U.S. patent number 10,385,033 [Application Number 15/746,082] was granted by the patent office on 2019-08-20 for process for preparing furan-2,5-dicarboxylic acid.
This patent grant is currently assigned to BASF SE. The grantee listed for this patent is BASF SE. Invention is credited to Rene Backes, Benoit Blank, Richard Dehn, Alvaro Gordillo, Markus Piepenbrink, Stephan A Schunk, Joaquim Henrique Teles, Holger Werhan, Lei Zhang.
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United States Patent |
10,385,033 |
Gordillo , et al. |
August 20, 2019 |
Process for preparing furan-2,5-dicarboxylic acid
Abstract
A process for preparing furan-2,5-dicarboxylic acid is
disclosed. The process includes the following steps: preparing or
providing a starting mixture including 5-(hydroxy-methyl)furfural
(HMF), 5,5'-[oxy-bis(methylene)]bis-2-furfural (di-HMF), and water;
subjecting said starting mixture to oxidation conditions in the
presence of an oxygen-containing gas and a catalytically effective
amount of a heterogeneous catalyst including one or more noble
metals on a support so that both HMF and di-HMF react to give
furane-2,5-dicarboxylic acid in a product mixture also including
water and oxidation by-products. The use of a catalyst is also
disclosed, the catalyst including one or more noble metals on a
support as an heterogeneous oxidation catalyst for catalyzing in an
aqueous starting mixture the reaction of both HMF and di-HMF to
furane-2,5-dicarboxylic acid.
Inventors: |
Gordillo; Alvaro (Heidelberg,
DE), Werhan; Holger (Rauenberg, DE), Dehn;
Richard (Ludwigshafen, DE), Blank; Benoit
(Edingen-Neckarhausen, DE), Teles; Joaquim Henrique
(Waldsee, DE), Schunk; Stephan A
(Heidelberg-Rohrbach, DE), Piepenbrink; Markus
(Telgte, DE), Backes; Rene (Lampertheim,
DE), Zhang; Lei (De Meern, NL) |
Applicant: |
Name |
City |
State |
Country |
Type |
BASF SE |
Ludwigshafen am Rhein |
N/A |
DE |
|
|
Assignee: |
BASF SE (Ludwigshafen am Rhein,
DE)
|
Family
ID: |
53724033 |
Appl.
No.: |
15/746,082 |
Filed: |
July 1, 2016 |
PCT
Filed: |
July 01, 2016 |
PCT No.: |
PCT/EP2016/065494 |
371(c)(1),(2),(4) Date: |
January 19, 2018 |
PCT
Pub. No.: |
WO2017/012842 |
PCT
Pub. Date: |
January 26, 2017 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20180215724 A1 |
Aug 2, 2018 |
|
Foreign Application Priority Data
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|
|
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Jul 22, 2015 [EP] |
|
|
15177884 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J
23/42 (20130101); C07D 307/46 (20130101); B01J
21/18 (20130101) |
Current International
Class: |
C07D
307/02 (20060101); B01J 21/18 (20060101); C07D
307/46 (20060101); B01J 23/42 (20060101) |
Field of
Search: |
;549/485 |
References Cited
[Referenced By]
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Jan 2017 |
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WO |
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Other References
International Search Report and Written Opinion for International
Application No. PCT/EP2016/065494, dated Sep. 12, 2016, 9 pages.
cited by applicant .
Hicham Ait Rass et al: "Selective aqueous phase oxidation of
5-hyfroxymethyl furfural to 2, 5-furandicarboxylic acid over Pt/C
catalysts: influence of the base and effect of bismuth promotion",
Green Chemistry, vol. 15, No. 8, Jan. 1, 2013 (Jan. 1, 2013), p.
2240, XP055214536. cited by applicant .
Ma et al: "The copolymerization reactivity of diols with
2,5-furandicarboxylic acid for furn-based copolyester materials",
Journal of Materials Chemistry, 2012, pp. 3457-3461, vol. 22. cited
by applicant .
Extended European Search Report for EP Application No. 15177884.2,
dated Nov. 2, 2015, 6 pages. cited by applicant.
|
Primary Examiner: Oh; Taylor V
Attorney, Agent or Firm: Armstrong Teasdale LLP
Claims
The invention claimed is:
1. Process for preparing furane-2,5-dicarboxylic acid comprising
the following steps: (a) preparing or providing a starting mixture
comprising 5-(hydroxymethyl)furfural (HMF),
5,5'-[oxy-bis(methylene)]bis-2-furfural (di-HMF), and water,
wherein a total amount of water in the starting mixture is at least
50 wt.-%, based on a total weight of the starting mixture and
wherein a pH of the starting mixture is in a range of from 4.0 to
7.0, (b) subjecting said starting mixture to oxidation conditions
in the presence of an oxygen-containing gas and a catalytically
effective amount of a heterogeneous catalyst comprising one or more
noble metals on a support so that both HMF and di-HMF react to give
furane-2,5-dicarboxylic acid in a product mixture also comprising
water.
2. The process according to claim 1, wherein the starting mixture
has a molar ratio of HMF to di-HMF in the range of from 100 to 0.8,
and/or a total weight of HMF and di-HMF in the starting mixture is
in a range of from 0.1 to 50 wt.-%, based on the total weight of
the starting mixture.
3. The process according to claim 1, wherein a pH of the product
mixture is below 7.
4. The process according to claim 1, wherein said starting mixture
at a temperature in a range of from 70.degree. C. to 200.degree.
C., is subjected to said oxidation conditions in the presence of
said oxygen-containing gas and said catalytically effective amount
of a heterogeneous catalyst comprising one or more noble metals on
a support, so that both HMF and di-HMF react to give
furane-2,5-dicarboxylic acid in the product mixture also comprising
water and oxidation by-products.
5. The process according to claim 1, wherein said starting mixture
is subjected to said oxidation conditions in a pressurized reactor,
wherein an oxygen partial pressure in the reactor at least
temporarily is in a range of from 1 to 100 bar, during the reaction
of both HMF and di-HMF to furane-2,5-dicarboxylic acid.
6. The process according to claim 1, wherein a total amount of
acetate ions and acetic acid in said starting mixture is below 10
wt.-%, wherein a total amount of carboxylic acid ions and
carboxylic acid in the starting mixture is below 10 wt.-%.
7. The process according to claim 1, wherein the step of preparing
said starting mixture comprises (a1) preparing or providing a
material mixture comprising one, two or more compounds selected
from the group consisting of hexoses, oligosaccharides comprising
hexose units, and polysaccharides comprising hexose units, and (a2)
subjecting said material mixture to reaction conditions so that a
mixture results comprising HMF, di-HMF, and water.
8. The process according to claim 1, wherein in said heterogeneous
catalyst comprising one or more noble metals on a support (i) at
least one of said noble metals is selected from the group
consisting of gold, platinum, iridium, palladium, osmium, silver,
rhodium and ruthenium, and/or (ii) said support is selected from
the group consisting of carbon, metal oxides, metal halides, and
metal carbides.
9. The process according to claim 1, wherein in said heterogeneous
catalyst comprising one or more noble metals on a support at least
one of said noble metals is selected from the group consisting of
platinum, iridium, palladium, osmium, rhodium and ruthenium, and
said support is carbon.
10. The process according to claim 1, wherein in said heterogeneous
catalyst comprising one or more noble metals on a support said one
or one of said more noble metals is platinum and said support is
carbon, and a content of platinum on the support is in a range of
from 0.1 to 20 wt.-%, based on a total weight of the heterogeneous
catalyst comprising one or more noble metals on a support.
11. The process according to claim 1, wherein in said heterogeneous
catalyst comprising one or more noble metals on a support a molar
ratio of said one or one of said more noble metals to a total
amount of HMF and di-HMF is in a range of from 1:1 000 000 to
1:10.
12. The process according to claim 1, wherein the product mixture
obtained in step (b) comprises furan-2,5-di carboxylic acid in
dissolved form.
13. A catalyst comprising one or more noble metals on a support as
an heterogeneous oxidation catalyst for accelerating in an aqueous
starting mixture a conversion of both HMF and di-HMF to
furane-2,5-dicarboxylic acid, wherein a pH of the starting mixture
is in a range of from 4.0 to 7.0.
14. The process according to claim 7, wherein the step of preparing
said starting mixture further comprises (a3) subjecting the mixture
resulting from step (a2) to additional treatment conditions,
without adding a carboxylic acid and/or without adding an acidic
solvent for dissolving HMF and di-HMF, so that said starting
mixture results.
15. The process according to claim 3, wherein the pH of the product
mixture is in a range of from 1 to 4.
16. The process according to claim 4, wherein said starting mixture
is at a temperature in a range of from 100.degree. C. to
135.degree. C.
17. The process according to claim 5, wherein the oxygen partial
pressure in the reactor at least temporarily is in a range of from
1 to 20 bar.
18. The process according to claim 9, wherein at least one of said
noble metals is platinum.
19. The process according to claim 10, wherein in the content of
platinum on the support is in a range of from 1 to 10 wt.-%.
20. The process according to claim 12, wherein the product mixture
obtained in step (b) does not comprise furan-2,5-dicarboxylic acid
in solid form.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a U.S. National Phase Application of
PCT/EP2016/065494, filed Jul. 1, 2016, which claims the benefit of
priority to EP Application No. 15177884.2, filed Jul. 22, 2015, the
contents of which are hereby expressly incorporated by reference in
their entirety.
The present invention relates to a process for preparing
furan-2,5-dicarboxylic acid (FDCA) (compound of the formula (I))
and to a corresponding use of a catalyst.
##STR00001##
Further aspects of the present invention and the preferred
configurations thereof are apparent from the description which
follows, the working examples and the appended claims.
FDCA is an important compound for production of various products,
for example surfactants, polymers and resins.
With increasing depletion of fossil feedstocks, starting materials
based on renewable resources are needed, e.g. as alternatives to
terephthalic acid (a compound used in the production of
polyethylene terephalate, PET). PET is based on ethylene and
p-xylene which are usually obtained starting from of oil, natural
gas or coal, i.e. from fossil fuels. While bio-based routes to
ethylene (e.g. dehydration of bio-ethanol) are operated on
commercial scale a straightforward access to bio-terephthalic acid
remains difficult. FDCA is the best bio-based alternative to
terephthalic acid (for further information see: Lichtenthaler, F.
W., "Carbohydrates as Organic Raw Materials" in Ullmann's
Encyclopedia of Industrial Chemistry, Wiley-VCH Verlag GmbH &
Co. KGaA, Weinheim, 2010).
FDCA can be co-polymerized with mono-ethylene glycol to give
polyethylene furanoate (PEF), a polyester with properties similar
to PET.
##STR00002##
FDCA is usually obtained starting from fructose and/or other
hexoses via a catalyzed, preferably acid-catalyzed, dehydration to
key intermediate 5-(hydroxymethyl)furfural (HMF) followed by
oxidation to FDCA.
##STR00003##
In the dehydration step by-products are formed, depending on the
specific design of the process. A typical by-product is
5,5'-[oxy-bis(methylene)]bis-2-furfural (di-HMF) (V, see
below).
In a typical process of preparing FDCA, a starting mixture
comprising 5-(hydroxymethyl)furfural (HMF) is prepared by
subjecting a material mixture, comprising one, two or more
compounds selected from the group consisting of hexoses (monomeric
hexose molecules, e.g. fructose), oligosaccharides comprising
hexose units, and polysaccharides comprising hexose units, to
reaction conditions so that a mixture comprising HMF, water and
by-products (e.g. di-HMF) results. Under the reaction conditions
oligo- and/or polysaccharides are usually depolymerised, and
subsequently the resulting monosaccharides, e.g. monomeric hexose
molecules, are converted into HMF. Hexoses, oligosaccharides and
polysaccharides are typically selected from the group consisting of
fructose, glucose, and cellulose.
During depolymerisation oligo- or polysaccharides are usually
converted into monomeric hexose molecules by hydrolytic cleavage of
the ether bonds connecting the different hexose units in an oligo-
or polysaccharide molecule (e.g. cellulose). The products of a
typical depolymerization process (monomeric hexose molecules) are
present in their aldehyde form.
Typically, according to routines at least in part previously
undisclosed, depolymerization is conducted by using a catalyst,
preferably in a one-pot-procedure. Typically a hydrophilic solvent
is used (in particular water), e.g. in order to increase the amount
of dissolved cellulose thus increasing the yield per process run.
It is typically advantageous to conduct the conversion of cellulose
into HMF by means of a heterogeneous catalyst in order to
facilitate post-synthetic workup. In a typical depolymerization
process, an aqueous solution is used as a solvent, sometimes
comprising 50 wt.-% of water or more, based on the total weight of
the depolymerization mixture used.
Alternatively, if monosaccharides are used as a starting material
for preparing a starting mixture comprising HMF, water, and
by-products, e.g. di-HMF, no depolymerisation step is needed.
Monosaccharides produced or provided are typically subjected to a
dehydration process, wherein the aldehyde form of monomeric hexose
molecules is typically transferred by isomerization (via e.g.
ketone-enone tautomerization) into its ketone form which is
subsequently converted into its ring form. After ring closure, the
formed ring-closed hexose molecules are typically dehydrated (and
optionally further isomerized) resulting in a mixture comprising
HMF, by-products (e.g. di-HMF) and water, which can be used as a
basic mixture in a process for preparing FDCA (preferably in a
purified form).
Due to the insolubility of specific monomeric hexose molecules
(e.g. fructose) in common organic solvents, the dehydration process
step is usually performed in an aqueous environment so that an
aqueous solution comprising HMF, by-products (e.g. di-HMF) and
water is obtained as a (crude) mixture.
Isolation of HMF from such mixtures is challenging since HMF often
undergoes side-reactions, e.g. (further) etherification to di-HMF.
This is usually the case when water is removed during work-up (see
for example U.S. Pat. No. 2,994,645). Since two HMF-molecules are
etherified the amount of by-products produced is correspondingly
high.
##STR00004##
Hence, the (crude) mixture comprising HMF and water is usually
contaminated with by-products, in particular di-HMF, to a certain
degree, as separation of HMF from the by-products, in particular
di-HMF, is not possible with justifiable effort.
Common by-products (e.g. by-products as described above) are for
example fructose in its ring form (RFF) (compound of the formula
(III)), partially dehydrated fructose in its ring form (de-RFF)
(compound of the formula (IV)), and
5,5'-[oxy-bis(methylene)]bis-2-furfural (di-HMF) (compound of the
formula (V)). HMF (compound of the formula (II)) and di-HMF can be
obtained in significant amounts from biomass, especially from
biomass comprising hexoses and/or oligo- and/or polysaccharides as
described above.
##STR00005##
Different teachings regarding the isolation or preparation of FDCA
have been reported in the patent literature:
WO 2008/054804 A2 relates to "Hydroxymethyl furfural oxidation
methods" (title). It is disclosed that a reaction mixture having a
mild basic pH can be provided by addition of sodium carbonate, the
salts of FDCA having a distinctly elevated solubility in said
reaction mixture compared to reaction mixtures having a neutral or
acidic pH (cf. paragraph [0049]).
WO 2008/054804 A2 additionally discloses that twice as high a
solubility of FDCA in an acetic acid/water mixture (volume ratio
40:60) is achieved, compared to the solubility in pure water (cf.
paragraph [0058]).
WO 2013/033081 A2 discloses a "process for producing both by-based
succinic acid and 2,5-furane dicarboxylic acid" (title). In example
46 and 47 a mixture of HMF and di-HMF (molar ratio HMF:di-HMF is
1:10) is converted to FDCA at 100.degree. C.
US 2008/103318 discloses "hydroxymethyl furfural oxidation methods"
(title) comprising the step of "providing a starting material which
includes HMF in a solvent comprising water into reactor". The
starting material is brought into contact "with the catalyst
comprising Pt on the support material where the contacting is
conducted at a reaction temperature of from about 50.degree. C. to
about 200.degree. C.".
WO 2012/017052 A1 discloses a "process for the synthesis of
2,5-furandicarboxylic acid" (title).
Hicham Ait Rass et al. disclose a "selective aqueous phase
oxidation of 5-hydroxymethyl furfural to 2,5-furandicarboxylic acid
over Pt/C catalysts" (see titel of article in GREEN CHEMISTRY, vol.
15, no. 8, 1 Jan. 2013, page 2240).
U.S. Pat. No. 2,994,645 discloses the "purification of
hydroxymethyl furfural" (title). A process is disclosed wherein
"gases and water by heating under a high vacuum" are initially
removed.
The solubility of FDCA in aqueous solutions can be increased by
addition of solubilizers. EP 0 356 703 A2 relates to a process for
oxidizing 5-hydroxymethylfurfural (HMF) and discloses that the
precipitation of reaction products during the oxidation of
5-hydroxymethylfurfural can be avoided, especially at relatively
high concentrations, when a solubilizer which is inert with respect
to the reaction participants under the selected reaction conditions
is added to the reaction mixture. EP 0 356 703 A2 additionally
discloses that suitable solubilizers are, for example, glycol
ethers lacking free OH groups, especially dimethyl glycol ether,
diethyl glycol ether and methyl ethyl glycol ether.
Very frequently, precipitation of FDCA leads to deactivation of the
heterogeneous catalyst. WO 2013/191944 A1 discloses that, because
of the very low solubility of FDCA in water, the oxidation of HMF
has to be conducted in very dilute solutions, in order to avoid
precipitation of the FDCA on the catalyst surface, since the
process otherwise can no longer be conducted economically (cf. page
3).
Own observations show that the precipitation of FDCA on the
internal and/or external catalyst surface of a heterogeneous
catalyst can lead to contamination and possible deactivation of the
heterogeneous catalyst. This involves coverage or coating of the
catalytically active constituents of the heterogeneous catalyst by
the precipitated FDCA, such that the catalytic constituents no
longer come into contact with the reactants. The effect of such a
contamination of the catalyst is that the catalyst does not display
the same initial activity, if at all, and has to be replaced by new
catalyst material which increases the costs. Especially in the case
of utilization of costly catalysts, for example platinum catalysts,
such a course of action is frequently uneconomic.
The aforementioned disclosure regarding the depolymerization or
dehydration step also apply to (i) a process for preparing FDCA and
(ii) a use of a catalyst according to the present invention as
described in detail hereinbelow. In particular, the dehydration
step or the successive steps of depolymerization and dehydration
can be used to prepare a starting mixture as employed according to
the present invention.
Despite the considerable efforts made by industry, there remains a
need to provide an improved process for preparing FDCA from a
starting mixture comprising HMF, di-HMF and water, which avoids or
at least alleviates the disadvantages of the processes known to
date and which can be operated in an economically advantageous
manner. The process to be specified should favourably allow to
reduce the complexity of reactor set-ups known in the prior art,
allow to use a catalyst which can readily be separated from the
product mixture after the reaction.
According to the invention, this object is achieved by a process
for preparing furane-2,5-dicarboxylic acid, comprising the
following step: (a) preparing or providing a starting mixture
comprising 5-(hydroxymethyl)furfural (HMF),
5,5'-[oxy-bis(methylene)]bis-2-furfural (di-HMF), and water, (b)
subjecting said starting mixture to oxidation conditions in the
presence of an oxygen-containing gas and a catalytically effective
amount of a heterogeneous catalyst comprising one or more noble
metals on a support so that both HMF and di-HMF react to give
furane-2,5-dicarboxylic acid in a product mixture also comprising
water.
The "heterogeneous catalyst" preferably is a substance which is not
soluble in water and/or is present in solid form.
The expression "both HMF and di-HMF react to give
furane-2,5-dicarboxylic acid" indicates that under the oxidation
conditions of step (b) HMF reacts and di-HMF reacts, and a first
portion of the resulting furane-2,5-dicarboxylic acid is a product
of HMF and a second portion of the resulting
furane-2,5-dicarboxylic acid is a product of di-HMF.
The product mixture may also contain oxidation by-products. A
non-limiting selection of oxidation by-products, which can be
formed under oxidation conditions in step (b) of the process of the
present invention, are 2,5-diformylfuran (DFF),
5-hydroxymethylfuran-2-carboxylic acid (HMFCA),
5-formylfuran-2-carboxylic acid (FFCA).
An "oxygen-containing gas" is a gas comprising gaseous compounds
having one or more oxygen atoms per molecule. A preferred gaseous
compound having one or more oxygen atoms per molecule is molecular
oxygen (O.sub.2).
Air is a preferred oxygen-containing gas.
The term "oxidation conditions" indicates conditions suitable for
causing both HMF and di-HMF to react and to give
furane-2,5-dicarboxylic acid in said product mixture also
comprising water.
The oxygen-containing gas acts as an oxidizing agent.
Various types of reaction vessels can be used in step (b) to
conduct the reaction of both HMF and di-HMF to
furan-2,5-dicarboxylic acid (FDCA). In many cases an autoclave is
used to conduct the reaction of HMF an di-HMF to FDCA. In many
cases the reaction of HMF and di-HMF to FDCA is conducted in a
batch reactor or in a semi-batch reactor. In other cases a plug
flow or a fixed bed reactor is used.
As described above, in typical processes of the prior art, the
reaction of two HMF molecules to one dimeric molecule (di-HMF)
results in a high content of by-products and therefore in a low
yield of FDCA. In contrast, the process according to the present
invention converts both HMF and di-HMF into valuable FDCA, and thus
the overall yield of the industrially important production of FDCA
from hexoses is increased. In contrast to the teaching of WO
2013/033081 A2, a heterogeneous catalyst is used in the process of
the present invention, thus allowing for a simplified work-up and
other treatments of the product mixture and its ingredients.
Moreover, HMF and di-HMF are highly soluble in water thus
increasing the maximum achievable starting concentration of HMF and
di-HMF and therewith optimizing the space-time-yield of FDCA.
Additionally, water is relatively inert under the oxidation
conditions of the present invention as it cannot be oxidized as
easily as other solvents (e.g. acetic acid). Thus, the
oxygen-containing gas employed as oxidizing agent is used in a more
efficient way.
Surprisingly, it has been found that the presence of HMF in the
starting mixture is favourable when di-HMF is subjected to
oxidation conditions in the presence of an oxygen-containing gas
and a catalytically effective amount of a heterogeneous catalyst
comprising one or more noble metals on a support, and is thereby
converted into FDCA. Without wishing to be bound by any theory, it
is presently believed that the conversion of the initially present
HMF into FDCA proceeds in a shorter time frame in comparison with
the conversion of di-HMF to FDCA. Upon conversion of the initially
present HMF into FDCA the pH of the reaction mixture decreases, as
the reaction product FDCA is a dicarboxylic acid. The increasing
concentration of protons in the reaction mixture catalyzes the
hydrolytic cleavage of di-HMF into two HMF molecules thus
increasing the concentration of HMF. In turn, the HMF formed by
cleaving di-HMF is subsequently quickly converted into FDCA thereby
further decreasing the pH and increasing the rate of the cleaving
reaction. This allows to produce FDCA from di-HMF in an
economically valuable time frame with no need of additional agents
as used according to the prior art, for example HBr (see example 46
and 47 in WO 2013/033081) or similarly corrosive agents. Hence, at
the beginning of the reaction the concentration of HMF should be
sufficiently high to initiate the conversion of di-HMF to FDCA (in
contrast to WO2013/033081). The deliberate presence of HMF for the
acceleration of a process for preparing FDCA from di-HMF is
therefore a primary reason for the advantages provided by the
present invention.
According to the present invention, the oxidation of HMF and di-HMF
into FDCA is conducted in a starting mixture comprising water.
Preferably, in the starting mixture of step a) the total amount by
weight of di-HMF, preferably resulting from a previous process step
(e.g. process step (a2) as described hereinbelow), and HMF is
higher than the total amount of other organic compounds. The
starting mixture used in the process according to the invention in
step a) may comprise a comparatively high total concentration of
reactant compound(s), HMF and di-HMF. This regularly leads to
precipitation of FDCA during the catalytic conversion in step (b)
and hence to the product mixture comprising FDCA in solid or
dissolved form and the heterogeneous catalyst in solid form.
In the process according to the invention, in step (b), both the
heterogeneous catalyst and FDCA can be present in solid form.
However, preferably the heterogeneous catalyst is present in solid
form and FDCA is present in its dissolved form. A heterogeneous
catalyst used in step (b) may be part of a mixture of two, three or
more than three heterogeneous catalysts. Typically, the product
mixture formed in step (b) of a process according to the invention
at least comprises water and a heterogeneous catalyst in separate
phases, but many times comprises as a further solid phase the
product FDCA. The proportion of the dissolved FDCA in the aqueous
phase is typically low, because of the low solubility product of
FDCA in water or aqueous solutions. Preferably, the aqueous phase
of the product mixture produced in step (b) of the present
invention is a saturated solution with respect to FDCA.
The product mixture obtained in step (b) can be optionally
subjected to further treatment conditions resulting in a second
product mixture.
WO 2013/191944 A1 discloses that, under pressure and at a
temperature in the range of 120.degree. C. to 240.degree. C., FDCA
in solid form is dissolved in an appropriate aqueous solvent. At
appropriate temperature and appropriate pressure, an overheated
aqueous solution may comprise a total proportion of dissolved FDCA
in the range of from 10 to 20% by weight, based on the total amount
of the aqueous solution.
Heating under pressure of the product mixture of step (b), or of
the second product mixture obtained by subjecting the product
mixture of step (b) to further treatment conditions, each
comprising both FDCA in solid or dissolved form and the
heterogeneous catalyst in solid form, regularly dissolves at least
some of the FDCA deposited on or within the pore-system of the
heterogeneous catalyst (e.g. the pore-system of the support
material). Preferably, a subsequent (further treatment) step
comprises heating the heterogeneous catalyst as present at the end
of step (b) or as present at the end of an intermediate step
following step (b) so that the activity of the heterogeneous
catalyst after heating (i.e. its capability to act as a catalyst
for the oxidation of HMF to FDCA) is increased in comparison with
the heterogeneous catalyst as present at the end of step (b).
More preferably, the process of the present invention comprises a
subsequent (further treatment) step as described above comprising
heating the heterogeneous catalyst as present at the end of step
(b) or as present at the end of an intermediate step following step
(b) so that the activity of the heterogeneous catalyst after
heating (i.e. its capability to act as a catalyst for the oxidation
of HMF to FDCA) is increased, wherein the activity of the
heterogeneous catalyst after the heating is increased by at least
5%, preferably by at least 10%, more preferably by at least 20%,
even more preferably by at least 30%, most preferably by at least
50% in comparison with the activity of the heterogeneous catalyst
as present at the end of step (b).
A process of the invention is preferred wherein the product mixture
resulting in process step (b) is subjected to additional
separation, purification and/or to (re-)crystallization steps to
obtain purified FDCA.
In many cases a process of the invention is preferred, wherein
the starting mixture has a molar ratio of HMF to di-HMF in the
range of from 100 to 0.8, preferably in the range of from 100 to
0.9
and/or
the total weight of HMF and di-HMF in the starting mixture is in
the range of from 0.1 to 50 wt.-%, preferably in the range of from
1 to 30 wt.-%, more preferably in the range of from 1 to 20 wt.-%,
based on the total weight of the starting mixture.
In many preferred practical situations the starting mixture has a
molar ratio of HMF to di-HMF in the range of from 100 to 20, in
many other situations the range of from 10 to 0.9 is preferred.
In the starting mixture, these ranges of molar ratios of HMF and
di-HMF and/or this range of the total weight of HMF and di-HMF are
preferred as those values represent optimum values for the
production of FDCA from HMF or di-HMF. When working within these
ranges, a relatively low amount of by-products is produced and the
reaction can be conducted in an economically acceptable time
frame.
A concentration of over 50 wt.-% of HMF and di-HMF, based on the
total starting mixture is in many cases disadvantageous, as the
solubility characteristic of the reaction mixture is changed so
that FDCA produced will likely precipitate, thus complicating
post-synthetic work-up.
In many cases, a process of the invention is preferred, wherein the
total amount of water in the starting mixture is at least 10 wt.-%,
preferably at least 25 wt.-%, more preferably at least 50 wt.-%,
based on the total weight of the starting mixture.
By using water as a solvent in a process of the invention an
environmentally friendly solvent is used. Moreover, the higher the
content of water in the starting mixture the more HMF and di-HMF
can be dissolved and thus the more FDCA can be produced per
batch.
Preferred is a process of the present invention, wherein the pH of
the starting mixture is 4.0 or higher, preferably 4.5 or higher,
more preferably 5.0 or higher, even more preferably 5.5 or higher,
or the pH of the starting mixture is in the range of from 4.0 to
7.0, preferably the pH of the starting mixture is in the range of
from 4.5 to 7.0, more preferably the pH of the starting mixture is
in the range of from 5.0 to 7.0, even more preferably the pH of the
starting mixture is in the range of from 5.5 to 7.0.
It is preferred to conduct the conversion of HMF into FDCA in a
starting mixture with a pH of 4.0 or higher, as the produced FDCA
is very well soluble in such a reaction mixture with a pH of 4.0 or
higher. Starting mixtures with a pH below 4.0 are disadvantageous
because a low pH in the starting mixture will result in a product
mixture with a correspondingly low pH causing unfavourable
precipitation of FDCA.
In the process of the present invention the addition of
solubilizers is optional. Preferably, the starting mixture in step
(b) does not comprise a solubilizer for FDCA.
Preferably, in step (b) of the process of the present invention the
development of the pH in the mixture subjected to oxidation
conditions is not controlled by the addition of alkaline
reagents.
A process of the present invention is preferred, wherein the total
amount of HMF in the starting mixture is in the range of from 0.1
to 40 wt.-%, preferably in the range of from 1 to 30 wt.-%, based
on the total weight of the starting mixture.
As mentioned above, FDCA produced from initially present HMF
accelerates the hydrolytic cleavage of di-HMF and thus accelerates
the overall reaction. Therefore, concentrations of HMF in the
starting mixture below 0.1 are not advantageous. On the other hand
is a concentration of over 40 wt.-% of HMF, based on the total
amount of the starting mixture, disadvantageous as the solubility
characteristic of the reaction mixture is changed so that FDCA
produced will likely precipitate.
In particular, a process of the invention is preferred, wherein the
total amount of di-HMF in the starting mixture is in the range of
from 0.1 to 40 wt.-%, preferably in the range of from 0.1 to 30
wt.-%, more preferably in the range of from 0.1 to 10 wt.-%, even
more preferably in the range of from 0.2 to 6 wt.-%, based on the
total weight of the starting mixture.
A concentration of over 40 wt.-% of di-HMF, based on the total
weight of the starting mixture, is disadvantageous as the
solubility characteristic of the reaction mixture is changed so
that the FDCA produced will likely precipitate.
Preferred is a process of the invention, wherein the pH of the
product mixture is below 7 and wherein preferably the pH of the
product mixture is in the range of from 1 to 4.
According to the present invention the pH of the reaction mixture
can be monitored in order to correspondingly monitor the conversion
to FDCA during the reaction process. It is preferred to have a
product mixture with a pH below 7 (preferably below 4) which
generally means that an economically valuable amount of HMF or
di-HMF to FDCA was converted.
A process of the invention is preferred, wherein said starting
mixture at a temperature in the range of from 70.degree. C. to
200.degree. C., preferably in the range of from 80.degree. C. to
180.degree. C., more preferably in the range of from 90.degree. C.
to 170.degree. C., even more preferably in the range of from
100.degree. C. to 140.degree. C., is subjected to said oxidation
conditions in the presence of said oxygen-containing gas and said
catalytically effective amount of a heterogeneous catalyst
comprising one or more noble metals on a support, so that both HMF
and di-HMF react to give furane-2,5-dicarboxylic acid in the
product mixture also comprising water and oxidation
by-products.
On the one hand, lower reaction temperatures typically result in a
reduced reaction rate thus significantly increasing the time needed
for the oxidation of HMF or di-HMF to FDCA and making the process
economically inefficient.
On the other hand, too high temperatures can lead to overoxidation,
a too high reaction rate, an increased production of oxidation
by-products and hardly controllable reaction conditions which
require costly safety measures.
In many cases, a process is preferred as described above (or as
preferably described above), wherein said starting mixture is
subjected to said oxidation conditions in a pressurized reactor,
wherein during said reaction of HMF and di-HMF to FDCA oxygen or an
oxygen-containing gas is continuously (or optionally and less
preferred discontinuously) fed into and simultaneously removed from
said reactor
In some cases the pressure at which the reaction is conducted,
depends on the headspace volume of the reactor used which has to
accommodate at least the required stoichiometric amount of
oxygen-containing gas to fully convert the reactants HMF and
di-HMF. A high pressure (of, for example, 20 or, for example, even
100 bar) is required in cases, where no continuous or
discontinuously feed of an oxygen-containing gas is used, e.g. in a
case where the reactor is once pressurized with an at least
stoichiometric amount of an oxygen-containing gas at the beginning
of the reaction without further manipulation of the pressure in the
reactor.
In other cases consumed oxygen-containing gas is continuously or
discontinuously replaced by fresh oxygen-containing gas. In such
cases an oxygen partial pressure in the range of from 200 mbar and
10 bar is preferred.
A process of the present invention is preferred, wherein said
starting mixture is subjected to said oxidation conditions in a
pressurized reactor, wherein the oxygen partial pressure in the
reactor at least temporarily is in the range of from 100 mbar to 20
bar, preferably in the range of from 200 mbar to 10 bar, during the
reaction of both HMF and di-HMF to furane-2,5-dicarboxylic
acid.
A skilled person will choose suitable oxidation conditions
according to his specific needs. In many cases, the oxidation is
conducted at a pressure of 1 to 100 bar, preferably at a pressure
of 1 to 20 bar in an atmosphere of an oxygen-containing gas or a
mixture of an oxygen-containing gas and another gas (which is
preferably inert under the reaction conditions).
Working under a pressure below 1 bar is not preferred as it
requires additional technical measures thus increasing the
complexity of the reaction system. In order to work at pressures
above 20 bar additional safety equipment is necessary in order to
fulfil specific safety requirements.
A process of the invention is preferred wherein said starting
mixture does not comprise a catalytically effective amount of a
homogeneous oxidation catalyst selected from the group of cobalt,
manganese, and bromide compounds, and mixtures thereof.
In order to separate a homogeneous oxidation catalyst from a
reaction mixture technically complicated separation units are
required in the overall product plant thus increasing material and
energy costs. Thus, according to the present invention the presence
of one or more homogeneous oxidation catalysts is not
preferred.
More specifically, a process of the invention is preferred wherein
the total amount of cobalt and manganese and bromide ions in the
starting mixture is below 100 ppm, preferably below 20 ppm.
It is of particular interest to avoid toxic or corrosive compounds,
in particular cobalt and manganese compounds as well as bromide
compounds. The latter drastically increases the corrosiveness of
the reaction mixture and therefore requires specially coated
reactor vessels which incur high costs.
A process of the invention is preferred wherein the total amount of
carboxylic acid ions and carboxylic acid in the starting mixture is
below 10 wt.-%, preferably below 5 wt.-%.
Depending on the nature of the acid, e.g. the number of acid groups
per molecule and its specific structure, the presence of a specific
carboxylic acid or of its anions modifies the pH of the reaction
mixture and therefore complicates the monitoring of the progress of
the FDCA forming reactions by pH. This effect is even more
pronounced as the carboxylic acids present can be oxidized by an
oxygen-containing gas under the oxidation conditions of step (b) as
described above to compounds with changed acidity, and this may
effect the pH further. In such a case the pH could no longer be
used as a measure for the progress of the FDCA forming
reactions.
Moreover, the side reactions between carboxylic acids and the
oxygen-containing gas results in an inefficient use of the
oxygen-containing gas as an oxidizing agent for HMF and di-HMF.
A process of the present invention is preferred, wherein the total
amount of acetate ions and acetic acid in said starting mixture is
below 10 wt.-%, preferably below 1 wt.-%.
A process of the invention is preferred, wherein the step of
preparing said starting mixture (according to step (a)) comprises
(a1) preparing or providing a material mixture comprising one, two
or more compounds selected from the group consisting of hexoses,
oligosaccharides comprising hexose units, and polysaccharides
comprising hexose units, (a2) subjecting said material mixture to
reaction conditions so that a mixture results comprising HMF,
di-HMF, and water, (a3) optionally subjecting the mixture resulting
from step (a2) to additional treatment conditions, preferably
without adding a carboxylic acid and/or without adding an acidic
solvent for dissolving HMF and di-HMF,
so that said starting mixture results.
The term "acidic solvent" designates an aqueous solvent mixture
having a pH below 6 and/or a solvent (aqueous or non-aqueous)
comprising a substance having a pKa below 5.
The process step of subjecting the mixture to reaction conditions
so that a mixture results comprising HMF, di-HMF, and water (i.e.,
process step (a2) as defined above) often comprises a
depolymerization and/or a dehydration step as described above. All
aspects of a depolymerization and/or a dehydration step discussed
herein above in the context of a process of preparing a starting
mixture for a process for preparing furane-2,5-dicarboxylic acid
apply mutatis mutandis for a process according to the present
invention.
In some cases, it is advantageous to conduct depolymerization and
dehydration step (step (a2) as defined above) by using the same
catalyst and/or the same reaction mixture and/or the same
reactor.
In particular, a step of preparing said starting mixture is
preferred as described above (or as preferably described above)
wherein process step (a3) is omitted (no additional treatment
conditions are needed, e.g. solvent change) and the mixture
resulting in process step (a2) is the starting mixture prepared in
process step (a) and subjected to oxidation conditions of process
step (b).
In some cases, it is advantageous to conduct depolymerization and
dehydration step (step (a2)), and the oxidation of HMF and di-HMF
to FDCA (step (b)) in the same reactor.
As described above, di-HMF is produced as a by-product during the
conversion of hexoses or oligosaccharides or polysaccharides (e.g.
cellulose) to HMF. It is therefore a further achievement of the
present invention that di-HMF like HMF is converted to FDCA and
thus contributes to an increase of the overall yield of the
process. The addition of acidic solvent and/or carboxylic acid
should be avoided in order to allow for a monitoring of the process
of the reaction by measuring the pH.
Another advantage of the process of the present invention as
described above is the use of water as a solvent. According to the
present invention it is preferred that after successful conversion
of said one, two or more compounds selected from the group
consisting of hexoses, oligosaccharides comprising hexose units,
and polysaccharides comprising hexose units into HMF (and di-HMF)
the aqueous material mixture obtained in step (a2) (or the aqueous
material mixture obtained after additional treatment in step (a3))
is directly fed into the reactor where the produced HMF and di-HMF
are converted into FDCA (according to step (b) of the present
invention).
It is however even more advantageous if process steps (a2) and (b)
are performed in the same reactor, with an intermediate step (a3)
in the same reactor or without an intermediate step (a3). Therewith
the need for complicated and costly solvent separation, solvent
exchange or solvent purification between steps (a2) and (b) is
reduced or prevented. In many cases, two heterogeneous catalysts
are used in step (a2) and step (b). However, in some cases, the
catalyst can be the same for both steps. Therefore, the overall
process can be simplified by using the same solvent system
throughout steps (a1) to (b).
In particular, a process of the invention is preferred, wherein in
said heterogeneous catalyst comprising one or more noble metals on
a support (i) at least one of said noble metals is selected from
the group consisting of gold, platinum, iridium, palladium, osmium,
silver, rhodium and ruthenium, and/or (ii) said support is selected
from the group consisting of carbon, metal oxides, metal halides,
and metal carbides.
The specific noble metals as stated above under item (i) catalyze
the reaction of HMF into FDCA. Suitable supports for immobilizing
the noble metals as mentioned above are the supports stated above
under item (ii) because they do not negatively affect the reaction
kinetics during the conversion of di-HMF and HMF into FDCA.
A process of the invention is particularly preferred, wherein in
said heterogeneous catalyst comprising one or more noble metals on
a support
at least one of said noble metals is selected from the group
consisting of platinum, iridium, palladium, osmium, rhodium and
ruthenium, preferably platinum,
and
said support is carbon.
Carbon is a suitable support for immobilizing noble metals as
described above, in particular platinum, as it does not negatively
influence the reaction kinetics of the conversion of HMF and di-HMF
into FDCA.
A process of the invention is preferred, wherein in said
heterogeneous catalyst comprising one or more noble metals on a
support said one or one of said more noble metals is platinum and
said support is carbon, and the content of platinum on the support
is in the range of from 0.1 to 20 wt.-%, preferably 1 to 10 wt.-%,
based on the total weight of the heterogeneous catalyst comprising
one or more noble metals on a support.
In order to sufficiently accelerate the reaction of HMF and di-HMF
into FDCA, the loading of platinum on the support should be at
least 0.1 wt.-% (preferably at least 1 wt.-%), based on the total
weight of heterogeneous catalysts comprising one or more noble
metals on a support.
In contrast thereto if too much platinum is immobilized on a
support the conversion per platinum atom decreases due to a lower
average accessibility of the platinum atoms thus leading to a
higher waste of noble metals and thus higher costs.
A process of the invention is preferred, wherein in said
heterogeneous catalyst comprising one or more noble metals on a
support the molar ratio of said one or one of said more noble
metals to the total amount of HMF and di-HMF is in the range of
from 1:1 000 000 to 1:10, preferably in the range of from 1:10 000
to 1:10, more preferably in the range of from 1:1 000 to 1:100,
preferably said one or one of said more noble metals is
platinum.
It is advantageous to convert as much HMF and di-HMF per noble
metal atom as possible to FDCA to increase the yield of FDCA per
batch and to efficiently use the precious noble metal.
A process of the present invention is preferred, wherein the
process is not a process comprising all of the following steps: A)
in an aqueous reactant mixture, catalytically converting one or
more organic reactant compounds by means of at least one
heterogeneous catalyst, so as to form a first product suspension
comprising furan-2,5-dicarboxylic acid in solid form and the
heterogeneous catalyst in solid form, B) heating under pressure 1.
this first product suspension, or 2. a second product suspension
prepared therefrom by further treatment, each comprising
furan-2,5-dicarboxylic acid in solid form and the heterogeneous
catalyst in solid form, such that furan-2,5-dicarboxylic acid
dissolves fully or partly, resulting in a first aqueous product
phase comprising dissolved furan-2,5-dicarboxylic acid, and then C)
separating the heterogeneous catalyst from this first aqueous
product phase comprising dissolved furan-2,5-dicarboxylic acid, or
from a second product phase which results therefrom through further
treatment and comprising dissolved furan-2,5-dicarboxylic acid.
A process of the invention is preferred wherein the product mixture
obtained in step (b) comprises FDCA in dissolved form, and wherein
the product mixture obtained in step (b) preferably does not
comprise FDCA in solid form.
As described above, the precipitation of FDCA in the presence of a
heterogeneous catalyst is highly disadvantageous, as the effect of
the precipitation of FDCA is that both heterogeneous catalyst and
FDCA are present in solid form and can no longer be separated from
one another in a simple manner. As described above, very
frequently, precipitation of FDCA leads, incidentally, to
deactivation of the heterogeneous catalyst. The precipitation of
FDCA on the internal and/or external catalyst surface of a
heterogeneous catalyst can lead to contamination and possible
deactivation of the heterogeneous catalyst. This involves coverage
or coating of the catalytically active constituents of the
heterogeneous catalyst by the precipitated FDCA, such that the
catalytic constituents no longer come into contact with the
reactants. The effect of such a contamination of the catalyst is
that the catalyst does not display the same initial activity, if at
all, and has to be replaced by new catalyst material which
increases the costs. Especially in the case of utilization of
costly catalysts, for example platinum catalysts, such a course of
action is frequently uneconomic.
The present invention also relates to the use of a catalyst
comprising one or more noble metals on a support as an
heterogeneous oxidation catalyst for accelerating in an aqueous
starting mixture the conversion of both HMF and di-HMF to
furane-2,5-dicarboxylic acid. Herein the catalyst preferably is a
catalyst as defined hereinabove or in the attached claims.
Preferred is the use of a catalyst comprising one or more noble
metals (preferably gold, platinum, iridium, palladium, osmium,
silver, rhodium and ruthenium) on a support (preferably carbon,
metal oxides, metal halides, and metal carbides). Moreover, the use
of a catalyst comprising one or more noble metals on a support as
an heterogeneous oxidation catalyst allows to conduct steps (a1),
(a2), optionally (a3), and (b) without solvent exchange and without
addition of expensive chemicals like acetic acid.
Generally, all aspects of the present invention discussed herein
above in the context of a process of preparing
furane-2,5-dicarboxylic acid according to the present invention
apply mutatis mutandis for the use of a catalyst according to the
present invention. And likewise, all aspects of the inventive use
of a catalyst discussed herein above or below apply mutatis
mutandis for a process for preparing furane-2,5-dicarboxylic acid
according to the present invention.
Preferred is the use of a catalyst according to the present
invention in processes as described above, in particular in
processes of making FDCA. All aspects of or associated with
processes of the invention as described above (or as preferably
described above) can also be conducted by or in combination with
the use of a catalyst according to the invention.
By using a catalyst according to the present invention, it is
possible to simultaneously convert di-HMF and HMF into valuable
FDCA and thus to increase the overall yield of the industrial
important production of FDCA from hexoses (e.g. fructose) etc.
Further advantages of a use of a catalyst according to the present
invention are as described herein above generally in the context of
the process of the present invention and more specifically with
respect to preferred aspects of this process.
In many cases the use according to the invention of a catalyst is
preferred, wherein the pH of the starting mixture is 4.0 or higher,
preferably 4.5 or higher, more preferably the pH of the starting
mixture is in the range of from 4.0 to 7.0, most preferably the pH
of the starting mixture is in the range of from 4.5 to 7.0. The
corresponding advantages are as discussed above.
It is thus an achievement of the present invention to allow for a
use of catalyst as defined above which is active in the conversion
of both HMF and di-HMF into FDCA and can readily be separated and
subsequently reused.
The invention is further described in detail hereinafter by
specific aspects:
1. Process for preparing furane-2,5-dicarboxylic acid comprising
the following step: (a) preparing or providing a starting mixture
comprising 5-(hydroxymethyl)furfural (HMF),
5,5'-[oxy-bis(methylene)]bis-2-furfural (di-HMF), and water, (b)
subjecting said starting mixture to oxidation conditions in the
presence of an oxygen-containing gas and a catalytically effective
amount of a heterogeneous catalyst comprising one or more noble
metals on a support so that both HMF and di-HMF react to give
furane-2,5-dicarboxylic acid in a product mixture also comprising
water.
2. Process according to aspect 1, wherein
the starting mixture has a molar ratio of HMF to di-HMF in the
range of from 100 to 0.8, preferably in the range of from 100 to
0.9,
and/or
the total weight of HMF and di-HMF in the starting mixture is in
the range of from 0.1 to 50 wt.-%, preferably in the range of from
1 to 30 wt.-%, more preferably in the range of from 1 to 10 wt.-%,
based on the total weight of the starting mixture.
3. Process according to any preceding aspect, wherein the total
amount of water in the starting mixture is at least 10 wt.-%,
preferably at least 25 wt.-%, more preferably at least 50 wt.-%,
based on the total weight of the starting mixture.
4. Process according to any preceding aspect, wherein the pH of the
starting mixture is 4.0 or higher, preferably 4.5 or higher, more
preferably 5.0 or higher, even more preferably 5.5 or higher, or
the pH of the starting mixture is in the range of from 4.0 to 7.0,
preferably the pH of the starting mixture is in the range of from
4.5 to 7.0, more preferably the pH of the starting mixture is in
the range of from 5.0 to 7.0, even more preferably the pH of the
starting mixture is in the range of from 5.5 to 7.0.
5. Process according to any preceding aspect, wherein the total
amount of HMF in the starting mixture is in the range of from 0.1
to 40 wt.-%, preferably in the range of from 1 to 30 wt.-%, based
on the total weight of the starting mixture.
6. Process according to any preceding aspect, wherein the total
amount of di-HMF in the starting mixture is in the range of from
0.1 to 40 wt.-%, preferably in the range of from 0.1 to 30 wt.-%,
more preferably in the range of from 0.1 to 10 wt.-%, even more
preferably in the range of from 0.2 to 6 wt.-%, based on the total
weight of the starting to mixture.
7. Process according to any preceding aspect, wherein the pH of the
product mixture is below 7 and wherein preferably the pH of the
product mixture is in the range of from 1 to 4.
8. Process according to any preceding aspect, wherein said starting
mixture at a temperature in the range of from 70.degree. C. to
200.degree. C., preferably in the range of from 80.degree. C. to
180.degree. C., more preferably in the range of from 90.degree. C.
to 170.degree. C., even more preferably in the range of from
100.degree. C. to 140.degree. C., is subjected to said oxidation
conditions in the presence of said oxygen-containing gas and said
catalytically effective amount of a heterogeneous catalyst
comprising one or more noble metals on a support, so that both HMF
and di-HMF react to give furane-2,5-dicarboxylic acid in the
product mixture also comprising water and oxidation
by-products.
9. Process according to any preceding aspect, wherein said starting
mixture is subjected to said oxidation conditions in a pressurized
reactor, wherein during said reaction of HMF and di-HMF to FDCA
oxygen or an oxygen-containing gas is continuously fed into and
simultaneously removed from said reactor.
10. Process according to any preceding aspect, wherein said
starting mixture is subjected to said oxidation conditions in a
pressurized reactor, wherein the oxygen partial pressure in the
reactor at least temporarily is in the range of from 200 mbar to 50
bar, preferably in the range of from 1 to 20 bar, during the
reaction of both HMF and di-HMF to furane-2,5-dicarboxylic
acid.
11. Process according to any preceding aspect, wherein said
starting mixture does not comprise a catalytically effective amount
of a homogeneous oxidation catalyst selected from the group of
cobalt, manganese, and bromide compounds, and mixtures thereof.
12. Process according to any preceding aspect, wherein the total
amount of cobalt and manganese and bromide ions in the starting
mixture is below 100 ppm, preferably below 20 ppm.
13. Process according to any preceding aspect, wherein the total
amount of acetate ions and acetic acid in said starting mixture is
below 10 wt.-%, preferably below 1 wt.-%.
14. Process according to any preceding aspect, wherein the total
amount of carboxylic acid ions and carboxylic acid in the starting
mixture is below 10 wt.-%, preferably below 5 wt.-%.
15. Process according to any preceding aspect, wherein the step of
preparing said starting mixture comprises (a1) preparing or
providing a material mixture comprising one, two or more compounds
selected from the group consisting of hexoses, oligosaccharides
comprising hexose units, and polysaccharides comprising hexose
units, (a2) subjecting said material mixture to reaction conditions
so that a mixture results comprising HMF, di-HMF, and water, (a3)
optionally subjecting the mixture resulting from step (a2) to
additional treatment conditions, preferably without adding a
carboxylic acid and/or without adding an acidic solvent for
dissolving HMF and di-HMF,
so that said starting mixture results.
16. Process according to any preceding aspect, wherein in said
heterogeneous catalyst comprising one or more noble metals on a
support (i) at least one of said noble metals is selected from the
group consisting of gold, platinum, iridium, palladium, osmium,
silver, rhodium and ruthenium, and/or (ii) said support is selected
from the group consisting of carbon, metal oxides, metal halides,
and metal carbides.
17. Process according to any preceding aspect, wherein in said
heterogeneous catalyst comprising one or more noble metals on a
support
at least one of said noble metals is selected from the group
consisting of platinum, iridium, palladium, osmium, rhodium and
ruthenium, preferably platinum
and
said support is carbon.
18. Process according to any preceding aspect, wherein in said
heterogeneous catalyst comprising one or more noble metals on a
support said one or one of said more noble metals is platinum and
said support is carbon, and the content of platinum on the support
is in the range of from 0.1 to 20 wt.-%, preferably 1 to 10 wt.-%,
based on the total weight of the heterogeneous catalyst comprising
one or more noble metals on a support.
19. Process according to any preceding aspect, wherein in said
heterogeneous catalyst comprising one or more noble metals on a
support
the molar ratio of said one or one of said more noble metals to the
total amount of HMF and di-HMF is in the range of from 1:1 000 000
to 1:10, preferably in the range of from 1:10 000 to 1:10, more
preferably in the range of from 1:1 000 to 1:100, preferably said
one or one of said more noble metals is platinum.
20. Process according to any preceding aspect, wherein the process
is not a process comprising all of the following steps: A) in an
aqueous reactant mixture, catalytically converting one or more
organic reactant compounds by means of at least one heterogeneous
catalyst, so as to form a first product suspension comprising
furan-2,5-dicarboxylic acid in solid form and the heterogeneous
catalyst in solid form, B) heating under pressure 1. this first
product suspension, or 2. a second product suspension prepared
therefrom by further treatment, each comprising
furan-2,5-dicarboxylic acid in solid form and the heterogeneous
catalyst in solid form, such that furan-2,5-dicarboxylic acid
dissolves fully or partly, resulting in a first aqueous product
phase comprising dissolved furan-2,5-dicarboxylic acid, and then C)
separating the heterogeneous catalyst from this first aqueous
product phase comprising dissolved furan-2,5-dicarboxylic acid, or
from a second product phase which results therefrom through further
treatment and comprising dissolved furan-2,5-dicarboxylic acid.
21. Process according to any preceding aspect, wherein the product
mixture obtained in step (b) comprises furan-2,5-di carboxylic acid
in dissolved form and wherein the product mixture obtained in step
(b) preferably does not comprise furan-2,5-dicarboxylic acid in
solid form.
22. Use of a catalyst comprising one or more noble metals on a
support as an heterogeneous oxidation catalyst for accelerating in
an aqueous starting mixture the conversion of both HMF and di-HMF
to furane-2,5-dicarboxylic acid, wherein the catalyst preferably is
a catalyst as defined in any of aspects 1 to 21.
23. Use of a catalyst according to aspect 22, wherein the pH of the
starting mixture is 4.0 or higher, preferably 4.5 or higher, more
preferably the pH of the starting mixture is in the range of from
45.0 to 7.0, most preferably the pH of the starting mixture is in
the range of from 4.5 to 7.0.
Throughout the present text, preferred aspects and features of the
present invention, i.e. the process of the present invention and
the use of the present invention, are preferably combined with each
other in order to arrive at particularly preferred processes and
uses in accordance with the present invention.
The invention is illustrated in detail hereinafter by examples.
EXAMPLES
Catalyst Screening Experiments:
Catalyst screening was carried out in a series of single
experiments designated "Experiment 1" to "Experiment 3". In each
single experiment "1" to "3" the organic reactant compounds HMF and
di-HMF were in parts catalytically converted by means of a
heterogeneous platinum catalyst to FDCA. The general experimental
procedure for each screening experiment of "1" to "3" was as
follows:
In a first step, by filling into a steel autoclave reactor (inner
volume 90 ml) specific amounts of deuterated water (D.sub.2O, 99.9
atom %, Sigma Aldrich (151882)), HMF (99+%), and di-HMF (99+%) an
aqueous starting material mixture was prepared having a composition
similar to the composition of HMF feed-streams usually obtained in
sugar dehydration). The amounts of the reactants and D.sub.2O are
identified in table 1 below:
TABLE-US-00001 TABLE 1 D.sub.2O 28.5 g total amount of reactants
1.5 g HMF and di-HMF HMF 1.0, 0.75 or 0.5 g di-HMF* 0.5, 0.75 or
1.0 g *di-HMF can, e.g., be synthesized according to WO
2013/033081, example 45.
The starting concentration C.sub.0[HMF+di-HMF] of HMF+di-HMF in
each aqueous reactant mixture was correspondingly 5% by weight,
based on the total mass of the aqueous reactant mixture (total mass
of deuterated water, HMF and di-HMF). The solid heterogeneous
catalyst (0.928 g of 5 wt % Pt/C, 50 wt % H.sub.2O) was added to
the respective aqueous reactant mixture and, thus, a reaction
mixture comprising deuterated water, HMF, di-HMF, and the
heterogeneous catalyst was obtained.
In a second step, the filled reactor was tightly sealed and
pressurized with synthetic air (total pressure 100 bar to obtain
conditions so that both HMF and di-HMF react to give FDCA. The
starting mixture in the reactor comprising HMF, di-HMF and
deuterated water was heated to a temperature of 100.degree. C.
while stirring at 2000 rpm. After reaching 100.degree. C., this
temperature was maintained for 18 hours while continuing stirring
the heated and pressurized reaction mixture during the reaction
time. A product mixture comprising FDCA, oxidation by-products,
deuterated water and the heterogeneous catalyst resulted.
In a third step, after the temperature had been maintained for 18
hours, to give a cooled product mixture the steel autoclave reactor
was (i) allowed to cool down to room temperature (approximately
22.degree. C.), (ii) depressurized and (iii) opened.
The product mixture obtained was in the form of a suspension.
For the purpose of product analysis of the cooled product mixture,
a solution of deuterated sodium hydroxide (NaOD, 40 wt.-% in
D.sub.2O, 99.5 atom % D, Sigma Aldrich) was carefully added to the
product mixture until a slightly alkaline product mixture having a
pH in the range of from 9 to 10 was reached. The slightly alkaline
product mixture comprised the disodium salt of FDCA in completely
dissolved form, and the heterogeneous catalyst in solid form.
In a fourth step, the heterogeneous catalyst in the slightly
alkaline product mixture was separated from the solution by syringe
filtration, and the filtrate (i.e. the remaining solution
comprising the disodium salt of FDCA in completely dissolved form)
was subsequently analyzed by .sup.1H-NMR spectroscopy. .sup.1H-NMR
spectroscopy was used to determine the concentration of FDCA, FFCA,
HMF and di-HMF.
NMR Analysis:
NMR sample preparation and NMR measurements:
3-(Trimethylsilyl)propionic-d.sub.4 acid sodium salt (Standard 1,
68.39 mg, corresponding to 0.397 mmol, 98+ atom % D, Alfa Aesar
(A14489)) and Tetramethylammonium iodide (Me.sub.4N+I-, Standard 2,
80.62 mg, corresponding to 0.397 mmol, 99%, Alfa Aesar (A12811))
were added as internal standards to 5.0 g of a slightly alkaline
product mixture, exhibiting a pH value in the range of from 9 to
10. Finally, 0.7 ml of this prepared sample liquid were transferred
into a NMR tube for .sup.1H NMR quantification experiments.
NMR-spectra were recorded in D.sub.2O at 299 K using a Bruker-DRX
500 spectrometer with a 5 mm DUL 13-1H/19F Z-GRD Z564401/11 probe,
measuring frequency 499.87 MHz. Recorded Data were processed with
the software Topspin 2.1, Patchlevel 6 (Supplier: Bruker BioSpin
GmbH, Silberstreifen 4, 76287 Rheinstetten, Germany).
Interpretation of NMR spectra:
Interpretation of NMR spectra is based on published reference data
as indicated below.
Disodium salt of FDCA (disodium salt of compound of formula
(I)):
.sup.1H NMR (500 MHz, D2O, 299 K): 6.97 ppm (2H, s, furan-H);
13C{1H} NMR: 166.1 ppm (--COO), 150.0 ppm (furan C atoms), 115.8
ppm (furan C atoms).
Reference: J. Ma, Y. Pang, M. Wang, J. Xu, H. Ma and X. Nie, J.
Mater. Chem., 2012, 22, 3457-3461.
Sodium salt of FFCA (sodium salt of compound of formula V):
.sup.1H NMR (500 MHz, D2O, 299 K): 9.49 ppm (1H, s, --CHO); 7.42
ppm (1H, d, 3J=3.67 Hz, furan-H); 7.03 ppm (1H, d, 3J=3.67 Hz,
furan-H).
Reference: A. J. Carpenter, D. J. Chadwick; Tetrahedron 1985,
41(18), 3803-3812.
Screening Experiments:
In each single experiment a cooled product mixture, and based
thereon a slightly alkaline product mixture comprising the disodium
salt of FDCA in completely dissolved form was obtained. As shown in
Table 1, HMF conversion in mol % and yield in mol % are
summarized.
TABLE-US-00002 TABLE 1 Relevant parameters of catalyst screening
experiments. HMF di-HMF Cat- di- Con- Con- alyst HMF HMF version
version Y.sub.FDCA Y.sub.FFCA Exp. [g] [g] [g] [mol %] [mol %] [mol
%] [mol %] 1 0.928 1.00 0.50 100 100 78.3 <1.0 2 0.928 0.75 0.75
100 100 63.4 1.4 3 0.928 0.50 1.00 100 100 48.2 3.3
TABLE-US-00003 TABLE 2 Relevant parameters of catalyst screening
experiments. HMF HMF di-HMF di-HMF ratio of FDCA Y.sub.FDCA
Y.sub.FFCA C.sub.HMF+di-HMF Y.sub.min, di-HMF Exp. [g] [mmol] [g]
[mmol] HMF:di-HMF [mmol] [mol %] [mol %] [mol %] [mol %] 1 1.00
7.93 0.50 2.13 3.72 9.58 78.3 <1.0 65.1 13.2 2 0.75 5.95 0.75
3.20 1.86 7.86 63.4 1.4 48.2 15.2 3 0.50 3.96 1.00 4.27 0.93 6.07
48.2 3.3 31.7 16.5
HMF conversion in mol % was calculated as follows (di-HMF
conversion was calculated accordingly): HMF Conversion[mol
%]=[1-(C.sub.final[HMF]/C.sub.0[HMF])]*100,
wherein C.sub.[HMF] is the concentration in % by weight measured in
the slightly alkaline product mixture and C.sub.0[HMF] is the
concentrations in % by weight measured based on the added amount of
HMF and the volume of the starting mixture.
"Conversion [mol %]" and "yield [mol %]" are average values
calculated from a first value based on internal standard 1 and a
second value based on internal standard 2 (general deviation is
less than 5%).
The yield definition (exemplified for FDCA):
.times..times. ##EQU00001##
wherein n.sub.[FDCA]=[mol FDCA (based on Standard 1)+mol FDCA
(based on Standard 2)]/2 n.sub.[HMF]=m.sub.0[HMF]/M.sub.[HMF] and
n.sub.[di-HMF]=M.sub.0[di-HMF]/M.sub.[di-HMF]
wherein C.sub.[FDCA] is the concentration of FDCA in % by weight in
the filtrate obtained in the fourth step, C.sub.0[HMF] is the HMF
starting concentration in % by weight, C.sub.0[di-HMF] is the
di-HMF starting concentration in % by weight, M.sub.FDCA, M.sub.HMF
and M.sub.di-HMF are the respective molecular weights in g/mol.
The yield [mol %] for FFCA was determined mutatis mutandis as for
the yield of FDCA.
The amount of converted HMF based on the amount of HMF and di-HMF
(C.sub.HMF+di-HMF) was calculated by the following formula:
.times..times..times..times. ##EQU00002##
The minimum yield of di-HMF (Y.sub.min,di-HMF) was calculated by:
Y.sub.min,di-HMF=Y.sub.FDCA-C.sub.HMF+di-HMF
In table 1, the results of the three experiments described above
are shown. In all three experiments the molar amount of FDCA
obtained after oxidation is larger than the molar amount of HMF
provided at the beginning of the corresponding experiment. Thus,
di-HMF was successfully converted into FDCA, with a considerable
yield.
Moreover, table 1 shows that the yield of FDCA is increasing with
increasing ratio n.sub.HMF/(h.sub.HMF+2n.sub.di-HMF).
* * * * *