U.S. patent application number 11/638348 was filed with the patent office on 2007-06-28 for production of biodiesel from triglycerides via a thermal route.
Invention is credited to Michio Ikura.
Application Number | 20070144060 11/638348 |
Document ID | / |
Family ID | 38162512 |
Filed Date | 2007-06-28 |
United States Patent
Application |
20070144060 |
Kind Code |
A1 |
Ikura; Michio |
June 28, 2007 |
Production of biodiesel from triglycerides via a thermal route
Abstract
A method is presented for producing biodiesel from a
triglyceride feedstock. The feedstock is pretreated by thermal
cracking or rapid pyrolysis to convert triglycerides to form a
middle distillate fraction rich in fatty acids. The middle
distillate fraction is then esterified the in the presence of an
alcohol and a catalyst to produce a biodiesel stream. The biodiesel
stream can be treated with a basic solution to convert unesterified
free fatty acids to non-foaming metallic soaps, which can be
removed by known means. A method is also provided for producing a
biodiesel/naphtha mixture, in which a triglyceride feedstock is
pretreated by thermal cracking or rapid pyrolysis to produce a
middle distillate fraction, a naphtha stream and a gas stream. The
naphtha stream and the middle distillate fraction are then
esterified to produce a mixed biodiesel/naphtha stream, which can
be treated with a basic solution to convert unesterified free fatty
acids to non-foaming metallic soaps, which are then removed by
known means.
Inventors: |
Ikura; Michio; (Kanata,
CA) |
Correspondence
Address: |
KIRBY EADES GALE BAKER
BOX 3432, STATION D
OTTAWA
ON
K1P 6N9
CA
|
Family ID: |
38162512 |
Appl. No.: |
11/638348 |
Filed: |
December 14, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11304658 |
Dec 16, 2005 |
|
|
|
11638348 |
Dec 14, 2006 |
|
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Current U.S.
Class: |
44/308 |
Current CPC
Class: |
C10G 2300/1018 20130101;
Y02E 50/10 20130101; C11C 3/00 20130101; Y02P 30/20 20151101; C10L
1/026 20130101; C10G 2300/1014 20130101; C10G 3/40 20130101; C10G
2300/807 20130101; C11C 3/003 20130101 |
Class at
Publication: |
044/308 |
International
Class: |
C10L 1/18 20060101
C10L001/18 |
Claims
1. A method of producing biodiesel from a triglyceride feedstock,
the method comprising: a. pretreating the triglyceride feedstock by
thermal cracking to remove contaminants and convert triglycerides
to form a middle distillate fraction rich in free fatty acids; b.
esterifying the middle distillate fraction in the presence of an
alcohol and a catalyst to produce a biodiesel stream; c. treating
the biodiesel stream with a basic solution to convert unesterified
free fatty acids to non-foaming metallic soaps; and d. removing the
non-foaming metallic soaps by centrifugation, filtering or a
combination thereof.
2. The method of claim 1 wherein the basic solution is an aqueous
solution of a compound selected from the group consisting of
lithium hydroxide (LiOH), magnesium hydroxide (Mg(OH).sub.2), and
calcium hydroxide (Ca(OH).sub.2).
3. The method of claim 2 wherein the basic solution is an aqueous
solution of calcium hydroxide or lithium hydroxide.
4. The method of claim 1 wherein the triglyceride feedstock is
selected from the group consisting of restaurant trap grease,
rendered animal fats, waste greases, low-quality vegetable oils and
combinations thereof.
5. The method of claim 1 wherein thermal cracking is conducted at a
temperature of from 390.degree. C. to 460.degree. C.
6. The method of claim 1 wherein thermal cracking is conducted at a
temperature of from 410.degree. C. to 430.degree. C.
7. The method of claim 1 wherein the middle distillate fraction is
esterified in the presence of methanol as the alcohol.
8. The method of claim 7 wherein esterifying is conducted at a
temperature of from 70.degree. C. to 120.degree. C.
9. The method of claim 8 wherein esterifying is conducted at a
temperature of from 85.degree. C. to 110.degree. C.
10. The method of claim 1, wherein the middle distillate fraction
is esterified in the presence of an acid catalyst.
11. The method of claim 10 wherein the acid catalyst is selected
from the group consisting of sulphuric acid (H.sub.2SO.sub.4(l)),
sulphamic acid (H.sub.2NSO.sub.3H.sub.(l)), formic acid
(HCO.sub.2H.sub.(l)), acetic acid (CH.sub.3CO.sub.2H.sub.(l)),
propionic acid (CH.sub.3CH.sub.2CO.sub.2H.sub.(l)), hydrochloric
acid (HCl.sub.(l)), phosphoric acid (H.sub.3PO.sub.4(l)), sulphated
metal oxides such as sulphated zirconia, and styrene divinylbenzne
copolymers having SO.sub.3H functional groups.
12. The method of claim 11 wherein the acid catalyst is a styrene
divinylbenzene copolymer having an SO.sub.3H functional group.
13. The method of claim 1, further comprising filtering the
triglyceride feedstock before thermal cracking to remove
macroscopic contaminant particles.
14. A method of producing a biodiesel/naphtha mixture from a
triglyceride feedstock, the method comprising: a. pretreating the
triglyceride feedstock by thermal cracking to remove contaminants
and convert triglycerides to produce a middle distillate fraction
rich in free fatty acids, a naphtha stream and a gas stream; b.
esterifying the naphtha stream and middle distillate fraction in
the presence of an alcohol and a catalyst to produce a mixed
biodiesel/naphtha stream; c. treating the mixed biodiesel/naphtha
stream with a basic solution to convert unesterified free fatty
acids to non-foaming metallic soaps; and d. removing the
non-foaming metallic soaps by centrifugation, filtering or a
combination thereof.
15. A method of producing biodiesel from a triglyceride feedstock,
the method comprising: a. pretreating the triglyceride feedstock by
rapid pyrolysis to remove contaminants and convert triglycerides to
form a middle distillate fraction rich in free fatty acids; b.
esterifying the middle distillate fraction in the presence of an
alcohol and a catalyst to produce a biodiesel stream; c. treating
the biodiesel stream with a basic solution to convert unesterified
free fatty acids to non-foaming metallic soaps; and d. removing the
non-foaming metallic soaps by centrifugation, filtering or a
combination thereof.
16. The method of claim 15 wherein the basic solution is an aqueous
solution of a compound selected from the group consisting of
lithium hydroxide (LiOH), magnesium hydroxide (Mg(OH).sub.2), and
calcium hydroxide (Ca(OH).sub.2).
17. The method of claim 16 wherein the basic solution is an aqueous
solution of calcium hydroxide or lithium hydroxide.
18. The method of claim 15 wherein the triglyceride feedstock is
selected from the group consisting of restaurant trap grease,
rendered animal fats, waste greases, low-quality vegetable oils and
combinations thereof.
19. The method of claim 15 wherein rapid pyrolysis is conducted at
a temperature of from 480.degree. C. to 600.degree. C.
20. The method of claim 15 wherein rapid pyrolysis is conducted at
a temperature of from 550.degree. C. to 600.degree. C.
21. The method of claim 15 wherein rapid pyrolysis is conducted at
a temperature of from 565.degree. C. to 585.degree. C.
22. The method of claim 15 wherein the triglyceride feedstock is
fluidized with steam.
23. The method of claim 22 wherein the steam to triglyceride
feedstock ratio ranges from 0.5 to 1.5.
24. The method of claim 23 wherein the steam to triglyceride
feedstock ratio is 0.9.
25. The method of claim 15 wherein an inert gas is used to purge
any oxidizing agents during rapid pyrolysis.
26. The method of claim 25 wherein the inert gas is nitrogen.
27. The method of claim 15 wherein a catalyst is used during rapid
pyrolysis to enhance the cracking of triglycerides to largely free
fatty acids.
28. The method of claim 27 wherein the catalyst is selected from
the group consisting of acid washed activated carbon, calcined
sewage sludge solids and silica sand.
29. The method of claim 15 wherein the middle distillate fraction
is esterified in the presence of methanol as the alcohol.
30. The method of claim 29 wherein esterifying is conducted at a
temperature of from 70.degree. C. to 120.degree. C.
31. The method of claim 30 wherein esterifying is conducted at a
temperature of from 85.degree. C. to 110.degree. C.
32. The method of claim 15, wherein the middle distillate fraction
is esterified in the presence of an acid catalyst.
33. The method of claim 32 wherein the acid catalyst is selected
from the group consisting of sulphuric acid (H.sub.2SO.sub.4(l)),
sulphamic acid (H.sub.2NSO.sub.3H.sub.(l)), formic acid
(HCO.sub.2H.sub.(l)), acetic acid (CH.sub.3CO.sub.2H.sub.(l)),
propionic acid (CH.sub.3CH.sub.2CO.sub.2H.sub.(l)), hydrochloric
acid (HCl.sub.(l)), phosphoric acid (H.sub.3PO.sub.4(l)), sulphated
metal oxides such as sulphated zirconia, and styrene divinylbenzne
copolymers having SO.sub.3H functional groups.
34. The method of claim 33 wherein the acid catalyst is a styrene
divinylbenzene copolymer having an SO.sub.3H functional group.
35. The method of claim 15, further comprising filtering the
triglyceride feedstock before thermal cracking to remove
macroscopic contaminant particles.
36. A method of producing a biodiesel/naphtha mixture from a
triglyceride feedstock, the method comprising: a. pretreating the
triglyceride feedstock by rapid pyrolysis to remove contaminants
and convert triglycerides to produce a middle distillate fraction
rich in free fatty acids, a naphtha stream and a gas stream; b.
esterifying the naphtha stream and middle distillate fraction in
the presence of an alcohol and a catalyst to produce a mixed
biodiesel/naphtha stream; c. treating the mixed biodiesel/naphtha
stream with a basic solution to convert unesterified free fatty
acids to non-foaming metallic soaps; and d. removing the
non-foaming metallic soaps by centrifugation, filtering or a
combination thereof.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation-in-part of U.S.
patent application Ser. No. 11/304,658 filed Dec. 16, 2005.
FIELD OF THE INVENTION
[0002] The present invention relates to a method of producing
biodiesel from triglycerides using thermal cracking. The present
invention specifically relates to the production of biodiesel from
waste triglycerides.
BACKGROUND OF THE INVENTION
[0003] In recent years, the area of biodiesels has drawn a great
deal of attention. Biodiesels are plant and animal based fuels
produced from the esterification of biomass-derived oils with
alcohol. Biodiesel can be produced from such sources as canola,
corn, soybean etc. Biodiesels are generally considered less
environmentally damaging than traditional fossil fuels.
[0004] Another potential source for biodiesels is the waste
triglycerides of animal rendering facilities and waste cooking
oils, such as those found as restaurant trap greases. However, this
potential is presently still under-explored and waste triglycerides
are most commonly dumped into landfills ("Biodiesel Production
Technology, August 2002-January 2004"; Van Gerpen, J. et al., July
2004, NREL/SR-510-36244). Waste triglycerides often have a high
contaminants content that must effectively be removed before
processing. Furthermore, waste triglycerides tend to have a high
content of free fatty acid (FFA), anywhere in the range of from 50%
to 100%. Mixtures of free fatty acids and triglycerides have been
found to be very difficult to convert to useful fuels by any
traditional methods.
[0005] Traditional methods of producing biodiesels include
transesterification and esterification with alcohol using either an
acid or base catalyst. However, the high FFA content in waste
triglycerides causes undesirable soap formation in base catalyzed
esterification processes, rendering this process inoperable.
[0006] Waste triglycerides are also often heavily contaminated by
contaminants, such as bacteria, detergents, silts and pesticides.
These contaminants must be removed before esterification can take
place, without adding significant additional cost to the overall
processes.
[0007] One known method of processing high FFA feedstocks involves
adding glycerol to the feedstock to convert FFA's to mono- and
diglycerides, followed by conventional alkali-catalyzed
esterification. This method addresses the high FFA content of waste
triglycerides, but does not treat or remove contaminants. A second
method involves performing both esterification and
transesterification of triglycerides using a strong acid such as
H.sub.2SO.sub.4. However, water formation by FFA esterification
prevents this process from going to completion. A third method
involves pre-treating an FFA-rich triglyceride feedstock with an
acid catalyst to convert FFA to alkyl-esters and reduce FFA
concentrations to less than about 0.5%, followed by traditional
base-catalyzed esterification. This method again, only deals with
the FFA content of waste triglycerides, and not the high
contaminant levels.
[0008] Thermal cracking of clean triglycerides under typical
cracking conditions with and without catalyst has been attempted,
but this process was found to yield mainly naphtha, not diesel
fuels. Furthermore, in typical thermal cracking of clean or waste
triglycerides in the presence of a catalyst, there is a tendency
for coke formation to occur on the catalyst, resulting in rapid
deactivation.
[0009] It is therefore greatly desirable to find a method of
converting waste triglycerides feedstocks to biodiesel that is both
efficient and economical. It is also desirable to find ways of
dealing with contaminants and high FFA content in waste
triglyceride feedstocks so that they can be converted into usable
fuels.
SUMMARY OF THE INVENTION
[0010] The present invention thus provides a method of producing
biodiesel from a triglyceride feedstock, comprising pretreating the
triglyceride feedstock by thermal cracking or rapid pyrolysis to
remove contaminants and convert triglycerides, to form a middle
distillate fraction rich in free fatty acids. The middle distillate
fraction can then be esterified in the presence of an alcohol and a
catalyst to produce a mixed biodiesel/diesel stream. The mixed
biodiesel/diesel stream can then be treated with a basic solution
to convert unesterified free fatty acids to non-foaming metallic
soaps, which non-foaming metallic soaps can be removed by
centrifugation, filtering or a combination thereof.
[0011] The present invention also provides a method of producing a
biodiesel/naphtha mixture from a triglyceride feedstock. The method
involves first pretreating the triglyceride feedstock by thermal
cracking or rapid pyrolysis to remove contaminants and convert
triglycerides, to produce a middle distillate fraction rich in free
fatty acids, a naphtha stream and a gas stream. Next, the naphtha
stream and middle distillate fraction are esterified in the
presence of an alcohol and a catalyst to produce a mixed
biodiesel/naphtha stream. The mixed biodiesel/naphtha stream can
then be treated with a basic solution to convert unesterified free
fatty acids to non-foaming metallic soaps, which non-foaming
metallic soaps are removed by centrifugation, filtering or a
combination thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The present invention will now be described in further
detail with reference to the following drawings, in which:
[0013] FIG. 1 is a flow sheet of a first preferred process for
carrying out the present invention; and
[0014] FIG. 2 is a flow sheet of a second preferred process for
carrying out the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] The present process employs a novel combination of thermal
cracking followed by esterification to convert low quality
triglycerides feedstock into usable biodiesel. In the present
process, thermal cracking is used as a pre-treatment step to break
down the triglycerides into a broad range of free fatty acids and
lower molecular weight components. Thermal cracking also serves to
remove contaminants found in waste triglycerides, which can cause
problems downstream. The resulting product from the cracking step
can then be esterified to convert fatty acids into alkyl esters
(biodiesel).
[0016] For the purposes of the present invention, thermal cracking
is considered to loosely cover the process of breaking down large
molecules into smaller molecules at a predetermined temperature and
pressure. Rapid pyrolysis of waste triglycerides can also be used
in the present process and is considered to be encompassed by the
term thermal cracking. Details of rapid pyrolysis are given
below.
[0017] A flow diagram of the process steps and streams of one
embodiment of the present invention is shown in FIG. 1. A feedstock
12 of low quality or waste triglycerides is fed to a thermal
cracking unit 10. The feedstock 12 can be any variety of waste
triglyceride, including restaurant trap greases, waste greases from
animal rendering facilities and other forms of waste oils and
greases and low-quality vegetable oils. The feedstock stream 12 can
be heterogeneous in nature and can contain water and other
contaminants. Waste triglycerides used as the feedstock stream 12
can also have free fatty acid (FFA) content as high as 50 to 100
wt. %. In an optional embodiment (not shown), the triglyceride
feedstock 12 may be filtered to remove any macroscopic contaminant
particles prior to thermal cracking.
[0018] In the thermal cracking unit 10, triglycerides in the
feedstock stream 12 are significantly reduced since they are
converted into free fatty acids, thus forming a mixture of free
fatty acids and conventional hydrocarbons, such as paraffins,
olefins and aromatics. Thermal cracking is preferably carried out
at mild cracking conditions which, for the purposes of the present
invention, are described as an operating temperature preferably in
the range of from 390 to 460.degree. C., more preferably from 410
to 430.degree. C., and preferably at an operating pressure of from
0 to 60 psig (6.9 to 515 kPa), more preferably from 30 to 40 psig
(308 to 377 kPa). Thermal cracking produces various fractions
including gases 14, naphtha 16, middle distillate 22, and residue
18. Contaminants from the feedstock 12 end up in the residue stream
18.
[0019] It was noted that the mild thermal cracking conditions used
in the present invention to crack waste triglycerides produces
mainly diesel, having a boiling range of between 165.degree. C. and
345.degree. C., rather than naphtha (IBP to 165.degree. C.), as was
produced from thermal cracking of triglycerides at higher
temperatures and pressures.
[0020] The middle distillate fraction 22 makes up more than half of
the thermally cracked product and has been found to have suitable
characteristics for further treatment by esterification. The middle
distillate fraction 22 comprises free fatty acids formed from
thermal cracking of triglycerides, the original free fatty acids
present in the feedstock and conventional hydrocarbons. Middle
distillates typically encompass a range of petroleum equivalent
fractions from kerosene to lubricating oil and include light fuel
oils and diesel fuel. In one embodiment of the present invention
the middle distillate fraction 22 was found to have a boiling point
range of from 150 to 360.degree. C., and more preferably from 165
to 345.degree. C. The middle distillate fraction 22 still has some
fuel quality issues such as high viscosity, high acid number, high
cloud point and high concentrations of nitrogen and/or sulphur.
[0021] The middle distillate fraction 22 is next fed to an
esterification unit 20, where it is reacted with an alcohol stream
24 in the presence of a catalyst to produce alkyl esters
(biodiesel). The esterification process is carried out at a
temperature preferably ranging from 70 to 120.degree. C., more
preferably in the range of from 90 to 110.degree. C., and
preferably at atmospheric pressure. The alcohol stream 24 can be
any suitable alcohol known in the art, or mixtures thereof. The
alcohol stream 24 is preferably methanol.
[0022] It is surprisingly noted that esterification could be
carried out well above the boiling temperature of the reacting
alcohol, despite low alcohol concentration in the liquid phase of
the reaction mixture. The ability to conduct the esterification at
higher temperatures is advantageous since this allows continuous
water stripping by the flashing alcohol stream. Since water is a
co-product of acid esterification, it can detrimentally quench the
esterification reaction if not removed continuously.
[0023] The catalyst can be either an acidic solid or liquid
catalyst. Preferably, the acid catalyst is chosen from sulphuric
acid (H.sub.2SO.sub.4(l)), sulphamic acid
(H.sub.2NSO.sub.3H.sub.(l)), formic acid (HCO.sub.2H.sub.(l)),
acetic acid (CH.sub.3CO.sub.2H.sub.(l)), propionic acid
(CH.sub.3CH.sub.2CO.sub.2H.sub.(l)), hydrochloric acid
(HCl.sub.(l)), phosphoric acid (H.sub.3PO.sub.4(l)), sulphated
metal oxides such as sulphated zirconia, and styrene divinylbenzene
copolymers having SO.sub.3H functional groups, such as Amberlyst
36.TM.. Amberlyst 36 is most preferred for the esterification
reaction, as this does not leave any trace in the esterification
product, and further washing of the esterification product is thus
not required.
[0024] Free fatty acids can be acid esterified by the following
reaction, here shown with the alcohol optionally being methanol:
##STR1##
[0025] The water byproduct can inhibit the reaction, and may
prevent esterification from going to completion. As mentioned
above, esterification at temperatures above the boiling temperature
of the alcohol has been surprisingly found to alleviate this
problem in the present invention.
[0026] Esterification produces a raw diesel stream 26 of
approximately 50% alkyl esters (biodiesel) and 50% hydrocarbons.
These hydrocarbons can include tetradecane, pentadecane,
1-hexadecene, hexadecane, heptadecane, 1-octadecene, octadecane,
nonadecane, 1-eicosene, eicosane, heneicosane, 1-docosene,
docosane, tricosane, tetracosane, pentacosane, hexacosane,
heptacosane, octacosane, nonacosane, triacontane, untriacontane,
dotriacontane, tritriacontane, tetratriacontane, pentatriacontane,
hexatriacontane, heptatriacontane, and octatriacontane.
[0027] It should be noted that, in addition to esterifying only the
middle distillates fraction 22 from thermal cracking, it is also
possible to esterify both the naphtha stream 16 and middle
distillates fraction 22 from the thermal cracking step. This
optional method circumvents an extra step of separating naphtha 16
from the middle distillates 22.
[0028] Depending on the type of catalyst used and the degree of
esterification achieved, the raw diesel stream 26 may exceed
acidity limits allowed by ASTM specifications for biodiesel, namely
0.8 mg KOH/g. To reduce acidity, the raw diesel stream 26 can
optionally be fed to a base treatment unit 30, together with a
basic solution 28. The basic solution 28 reacts with any unreacted
fatty acids in the raw diesel stream 26 to produce non-foaming
metallic soaps with low solubility in biodiesel. These non-foaming
metallic soaps can then be removed by either centrifugation or
filtering or a combination thereof. Base treatment is preferably
carried out at temperatures of from 30 to 60.degree. C., and more
preferably at temperatures of from 40 to 50.degree. C. and
preferably at atmospheric pressure. The basic solution is
preferably chosen from lithium hydroxide (LiOH), magnesium
hydroxide (Mg(OH).sub.2), and calcium hydroxide (Ca(OH).sub.2).
Most preferred are LiOH and Ca(OH).sub.2.
[0029] The base treatment step results in a mixed biodiesel/diesel
product 32 that has been found to have excellent fuel properties.
The boiling point of the resultant biodiesel/diesel product 32 is
found to be lighter and the boiling point distribution broader than
that of biodiesel produced by conventional transesterification
alone. The mixed biodiesel/diesel product 32 can be used both neat
or can optionally be further blended with regular diesel.
[0030] The naphtha stream 16 from the thermal cracking unit 10
contains oxygenates and can optionally be sold as a valuable
by-product such as octane improver. The residue stream 18 can be
discarded by well known means in the art.
[0031] As mentioned earlier, the step of thermal cracking can
optionally be replaced by a step of rapid pyrolysis. This process
is shown in FIG. 2. Rapid pyrolysis is a process of decomposing a
chemical at very high temperatures and in the absence of an
oxidizing agent. Rapid pyrolysis has very short residence times
when compared to thermal cracking.
[0032] In the present invention, rapid pyrolysis of triglycerides,
more specifically trap grease, was conducted at temperatures
ranging from 480.degree. C. to 600.degree. C. for approximately 2
seconds. The triglycerides 12 are fed to a fluidized bed reactor 34
which is preferably fluidized with steam 36, although other
suitable fluidizing media known in the art can also be used and are
encompassed by the present invention. Steam 36 may be fed to the
reactor at a ratio ranging from 0.5 to 1.5, relative to the
triglyceride feed stream. The preferred steam to triglyceride feed
ratio is 0.9.
[0033] Any known inert gas 38 can optionally be added to the
reactor to purge the reactor of free oxygen during pyrolysis. The
inert gas 38 is preferably nitrogen. A catalyst may also be added,
and suitable catalysts include, but are not limited to acid washed
activated carbon, calcined sewage sludge solids and silica sand,
such as silica alumina. The catalyst acts to enhance the selective
cracking of triglyceride molecules to largely free fatty acid
molecules.
[0034] Sample data of rapid pyrolysis conducted by the inventor on
a trap grease feedstock is listed in Table 1 below. The resultant
pyrolysis products are shown in Table 2. TABLE-US-00001 TABLE 1
Rapid pyrolysis conditions Run ID 261 265 253 Temperature (.degree.
C.) 511 575 580 Fluidizing media Steam Steam Steam Steam/Feed ratio
.about.0.9 .about.0.9 .about.0.9 by weight N.sub.2 purge/Feed
.about.7 .about.7 .about.7 ratio by weight Catalyst Acid washed
Sewage sludge Silica sand activated solids, carbon, 35 calcined at
mesh minus 750.degree. C. Gas phase .about.2 .about.2 .about.2
contact time (s)
[0035] TABLE-US-00002 TABLE 2 Rapid Pyrolysis Products 261 265 253
Gas 28.2 11.3 7.6 Liquid 50.3 89.4 90.7 Solids (coke) 9.0 Trace 1.4
Total above 87.5 100.7 99.7
[0036] The liquid fraction identified in Table 2 above contains
middle distillates 22 as well as naphtha 16 and some residue 18.
The boiling point distribution of the liquid fraction was
determined by thermogravimetric analysis (TGA) and is given in
Table 3 below. The middle distillates yield is given in Table 4.
These tables indicate that rapid pyrolysis of triglycerides
produces an even larger proportion of desirable middle distillates
than thermal cracking. TABLE-US-00003 TABLE 3 Boiling point
distribution of the liquid fraction (from TGA) 261 265 253 Naphtha
(IBP.about.165.degree. C.) 86% 10% 8% Middle distillate
(165.about.345.degree. C.) 12% 75% 64% Residue (345.degree. C.
plus) 2% 15% 28%
[0037] TABLE-US-00004 TABLE 4 Middle distillate yield with respect
to feed 261 265 253 Middle distillate (wt % of feed) 6% 67% 58%
[0038] The middle distillate fraction 22 produced by rapid
pyrolysis was found to have varying free fatty acids (FFA) content,
depending on the pyrolysis conditions. These details are shown in
Table 5 below: TABLE-US-00005 TABLE 5 Fatty acids in the middle
distillate fraction Run ID 261 265A 265B 253 Pyrolysis Temperature
(.degree. C.) 511 575 575 580 Total FFA wt % 0.63 45.70 45.50
33.17
[0039] The present inventor noted that the largest middle
distillates fraction was produced by rapid pyrolysis at a
temperature of 575.degree. C. As well, FFA content was highest for
this temperature range. A preferred temperature range for rapid
pyrolysis of the present process is therefore from 550.degree. C.
to 600.degree. C. and a most preferred range is from 565.degree. C.
to 585.degree. C.
[0040] The difference in middle distillates yield between the run
at 575.degree. C. and the run at 580.degree. C. is thought to be
due to the difference in catalysts rather than the small difference
in temperature. Catalyst derived from sewage sludge is less acidic
than silica sand. Thus, although the run with silica sand produced
a slightly larger liquids fraction by deoxygenation, this was
accompanied by higher coke and residue formation, resulting in an
overall lower level of middle distillates. Thus the sewage sludge
appears to provide a preferred balance between higher middle
distillate yield and lower coke formation.
[0041] It has also been noted that the middle distillate stream
produced by rapid pyrolysis comprises practically no nitrogen.
Nitrogen content in the middle distillate obtained by mild thermal
cracking was in the order of 5200 ppm whereas that in the middle
distillate obtained by rapid pyrolysis was 0.3 ppm. This is
particularly advantageous since the presence of nitrogen diminishes
the quality of the final biodiesel product.
[0042] As well, total sulphur in the middle distillate obtained by
mild thermal cracking was in the order of 500 ppm whereas that in
the middle distillate obtained by rapid pyrolysis was 150 ppm. Both
pre-treatment steps produce free fatty acids and other components
containing sulphur and nitrogen. However, it is thought that
products from rapid pyrolysis leave the reactor before the sulphur
and nitrogen-containing components start to react with each other
and become an integral part of the middle distillates fraction.
Once nitrogen and sulphur enter the middle distillate stream, it
can be very difficult to remove them from the final alkyl ester
(biodiesel) product.
[0043] The following examples serve to better illustrate the
process of the present invention, without limiting the scope
thereof:
EXAMPLE 1
Conversion of Restaurant Trap Grease into Mixed Biodiesel/Diesel
Product
[0044] Restaurant trap grease having an average density of 0.925
g/mL was fed to a thermal cracking unit where it was cracked at a
temperature of 418.5.degree. C. and a pressure of 29 psig (301 kPa)
for 40 minutes. Thermal cracking produced a gas stream, a naphtha
stream, a middle distillate stream with a maximum boiling point of
approximately 343.degree. C., as well as water and residue. The
middle distillates stream made up 63.0 wt % of the total cracked
product and had an acid number of 83.93 mg KOH/g.
[0045] The middle distillate stream was then fed to an acid
esterification unit, where it was contacted with methanol in the
presence of an Amberlyst 36 catalyst. Esterification was conducted
at a temperature of 90.degree. C. and at atmospheric pressure for
20 hours.
[0046] Esterification produced a raw diesel stream which was then
treated with a calcium hydroxide solution, Ca(OH).sub.2(aq), to
produce a final mixed biodiesel/diesel product having an acid
number of 0.45 mg KOH/g. The final product was found to have 0.22
wt. % nitrogen, 136 ppm sulphur and a viscosity of 5.02 cSt; the
sulphur content and viscosity being well within ASTM 6751 standards
for biodiesel
EXAMPLE 2
Conversion of Rendered Animal Fat into Mixed Biodiesel/Diesel
Product
[0047] Rendered animal fat, having an average density of 0.918 g/mL
was fed to a thermal cracking unit in which it was cracked at
411.degree. C. and atmospheric pressure for 40 minutes. The
thermally cracked product contained 68.6 wt % middle distillates
having a maximum boiling point of 345.degree. C., naphtha and the
remainder gas, water and residues.
[0048] The middle distillate stream, having a viscosity of 8.50
cSt, and an acid number of 146.96 mg KOH/g, was then fed to an acid
esterification unit, where it was contacted with methanol in the
presence of an Amberlyst 36 catalyst. Esterification was conducted
at a temperature of 90.degree. C. and at atmospheric pressure for
20 hours.
[0049] The resultant raw diesel stream was then treated with a
calcium hydroxide solution, Ca(OH).sub.2(aq), to produce a final
mixed biodiesel/diesel product having an acid number of 0.75 mg
KOH/g. The final product was found to have 18 ppm sulphur and 158
ppm nitrogen, and a viscosity of 4.84 cSt.
[0050] This detailed description of the process and methods is used
to illustrate certain embodiments of the present invention. It will
be apparent to those skilled in the art that various modifications
can be made in the present process and methods and that various
alternative embodiments can be utilized. Therefore, it will be
recognized that various modifications can also be made to the
applications to which the method and processes are applied without
departing from the scope of the invention, which is limited only by
the appended claims.
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