Preparation of a sulfonated carbonaceous material from lignosulfonate and its usefulness as an esterification catalyst

Article abstract of DOI:10.3390/molecules18078168

Sulfonated carbonaceous material useful as a solid acid catalyst was prepared from lignosulfonate, a waste of the paper-making industry sulfite pulping process, and characterized by 13C-NMR, FT-IR, TGA, SEM and elemental analysis, etc. The sulfonic acid group density and total density of all acid groups in the sulfonated carbonaceous material was determined by titration to be 1.24 mmol/g and 5.90 mmol/g, respectively. Its catalytic activity in the esterification of cyclohexanecarboxylic acid with anhydrous ethanol was shown to be comparable to that of the ionic exchange resin Amberlyst-15, when they were used in the same amount. In the meantime, the sulfonic acid group was found to be leached out by 26%-29% after it was exposed to hot water (95 °C) for 5 h. The catalytic usefulness of the prepared carbonaceous material was investigated by performing esterifications.

Full text of DOI:10.3390/molecules18078168

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Molecules 2013, 18, 8168-8180; doi:10.3390/molecules18078168
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molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Preparation of a Sulfonated Carbonaceous Material from
Lignosulfonate and Its Usefulness as an Esterification Catalyst
Duckhee Lee
The Division of Bionanochemistry, the College of Natural Sciences, the Wonkwang University,
Iksan City, Chonbuk 570-749, Korea; E-Mail: dl202@wku.ac.kr; Tel.: +82-63-850-6225;
Fax: +82-63-850-7312
Received: 3 May 2013; in revised form: 26 June 2013 / Accepted: 8 July 2013 /
Published: 10 July 2013
Abstract: Sulfonated carbonaceous material useful as a solid acid catalyst was prepared
from lignosulfonate, a waste of the paper-making industry sulfite pulping process, and
13
characterized by C-NMR, FT-IR, TGA, SEM and elemental analysis, etc. The sulfonic
acid group density and total density of all acid groups in the sulfonated carbonaceous
material was determined by titration to be 1.24 mmol/g and 5.90 mmol/g, respectively. Its
catalytic activity in the esterification of cyclohexanecarboxylic acid with anhydrous
ethanol was shown to be comparable to that of the ionic exchange resin Amberlyst-15,
when they were used in the same amount. In the meantime, the sulfonic acid group was
found to be leached out by 26%–29% after it was exposed to hot water (95 °C) for 5 h.
The catalytic usefulness of the prepared carbonaceous material was investigated by
performing esterifications.
Keywords: sulfonated carbonaceous material; lignosulfonate; solid acid catalyst
1. Introduction
Over the recent two decades or so carbon-based solid acids have received much attention in the
fields of catalysis and organic synthesis [1–14]. Like other solid acids, they have several advantages
such as readiness of separation from the reaction mixture, resulting reusability, and reduction in the
amount of waste water generated in washing processes for removing the remaining acid from products,
compared to homogenous catalysts such as p-toluenesulfonic acid or sulfuric acid when used in
organic reactions. Among the carbon-based solid acids reported so far in the literature, sulfonated
carbonaceous materials are most noteworthy since they are strong enough acids to be used as a catalyst

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Molecules 2013, 18
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for several types of organic reactions, thermally stable up to 150–200 °C, and are also prepared from
cheap raw materials such as aromatic hydrocarbons, carbohydrates, and sulfuric acid. Since first
reported by Hara et al. [15], several research groups have shown that amorphous carbon bearing
SO3H groups could be prepared by treating various types of organic compounds with conc. sulfuric
acid [16–25]. In this preparation, a series of reactions like elimination, rearrangement of the carbon
back bone, gas evolution, condensation, and sulfonation, etc., were known to occur in one pot to give
carbonaceous compounds with graphene-like structures containing SO3H, OH, and CO2H groups on
the edge of their sheet-structure molecules. Here a new preparative method for such catalysts using as
a raw material lignosulfonate, which is a by-product of the sulfite pulping process of the paper-making
industry, is presented, together with some catalytic characteristics of the product. As a starting
material, lignosulfonate is an interesting compound because it already has a sulfonic acid group on the
sp3 carbon of the molecule and an activated aromatic ring available for electrophilic sulfonation.
Therefore it was chosen as a starting material with a hope that some catalyst characteristics such as
density of SO3H groups and resistance to hydrolysis might be improved.
2. Results and Discussion
2.1. Material Synthesis and Acid Density, BET Surface Area
The catalyst was prepared from the lignosulfonate according to Scheme 1. Conc. sulfuric acid and
fuming sulfuric acid were used as a sulfonating agent in the reactions. The same type of reaction was
carried out with glycerol to obtain a standard material for comparison.
Scheme 1. Preparation of the sulfonated carbonaceous material.
H3CO
SO3Na
HO
H2SO4
+
OH
H(or Lignin)
Lignin
CO2H
CO2H
SO3H
SO3H SO3H
H3CO
HO2C
OH
HO3S
H
SO3H SO3H

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After the initial exothermic reaction settled down, the reaction product was filtered and
thoroughly washed with deionized water until no sulfate ion was detected by a test using aqueous
barium chloride solution.
The reaction conditions and acid density values obtained by titration on the products are
summarized in Table 1 together with the elemental analysis data and BET surface area data. The
surface areas of the synthesized carbonaceous materials were small, 2.18–3.19 m2/g and not much
different from that of the material made of glycerol, 1.79 m2/g. The low surface area may be
attributable to the non-porous structure of the materials. The density of SO3H groups in the material
was 1.24 mmol/g, indicating a much lower value than that of the commercial ion exchange resin ,
Amberlyst-15 while the total acidity expressed as a sum of all acidic groups such as phenolic OH,
CO2H, and SO3H was found to be similar to that of the well-known ion exchange resin Amberlyst-15.
The higher value of the total acidity than the density of SO3H group can be interpreted as due to the
presence of many acidic groups like phenolic OH or CO2H groups in addition to SO3H groups in the
materials. It is interesting that the sulfonated carbonaceous material prepared with fuming sulfuric acid
(run 3) has a higher total acidity value than the other samples. This can be attributed to the higher
oxidizing ability of the fuming sulfuric acid, compared with normal sulfuric acid.
Table 1. The acid density and surface area of the prepared carbonaceous material with
SO3H groups.
Samples
N2 adsorption
(Surface area)
1.79 m2/g
3.19 m2/g
2.18 m2/g
T. A
SO3H
CO2H
OH
(mmol/g)
0
E.A
(mmol H+/g) (mmol/g) (mmol/g)
Run
(Raw materials)
Gly(100%), Sul
1)Lig(100%), Sul
2)Lig(100%),Sul(fum)
3)Amberlyst-15
1
2
3
4
4N.A
4.86
4.64
5.90
4.66
1.24
0.96
1.24
4.60
3.66
3.36
3.66
N.A
CH0.72O0.53S0.017
CH0.59O0.26S0.015
4)N.A
0.32
1.04
45 m2/g
N.A
Abbreviations: Gly: Glycerol, Lig: Sodium Lignosulfonate, Sul: 96% sulfuric acid, Sul(fum): sulfuric acid (20% fuming)
E.A: Elemental analysis, T. A: Total acidity, SO3H, CO2H, and OH represent their density respectively. 1) Reaction
temperature: 150–175 °C, Reaction time: 0.5 h; 2) Two continuous reactions: the first reaction; Reaction temperature:
150–175 °C, Reaction time: 50 min, and then followed by the second reaction; reaction temperature: 150–175 °C,
reaction time: 12 hr, sulfonating agent: 20% fuming H2SO4; 3) The data on Amberlyst-15 were adapted from
reference [11]; 4) N.A: not available.
2.2. Spectroscopic Studies by IR and Solid-state 13C-NMR
The FT-IR spectrum of the SO3H group-bearing carbonaceous material is shown in the Figure 1.
The peaks at 1709 cm−1 and at 1159 cm−1 are due to the presence of CO2H and C-O functional groups,
respectively. The peaks due to the SO3H group are seen at 1032 cm−1 and at 872 cm−1. The peaks
attributable to aliphatic C-H bond, aromatic C-H bond, O-H bond in a carboxylic acid group, and O-H
bond in a phenol group are seen as a broad peak between 3600 cm−1 and 2400 cm−1.
In the meantime a 13C-MAS-NMR experiment was carried out to obtain clues regarding the
structure of the sulfonated carbon. The spectrum is shown below in Figure 2.

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Figure 1. FT-IR spectrum of the prepared carbonaceous material made from lignosulfonate.
90
80
70
60
50
40
2269.7
2564.6
3067.1
3394.8
1708.8
1574.5
871.5.1
1031.6.1
1159.6.1
4000
3000
2000
1500
1000
Wavenumbers (cm-1)
13
Figure 2. C CP/MASNMR spectrum of the sulfonated carbon obtained with the magic
angle spinning technique.
The peaks at around 127, 146, and 188 ppm can be assigned to polycyclic aromatic carbon atoms,
phenolic OH-bearing carbons, and carbonyl carbon atoms of carboxylic acid groups, respectively, as
reported previously in the literature [26]. The resonance peak due to SO3H group-bearing aromatic
carbons is seen as a little obscure peak around 139 ppm in this spectrum because of the overlapping
peaks due to phenolic OH-bearing carbons and polycyclic aromatic carbons.
2.3. Hydrolytic Stability Studies
The hydrolytic stability of the sulfonated carbonaceous material was studied by exposing it to hot
(95 °C) water for 5 h. The amount of sulfonic acid groups leached during the exposure was determined