U.S. patent application number 13/812815 was filed with the patent office on 2013-05-16 for thermal treatment.
This patent application is currently assigned to Aston University. The applicant listed for this patent is Anthony Victor Bridgwater, Gouzhan Jiang. Invention is credited to Anthony Victor Bridgwater, Gouzhan Jiang.
Application Number | 20130118886 13/812815 |
Document ID | / |
Family ID | 42984470 |
Filed Date | 2013-05-16 |
United States Patent
Application |
20130118886 |
Kind Code |
A1 |
Bridgwater; Anthony Victor ;
et al. |
May 16, 2013 |
Thermal Treatment
Abstract
The invention provides methods and apparatus for thermal
treatment, e.g. for pyrolysis of lignin. The lignin is provided to
a reaction chamber as a paste, which can reduce or avoid process
difficulties encountered when heating lignin.
Inventors: |
Bridgwater; Anthony Victor;
(Solihull, GB) ; Jiang; Gouzhan; (Birmingham,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bridgwater; Anthony Victor
Jiang; Gouzhan |
Solihull
Birmingham |
|
GB
GB |
|
|
Assignee: |
Aston University
Birmingahm
GB
|
Family ID: |
42984470 |
Appl. No.: |
13/812815 |
Filed: |
August 19, 2011 |
PCT Filed: |
August 19, 2011 |
PCT NO: |
PCT/GB2011/001255 |
371 Date: |
January 28, 2013 |
Current U.S.
Class: |
201/20 ;
202/105 |
Current CPC
Class: |
Y02E 50/14 20130101;
C10C 5/00 20130101; D21C 11/125 20130101; Y02E 50/10 20130101; C10B
53/02 20130101; D21C 11/0007 20130101; C10B 47/24 20130101; C10G
1/002 20130101 |
Class at
Publication: |
201/20 ;
202/105 |
International
Class: |
C10B 53/02 20060101
C10B053/02 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 20, 2010 |
GB |
1014020.0 |
Claims
1. A process for the pyrolysis of lignin comprising the steps: (a)
feeding a paste comprising lignin into a reaction chamber; and (b)
performing pyrolysis on the paste in the reaction chamber.
2. A process according to claim 1 wherein the paste is a mixture of
lignin with one or more further components.
3. A process according to claim 2 wherein the paste is a suspension
of lignin in a further component.
4. A process according to claim 3 wherein a portion of the lignin
is dissolved in the at least one further component and a portion of
the lignin is suspended in the further component.
5. A process according to claim 2 wherein the mass ratio of lignin
to the further component is from 1:5 to 10:1.
6. A process according to claim 2 wherein the further component is
a polar solvent.
7. A process according to claim 6 wherein the further component is
an alcohol.
8. A process according to claim 7 wherein the further component is
methanol.
9. A process according to claim 2 wherein the further component is
a non-polar compound.
10. A process according to claim 2 wherein the process further
comprises the step of mixing together lignin and the one or more
further components to form the paste.
11. A process according to claim 1 wherein the temperature inside
the reaction chamber is at least 300.degree. C. when the paste is
fed into the chamber.
12. A process according to claim 1 wherein the reaction chamber is
a fluidised bed reaction chamber, a fixed bed reaction chamber or a
heated vessel.
13. A process according to claim 1 wherein the paste is fed into
the reaction chamber via a feeding assembly, the feeding assembly
being provided with a cooling system.
14. A process according to claim 13 comprising feeding the paste
into the reaction chamber at a position toward or at the base of
the reaction chamber.
15. A process according to claim 1 wherein agitation is provided to
the interior of the reaction chamber during feeding and/or
pyrolysis.
16. Apparatus for the pyrolysis of lignin, comprising: a pyrolysis
reaction chamber; and a feeding assembly adapted to supply paste
comprising lignin into the reaction chamber.
17. Apparatus according to claim 16 further comprising a paste
supply.
18. Apparatus according to claim 16 wherein the feeding assembly is
provided with a cooling system.
19. Apparatus according to claim 16 wherein the feeding assembly is
arranged to deliver paste to the reaction chamber at a position
toward or at the base of the reaction chamber.
20. Apparatus according to claim 19 further comprising an agitator
arranged to provide agitation in the reaction chamber.
Description
BACKGROUND TO THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to thermal treatment, such as
thermal treatment of lignin, and apparatus for thermal treatment
e.g. of lignin. In particular, it relates to pyrolysis of
lignin.
[0003] 2. Related Art
[0004] Lignin is a component of cell walls of plants. It provides
strengthening support to trees, and contributes to enabling plants
to conduct water efficiently.
[0005] Lignin is available as a by-product of industrial processes
including pulping and paper making. In these processes, lignin may
be removed from plant material such as wood, and so may be produced
as a by-product.
[0006] Processing of lignin is of particular interest because it
can result in the production of useful and valuable products, such
as phenolic compounds. Phenolic compounds include those having the
moiety Ph-O--, wherein the phenyl group may be further substituted.
Examples include phenol, catechol, guaiacol, syringol and vanillin.
Other products of lignin processing include aromatic hydrocarbon
products, for example benzene, toluene and naphthalene.
[0007] The phenolic compounds produced from lignin processing may
be useful as they are, or as starting materials in chemical
synthesis of other products.
[0008] Processing of lignin into phenolic compounds has been
attempted since the beginning of modern paper and pulp industry
because of its aromatic nature (1). In recent years, with an
increasing production of cellulosic ethanol and the use of
organosolv pulping processes, lignin processing has become more
urgent and challenging. This is because the lignin produced in
these two processes may not be burned to get process energy and to
recycle pulping agents. In the Kraft pulping process, in contrast,
lignin by-product can be recycled and used in the process (2,
3).
[0009] Lignin may be processed by pyrolysis in order to produce,
among other products, phenolic compounds. Pyrolysis is thermal
decomposition of a substance (e.g. biomass, or lignin) in the
substantial absence of oxygen (21).
[0010] The rate and extent of decomposition of the substance
subjected to pyrolysis depends on the process parameters of the
pyrolysis, for example the rate of heating of the substance, the
mode of heating the substance, and the residence time of the
products. In turn, these process parameters may also have an effect
on the subsequent behaviour of the product, e.g. by secondary
reactions such as cracking (of the higher molecular mass products)
or condensation reactions (of lower molecular mass products).
[0011] Pyrolysis can be carried out using fast heating rates and
short hot vapour residence times. Such "fast" pyrolysis processes
are reviewed in Bridgwater et al (10, 22), which focuses on
pyrolysis of biomass. For example, fast pyrolysis may employ
reaction temperatures of about 500.degree. C. and hot vapour
residence times of less than around 1 second.
[0012] In general, pyrolysis is a relatively simple process, which
can be conducted at atmospheric pressure. However, pyrolysis of
lignin (e.g. lignin derived from plant material such as wood) has
not been straightforward. This is at least in part due to the low
melting point range of lignin (80-200.degree. C.), and the fact
that lignin, and particularly lignin melt, is very adhesive. As a
result, it tends to melt before entering a pyrolysis reaction
chamber, which is usually above about 500.degree. C., leading to
blocking of the feeding system. In addition, lignin tends to cause
char and other solids present in the reaction chamber to
agglomerate. This can lead to the formation of solid deposits, for
example on the feeding system and reaction chamber walls. This can
block the reactor and stop it from functioning properly.
[0013] In the case of a fluidised bed pyrolysis reactor, pyrolysis
of the melted lignin tends to produce a char agglomerate with the
solid particles (e.g. sand) of the fluidised bed, which forms large
pieces, leading to defluidization of the bed.
[0014] These problems have significantly limited the success of
reported lignin pyrolysis. Some papers report success in
micro-scale experiments with a sample size of milligrams (4, 5 and
6).
[0015] There are some reports of bench-scale pyrolysis. In 1980s,
Kaminsky et al (7) studied the fast pyrolysis of ethanol lignin and
Kraft lignin using fluid bed reactor. The use of screw feeders was
not successful due to the blockage at the end of the screw. Finally
they compressed the lignin into pellets with the addition of 3%
stearic acid and 2% polyvinylpyrrolidone and fed the pellets
batchwise from the top of the reactor via two air-lock valves in
serial. However, the maximum feeding was only 30-40 g because of
the defluidization caused by char-sand agglomeration.
[0016] Fluid bed reactor bench-scale pyrolysis of lignin has been
conducted at Aston University (UK) (8) and ECN (Netherlands) (9).
The work at Aston allowed only several grams of feeding. ECN tested
two types of feeding methods to a fluid bed reactor. One was
batchwise, in which 50 g Alcell lignin was fed into the reactor.
The reactor was defluidised immediately. ECN also designed a new
type of screw feeder with a cooling system in the centre of the
screw. Two hours' continuous running was achieved at 400.degree. C.
This is a rather low temperature for lignin pyrolysis. They did not
report the results of higher temperature. Probably, the screw
feeder did not work well at high temperatures due to the effect of
the cooling system reducing at these higher temperatures.
SUMMARY OF THE INVENTION
[0017] The present inventors have devised the present invention in
order to address one or more of the above problems.
[0018] The present inventors have found that providing lignin to a
pyrolysis reactor in the form of a paste can reduce the problems
discussed above, associated with the low melting point and
adhesiveness of lignin.
[0019] Accordingly, in a preferred aspect the present invention
provides a process for the pyrolysis of lignin comprising the
steps: [0020] (a) feeding a paste comprising lignin into a reaction
chamber; and [0021] (b) performing pyrolysis on the paste in the
reaction chamber.
[0022] In a further preferred aspect, the present invention
provides apparatus for the pyrolysis of lignin, comprising [0023] a
pyrolysis reaction chamber; and [0024] a feeding assembly adapted
to supply paste comprising lignin into the reaction chamber.
[0025] The apparatus may comprise a paste supply.
[0026] It will be understood that the present invention is also
applicable to pyrolysis of substances other than lignin. In
particular, it is applicable to other substances which are
similarly difficult to pyrolyse, for example due to difficulty of
feeding the substances into the reaction chamber, and/or problems
associated with agglomeration in the reaction chamber. For example,
the present invention may be applicable to pyrolysis of substances
which have a melting point below typical pyrolysis temperatures,
such as substances with similar melting points to lignin. In the
following discussion of optional features of the invention, it will
be understood that references to lignin are also applicable to
other substances which may be pyrolysed in accordance with the
present invention.
[0027] Preferably, the paste is a mixture of lignin with one or
more further components. The present inventors have found that
lignin is able to form a stable paste, when mixed with a further
component, without phase separation after several days'
standing.
[0028] For example, the paste may be a suspension of lignin in a
further component, for example in a liquid. In this way, the lignin
may be the internal phase of the suspension, and the liquid may be
the external phase of the suspension.
[0029] It may be preferred that a portion of the lignin is
dissolved in the liquid, and a portion of the lignin is suspended
in the liquid. For example, lower molecular weight lignin fractions
may be dissolved, and higher molecular weight lignin fractions may
be suspended. It is believed that dissolving a portion of the
lignin in this way may contribute to the reduction in problems
associated with lignin melting and adhesion discussed above.
[0030] The mass ratio of lignin to the further component may range
from 1:5 to 10:1. Preferably, the mass ratio of lignin to the
further component is at least 1:2, more preferably at least 1:1.
Preferably, the mass ratio of lignin to the further component is
not more than 10:1, more preferably not more than 5:1, 4:1 or 3:1.
In a particularly preferred embodiment, the mass ratio of lignin to
the further component may be from 1:1 to 3:1, for example from
1.5:1 to 2.5:1. Most preferably, the ratio is 2:1.
[0031] The viscosity of the paste may range from a lower limit at
which the viscosity is approximately equal to or slightly higher
than the viscosity of the further component alone (for example, the
viscosity of the further component alone at 25.degree. C. at
atmospheric pressure), to an upper limit where it is significantly
more viscous than the further component but still flowable into the
reaction chamber. For example, the paste may be a slurry.
[0032] It will be understood that the present invention is
particularly applicable to extracted lignin, e.g. lignin which has
been extracted from biological material, such as plant material.
The lignin may be provided to the paste in the form of lignin
powder or granules.
[0033] Suitable sources of lignin (e.g. extracted lignin) include
lignin produced in processes for the production of cellulosic
ethanol, and pulping processes such as organosolve pulping
processes. For example, when cellulose is hydrolyzed into sugars
for fermentation to ethanol, typically the insoluble residue
includes lignin and incompletely hydrolysed cellulose. This solid
residue may be used in the process of the invention. The proportion
of lignin included in the residue may be increased by dissolving
the lignin from the cellulose then precipitating it.
[0034] Accordingly, the skilled person will understand that in some
embodiments the lignin (e.g. extracted lignin) may be provided to
the paste as a lignin-containing composition. Typically, the
lignin-containing composition comprises at least 50 wt % lignin,
more preferably at least 60 wt %, at least 65 wt %, at least 70 wt
%, at least 75 wt % or at least 80 wt % lignin. The
lignin-containing composition may comprise 100 wt % of lignin, or
may comprise 99 wt % or less, 98 wt % or less, 97 wt % or less, 96
wt % or less, 95 wt % or less, 93 wt % or less, or 90 wt % or less
of lignin.
[0035] The further component may be any substance which is capable
of forming a paste when it is mixed with lignin. Preferably, the
further component is capable of dissolving a portion of the lignin
and suspending a portion of the lignin, as described above.
[0036] It may be preferred that the further component is a
liquid.
[0037] Particularly preferred as the further component is a polar
compound, for example a polar solvent. The term polar solvent is
well understood by the skilled person. It will be understood that
the use of the word solvent here does not imply that the lignin is
dissolved, either fully or partially, in the solvent (although
partial dissolving may be preferred as discussed above). Rather,
the use of this term is based on the inventors' realisation that
compounds commonly employed as polar solvents are particularly
useful as components of the paste in the present invention.
[0038] The polar solvent may be, for example a polar organic
solvent. The polar solvent may be a polar protic solvent, or a
polar aprotic solvent. Of course, these terms are well understood
by those skilled in the art.
[0039] Examples of polar solvents (protic and aprotic) useful as
the further component include water, alcohols, ethers, esters,
amides, ketones, haloalkyls, sulfoxides, nitriles and organic acids
such as carboxylic acids.
[0040] Examples of suitable polar solvents for use as the further
component include methanol, ethanol, n-propanol, i-propanol,
n-butanol, i-butanol, t-butanol, methanoic acid, ethanoic acid,
propionic acid, butyric acid, ethyl acetate, acetone,
dimethylformamide (DMF), dichloromethane (DCM), tetrahydrofuran
(THF), acetonitrile and dimethylsulfoxide (DMSO).
[0041] Most preferably, the further component is an alcohol.
[0042] Where the further component is an alcohol, it may be a
C.sub.1-C.sub.10 alcohol, for example C.sub.1-C.sub.4 alcohol. The
alcohol may have the formula R.sup.1--OH, wherein R.sup.1 is
C.sub.1-C.sub.10 alkyl, alkenyl or alkynyl which may be straight,
branched or cyclic, preferably C.sub.1-C.sub.4 alkyl which may be
straight or branched, for example straight. R.sup.1 may be
substituted, for example, with zero, one, two or three
substituents. For example, the substituents may be selected from a
halogen atom and a further hydroxyl group. The halogen atom may be,
for example, fluorine, chlorine, bromine or iodine, preferably
chlorine. However, it may be preferred that R.sup.1 is
unsubstituted.
[0043] Particularly preferred alcohols include methanol, ethanol,
n-propanol, i-propanol, n-butanol, i-butanol and t-butanol. Most
preferred is methanol.
[0044] Methanol is particularly preferred, as it is believed to be
capable of dissolving a portion of the lignin, and suspending a
portion of the lignin, as described above.
[0045] The present inventors have also realised that the use of
alcohol, and particularly methanol, as the further component is
desirable, as it is a hydrogen rich material (11) and a potential
hydrogen transferring agent (12), for example due to thermal
decomposition of the alcohol. This may reduce the formation of
char, which may further reduce the problems associated with char
agglomeration during pyrolysis.
[0046] As an alternative to the polar compounds discussed above,
non-polar compounds are also suitable the further component. For
example, hydrocarbons such as alkanes, alkenes or alkynes may be
suitable. Preferred are C.sub.1-C.sub.15 hydrocarbons, such as
C.sub.1-C.sub.15 alkanes or alkenes, more preferably
C.sub.1-C.sub.15 alkanes. More preferred at are C.sub.1-C.sub.10
hydrocarbons, such as C.sub.1-C.sub.10 alkanes or alkenes, more
preferably C.sub.1-C.sub.10 alkanes. Most preferred are
C.sub.5-C.sub.15, or C.sub.5-C.sub.10, hydrocarbons, such as
C.sub.5-C.sub.15, or C.sub.5-C.sub.10, alkanes or alkenes, more
preferably C.sub.5-C.sub.15, or C.sub.5-C.sub.10, alkanes.
[0047] It may be preferred that the further component(s) are
sourced from renewable sources. For example, the further component
may be bio-ethanol, or a vegetable oil. Alternatively, bio-diesel
(esterified vegetable oil) may be used. In this way, the pyrolysis
products (e.g. phenolic compounds) may be derived from
substantially or entirely renewable starting materials.
[0048] It will be understood that the paste may comprise a mixture
of one or more further components, for example a mixture of one or
more of the further components described above.
[0049] The process may further comprise the step, before the paste
is fed into the reaction chamber, of mixing together lignin and one
or more further components (for example, a further component as
described above) in order to form the paste. For example, extracted
lignin or lignin powder/granules may be mixed with one or more
further components in order to from the paste.
[0050] Similarly, the apparatus may include a mixing chamber for
mixing together lignin and one or more further components to form a
paste for introduction into the reaction chamber. The feeding
assembly of the apparatus may be arranged to convey the paste from
the mixing chamber into the reaction chamber.
[0051] The reaction chamber may be at a pyrolysis temperature when
the paste is fed into the chamber. For example, the temperature
inside the reaction chamber may be at least 300.degree. C., at
least 400.degree. C., or at least 500.degree. C. when the paste is
fed into the chamber. Preferably, the temperature inside the
reaction chamber is not more than 900.degree. C., for example not
more than 800.degree. C., not more than 700.degree. C., not more
than 650.degree. C. or not more than 600.degree. C. when the paste
is fed into the chamber.
[0052] During pyrolysis, the temperature inside the reaction
chamber may be at least 300.degree. C., at least 400.degree. C., or
at least 500.degree. C. Preferably, the temperature inside the
reaction chamber is not more than 900.degree. C., for example not
more than 800.degree. C., not more than 700.degree. C., not more
than 650.degree. C. or not more than 600.degree. C. during
pyrolysis.
[0053] The pyrolysis of lignin may be "fast" pyrolysis. For
example, the residence time of hot vapour products of the pyrolysis
in the reaction chamber may be less than a minute, for example less
than 30 s, 20 s, 10 s or 5 s. Most preferably, the residence time
of the hot vapour products may be less than 1 s, or may be less
than 2 s.
[0054] The reaction chamber may be, for example, a fluidised bed
reactor, or a fixed bed reactor. The present invention is
particularly relevant to these types of pyrolysis reactors. This is
because lignin can cause agglomeration of solid particles of a
fluidised bed (e.g. silica particles) causing defluidization.
Similarly, agglomeration of lignin and/or char can cause pressure
drop in fixed bed reactors. The present inventors have found that
processes and apparatus according to the present invention can
reduce these problems.
[0055] In embodiments employing a fluidised bed reactor, the bed
may comprise silica sand, for example having a diameter in the
range 150 to 300 .mu.m. Nitrogen may be employed as a fluidising
gas. The fluidising gas may be heated before it enters the reaction
chamber.
[0056] Alternatively, the reaction chamber may be a heated
vessel.
[0057] A feeding assembly may be provided, for feeding the paste
into the reaction chamber. For example, the feeding assembly may
comprise a tube, channel or screw feeder. The paste may be extruded
into the chamber via the feeding assembly. The paste may be
extruded into the chamber due to pressure exerted on the paste in
order to move it into the reactor. For example, the pressure may be
provided by gas flow, for example nitrogen flow.
[0058] The feeding assembly may be made from an insulating
material, to reduce heat transfer from the reaction chamber to the
paste as it is fed into the chamber. For example, the feeding
assembly may be made from PTFE. For example, it may be a PTFE
tube.
[0059] A cooling system may be provided to the feeding assembly.
For example, a water cooling system may be provided. In one
embodiment, the feeding assembly may comprise a PTFE tube cooled by
a water cooling system.
[0060] The process of the present invention may comprise feeding
the paste into the reaction chamber at a position toward or at the
base of the reaction chamber. This can reduce lignin and char build
up in the interior of the reaction chamber, for example on the
reaction chamber walls. For example, the process may comprise
feeding the paste into the reaction chamber at a position in the
lower half of the reaction chamber. In the case of a fluidised bed
reactor, it is particularly preferred that the process comprises
feeding the paste into the reaction chamber at a position below the
level of the fluidised bed.
[0061] In this way, the paste may be delivered directly into the
fluidised bed. The feeding assembly may by arranged in order to
deliver the paste to the reaction chamber at these preferred
positions.
[0062] The problems caused by adhesion of lignin and/or char to
components of the pyrolysis reactor, and by agglomeration of
lignin, char and/or the solid phase of a fluidised bed may be
further reduced by agitation during feeding and/or pyrolysis.
[0063] For example, an agitator may be provided to provide
agitation in the interior of the reaction chamber. The agitator may
be arranged to reduce build-up of deposits, for example deposits of
lignin and/or char, on the walls of the reaction chamber and/or on
the feeding assembly. In the case of a fluidised bed reactor,
alternatively or in addition, the same or an additional agitator
may be provided to agitate the fluidised bed. The agitator(s) may
be, for example, a stirrer.
[0064] Similarly, the process of the present invention may comprise
providing agitation to the interior of the reaction chamber during
feeding and/or pyrolysis. Agitation may be provided to reduce the
build-up of deposits, for example deposits of lignin and/or char,
on the walls of the reaction chamber and/or on the feeding
assembly. Alternatively or in addition, in the case of a fluidised
bed reactor, the process may comprise agitating the fluidised
bed.
[0065] As mentioned above, pyrolysis of lignin is of particular
interest as it results in the production of useful phenolic
products. In general, phenolic products are those including the
moiety Ph-O--, wherein the phenyl group may be further substituted.
In some cases, phenolic compounds may also include compounds
including a benzeneacetaldehyde moiety. Monomeric phenolic
compounds are those including only a single Ph-O-- moiety, or only
a single benzeneacetaldehyde moiety as the case may be.
[0066] Example phenolic compounds which may be produced from lignin
hydrolysis include phenol, guaiacol, 2-methylphenol,
2-methoxy-4-methylphenol, 2,3-dimethylphenol,
4-ethyl-2-methoxyphenol, 2-methoxy-4-vinylphenol, 1,2-benzenediol,
2,6-dimethoxyphenol (syringol), 3-methyl-1,2-benzenediol,
3,4-dimethoxyphenol, 4-methyl-1,2-benzenediol,
2-methoxy-4-(1-propenyl)phenol, 1,2,3-trimethoxybenzene, vanillin,
5-methyl-1,2,3-trimethoxybenzene,
1-(4-hydroxy-3-methoxyphenol)ethanone,
1-(2-hydroxy-5-methoxy-4-methylphenol)ethanone,
.beta.-phenyl-benzeneacetaldehyde,
2,6-dimethoxy-4-(2-propenyl)phenol,
2,5-dimethoxy-4-ethylbenzaldehyde,
4-hydroxy-3,5-dimethoxybenzaldehyde, 3,4,5-trimethoxybenzaldehyde,
1-(2,4,6-trimethoxy-3-methylphenyl)-1-butanone, and
(1,1'-biphenyl)-2,2'-dicarboxaldehyde.
[0067] One or more additives may be included in the process, for
example to enhance production of preferred products. For example,
the additives may be included to enhance the production of
particularly preferred phenolic products. Additives may be added to
the reaction chamber. For example, additives may be added to the
paste. For example, the additives may be added when the lignin is
mixed with the further component.
[0068] For example, one or more catalysts may be added to the
paste, or to the reaction chamber, for example in the fluidised
bed. Alternatively or in addition, a carbon dioxide absorber could
be included. This may be used to tune the pyrolysis reaction by
affecting the equilibrium.
[0069] The process of the present invention may comprise additional
steps. For example, the process may comprise removing pyrolysis
products from the reaction chamber. For example, hot vapour
products may be removed from the reaction chamber. Particulate
products may be present in the thus removed vapour. These may be
removed by any suitable method, for example using an electrostatic
precipitator and/or a cyclone.
[0070] The process may comprise additional cooling, condensation,
separation and/or purification steps, for obtaining the products of
pyrolysis, such as phenolic compounds.
[0071] Similarly, the apparatus of the present invention may
comprise a removal port for removing components from the reaction
chamber. It may comprise one or more components for removing
particulate from gaseous, vapour and/or liquid pyrolysis products,
such as an electrostatic precipitator and/or a cyclone.
Additionally, it may comprise one or more cooling assemblies,
condensation assemblies and/or separation assemblies for further
processing, separating and/or purifying the pyrolysis products.
[0072] Any of the preferred or optional features of any aspect may
be combined, either singly or in combination, or with any other
aspect, unless context demand otherwise.
BRIEF DESCRIPTION OF THE DRAWINGS
[0073] Preferred embodiments of the invention will now be
described, by way of example, with reference to the accompanying
drawings in which:
[0074] FIG. 1 shows apparatus for conducting pyrolysis of lignin
according to an embodiment of the invention.
[0075] FIG. 2 shows the molecular mass of oil collected in the
first oil pot in the pyrolysis processes carried out in the
Examples at various pyrolysis temperatures. Mn is number average
molecular mass, and Mw is weight average molecular mass.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS AND FURTHER
OPTIONAL FEATURES OF THE INVENTION
[0076] FIG. 1 shows pyrolysis apparatus according to an embodiment
of the invention. The apparatus includes a furnace 1, containing a
fluid bed reaction chamber 2, a cyclone 3 and a char pot 4. The
cyclone and the char pot are provided for removing and collecting
solid particles from the gasses leaving the reaction chamber 2. The
gasses leave the reaction chamber 2 via a removal port 5.
[0077] Nitrogen fluidising gas is provided to the fluid bed
reaction chamber 2 from a nitrogen cylinder 6.
[0078] The apparatus comprises a lignin paste feeder 7, located
above the reaction chamber 2. This is connected to the reaction
chamber 2 by a PTFE tube 8. The PTFE tube is held within a vertical
tube passing into the reaction chamber 2 and provided with a water
cooling jacket 9 (49.5.times.50 mm). "CW" indicates the input of
cold water, and "RW" indicates the output of water from the water
cooling jacket 9.
[0079] The lignin paste feeder 7 is provided with a nitrogen gas
source 10 to urge paste through the PTFE tube 8 into the reaction
chamber 2.
[0080] The reaction chamber 2 is additionally provided with a
stirrer 11 having several plate-shaped blade layers. The stirrer 11
is installed from the top of the vertical tube into the reaction
chamber. It is operable to break lignin char agglomerate in the
reaction chamber during the pyrolysis process.
[0081] As mentioned above, the reaction chamber 2 is connected to a
cyclone 3 and char pot 4, via a removal port 5. The char pot 4 is
located underneath the cyclone 3 for collecting solid particles,
e.g. char particles, from the gasses in the cyclone 3. The cyclone
3 is connected, in sequence, to a water condenser 12, an
electrostatic precipitator 13, two serial dry ice condensers 14 and
15 and a cotton filter 16. Oil pots 17, 18 and 19 are connected to
each of the dry ice condensers 14 and 15, and to the electrostatic
precipitator 13, for collecting condensate.
[0082] In the water condenser 12, "CW" indicates the input of cold
water, and "RW" indicates the output of water. The electrostatic
precipitator 13 is connected to a voltage multiplier 21.
[0083] A meter 20 is provided for metering the non-condensable
gasses. The non-condensable gasses are then directed to a venting
system. The venting system includes a gas chromatography
apparatus.
[0084] In an example process according to the present invention,
the reaction chamber 2 is heated to a pyrolysis temperature and the
bed is fluidised with heated nitrogen. The lignin paste is fed into
the heated reaction chamber 2 by connecting the lignin paste feeder
7 to a pressurised nitrogen line. The lignin paste is extruded into
the reaction chamber 2 as a thread. Pyrolysis gasses leave the
chamber via the removal port 5 and pass into the cyclone 3 where
solid particulate is collected in the char pot 4. The gasses then
enter, in sequence, the water condenser 12, the electrostatic
precipitator 13, the two serial dry ice condensers 14 and 15 and
the cotton filter 16. Condensate is collected in the oil pots 17,
18 and 19.
EXAMPLES
[0085] Materials
[0086] The Alcell lignin used in this work was supplied by Energy
Research Centre of Netherlands (ECN). The ash content of the lignin
was derived by ashing at 575.degree. C. for 3 hours (ASTM
E1534-93). The moisture content of the lignin was analysed using a
moisture analyser (Sartorius MA35), in which a sample of about 1 g
was placed in an aluminium pan and then dried at 105.degree. C. to
a constant weight. The reported data for ash and moisture content
was the average of three measurements. The volatiles and fixed
carbon was determined using a PerkinElmer Pyris 1 Thermogravimetric
analyser (TGA). The sample was heated from 105.degree. C. to
950.degree. C. at a heating rate of 10.degree. C./min under a
nitrogen atmosphere. The final weight after correction for ash and
moisture content was the fixed carbon. The volatiles were
calculated on a dry ash free basis as the difference between fixed
carbon and original weight.
[0087] The carbon, hydrogen and nitrogen contents in the sample
were analysed by Medac Ltd (Surrey, UK) by duplicate analysis. The
oxygen content was determined by difference. The analytical results
are given in Table 1.
TABLE-US-00001 TABLE 1 Proximate and elemental analysis of Alcell
lignin Proximate analysis (wt % daf) Moisture 2.23 Ash 0.18 Fixed
carbon 34.31 Volatiles 65.69 Pyrolysis temperature (.degree. C.)
396.1 CHNO analysis (wt % daf) Carbon 66.52 Hydrogen 5.94 Nitrogen
<0.10 Oxygen 27.54
[0088] Pyrolysis Procedure
[0089] All pyrolysis experiments were conducted in a 100 g/h fluid
bed fast pyrolysis reactor. The fluid bed reactor had an internal
diameter of 41 mm and a length of 250 mm, which was placed in a
furnace for heating it up. Nitrogen was used as the fluidising gas
on a once through basis. The volume flow rate of the nitrogen was
kept at 4 L/min (20.degree. C.), which gave a good bubbling fluid
bed. Silica sand with a diameter of 150-300 .mu.m was used as the
bed material. A flow diagram of the processing system is shown in
FIG. 1, which is described above. Nitrogen was metered from a
cylinder to the reactor as the fluidising gas. The fluidising gas
was pre-heated in the furnace before entering the bottom of the
reactor. The temperatures of the reactor were measured using K-type
thermocouples, which were installed on the wall of the freeboard
and the lower wall of the reactor at a position lower than the
height of the static bed. The pyrolysis temperature was reported as
the average of the two temperatures.
[0090] The Alcell lignin was fed in the form of paste. The lignin
powder was mixed with methanol at a mass ratio of 2:1 in a glass
beaker. The mixture was then stirred using a glass rod for 2
minutes to form a paste. Since methanol can dissolve lignin
fraction with low molecular mass, the paste was very viscous at
this ratio. The lignin paste was then transferred into a stainless
steel cylindrical vessel with an upside conical bottom, which was
connected with a flexible PTFE tube with an inner diameter of 0.5
mm and a wall thickness of 1.0 mm. The weight of the transferred
lignin was calculated by the weight difference of the vessel
(including the connected PTFE tubing) before and after the
transferring. Due to the high viscosity and the short duration of
the transferring process, the ratio of lignin to methanol in the
vessel was considered the same as that in the glass beaker.
[0091] The vessel containing the lignin paste was placed above the
reactor. The PTFE tubing was then inserted into the vertical tube
with a cooling water jacket (.PHI.9.5.times.50 mm), which was
connected to the cap of the reactor. The PTFE tubing reached the
lower end of the vertical tube to avoid the high temperature of the
reactor. A stirrer with several layers of plate-shape blade was
installed from the top of the vertical cooling tube into the
reactor to break lignin char agglomerate in the reactor during the
pyrolysis process.
[0092] When the fluid bed reached the pyrolysis temperature,
feeding was started by connecting the lignin feeder to 3 bar
nitrogen line to compress the lignin paste into the fluid bed
reactor via the PTFE tubing. The lignin paste was extruded from the
feeder in a form of thread. The pyrolysis vapour left the reactor
to a cyclone where most of the entrained solids were separated and
collected in a char pot under the cyclone. The char pot and cyclone
were also contained in the furnace. The gases then entered in
sequence a water condenser, an electrostatic precipitator (ESP),
two serial dry ice condensers and a cotton filter. The condensate
was collected in three oil pots. The condensates were collected
from the ESP and the two dry ice condensers. The non-condensable
gases were metered and then entered the venting system. The
condensate trapped in the cotton filter was very small, less than
1% of the total condensates.
[0093] A part of the non-condensable gases after being metered went
to a Micro-GC (Varian CP 4900) with a thermal conductivity detector
to measure its volumetric composition. Hydrogen, methane and CO
were separated using a column packed with molecular sieve 13X,
while CO.sub.2 and C.sub.2-C.sub.4 hydrocarbons were separated
using a column packed with Porapak QS with a thermal conductivity
detector.
[0094] Since each unit, as well as the connecting lines of the
pyrolysis system, could be disassembled, a complete mass balance
was obtained by weighing before and after the experiment. The yield
of liquid product was the sum of mass differences of the three oil
pots, the water condenser, the ESP, the two dry ice condensers and
the cotton filter, after the solids contained in water condenser,
ESP and the first oil pot was subtracted. The yield of char was the
sum of the mass differences of the reactor, the cyclone, the char
pot and the solids in the water condenser, the ESP and the first
oil pot, which were determined as follows. The water condenser and
the ESP were washed using acetone until the liquid become clear.
The acetone solution was then filtered using filter paper with a
pore size of 1 .mu.m, and the solids on the filter paper was rinsed
with fresh acetone several times until the acetone passing through
the filter become clear. The filter paper together with solids on
it was dried in a fume-hood and then dried in a 60.degree. C. oven
overnight. The mass of the solids in the ESP and water condenser
was then determined by the difference of the filter paper and
filter paper plus dried solids. The solid content in the first oil
pot was determined similarly as above by using about 1 g sample
taken from the oil.
[0095] The water content of the three condensates in the three oil
pots was analysed using Karl-Fischer titration. The methanol
content of the three condensates was determined by GC-FID, as
described in the analytical section. The chemical species in the
oil was then quantitatively analysed by GC-MS-FID as shown in the
analytical section.
[0096] The total mass of the permanent gases produced by pyrolysis
of the feedstock was calculated according to Eq. (1)
m = i = 1 n pV i M i RT ( 1 ) ##EQU00001##
where p is the atmospheric pressure, which was taken as 101325 Pa;
V.sub.i is the volume of gas i, which can be calculated by the
volume concentration multiplied by the total volume of the gas
obtained from the gas meter; M.sub.i is the molar mass of gas i; R
is the Universal gas constant, which is 8.314 J mol.sup.-1
K.sup.-1; and T is the temperature of the gas before entering the
gas meter in Kelvin.
[0097] The maximum residence time of gases and vapours was
calculated as the free volume of the reactor divided by the inlet
gas volumetric flow rate expressed at the reactor conditions, which
was about 1 second in this work.
[0098] Analysis
[0099] The light oil was analysed using GC-MS-FID. A Perkin-Elmer
AutoSystem XL Gas Chromatograph fitted with a DB 1701 column (60
m.times.25 .mu.m with 0.25 .mu.m film thickness) was used to
separate the pyrolysis oil. At the end of the GC column, a splitter
was fitted, which split the sample gas into two streams, one to MS
detector and one to FID detector. The carrier gas was helium with a
flow rate of 2 ml min.sup.-1. The injection volume was 1 .mu.L with
a split ratio of 1:24. The oven program held temperature at
45.degree. C. for 5 minutes then heated to 250.degree. C. at a rate
of 5.degree. C. min.sup.-1. The oven was held at the upper
temperature for 5 minutes.
[0100] The compounds in the oil were identified by the retention
time of the standards and MS library. The MS was a Perkin Elmer
Turbomass GOLD mass spectrometer. The detector temperatures were
set at 280.degree. C. Electron impact mass spectra were obtained at
70 eV. The mass range scanned from m/z 35 to 400 was. Data
processing was performed using NIST-98 Mass Spectral library. The
quantitative determination of the compounds in the oil was
determined by GC-FID, which was calibrated using standard
compounds. The FID detector was maintained at 250.degree. C. The
hydrogen flow rate was set at 45.0 ml/min and the air was set at
450 ml/min.
[0101] The following compounds were calibrated using standard
compounds: phenol, catechol, eugenol, 2-methoxy-4-methylphenol,
guaiacol, 1,2,3-trimethoxybenzene, syringaldehyde,
3-methylcatechol, acenaphthene, furfuryl alcohol,
2-methyoxy-4-vinylphenol, 2-furfuraldehyde (fufural), vanillin,
3,4-dimethoxyphenol, 1,6-anhydro-b-D-glucose, toluene, methanol,
acetic acid. The response factors of these compounds were then
calculated. The response factors of other compounds were calculated
according to the relationship between their effective carbon
numbers to the response of flame ionisation detector (FID)
(13-16).
[0102] The molecular mass of the oil in the first oil pot was
analysed using PolymerLabs GPC PL50 with a refractive index
detector. The mobile phase used was tetrahydrofuran with a flow
rate of 1.0 mL/min. The column was mixed D calibrated against
polystyrene narrow standards. The oven temperature was set at
40.degree. C.
[0103] Results and Discussion
[0104] Feeding and Char Agglomeration In the first few trial
experiments, it was recognized that lignin could be fed smoothly
into a fluid bed reactor in a form of paste. A stirrer in the
freeboard was used to break any agglomerates forming during
running. The running could last as long as 70 g lignin paste was
fed (the maximum mass that the vessel could hold). No blockage was
formed during feeding, but some char stuck to the wall of the
reactor freeboard. Most of the broken char was not elutriated from
the reactor because of the large size. After pyrolysis, char and
sand were poured out of the reactor. The broken char agglomerates
by the stirrer could clearly be seen clearly in the sand. There
were also fine char particles.
[0105] Five runs were conducted at a temperature range between 400
and 800.degree. C. The product distributions of the five runs are
given in Table 2, and the main components in the pyrolysis oils are
given in Table 3. The yield of the gaseous products increased
rapidly from 17.55% at 480.degree. C. to 45.55% at 780.degree. C.
The gas was mainly composed of CO, CO.sub.2 and CH.sub.4. All of
the gas components increased rapidly with an increase in pyrolysis
temperature. It should be noted that H.sub.2 accounted 0.1 wt % of
the gas at 480.degree. C., and this value increased to 0.3 wt %.
Hydrogen was not reported in previous reports of lignin pyrolysis.
It is therefore believed to originate from thermal decomposition of
methanol, which produces CO and hydrogen (17, 18). The presence of
hydrogen generated from the thermal decomposition of methanol was
probably the reason for the production of aromatic hydrocarbons,
which account for 0.2% at 680.degree. C., as shown in Table 2.
[0106] The yield of char reached a maximum of 37.7% of the total
feed at 555.degree. C. With an increase in temperature, the yield
of char decreased to 22.3%. This may be due to the gasification of
the char at higher temperatures in the presence of methanol. In the
liquid product, there were three parts: water, methanol and
organics. The yield of water was around 7 wt % without significant
variations with the temperature. This is in agreement with the
literature reports (4, 5, 19). The consumption of methanol
increased with pyrolysis temperature. From the product distribution
in Table 2 and the compounds in the liquid product shown in Table
3, it can be seen that methanol may have been consumed in two ways.
First, it is believed that methanol was decomposed into CO and
hydrogen. Secondly, it is believed that methanol reacted with acids
and ketones from lignin pyrolysis to form esters (4.88 min) and
acetals (5.52 min).
[0107] The organic part of the lignin pyrolysis includes aromatic
hydrocarbons, monomeric phenolics, pyrolytic lignin and
non-aromatic compounds such as acetic acid, formic acid esters. The
aromatic hydrocarbons produced in the pyrolysis include benzene
(6.96 min), toluene (10.14 min) and indene (20.89 min). The
mechanism for the formation of aromatic hydrocarbons is most
probably due to the hydrogenation of the phenolic compounds.
[0108] (The term pyrolytic lignin will be well understood by the
skilled person. It relates to lignin fragments which have not been
fully broken down into monomers in the pyrolysis process. It may
have an average molecular weight in the region of 2500.)
[0109] The pyrolytic lignin increased steadily from 480.degree. C.
to 632.degree. C. and decreased slowly. The change in the pyrolytic
lignin concentration was reflected in the change in molecular mass
of the liquid in the first oil pot, as shown in FIG. 2. At lower
temperatures, the thermal energy is not enough to break down
carbon-carbon linkages, leading to more large fragments. At higher
temperatures, the thermal energy is enough to break down the
carbon-carbon linkages, leading to small fragments. However, the
total liquid is also reduced due to the gasification reaction. The
two effects together resulted in lower yields of pyrolytic lignin
at higher temperatures (20).
[0110] The monomeric phenolics reached the maximum at 555.degree.
C. and decreased rapidly with pyrolysis temperature, but the
aromatic hydrocarbons increased rapidly with pyrolysis temperature.
This indicates that monomeric phenolics underwent
hydrodeoxygenation reactions with the hydrogen from the thermal
decomposition of methanol. The main phenolic compounds are
2-methoxy-4-vinylphenol (30.82 min), 1,2,3-trimethoxybenzene (34.48
min), .beta.-phenyl-benzeneacetaldehyde (37.93 min),
2,5-dimethoxy-4-methylbenzaldehyde (40.37 min),
4-hydroxy-3,5-dimethoxybenzaldehyde (41.11 min). These compounds
have also been reported as the main monomeric phenolics in the
microscale pyrolysis (4, 5, 19) and fluid bed reactors (7, 8, 9).
The structures of the compounds are shown below. They are
characteristic monolignols.
##STR00001##
[0111] The maximum yield of phenolic compounds can be achieved at
550-630.degree. C. At this temperature, the yield of phenolic
compounds can be up to 26.7 wt % of lignin, in which monomeric
phenolics account for 17.9% of the total phenolics (calculated from
Table 2).
TABLE-US-00002 TABLE 2 Fast pyrolysis yields from Alcell lignin
paste as a function of pyrolysis temperature (wt % mf feed)
Temperature 480 555 632 682 780 Paste fed (g) 59.33 68.60 49.77
46.35 42.68 Methanol (wt % of paste) 33.3 33.3 33.3 33.3 33.3 Gas
17.6 16.4 17.5 26.6 45.6 Char 27.7 37.7 26.5 29.1 22.3 Water 9.9
6.6 10.1 5.9 6.4 Methanol 19.8 15.2 20.1 15.6 12.5 Organics 16.4
18.3 18.3 12.8 8.4 Mass balance 91.3 94.1 92.5 90.0 95.2 H.sub.2
0.06 0.14 0.33 0.31 0.33 CO 5.59 6.75 6.32 12.49 20.68 CO.sub.2
8.07 5.64 6.49 5.19 10.64 CH.sub.4 2.92 3.06 2.80 3.81 8.35
C.sub.2-C.sub.4 hydrocarbons 0.91 0.85 1.56 4.79 5.50 Aromatic
hydrocarbons 0.01 0.01 0.04 0.22 0.21 Monomeric phenolics* 3.1 3.2
1.2 0.6 0.2 Pyrolytic lignin** 10.8 14.6 15.1 9.1 7.5 *The value
was the sum of all the phenolic compounds that was GC detectable.
**The value was obtained by the subtraction of water, methanol, GC
detectable from total liquid yield.
TABLE-US-00003 TABLE 3 Compounds of the pyrolysis oil determined by
GC-MS-FID at different temperatures (mass % of whole liquid) RT
Temperature (.degree. C.) Compound name (min) 479 555 632 682 780
formic acid, 1-methylethylester 4.79 0.087 0.453 0.362 0.412 1.368
acetic acid, methylester 4.88 0.000 0.085 0.088 0.153 0.208 ethane,
1,1-dimethoxy- 5.52 0.069 0.157 0.176 0.328 0.433 benzene 6.96
0.010 0.014 0.019 0.138 0.147 acetic acid 8.84 0.974 0.801 0.576
0.659 0.490 toluene 10.14 0.006 0.008 0.013 0.107 0.098 furfural
15.80 0.021 0.386 0.298 0.293 0.137 indene 20.89 0.000 0.000 0.021
0.092 0.118 phenol 23.53 0.136 0.145 0.119 0.298 0.346 guaiacol
24.10 0.648 0.504 0.201 0.000 0.000 2-methylphenol 24.93 0.039
0.059 0.073 0.183 0.138 2-methoxy-4-methylphenol 27.05 0.777 0.627
0.227 0.071 0.016 2,3-dimethylphenol 27.26 0.034 0.056 0.083 0.152
0.127 4-ethyl-2-methoxyphenol 29.31 0.250 0.213 0.095 0.000 0.000
2-methoxy-4-vinylphenol 30.82 1.350 1.245 0.498 0.111 0.000
1,2-benzenediol 31.99 0.198 0.287 0.392 0.750 0.523
2,6-dimethoxyphenol (syringol) 32.23 1.647 1.200 0.456 0.132 0.034
3-methyl-1,2-benzenediol 32.91 0.041 0.133 0.162 0.279 0.148
3,4-dimethoxyphenol 33.14 0.212 0.285 0.178 0.000 0.000
4-methyl-1,2-benzenediol 33.90 0.000 0.118 0.241 0.414 0.275
2-methoxy-4-(1-propenyl)phenol 34.13 0.552 0.475 0.136 0.049 0.000
1,2,3-trimethoxybenzene 34.48 1.564 1.164 0.379 0.077 0.000
vanillin 34.78 0.284 0.272 0.248 0.219 0.000
5-methyl-1,2,3-trimethoxybenzene 36.18 0.501 0.335 0.134 0.041
0.000 1-(4-hydroxy-3-methoxyphenol)ethanone 36.67 0.271 0.241 0.076
0.000 0.000 1-(2-hydroxy-5-methoxy-4-methylphenol)ethanone 37.51
0.975 0.831 0.151 0.000 0.000 .beta.-phenyl-benzeneacetaldehyde
37.93 1.089 0.838 0.364 0.000 0.000
2,6-dimethoxy-4-(2-propenyl)phenol 39.05 0.386 0.364 0.114 0.000
0.000 2,5-dimethoxy-4-ethylbenzaldehyde 40.37 1.533 1.321 0.253
0.122 0.000 4-hydroxy-3,5-dimethoxybenzaldehyde 41.11 1.358 1.111
0.376 0.144 0.000 3,4,5-trimethoxybenzaldehyde 42.51 0.615 0.512
0.187 0.080 0.000 1-(2,4,6-trimethoxy-3-methylphenyl)-1-butanone
43.41 0.517 0.389 0.000 0.000 0.000
(1,1'-biphenyl)-2,2'-dicarboxaldehyde 44.02 0.265 0.236 0.000 0.000
0.000 Sum 16.409 14.865 6.696 5.304 4.606
[0112] Shown in Table 4 below is a comparison with previous reports
using fluid bed reactor (7,9). Generally, the present work agrees
well with the literature reports for the temperature at which
maximum liquid can be obtained, which is around 600.degree. C. In
this work, the yield of phenolics (pyrolytic lignin and monomeric
phenolics) was higher than that Kaminsky et al (7) reported.
However, the yield of monomeric phenolics was lower than that in
Kaminsky's work for ethanol lignins but at similar level for Kraft
lignins. This may be due to the difference in the molecular
structures of the lignins. The yield of phenolics is much higher
than that in de Wild et al's work (9), since they conducted the
pyrolysis of Alcell lignin at only 400.degree. C.
TABLE-US-00004 TABLE 4 A comparison of this work with literature
reports using fluid bed reactor Temperature Temperature for max
Organics Phenolics Monomeric range liquid yield (% (% phenolics
Authors Feedstock studied (.degree. C.) (.degree. C.) lignin)
lignin) (% lignin) Kaminsky Ethanol 450-850 600 -- 21.5 14.1 et al
(7) lignin (beech) Ethanol 450-850 600 -- 24.7 9.7 lignin (spruce)
Kraft lignin 450-850 500 -- 12.0 3.4 (beech) Kraft lignin 450-850
500 -- 14.9 5.4 (spruce) de Wild Alcell 400 400 13.0 et al (9)
lignin (mixed hardwood) Granit 400 400 21.0 lignin (mixed grass)
This work Alcell 450-800 550-630 27.7 26.7 4.8 lignin (mixed
hardwood)
[0113] The preferred embodiments have been described by way of
example only. Modifications to these embodiments, further
embodiments and modifications thereof will be apparent to the
skilled person and as such are within the scope of the present
invention.
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