units
C
C
OH H
(glucose molecules less H2O) are
CH2OH
H
C
C
C
O O
bonded together:
H
OH
H H
Cellulose is the most abundant
C OH H C
H
natural material produced by
C
C
(C6H11O5)1500-6000
organisms
H
OH
Bond to remainder of polymer
• Annual world production around
500 billion metric tons
Preparation of Cellulose from Plant Sources
Preparation of cellulose
• Separation from matrix of lignocellulose (hemicellulose and lignin)
• Harsh chemical processing required
• Cellulose product may require bleaching with potentially
hazardous chemicals
Microcrystalline cellulose used in foods, pharmaceuticals, and
cosmetics
Cellulose Products
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
Cellulose acetate, an ester in which most of the -OH groups on
cellulose are replaced by acetate groups by reaction with acetic
anhydride
H O
H C C O
H
Acetate group
H O
O H
H C C O C C H
H
H
Acetic anhydride reagent
Cellulose Nitrate
Cellulose 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 WASTES
Large 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 residues
Rumen bacteria acting on cellulose wastes treated with lime in large
fermentors from which oxygen is excluded
Produce calcium acetate, calcium propionate, and calcium butyrate
that can be acidified to produce corresponding acids
H O
H H O
H C C OH H C C C OH
H
H H
Acetic acid
Propionic acid
H H H O
H C C C C OH
H H H
Butyric acid
Feedstocks from Cellulose Wastes (Cont.)
Hydrogenation to convert organic acids to alcohols:
H H
H C C OH
H H
Ethanol
H H H
H H H H
H C C C OH H C C C C OH
H H H
H H H H
Propanol
Butanol
Heat treatment of the organic acids at 450˚C to produce ketones
H O H
H C C C H
H
H
H O H H
H C C C C H
H
H H
Acetone
Methylethyl ketone
H H O H H
H C C C C C H
H H
H H
Diethyl ketone
12.8. LIGNIN
Lignin 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 plants
Lignin 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
H
H C O
H C H
O
O
H
H C
HO C
H
C
OH
OH
H
OCH3
O
Aromatic (benzene) ring
OCH3
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 chemistry
Some 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 POLYMERS
Cellulose in wood and cotton
Protein polymers in wool and silk
Environmental advantage in that polymers made biologically are
also the ones that are most likely to be biodegradable
From 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 3hydroxybutyric acid: O H H H
HO C C C C H
3-Hydroxybutyric acid
H O H
H
• 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 vats
Poly(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
O
HO C
OH p-Hydroxybenzoic acid
This compound is an important intermediate used in the synthesis of
pharmaceuticals, pesticides, dyes, preservatives, and liquid crystal
polymers
Currently 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 Toluene
Biosynthetic alternative synthesis of p-hydroxybenzoic acid from
toluene with genetically engineered Pseudomonas putida bacteria
1. 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:
H3C
O2
T4MO
H3C
OH
(12.10.1)
p -Cresol
Para position on the aromatic ring
2. p-Cresol methylhydroxylase (PCMH) enzyme from a strain of
Pseudomonas putida to give p-hydroxybenzyl alcohol followed by
conversion to p-hydroxybenzaldehyde:
H
H2O
H3C
OH
HO C
PCMH
H
O
C
p-Hydroxybenzaldehyde
H
OH
H2O
PCMH
p-Hydroxybenzyl alcohol
OH
(12.10.2)
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:
H
O
C
OH
H2O
O
HO C
OH
(12.10.1)
Biosynthesis of 5-Cyanovaleramide
Production of 5-Cyanovaleramide
Currently performed chemically with a stoichiometric mixture of
adiponitrile with water and a manganese dioxide catalyst under
pressure at 130˚C:
H H H H
MnO2
N C C C C C C N + H2O
H H H H Adiponitrile
Amide group
5-Cyanovaleramide
O H H H H
N C C C C C C N
H
H H H H
H
(12.10.4)
• 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 CN 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