Polyurethane as Novel Catalyst for the Propoxylation of Fatty Amines

Article abstract of DOI:10.1002/cctc.202000337

The propoxylation of fatty amines is a crucial reaction in the industrial production of surfactants. Catalyzing this reaction has so far proven unrewarding due to severe selectivity losses. In this study, rigid foam-structured polyurethane, i. e., an extremely inexpensive material which has not been used as a catalyst ever before, shows an unprecedented catalytic activity during the in-flow propoxylation of octylamine. The foam cells contain bound hydroxyl and amine groups that result in a bifunctional catalyst able to destabilize the ring structure of propylene oxide, and thus catalyze further propoxylation of fatty amines. An outstanding 10-fold reduction of the residence time without any loss of selectivity is achieved with respect to the un-catalyzed process. Furthermore, the polyurethane foam showed stable time-on-stream performance up to 10 bar and 110 °C.

Full text of DOI:10.1002/cctc.202000337

The European Society Journal for Catalysis
Supported by
Accepted Article
Title: Polyurethane as Novel Catalyst for the Propoxylation of Fatty
Amines
Authors: Pia Mueller, Maria Fernanda Neira d'Angelo, and John van
der Schaaf
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: ChemCatChem 10.1002/cctc.202000337
Link to VoR: https://doi.org/10.1002/cctc.202000337
01/2020

10.1002/cctc.202000337
ChemCatChem
COMMUNICATION
Polyurethane as Novel Catalyst for the Propoxylation of Fatty
Amines
Pia Müller[a], Maria Fernanda Neira d’Angelo[a] and John van der Schaaf*[a]
Abstract: The propoxylation of fatty amines is a crucial reaction in the
industrial production of surfactants. Catalyzing this reaction has so far
proven unrewarding due to severe selectivity losses. In this study,
rigid foam-structured polyurethane, i.e., an extremely inexpensive
material which has not been used as a catalyst ever before, shows an
unprecedented catalytic activity during the in-flow propoxylation of
octylamine. The foam cells contain bound hydroxyl and amine groups
that result in a bi-functional catalyst able to destabilize the ring
structure of propylene oxide, and thus catalyze further propoxylation
of fatty amines. An outstanding 10-fold reduction of the residence time
without any loss of selectivity is achieved with respect to the un-
catalyzed process. Furthermore, the polyurethane foam showed
stable time-on-stream performance up to 10 bar and 110 °C.
While the single functionality did show some catalytic
enhancement (e.g. PVA showed 1.5 times the activity of the
blank), the bi-functionality prompted a much stronger catalytic
enhancement (i.e., 16 times the blank, Table S2 in SI). In this
context, polyurethane foams containing the desired bi-
functionality and showing an open cell structure that is ideal for
heterogeneous catalysis became particularly attractive, and thus
the focus of this study. While the effect of the hydroxyl groups
(PU-OH) is clear, the role of the amine on the PU is yet uncertain.
One possible explanations its involvement as a proton “shuttle” in
the overall process, as the octylamine protons have to be
transferred back to the newly deprotonated PU-OH groups
(Figure 1).
As recently reviewed, polyurethane is a versatile material for
manifold applications,[13] including catalytic support and as
structural copolymer.[14–17] However, its use as catalytically active
material has not been reported, to the best of our knowledge.
Herein we report, for the first time, the use of rigid polyurethane
foams (hereafter PU foam) as a bi-functional catalyst for the
propoxylation of octylamine. The two catalytic active sites are as
following:
1) hydroxyl groups, resulting from excess diols used in the
formation of urethane groups.
2) amine groups, produced during foam blowing with water,
which reduces isocyanates to amines and CO2.
Propoxylated fatty amines are widely used as non-ionic
surfactants, with a steady increase in industrial demand over the
past six decades. Since the 1950’s, the propoxylation of fatty
amines has been known to proceed auto-catalytically (i.e., in the
absence of an additional catalysts[1]) and is therefore performed
semi-batch wise. Concerns about safety and product quality due
to formation of side products under intensified or catalytic
conditions have justified a lack of innovation in this field in the last
decades. While a number of new reactor systems have been
proposed[2–4], research about catalytic enhancement has proven
futile for this system. Catalysts used in the ethoxylation of phenols
and acids, e.g., hydroxide salts[5–7], zeolites [8,9] or organometallic
compound[10], are not active enough nor selective in the amine
process.
OH
PU
O
NH2
+
2
R

C
10 bar, 70 -130
N
R
OH
In our previous work, the butoxylation of dodecylamine was found
to be auto-catalytic, being both the amine and hydroxyl groups in
the formed products the active species.[11] It is generally
understood that the reaction mechanism proceeds via
destabilization of the epoxide ring in the presence of proton
donating groups[12].Our work concluded that the amine group
adds to the destabilizing effect, and interacts with the resulting
species to forming an even more reactive intermediate than the
epoxide alone with hydroxyl groups. In this study, a preliminary
screening of various catalyst materials was added to the
previously performed screening of homogenous catalysts (Table
S2 in SI and Figure S8). The screenings reveal that, for the
propoxylation and butoxyilation of fatty amines, the co-addition of
catalysts containing both amine and alcohol groups (e.g. ethanol-
ethylamine) is essential to significantly increase the reaction rate.
PU O
H
H
O
H
O
PU O
- H
+
N
R
NH2
R
Figure 1. Propoxylation of fatty amines. Amine and alcohol groups destabilize
the propylene oxide ring, thus increasing the effective collision. Epoxide ring
opening catalysed by hydroxyl group of polyurethane.
The rigid PU foam with the tradename Tricast 5 was purchased
from Goodfellow. According to mercury porosimetry
measurements, the pore area is 1.87 m2/g and the pore diameter
is narrowly distributed around 2.5 μm. Initially, the foam contains
over 95% closed cells, as reported by the purchaser. The supplied
[a]
P. Müller Msc, Dr. M.F. Neira d’Angelo, Dr. J. van der Schaaf
Group of Sustainable Process Engineering ,
Department of Chemical Engineering and Chemistry
Eindhoven University of Technology
P.O. Box 513, 5600 MB Eindhoven (The Netherlands)
E-mail: j.vanderschaaf@tue.nl
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/cctc.202000337
ChemCatChem
COMMUNICATION
Figure 3. FTIR of PU foam normalized for as received foam and washed foam
after reaction.
The used PU foams show similar FTIR spectrum, with additional
peaks around 2800 cm-1 ν(C-H), corresponding to the alkyl chain
skeleton of residual octylamine and its products. A smaller peak
around 1750 cm-1 ν(C=O stretch) also appeared after the reaction
at 110 °C, which Mishra et al. described, in regard to PU-urea-
imide copolymers, as free and proton bond carbonyl groups.[15] In
the reaction stream two additional absorption peaks were formed
at 1030 and 1100 cm-1 after the conversion started dropping at
130 °C (> 90 min). These absorption overlap with the PU foams,
amine and ether vibrations (Figure 3). Therefore showing only the
decomposed PU particles flowing in the product stream. No other
side or decomposition products were found (compare SI).These
observations suggest that the PU foams are chemically stable
until 70 °C and can be used as heterogeneous catalyst. During
the reaction at 110 °C some degree of polymer chain cleavage
occurs, breaking the urethane bond close to the carbonyl
group.[19] At this point some contribution of homogeneous
catalysts cannot be discarded entirely. Yet, the time-on-stream
catalytic performance remains stable up to 110 °C (Figure 2c).
SEM images reveal that the initially closed foam cells (supplied
with 95% closed cell, (Figure 4b), open upon exposure to flow
conditions, even at room temperature, resulting in an open foam
structure (<5% closed, Figure 4c). This mechanical opening of the
foam structure at the start of the operation is believed to be
beneficial for the catalytic activity since it improves the
accessibility of the reactants to the active sites. The structural
integrity of the open cell foams during operation was confirmed
up to 110 °C by a stable time-on-stream catalytic performance
(Figure 2c), and by visual inspection of the used foams after the
reaction.
Figure 2. Conversion of propylene oxide in the reaction with octylamine versus
(a) residence time at 90 °C and 0.22 gcat; (b) weight of catalyst at τ= 55 min; (c)
time-on-stream (expressed as number of successive cycles) and temperature
at τ= 18 min and 0,22 gcat
.
foam is slightly basic (pH 9 in solution). For the catalytic tests, the
as received PU foam is cut into cylinders with the dimensions of
ø 7.5 x 10 mm (Figure 4a).
The catalytic activity of the PU foams during the propoxylation of
octylamine is demonstrated by performing flow-through
experiments in the ranges of 20 to 90 min residence time (Figure
2a), using a range of catalytic weight from 0 to 0.5 g of PU (Figure
2b), and temperatures from 70 to 130 °C (Figure 2c). The
selectivity was in the pretest 0.95, in the flow experiments a
selectivity of 0.99 was even observed. Figure 2a shows that,
under same reaction conditions, the conversion increases by a
factor 10 in the PU foam-catalyzed reaction with respect to the
un-catalyzed benchmark at 90 °C. This could lead to a potential
process intensification by reduction of reactor sizes or reaction
temperature (e.g. from 180 °to 110 °C) to reach equal productivity.
Furthermore, the linear dependence of conversion on the catalyst
weight (Figure 2b) clearly demonstrates that the PU foam acts as
catalyst during this reaction. The strong dependence of
conversion on temperature (Figure 2c) further suggests absence
of (external) mass transport limitations. Although the maximum
reaction rate is achieved at 130 °C (i.e., the highest temperature
explored in this work), clear evidences of catalyst deactivation
under these reaction conditions are observed. Below 130 °C, the
PU shows stable catalytic performance during the total explored
time-on-stream of 200 minutes.
The chemical stability of the PU foams is analyzed by FTIR
(Figure 3). The spectrum of the as received PU foam corresponds
to the spectra found in the polymers and plasticizers.[18] The main
characteristic bands are marked in Figure 3.
This article is protected by copyright. All rights reserved.

10.1002/cctc.202000337
ChemCatChem
COMMUNICATION
an inline FTIR coupled with a sampling point for GC samples, leading to
continuous process analysis. A more detailed description of the set-up,
parts and chemicals can be found in the SI.
Acknowledgements
This research was carried out within the HighSinc program – a
joint development between Nouryon Specialty Chemicals and
the Department of Chemical Engineering and Chemistry from
Eindhoven University of Technology. The authors thank T. di
Martino for support in SEM data acquisition.
Conflict of interest
The authors declare no conflict of interest.
Keywords: amines • autocatalysis • epoxidation •heterogeneous
catalysis • polyurethane foam
Figure
4. PU Foam. a) image of PU foam as used in reaction, b-d) SEM images
[1]
[2]
S. Komori, T. Karaki, Chem. Soc. Jpn. 1959, 62, 538–542.
L. L. van Dierendonck, J. Zahradnik, V. Linek, Ind. Eng. Chem. Res.
1998, 37, 734–738.
of PU foam cells as received and used after reactions at two temperatures
.
[3]
[4]
M. Di Serio, R. Tesser, E. Santacesaria, Ind. Eng. Chem. Res. 2005,
44, 9482–9489.
F. Sirovski, S. Mulyashov, V. Shvets, Chem. Eng. J. 2006, 117, 197–
203.
At even higher reaction temperatures, more severe structural
changes take place (Figure 4d). While in tests at ambient
conditions the PU foam proved catalytically stable over a period
of more than a month, the loss of catalytic activity at 130 °C is
attributed to: 1) thermal instability of the polyurethane foam,[20]
which has an upper service temperature at around 90 °C; and/or
2) chemical instability caused by attack of propylene oxide and
consequent decomposition of the polyurethane structure above
120 °C to polyols, ureas and amine species’.[19] Overall, the PU
foam loses its structural integrity and reduces to particles smaller
than 0.75 mm, thus passing through the filter at the reactor outlet,
and impeding further characterization of the spent sample.
[5]
[6]
[7]
R. M. Laird, R. E. Parker, J. Chem. Soc. B 1969, 1062–1068.
M. Lukosek, K. Alejski, Przem. Chem. 2016, 95, 2352–2358.
Y. N. Chiu, J. Naser, A. Easton, K. F. Ngian, K. C. Pratt, Chem. Eng.
Sci. 2010, 65, 1167–1172.
I. N. Senchenya, V. B. Kazansky, Catal. Lett. 1991, 8, 317–325.
J. Trejbal, M. Petrisko, J. Pašek, Pet. Coal 2012, 54, 340–347.
J. Herzberger, K. Niederer, H. Pohlit, J. Seiwert, M. Worm, F. R.
Wurm, H. Frey, Chem. Rev. 2016, 116, 2170–2243.
P. Müller, R. D. E. Krösschell, W. Winkenwerder, J. van der Schaaf,
Chem. Eng. J. 2019, 122939.
J. W. Holubka, R. D. Bach, J. L. Andres, Macromolecules 1992, 25,
1189–1192.
H.-W. Engels, H.-G. Pirkl, R. Albers, R. W. Albach, J. Krause, A.
Hoffmann, H. Casselmann, J. Dormish, Angew. Chem., Int. Ed. 2013,
52, 9422–9441.
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
L. Lefebvre, J. Kelber, L. Jierry, V. Ritleng, D. Edouard, J. Environ.
Chem. Eng. 2017, 5, 79–85.
A. K. Mishra, D. K. Chattopadhyay, B. Sreedhar, K. V. S. N. Raju,
Prog. Org. Coat. 2006, 55, 231–243.
P. A. Charpentier, K. Burgess, L. Wang, R. R. Chowdhury, A. F.
Lotus, G. Moula, Nanotechnology 2012, 23, 425606.
S. Gunashekar, N. Abu-Zahra, Int. J. Polym. Sci. 2014, 2014, DOI
10.1155/2014/570309.
“Polymer Additives and Plasticizers Spectral Library,” can be found
under http://www.thermofisher.com/order/catalog/product/834-008300,
2018.
M. B. Sheratte, Process for Converting the Decomposition Products of
Polyurethane and Novel Compositions Thereby Obtained, 1978,
US4110266A.
D. K. Chattopadhyay, D. C. Webster, Prog. Polym. Sci. 2009, 34,
1068–1133.
In conclusion, we have shown unprecedented catalytic activity of
commercially available polyurethane foam on the propoxylation of
octylamine; i.e., an industrially relevant reaction that could not be
catalyzed selectively before. The catalytic activity of PU foam is
attributed to the hydroxyl and amine groups present in the blown
foam cells. The currently available polyurethane foams are not
stable enough to operate at elevated temperatures (i.e., 130 °C
and above) but show great potential to intensify the reaction
without loss of selectivity up to 110 °C. While common methods
to avoid or reduce catalyst degradation/deactivation involve
modification of the process conditions,[21] in this case, further
material development would likely be a more efficient solution.
The design of a heterogeneous catalyst with the same hydroxyl
and amino functionalities of the PU, but with increased thermo-
chemical- stability at elevated temperatures, could potentially lead
to a paradigm shift in the propoxylated amine production.
[19]
[20]
[21]
W. Wang, L. Cui, P. Sun, L. Shi, C. Yue, F. Li, Chem. Rev. 2018, 118,
9843–9929.
Experimental Section
The experiments were performed in a tubular reactor connected to a flow
set-up. The foam was cut into cylinders and placed in the reactor
separated by glass beads to avoid a large pressure drop. Both propylene
oxide and octylamine were stoichiometrically mixed and pumped through
the reactor, which was immersed in an oil bath. The backpressure of 10
bar guaranteed a one liquid phase mixture. The set-up was connected to
This article is protected by copyright. All rights reserved.

10.1002/cctc.202000337
ChemCatChem
COMMUNICATION
COMMUNICATION
Text for Table of Contents
Pia Müller, Maria Fernanda Neira
d’Angelo and John van der Schaaf*
Page No. – Page No.
Polyurethane as Novel Catalyst for
the Propoxylation of Fatty Amines
Kitchen Sponge goes catalyst: Polyurethane foam was discovered as novel catalyst for production of nonionic surfactants by
supporting the epoxide ring opening without side product formation. A conversion increase of a factor 10 was observed with a
chemically stable foam till 110 °C.
Institute Twitter username: @TUe_ST
This article is protected by copyright. All rights reserved.