U.S. patent application number 12/181217 was filed with the patent office on 2009-03-19 for continuous algal biodiesel production facility.
Invention is credited to Mark T. Machacek, Thomas Gordon Smith.
Application Number | 20090071064 12/181217 |
Document ID | / |
Family ID | 40304795 |
Filed Date | 2009-03-19 |
United States Patent
Application |
20090071064 |
Kind Code |
A1 |
Machacek; Mark T. ; et
al. |
March 19, 2009 |
CONTINUOUS ALGAL BIODIESEL PRODUCTION FACILITY
Abstract
Embodiments of the present invention concern methods,
compositions, and apparatus for the continuous conversion of algal
lipids into biodiesel. In some embodiments, the biodiesel is formed
in a multi-step sequence, the first steps occurring in the presence
of water and a strong acid wherein the lipids are released from the
algae by means of mechanical and chemical action and are then
hydrolyzed to free fatty acids. In a subsequent step, this free
fatty acid mixture is reacted with methanol to generate fatty acid
methyl esters (also known as biodiesel). Such methods produce
biodiesel from algal lipids without the requirement for separate
algal cell lysis or lipid extraction or purification prior to the
acid catalysis sequence. In other embodiments, the multi-step acid
catalysis sequence occurs at 100.degree. C. at two atmospheres of
pressure.
Inventors: |
Machacek; Mark T.; (Fort
Collins, CO) ; Smith; Thomas Gordon; (Livermore,
CO) |
Correspondence
Address: |
FAEGRE & BENSON LLP;PATENT DOCKETING
2200 WELLS FARGO CENTER, 90 SOUTH SEVENTH STREET
MINNEAPOLIS
MN
55402-3901
US
|
Family ID: |
40304795 |
Appl. No.: |
12/181217 |
Filed: |
July 28, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60952443 |
Jul 27, 2007 |
|
|
|
Current U.S.
Class: |
44/308 |
Current CPC
Class: |
Y02E 50/10 20130101;
C11C 3/003 20130101; Y02E 50/13 20130101; C11C 1/08 20130101; Y02P
30/20 20151101; C10G 2300/1011 20130101; C10L 1/026 20130101 |
Class at
Publication: |
44/308 |
International
Class: |
C10L 1/18 20060101
C10L001/18 |
Claims
1. A method for continuous production of biodiesel from algae
comprising: a. continuously feeding an aqueous suspension
comprising algae into a biodiesel production plant; and b.
converting lipids from the algae into biodiesel without an initial
purification or extraction step.
2. The method of claim 1, wherein the algal lipids are converted
into biodiesel using an acid catalyzed reaction at 100.degree. C.
and 2 atmospheres of pressure.
3. The method of claim 2, wherein the acid catalyzed hydrolysis
step produces free fatty acids from the algal lipids.
4. The method of claim 2, wherein the acid catalyzed hydrolysis
step breaks down algae cell walls and releases the algal
lipids.
5. The method of claim 3, further comprising adding methanol to the
fatty acids to form fatty acid methyl esters (FAME).
6. The method of claim 5, wherein the amount of methanol added is
twice the amount of free fatty acid.
7. The method of claim 6, wherein there is an eighty-five percent
conversion of free fatty acids to FAME in one hour of reaction.
8. The method of claim 5, further comprising centrifuging the
suspension to form liquid and solid components.
9. The method of claim 8, further comprising decanting the liquid
component by a phase separation procedure to form a heavy phase and
a light phase.
10. The method of claim 9, wherein the heavy phase comprises water,
glycerol, acid and methanol.
11. The method of claim 9, wherein the light phase comprises FAME
and free fatty acids (FFA).
12. The method of claim 10, wherein the heavy phase is preheated by
flashing to separate glycerol and acid from water and methanol.
13. The method of claim 12, further comprising removing the
glycerol and acid in a liquid bottoms stream.
14. The method of claim 12, wherein the water and methanol are
distilled to separate the methanol from the water.
15. The method of claim 14, further comprising recycling the
distilled methanol to react with free fatty acids.
16. The method of claim 11, wherein the FFA and FAME are reacted
with additional acid and methanol to complete the production of
FAME from FFA.
17. The method of claim 16, wherein over ninety-five percent of the
FFA are converted into FAME.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 60/952,443, filed on Jul. 27, 2007, and
entitled, "Continuous Algal Biodiesel Production Facility," which
is incorporated by reference herein in its entirety for all
purposes.
BACKGROUND
[0002] 1. Field
[0003] Embodiments of the present invention concern methods,
compositions and apparatus for continuous algal biodiesel
production. In particular, methods are provided for continuous
biodiesel production from algal biomass, without the need for
extraction or separation of algal lipids for esterification into
biodiesel. More particularly, such embodiments concern an in-situ
hydrolysis and esterification process for production of fatty acid
methyl esters (FAME), commonly referred to as biodiesel.
[0004] 2. Discussion of Related Art
[0005] Reducing the reliance of the United States on imported
fossil fuels is of concern for the future. Two-thirds of the oil
consumed in the U.S. is imported, and that number will continue to
rise unless reasonably priced, domestically produced alternatives
can be created. At the same time, the long-term supply of oil is
limited, and a large percentage of proven oil reserves are in
countries with unstable or hostile governments. Cutoffs in foreign
oil supply have been used as a political tool in attempts to coerce
U.S. policy. Combustion of petroleum based products releases
enormous amounts of CO.sub.2 into the atmosphere, contributing to
global warming. Thus, foreign petroleum use is a national concern,
as well as an environmental concern.
[0006] Various attempts have been made to develop biofuels from
non-petroleum sources. A large scale effort has been made to
develop ethanol from plant materials, primarily from corn grain.
Although substantial progress has been made, with almost five
billion gallons of corn ethanol produced in 2006, the resulting
impact on corn and food prices suggests that there are limits to
how much further production is feasible. Present corn ethanol
production is only sufficient to provide about 1.5% of U.S. fuel
needs and consumes over 20% of total U.S. corn production.
[0007] Other technologies have been developed to produce biodiesel
from plant sources. Many different irrigated crops, such as
soybean, rapeseed, jathropa, palm and sunflower, are currently
being used to produce biodiesel. Current biodiesel production often
utilize some form of transesterification process, wherein
triglycerides or other starting materials undergo an alkali or acid
catalyzed transesterification reaction between the fatty acid
component of the triglyceride and a low molecular weight alcohol,
such as methanol. Glycerol is released as a byproduct of
transesterification and fatty acid methyl esters are produced. Such
processes may be operated in either a batch or continuous mode.
However, it is currently necessary to first separate the
triglycerides or other source material from the bulk plant matter
before the transesterification reaction can proceed. Using such
technologies, current biodiesel production is only a small fraction
of corn ethanol production, with present U.S. capacity of less than
100 million gallons per year. In addition, biodiesel production
from food crops, such as soybeans, will ultimately encounter the
same problems that currently limit corn ethanol production.
[0008] Alternatives to increase biofuels production capacity have
been proposed, such as conversion to cellulosic ethanol production,
utilizing wood, switchgrass or other non-food starting materials.
However, cellulosic ethanol technology, while promising, has not
yet been developed to the point of full commercial scale production
and the time required to reach that point remains uncertain. Other
proposals have involved biofuel crop production on marginal or idle
land, such as the Conservation Reserve Program (CRP) acreage. Such
proposals ignore the practical difficulties of obtaining water
supplies to grow such crops, requirements for fertilizer input, low
productivity of marginal land, etc.
[0009] Another alternative source of biofuels production has been
proposed for algal culture systems. The National Renewable Energy
Laboratory (NREL) in Golden, Colorado spent 10 years and $25
million on an Aquatic Species program that focused on extracting
biodiesel from unusually productive species of algae. Before losing
funding, the government scientists demonstrated oil production
rates two hundred times greater per acre than achievable with fuel
production from soybean farming. However, the open pond system
utilized by NREL was susceptible to invasion by contaminating
algae, bacteria or algal-consuming organisms and algal productivity
was adversely impacted by fluctuating environmental temperature and
solar radiation. Further, in a pond type of system the light
penetration depth into dense algal cultures results in only a
limited band of photosynthetic productivity, with the majority of
algae being shaded by overlying organisms.
[0010] Closed system bioreactors for algal culture have been
proposed to provide better control of algal growth conditions,
limit invasion by undesired species, and enhance algal growth by
supplementing environmental gases with, for example, CO.sub.2
emissions from power plants or other fixed carbon sources. While
closed systems represent an improvement over open system
alternatives, such designs are often expensive to construct and
maintain, poorly scalable, and not optimized for maximal algal
lipid production under continuous culture conditions. Thus, a need
exists in the field for closed system, inexpensive, scalable
bioreactors capable of growing algae and producing biodiesel or
other products, and methods of use of such bioreactors for
continuous production of biodiesel from algae. A further need
exists for methods of biodiesel production from algae that does not
require separation or extraction of lipids from algal cells, prior
to conversion of algal lipids into biodiesel.
SUMMARY
[0011] Embodiments of the present invention include methods,
compositions and apparatus for continuous production of FAME from
algae, without the need for purification and/or extraction of
lipids from algal cells. Certain embodiments concern methods
involving a novel in-situ hydrolysis-esterification reaction
process. Lipids, or triglycerides, are first hydrolyzed to create
fatty acids at a 99 percent conversion rate. These are then
esterified to fatty acid methyl esters (FAME), commonly referred to
as biodiesel.
[0012] In some embodiments, in order to drive this reaction to
completion, a multiplicity of continuously stirred tank reactors
are used and are split into three parallel streams. Following the
reaction section, continuous centrifuge and decanter units may be
used to separate the solid, liquid and oil phases. As methanol is
non-renewable and somewhat expensive, about 98 percent of the feed
methanol may be recycled. Additional washing and reaction steps may
be used to create FAME with 99 percent purity.
[0013] Various embodiments concern use of one or more closed system
bioreactors for algal culture, to provide starting material for the
methods of continuous biodiesel production. Additional details of
such closed system bioreactors for algal culture are disclosed in
U.S. patent application Ser. Nos. 11/510,148 and 11/510,442; PCT
Patent Application Ser. No. PCT/US2006/033252; and provisional U.S.
Patent Application Ser. Nos. 60/894,082, filed Mar. 9, 2007;
60/877,907, filed Dec. 20, 1996, and 60/878,506, filed Jan. 3,
2007; the text of each of which is incorporated herein by
reference.
[0014] Certain embodiments may concern methods, compositions and
apparatus for fermentation of glycerin or glycerol into ethanol. In
some embodiments, the fermentation may be accomplished using
bacterial fermenters, such as E. coli.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 illustrates a mechanism for acid-catalyzed ester
hydrolysis, according to embodiments of the present invention.
[0016] FIG. 2 illustrates a process flow diagram for a reaction and
separation process for converting algae into biodiesel, according
to embodiments of the present invention.
[0017] FIG. 3 illustrates a reaction flow diagram, according to
embodiments of the present invention.
[0018] FIG. 4 illustrates a separation flow diagram, according to
embodiments of the present invention.
[0019] FIG. 5 illustrates a methanol purification flow diagram,
according to embodiments of the present invention.
[0020] FIG. 6 illustrates a biodiesel purification flow diagram,
according to embodiments of the present invention.
[0021] FIG. 7 illustrates an upper-left quadrant of an overall flow
process diagram, according to embodiments of the present
invention.
[0022] FIG. 8 illustrates an upper-right quadrant of an overall
flow process diagram, according to embodiments of the present
invention.
[0023] FIG. 9 illustrates an lower-left quadrant of an overall flow
process diagram, according to embodiments of the present
invention.
[0024] FIG. 10 illustrates an lower-right quadrant of an overall
flow process diagram, according to embodiments of the present
invention.
[0025] FIG. 11 illustrates a sample specification sheet for a
hydrolysis reactor that may be used according to embodiments of the
present invention.
[0026] FIG. 12 illustrates a sample specification sheet for an
esterification reactor that may be used according to embodiments of
the present invention.
[0027] FIG. 13 illustrates a sample specification sheet for a final
esterification reactor that may be used according to embodiments of
the present invention.
[0028] FIG. 14 illustrates a sample specification sheet for a heat
exchanger that may be used according to embodiments of the present
invention.
[0029] FIG. 15 illustrates a sample specification sheet for another
heat exchanger that may be used according to embodiments of the
present invention.
[0030] FIG. 16 illustrates a sample specification sheet for yet
another heat exchanger that may be used according to embodiments of
the present invention.
[0031] FIG. 17 illustrates a sample specification sheet for a
decanter that may be used according to embodiments of the present
invention.
[0032] FIG. 18 illustrates a sample specification sheet for another
decanter that may be used according to embodiments of the present
invention.
[0033] FIG. 19 illustrates a sample specification sheet for a
distillation tower that may be used according to embodiments of the
present invention.
[0034] FIG. 20 illustrates a sample specification sheet for a
centrifuge that may be used according to embodiments of the present
invention.
[0035] FIG. 21 illustrates a sample specification sheet for a flash
drum that may be used according to embodiments of the present
invention.
[0036] FIG. 22 illustrates a sample specification sheet for
parallel pumps that may be used according to embodiments of the
present invention.
[0037] FIG. 23 illustrates a sample specification sheet for a pump
that may be used according to embodiments of the present
invention.
[0038] FIG. 24 illustrates a sample specification sheet for another
pump that may be used according to embodiments of the present
invention.
[0039] FIG. 25 illustrates a sample energy balance chart for a
methanol mixer, according to embodiments of the present
invention.
[0040] FIG. 26 illustrates a sample energy balance chart for
methanol purification, according to embodiments of the present
invention.
[0041] FIG. 27 illustrates a sample energy balance chart for
parallel heaters, according to embodiments of the present
invention.
[0042] FIG. 28 illustrates a sample energy balance chart for a
methanol pre-heater, according to embodiments of the present
invention.
[0043] FIG. 29 illustrates a sample energy balance chart for a
product pre-heater, according to embodiments of the present
invention.
[0044] FIG. 30 illustrates a sample energy balance chart for
parallel pumps, according to embodiments of the present
invention.
[0045] FIG. 31 illustrates a sample energy balance chart for a
supplemental reactant pump, according to embodiments of the present
invention.
[0046] FIG. 32 illustrates a sample energy balance chart for a
methanol pump, according to embodiments of the present
invention.
[0047] FIG. 33 illustrates a sample energy balance chart for a
supplemental reactor, according to embodiments of the present
invention.
[0048] FIG. 34 illustrates a sample energy balance chart for a
parallel reaction branch, according to embodiments of the present
invention.
[0049] While the invention is amenable to various modifications and
alternative forms, specific embodiments have been shown by way of
example in the drawings and are described in detail below. The
intention, however, is not to limit the invention to the particular
embodiments described. On the contrary, the invention is intended
to cover all modifications, equivalents, and alternatives falling
within the scope of the invention as defined by the appended
claims.
DETAILED DESCRIPTION
[0050] Biofuel Production from Algal Culture
[0051] Algae are a very diverse and simple group of aquatic plant
that are widespread across the world. Algae can vary in form from
Eukaryote to Bacteria, and are spread across the kingdoms Plantae,
Protista, and Protozoa. All forms contain biomass, which can be
converted to various renewable fuels. In some embodiments, the
types used for culture are photosynthetic Plantae algae, although
the skilled artisan will realize that alternative algal types may
be utilized in the practice of the disclosed methods. The algae are
selected for their high lipid content and efficient growth under a
variety of conditions.
[0052] Algae is a beneficial feed stock because it has the
potential to provide over one hundred twenty times the fuel output
(per acre) of soybeans, the primary crop used for present biodiesel
production. Even palm oil, which has gained popularity recently,
has a lower order of magnitude for production per acre. Algae farms
are also advantageous in their ability to provide growth within a
contained environment, drastically reducing water usage compared to
conventional agriculture. Furthermore, livestock feed and general
food supply (a current concern for corn based ethanol, soybean oil,
and other biofuels ) will not be impacted by such a system.
[0053] An optimal location to grow algae quickly is next to a coal
or natural gas fired power plant, where large amounts of CO.sub.2
are released through combustion of fuel. The carbon dioxide, a
greenhouse gas, can be sequestered by the algae and some of it can
be converted into the carbon-containing lipids. Additional biomass
may be created, resulting in a reduction of atmospheric carbon
dioxide, even after the biodiesel is burned in a combustion engine.
At the same time, the CO.sub.2 enrichment provides for enhanced
algal growth.
Production of Biodiesel from Triglycerides
[0054] Certain embodiments of the present invention concern a
continuous process for converting algae to biodiesel (fatty acid
methyl esters-FAME). Current methods for production of biodiesel
from oil primarily utilize batch processes using a base catalyzed
reaction in a dry environment. Harvested algae contain a relatively
high percentage of water which obviates use of the current
technology in either the batch or continuous mode (soap, not
biodiesel, would be produced).
[0055] According to some embodiments of the present invention, a
process utilizes a two step water based acid catalyzed reaction
system to convert the algae lipids to biodiesel. At least one novel
feature of such a process is that the conversion of the lipids
(embedded in the algae) to fatty acids in the first stage reactors
proceeds without the prior extraction of the lipids. Extraction of
lipids from algae can be problematic and inevitably introduces at
least one additional chemical component which requires subsequent
separation from the product, by-products, and other feed
chemicals.
[0056] Another novel feature is the use of a water-based two stage
reaction system to produce biodiesel. Transesterification of the
lipids to FAME, the current route to biodiesel, proceeds
exceedingly slowly when acid catalyzed. However, if the lipids are
converted first to free fatty acids which are then reacted with
methanol and an acid catalyst, both reactions occur rapidly and to
a high extent. Further, after the biodiesel has been produced in
the two stage reactor system, it can be readily,
energy-efficiently, and economically separated from the other
chemicals in the reactor effluent using equipment common in the
chemical industry. All unreacted methanol is recovered and
recycled.
[0057] The manner in which the by-product, glycerol, is upgraded is
also new. Huge quantities of biodiesel will need to be produced to
have a significant effect on oil imports. The amount of glycerol
accompanying this biodiesel would flood the market, driving prices
down dramatically and thus resulting in an almost worthless
by-product. Embodiments of the present invention take advantage of
a new genetically-engineered strain of E-coli to convert the
glycerol primarily to ethanol, which can be sold as automobile
fuel. The ethanol itself is purified in the process by employing
novel ceramic/molecular sieve membrane technology. This drastically
reduces the energy requirement for this step of the process by
eliminating the need for high purity distillation.
[0058] The residual cell matter from the algae is energy-rich and
is burned to generate most of the steam and electricity needed for
the overall process (the carbon dioxide from this combustion can be
captured and used to grow additional algae), according to
embodiments of the present invention. The overall energy balance
for the process is exceptionally favorable, estimated at about 6
units of energy produced for every unit consumed, according to
embodiments of the present invention. For comparison, ethanol
plants are at an overall energy balance of approximately 1.2.
[0059] Existing biodiesel technology uses oils from various plants,
such as soybeans, as the feedstock. This oil is naturally free of
water so a base catalyzed transesterification reaction is feasible.
Industrially, the reaction is promoted by the conjugate base of the
alcohol (methanol), as shown below:
CH3O - Lipids + Methanol < -> FAME + Glycerol ( 1 )
##EQU00001##
where the methoxide ion provides a strong nucleophile for the
reaction mechanism. The methoxide is generated by dissolving a
small amount of base (e. g., potassium hydroxide) in the methanol.
The transesterification reaction is reversible and so is carried
out in an excess of methanol. The absence of water prevents the
formation of soap.
[0060] The conversion of algae-based lipids into FAME presents a
unique challenge with respect to existing technologies because the
algae itself contains water as part of its biological makeup and
also due to the harvested algae containing residual, water-based
growth media. Consequently, the base promoted technology employed
today by the biodiesel industry will not work. As described below,
embodiments of the current invention solve this problem. The
release of the lipids from the algae takes place in the first
reactor, avoiding an expensive extraction step.
[0061] Thus, while the lipids are being freed from the somewhat
fragile algae structure by means of vigorous mixing in the presence
of a strong acid, the first step in the transformation of these
lipids to FAME proceeds by means of their acid catalyzed hydrolysis
to free fatty acids. For example, using triolein, the major oil
component occurring in many plants, as a model lipid, the triolein
would be converted to oleic acid as follows:
Triolein+Water.fwdarw.Oleic Acid+Glycerol (2)
[0062] The general reaction mechanism for this is shown in FIG. 1.
Significantly, for Equation 2, the reverse reaction normally
associated with the hydrolysis of an ester (equilibrium
conversion=50%) is eliminated by the appearance of two liquid
phases, generated by the presence of the lipids. Since a lipid such
as triolein is, by definition, insoluble in water, the reaction
must occur at the interface between the lipid droplet and the
surrounding continuous water phase containing the strong acid
catalyst. However, the by-product glycerol is soluble in the water
phase and is also relatively dilute so that it does not react to
any significant extent with the water insoluble oleic acid to
sustain the reverse reaction. Thus, this reaction system not only
allows for the subsequent production of FAME in a water based acid
catalyzed medium (see equation 3 below) but eliminates the
potentially severe reversibility of the first reaction (equation
2), while at the same time avoiding the extraneous extraction of
the lipids themselves. This is accomplished all in the first
reactor, according to embodiments of the present invention.
[0063] The reaction of the oleic acid with methanol to form
biodiesel is carried out in a second reactor, according to
embodiments of the present invention, as follows:
Oleic Acid+Methanol<.fwdarw.Methyl Oleate+Water (3)
[0064] This type of reaction has been shown by others to occur
rapidly at seventy degrees centigrade using an excess of methanol
in the presence of a strong acid, with 99% conversion within a one
hour residence time. Others have also demonstrated that the acid
catalyzed transesterification of lipids directly to biodiesel is
very slow (36 hours to achieve 80% conversion) and would be
commercially impractical. So the multi-step sequence described
above (algae release>Equation 2>Equation 3) significantly
improves a design of an algae-to-biodiesel process.
[0065] Currently, there is no continuous technology of any kind
commercially producing biodiesel. For an algae feedstock, processes
according to embodiments of the present invention could readily
provide for this because their design is based on standard chemical
equipment commonly used for continuous processes, according to
embodiments of the present invention. Such processes should
therefore be scalable to very large capacities while producing
biodiesel at an economical price. Acid catalysis was selected for
the present methods. In some embodiments, the esterification takes
place at 100.degree. C. and at roughly twice atmospheric pressure.
The mechanism of this acid catalyzed reaction is shown as FIG.
1.
[0066] A difference in this synthesis is that a combination of
in-vitro hydrolysis and esterification reactions are utilized. The
use of a hydrolysis reaction, which converts the triglycerides to
free fatty acids, increases the overall rate of conversion to the
product. Free fatty acids produced from the hydrolysis readily
undergo acid catalyzed esterification with a residence time of
about one hour with ninety-nine percent conversion, according to
embodiments of the present invention. This can be contrasted with a
direct acid catalyzed transesterification of triglycerides, which
requires about thirty-six hours to achieve 80 percent conversion.
Such a two-step, acid-catalyzed, in vitro reaction sequence
drastically simplifies the process, as the lipids do not need to be
extracted from the cells, and they can be quickly converted to
product. The acid not only catalyzes the esterification reaction
but also breaks down the algal cell walls and releases the lipids
for conversion. This is considerably less expensive than methods
utilizing an extraction step prior to esterification.
[0067] Certain embodiments concern design of commercial scale
plants that will allow continuous production of 100 million gallons
per year of biodiesel from algae. As discussed above, in-situ
acid-catalyzed hydrolysis followed by esterification is used as the
reaction for the conversion of algae biomass to biodiesel. The
design focuses on the downstream processes that will convert an
algae stream into biodiesel, according to embodiments of the
present invention.
[0068] In determining efficient design of a biodiesel production
facility, certain assumptions were made according to embodiments of
the present invention: [0069] Methanol should be 2 times the
stoichiometric ratio. [0070] The incoming algae contain 40 percent
lipid content by dry weight. [0071] The incoming algae slurry is 25
percent water by weight. [0072] The algae growth facility is
located close to the plant. [0073] The acid-methanol solution will
be 4 percent sulfuric acid by volume. [0074] The overall conversion
of triglycerides to biodiesel will be 85 percent in the first
reaction series, and finalized to 99 percent in the last reactor.
[0075] A basic block flow diagram for the process is shown in FIG.
2.
Process Flow Diagram
[0076] The full process flow diagram (FIGS. 7-10) encompasses the
many different parts of the design, according to embodiments of the
present invention. For simplification, it can be broken down into
several sections: one for the main reaction, another for the
separation of the byproducts, and the final two for the
purification of the biodiesel product and the methanol recycle
stream. These sections may be broken down further into their
specific parts and analyzed individually.
[0077] Feeds
[0078] according to embodiments of the present invention, there are
three main feeds to the plant. The first is the algae feed. Its
composition is 25 percent water, 30 percent triglycerides (as
triolene), and the cell matter which accounts for the other 45
percent. The cell matter contains carbohydrates (as energy storage
or as cell wall material), proteins, and other cell mass.
Additionally the phospholipids that make up each cell membrane are
potential feed stocks for the reaction, but in the treatment below
are assumed to be accounted for as part of the lipid content. This
algae slurry enters the system at approximately 27.degree. C. and 1
atmosphere. Prior to entering the first reactor sequence, it is
combined with the second stream, sulfuric acid at 18 M. This second
stream arrives at the same temperature and pressure. These streams
are mixed before being split and sent to the three individual
reaction chains.
[0079] A methanol feed stream for the Fisher Esterification section
of the reaction scheme is an additional inlet and is fed at
27.degree. C. and 1 atm.
[0080] There is an additional sulfuric acid feed stream entering at
the same conditions that is utilized to feed the secondary
esterification reaction. It is mixed with a methanol stream.
[0081] Reaction Scheme
[0082] The reaction scheme is run in parallel to reduce reactor
size and individual flow rates, while maintaining the overall flow
rates. Prior to reaction, the streams are pressurized by pump P-101
(P-201 and P-301 in the parallel chains) up to 2 atm. This keeps
the methanol liquid at the reaction temperature. The pressurized
stream is then heated by H-101 (H-201, H-301) to 100.degree. C.,
the preferred hydrolysis temperature.
[0083] The first section of the reaction scheme focuses on the
triglyceride hydrolysis. Under appropriate conditions, three water
molecules will combine with each triglyceride to form three stable
fatty acids and glycerol. Reactors R-101 and R-102 combine to
provide the one hour residence time required for ninety-nine
percent hydrolysis. They are operated at 100.degree. C. and 2 atm.
The output of the reactors reflects the ninety-nine percent
conversion of triglycerides to free fatty acids.
[0084] The second section of the reaction scheme converts the free
fatty acids to form the biodiesel end product. A methanol stream is
added, fed at two times the required stoichiometric amount to drive
the reaction further to completion. Part of this stream consists of
the methanol recycle stream. The combined stream will be around
65.degree. C., but only makes up about six percent of the total
mass flow. Therefore, no additional heater is included, as the
reactors are jacketed, and the reactions themselves are exothermic.
Reactors R-103 and R-104 combine to allow for a one hour residence
time at 100.degree. C. and 2 atm, resulting in an 85 percent
conversion of the free fatty acids to methyl esters
(biodiesel).
[0085] Separation Scheme
[0086] The stream leaving the reaction section is then sent to the
separation section. It is first centrifuged in C-101 to remove the
algae cell matter. The supernatant includes all liquid components
that left the reaction section. The solids are removed at a rate
such that the mass flow rate downstream is reduced by almost 50
percent. The liquid stream enters a decanter, which allows for a
phase separation with a residence time of two hours. Water,
glycerol, acid, and methanol leave in the heavy phase and are sent
to the methanol purification section of the plant. The light phase,
consisting of fatty acid methyl esters and free fatty acids, is
sent to the secondary reaction section of the plant.
[0087] Methanol Purification
[0088] The heavy streams from the decanters are combined and
preheated for flashing by H-401. This stream is then flashed,
resulting in a separation of the glycerol and acid from the water
and methanol. Glycerol and acid leave the flash drum as a liquid
bottoms stream, which is then sent on for further processing. The
vapor overhead stream is combined with the aqueous phase from the
secondary esterification reaction, for a total flow into tower
T-101. The distillate leaving the tower consists of 99.1 percent
methanol, which leaves a bottoms product of mainly water and trace
sulfuric acid and glycerol. The methanol distillate stream is
recycled back to the esterification portion of the reaction
sequence, allowing for a significant reduction in the required
methanol input.
[0089] Biodiesel Purification
[0090] The product stream of free fatty acids and fatty acid methyl
esters is sent to the biodiesel purification. Acid and methanol is
added to reactor R-401 along with the product stream and allowed to
react for one hour. The conversion approaches 99 percent and the
outlet consists of 96.3 percent methyl ester. This stream is washed
in M-101 by water in order to create a two phase system. It then is
phase separated in D-401, resulting in a final product stream of 99
percent biodiesel, and a waste stream of methanol and water that
goes to T-101.
[0091] A large scale view of the overall process flow diagram is
presented in FIGS. 7-10.
Energy Balance and Utility Requirements
[0092] The energy consumption of the plant can be a concern during
the development of an overall process flow diagram, according to
embodiments of the present invention. In a plant, it may be
beneficial to recycle as much of the feed stocks as possible,
including methanol and water. Furthermore, it may be advantageous
to utilize as many byproducts as possible in order to offset the
costs of production. A method used to separate the product
biodiesel from the byproducts may be chosen with lower energy
requirements. Byproducts may be used in a manner that benefits the
overall energy balance and cost of the process. For example, the
glycerol produced in the esterification reaction may be processed
downstream to produce ethanol, which can either be sold or used as
fuel. Methodologies according to embodiments of the present
invention can be shown to produce significantly more energy in the
form of biodiesel than was required by the process to produce the
biodiesel.
[0093] Energy Requirements
[0094] Calculation of an overall energy requirement for a
particular factory design takes into account each individual
process component, according to embodiments of the present
invention. However, it may be assumed that the decanters, pumps and
centrifuges are perfectly insulated; that is, there was no heat
lost from these instruments. Following this method, it was found
that this process design according to embodiments of the present
invention has an overall energy requirement of 306 MBtu/hr. This
energy is used for the heating of incoming streams, preparing a
stream for flash, and distillation. Additionally, energy is needed
to keep the reactors at the target temperatures. Once the initial
feed stream is broken into three streams each one goes through a
heat exchanger to reach the target 100.degree. C. Each heat
exchanger has a heat duty of 4.4 MBtu/hr. The esterification
reactors experience an exothermic reaction, which may require
cooling to avoid thermal runaway. Therefore jacketed reactors may
be chosen, but cooling water may be useful in such cases. Cooling
water is usually a minimal cost in plant design.
[0095] In order to separate the water and other by products without
using an extremely large distillation column, a flash drum is
situated in front of the distillation column. The product stream is
heated to 125.degree. C. before entering the flash drum. This heat
exchanger has a heat duty of 77 MBtu/hr. The flash drum has a heat
duty of 6.5 MBtu/hr in order to keep it at 125.degree. C. The
distillation column used to purify methanol has a heat duty of 198
MBtu/hr. The reactors and smaller heat exchangers make up the
balance of the total heat duty.
[0096] Utilities
[0097] The heat for this process is mainly supplied by steam at 100
psi, which makes up most of the annual utility cost. The 100 psi
steam may be used for the feed heat exchangers, distillation
column, and the reactors. For the pre-flash heat exchanger, 450 psi
steam may be utilized. Additionally, cooling water may be used in a
number of applications. It may be used to condense the methanol
leaving the distillation column. More cooling water may be
necessary for the reactors as mentioned before, as well as cooling
any product streams that may require further processing on site.
Table 1 shows the costs and amount of each utility that may be
used, according to embodiments of the present invention.
Electricity is used to power the pumps and centrifuges. Process
water is calculated as the overall requirement, and could be
potentially supplemented by a recycle later on in the system, but
the full requirement is only 0.1 percent of the total annual cost
and would not impact the pricing in any significant way, according
to embodiments of the present invention.
TABLE-US-00001 TABLE 1 Utility Units Requirement Cost per Year 100
lb steam (lb) 5.29E+09 $ 17,204,000 450 lb steam (lb) 6.00E+08 $
3,300,000 Process Water (gal) 4.01E+07 $ 20,000 Cooling Water (gal)
3.12E+09 $ 156,000 Electricity (kW-hr) 5.84E+06 $ 233,000 TOTAL $
20,913,000
[0098] Energy Saving
[0099] A gravity separator may be used instead of a distillation
column or other energy consuming unit, to conserve energy. The
biodiesel and water exist in different phases and will separate if
given enough time, according to embodiments of the present
invention. Decanters help to not only separate the water from the
biodiesel, but since the acid, methanol, and glycerol are miscible
in water they are also removed from the product stream. This leaves
only biodiesel and unreacted free fatty acids in the product
stream, and allows for continuous plant operation.
[0100] In order to get biodiesel of 99 percent purity, the
biodiesel and unreacted free fatty acids may be run through another
reactor which converts almost all the free fatty acids to
biodiesel. A decanter is once again used to remove the added
methanol and sulfuric acid. To make the product as pure as possible
it is then washed with water to remove any trace amounts of acid,
methanol, and glycerol. If the concentration of free fatty acids in
the final product is too high, residence time in the reaction can
increase to reduce FFA levels.
Energy Balance
[0101] Table 2 shows that the disclosed process has a positive
energy balance, according to embodiments of the present invention.
The amount of sun used to make algae grow was not included in the
energy balance. The positive energy balance is an important
consideration in the design and construction of a plant, in
comparison to alternative methods. Concerns have been expressed
about the net energy produced in the production of ethanol and
rapeseed derived biofuels. The energy balance for the disclosed
plant shows that 5.6 units of energy are produced for every one
unit input into the system.
TABLE-US-00002 TABLE 2 Energy Balance Values Energy Balance
Source/Sink BTU/yr Production Use -2.40E+12 Biodiesel Fuel 1.35E+13
Overall 1.11E+13
Equipment
[0102] Embodiments of the present invention employ many different
types of equipment, including reactors, centrifuges, decanters, a
distillation column and many pumps and heat exchangers. Units
discussed in this section have specification sheets that may be
found at FIGS. 11-24.
[0103] Reactors
[0104] According to an embodiment of a production process, there
are three different types of reactors used. The first is the
reactor used for the hydrolysis of the triglyceride into free fatty
acids. These reactors are listed as R-101 and R-102, R-201 and
R-202, and R-301 and R-302 in the process flow sheet. In these
reactors the algae and acid are fed at a pressure of 2 atm and a
temperature of 100.degree. C. The conditions in the reactors are
the same as the feed conditions, so no heating or pressurization
needs to be done in the reactors, just the maintenance of these
conditions. The reactors are glass-lined continuous stirred tank
reactors (CSTR) and are agitated and jacketed. The glass lined
reactors may assist with the acidic nature of the feed. The
volumetric flow rates into each reactor are 8,585 gal/hr, according
to embodiments of the present invention. The residence time for
each reactor is half an hour, according to embodiments of the
present invention. A half hour residence time may be chosen to
reduce the size of each reactor and help in achieving the 99
percent hydrolysis of triglycerides into free fatty acids in a
smaller volume. Once the volumetric flow rate and residence time
are known, the size of each reactor may be calculated; according to
some embodiments of the present invention, each reactor is
calculated to be 4,293 gal. An oversize factor of 1.16 may be used,
leading to the choice of a a 5,000 gallon reactor. Such a rector
size may allow for head space and help minimize overfilling.
Challenges in designing the reactors include selecting a residence
time and operating conditions, according to embodiments of the
present invention.
[0105] Each reactor may be jacketed to help maintain a selected
temperature, for example 100.degree. C. Cooling water and 100 psi
steam may be used to heat and cool the reactor as necessary. The
reactors have very little heat duty overall compared to other units
in the process, as the inlets are already at operating conditions,
according to embodiments of the present invention. The overall
operating costs of the reactor are minimal due to low utility usage
and maintenance cost, according to embodiments of the present
invention. If one hydrolysis reactor must stop production for
maintenance, then there are two other chains that can still produce
biodiesel, according to embodiments of the present invention. The
overall production of the plant will decrease but will not have to
stop if one reactor needs maintenance, according to embodiments of
the present invention.
[0106] The second type of reactor that may be used is for the
esterification of the free fatty acids into the fatty acid methyl
esters or biodiesel, according to embodiments of the present
invention. These reactors are listed as R-103 and R-104, R-203 and
R-204, and R-303 and R-304 in the overall process flow diagram. The
feed to these reactors contains the components leaving the
hydrolysis reactors which, according to embodiments of the present
invention, may include: cell matter, water, glycerol, acid, and
free fatty acids. Another feed stream to the reactor is the
methanol for the esterification reaction. The total volumetric flow
rate of both streams is 9,472 gal/hr, according to embodiments of
the present invention. The conditions in these reactors are the
same as the hydrolysis reactors with a temperature of 100.degree.
C. and a pressure of 2 atm, according to embodiments of the present
invention. The esterification reactors may be glass-lined due to
the corrosive nature of the feed. Glass-lined may be preferred in
some cases over stainless steel due to the high cost of stainless
steel. All of these reactors are CSTRs and are jacketed and
agitated as well, according to embodiments of the present
invention. The residence time of these reactors is also half an
hour, according to embodiments of the present invention. The total
residence time may be selected to be 30 minutes, according to
embodiments of the present invention. In order to ensure the 85
percent conversion a total residence time may be selected to be one
hour between the two reactors, according to embodiments of the
present invention. The one hour may be divided across two reactors
to help reduce the size of each reactor and help in achieving the
desired conversion, according to embodiments of the present
invention. The calculated volume for each reactor is 9,023 gallons,
according to embodiments of the present invention.
[0107] The esterification reaction is an exothermic reaction that
may result in a need to cool the reactors. The reactors may be
cooled with cooling water through their jackets. The overall usage
of cooling water to maintain the desired temperature in the
reactors may be minimal, which leads to low operating cost due to
utilities. Another operating cost is maintenance. If, for some
reason, a reactor needs stop production due to maintenance, the
other two branches may still be able to continue making biodiesel,
according to embodiments of the present invention.
[0108] The final reactor is used to complete the esterification of
free fatty acids to biodiesel, according to embodiments of the
present invention. This reactor is listed as R-401 on the process
flow diagram. After the product stream is separated from the
byproducts (glycerol, water, etc), the biodiesel product stream is
fourteen percent free fatty acids. The final reactor may be added
to convert the remaining free fatty acids to biodiesel. The reactor
feed may be an acid and methanol mixture, along with the biodiesel
product containing fourteen percent free fatty acids. The
conditions in the reactor are 100.degree. C. and 2 atm, according
to embodiments of the present invention. The volumetric flow rate
through the reactor is 11,923 gal/hr, according to embodiments of
the present invention. This reactor may also be a jacketed and
agitated glass-lined CSTR. The residence time may be chosen to be
one hour for reasons stated for the other esterification reactors.
The size for the reactor is 11,923 gal, according to embodiments of
the present invention. This reactor houses a low concentration of
free fatty acids that need to react, according to embodiments of
the present invention.
[0109] As with the other reactors, the temperature may be
maintained using cooling water. Also, the amount of cooling water
required is a minimal expense and so the overall yearly maintenance
and cost is minimal, according to embodiments of the present
invention. According to some embodiments of the present invention,
if for some reason this reactor has to be shut down for
maintenance, the whole plant would have to either stop production
or the biodiesel product would have to be stored until the
maintenance is completed. Therefore, two intermediate storage tanks
may be included to allow for twenty-four hours of storage.
Alternatively, a backup reactor may be provided to allow for
maintenance during continuous production.
[0110] Centrifuges
[0111] A process according to embodiments of the present invention
utilizes three centrifuges to separate the cell matter from the
liquid after the hydrolysis and esterification reactor sequence.
After the triglycerides in the algae cells have been extracted and
reacted, they may need to be separated out. The centrifuges are
listed as C-101, C-201 and C-301 in the process flow diagram. 316
stainless steel may be used for the material due to the acidity of
the solution. The centrifuges may be designed based upon the number
of tons of solid per hour they were required to separate. The
amount of cell matter removed is estimated at 23.85 tons/hr for
each centrifuge, according to embodiments of the present
invention.
[0112] Decanters
[0113] According to embodiments of the present invention, decanters
separate the heavy byproducts from the biodiesel product. Decanters
are referred to as D-101, D-201, D-301 and D-401, according to
embodiments of the present invention. The decanters are designed to
allow a sufficient time for the aqueous phase (water, glycerol,
acid, and methanol) to separate from the oil phase (biodiesel, free
fatty acids). This is accomplished by a gravity separation due to
the significant difference in density of the phases, according to
embodiments of the present invention. The time taken for a
separation is given by Equation 4:
t = 100 .mu. .rho. H - .rho. L ( 4 ) ##EQU00002##
In this equation .mu. is the viscosity of the light phase,
.rho..sub.H is the density of the heavy phase, and .rho..sub.L is
the density of the light phase. A calculation time for separation
of two hours may be used as the residence time of the liquid in the
decanter. The volumetric flow rate through D-101, D-201 and D-301
is 7,112 gal/hr, according to embodiments of the present invention.
The volume of these decanters may be 14,107 gal, according to
embodiments of the present invention. The decanters may be
horizontal vessels. The length to diameter ratio may be selected as
6, to allow for proper settling of the heavy phase from the light
phase. With such volume, the length of each decanter may be 60 ft.
with a diameter of 10 ft., according to embodiments of the present
invention. The decanters may be constructed out of 316 SS due to
the acidity of the feed, according to embodiments of the present
invention. D-401 has a different size, due to a volumetric flow
rate of 16,791 gal/hr, according to embodiments of the present
invention. With this flow rate the decanter size may be 33,305 gal,
according to embodiments of the present invention. This volume with
a length to diameter ratio of 6 yields a length of 58.9 fit and a
diameter of 9.8 ft. According to some embodiments of the present
invention, 100 percent the aqueous phase is removed from the oil
phase in the decanters. The decanters require very little utilities
to ensure proper operating conditions, resulting in a minimal
yearly operating cost. If any of the decanters after the initial
reaction scheme have to be repaired there may be others that can
function while maintenance is completed. If the decanter after the
final reactor were to need maintenance, then the flow from that
reactor could be stopped or moved to a storage tank elsewhere,
according to embodiments of the present invention. However,
decanters are unlikely to require maintenance due to their simple
design.
[0114] Flash Drum
[0115] A flash drum reduce the volume of liquid sent to the
distillation column by flashing off about half the water and almost
all the methanol, leaving glycerol, acid and some water in the
liquid phase, according to embodiments of the present invention.
The flash drum is referred to as F-101 on the process flow diagram.
The inlet flow is the combination of the three aqueous streams from
the decanters, and the total volumetric flow rate is 10,100 gal/hr,
according to embodiments of the present invention. Heuristics may
be used to determine a residence time in the flash drum of 10
minutes, and that the volume of the flash drum may be twice the
value of the volumetric flow rate times the residence time,
according to embodiments of the present invention. From this, the
volume of the flash drum may be calculated to be 3,972 gal. The
conditions inside the column are 125.degree. C. and 1 atm.,
according to embodiments of the present invention. At this
temperature and pressure there is a 95 percent vapor fraction in
the column. Flash drums may be vertical columns with a length to
diameter ratio of five; such value may also be calculated with
heuristics, according to embodiments of the present invention. The
height of the flash drum may be 39.8 fit with a diameter of 8 ft,
according to embodiments of the present invention.
[0116] Distillation Column
[0117] The unit identification for the distillation column is T-101
on the process flow diagram. A distillation column separates the
water and any residual glycerol and acid from the methanol,
according to embodiments of the present invention. The purified
methanol may then be recycled to become part of the reactor feed.
This recycle process greatly reduces chemical costs. The water that
leaves the bottoms of the column may be further processed. A
software simulation engine, for example ASPEN, may be used to
determine the number of trays required for the column, the reflux
ratio and the flow rates of liquid and vapor through the column,
according to embodiments of the present invention. The total number
of trays for the column is 17 and the reflux ratio is 18.9,
according to embodiments of the present invention. The methanol
product leaving the top of the column may be 99 percent pure. The
height of the column may be determined by the number of trays with
2 foot spacing, which would make the column 34 feet tall. The tray
type may be selected to be sieve trays, and the tray material may
be determined to be 316 SS due to the possibility of acidic
conditions in the column. The flow rates for the liquid and vapor
may be used to calculate the column diameter, which is 5.45 fit in
some embodiments. The overall weight of the column is 8,421 lbs.,
according to embodiments of the present invention. The column
material may be selected to be 316 SS as well due to the acidity of
the solution. The column pressure is 2 atm to make for a smaller
diameter and a higher temperature of vapor leaving the column,
according to embodiments of the present invention.
[0118] The main operating cost of the distillation column consists
of utilities for the reboiler and the condenser. The reboiler may
be supplied with 100 psi steam and the condenser may be supplied
with cooling water, according to embodiments of the present
invention.
[0119] Pumps
[0120] Pumps in the system may operate to raise the pressure in the
feed streams from one atmosphere to a pressure of two atmospheres,
according to embodiments of the present invention. The pumps are
designated as P-101, P-201, P-301, P-401 and P-501. The pumps may
be constructed of 316 SS. The sizes of the individual pumps are
described in FIGS. 23-24.
[0121] Heat Exchangers
[0122] Heat exchangers H-101, H-201, H-301, and H-501 heat feed
streams from their initial temperature to the production
temperature of 100.degree. C., according to embodiments of the
present invention. H-401 may be used to heat the aqueous solution
from the decanters to 125.degree. C. to prepare it for the flash
drum, according to embodiments of the present invention. Heat
exchangers may be made of 316 SS due to the acidity in the
solution. The surface area in the heat exchanger and overall heat
transfer coefficients may be calculated using a facility design
software program, for example ASPEN, according to embodiments of
the present invention. Heat exchangers are not duplicated according
to embodiments of the present invention, and due to the fact that
three parallel streams exist, if H-101, H-201, or H-301 need
maintenance only one of the three branches needs to stop
production.
[0123] Various modifications and additions can be made to the
exemplary embodiments discussed without departing from the scope of
the present invention. For example, while the embodiments described
above refer to particular features, the scope of this invention
also includes embodiments having different combinations of features
and embodiments that do not include all of the described features.
Accordingly, the scope of the present invention is intended to
embrace all such alternatives, modifications, and variations as
fall within the scope of the claims, together with all equivalents
thereof.
* * * * *