Sulfonated porous organic polymer as a highly efficient catalyst for the synthesis of biodiesel at room temperature

https://doi.org/10.1016/j.molcata.2015.10.016Get rights and content

Highlights

  • Synthesis of a sulfonic acid grafted porous organic polymer PDVTA-SO3H, by post synthetic functionalization method.

  • The polymer possess high surface area (SBET = 406 m2 g−1) and high surface acidity 2.3 mmol g−1.

  • PDVTA-SO3H showed high catalytic activity for the synthesis of biodiesel compounds from long chain fatty acids.

Abstract

A new functionalized porous organic polymer bearing sulfonic acid groups (PDVTA-SO3H) at the pore surface with high surface area (SBET = 406 m2 g−1) and Brønsted acidity is reported. The material has been synthesized via post-synthetic sulfonation of the porous co-polymer poly-divinylbenzene-co-triallylamine (PDVTA-1) using chlorosulfonic acid as sulfonating agent. A detailed characterization of the single bondSO3H functionalized porous polymeric material has been carried out using N2 sorption, FT-IR and UV–vis spectroscopy, HR-TEM, FE-SEM, thermogravimetric and elemental analyses. Temperature programmed desorption of NH3 (TPD-NH3 analysis) of PDVTA-SO3H revealed a very high surface acidity of 2.3 mmol  g−1. Such high acidity of PDVTA-SO3H has been explored to investigate its catalytic efficiency towards eco-friendly production of biodiesel via esterification of long-chain free fatty acids (FFA) to the respective fatty acid monoalkyl esters (FAMEs) at room temperature using methanol as reactant as well as solvent. The sulfonated porous polymer is found to be a very active and reusable solid acid catalyst giving high yields (∼92–98%) of various biodiesel compounds under very mild reaction conditions.

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A new porous organic polymer functionalized with sulfonic acid groups and high Brønsted acidity is reported. The material showed excellent catalytic activity for the biodiesel synthesis at room temperature.

Introduction

Synthesis of biofuel compounds i.e. fatty acid monoalkyl esters (FAMEs) are of huge demand as they provide renewable, non-toxic and eco-friendly source of energy and a possible replacement of fossil fuels [1]. Large scale use of the fossil fuels with the advancement of today's world would cause severe energy crisis in future due to its limited reserves, emission of greenhouse gases and environmental pollution caused during their ignition. Biofuel compounds can overcome such problems as they are renewable and can be produced from low cost resources such as animal fat and vegetable oil containing free fatty acids (FFA) [2], [3], [4], [5], [6]. The biodiesel compounds can be synthesized by esterification of long chain fatty acids with aliphatic alcohols. However, the commercial production of biodiesel is associated with major problems of high production cost, product isolation, catalyst separation etc. as the synthesis involves homogeneous strong acid or base catalyzed esterification of fatty acids. The conventional use of concentrated sulfuric acid as homogeneous acid catalyst is not very favorable due to its corrosive nature. Although the base catalyzed synthesis of biodiesel via transesterification reaction occurs at low temperature and lesser reaction time but the process requires a pre-esterification step to prevent saponification between the FFAs and base. This is because of the fact that low-cost feedstock containing high FFA causes saponification under basic condition, which leads to a major problem in product separation and the process consumes large excess of catalyst. Thus, a wide scale research focusing on the design of suitable heterogeneous solid acid catalysts has been undertaken [7], [8]. Several solid acids have been reported till date to catalyze the esterification reaction, such as transition metal oxides [9], [10], [11], Au NP/nanoporous polymer [12], ion exchange resins [13], molecular sieves [14], functionalized silica [15], zeolites [16], metallo phosphates [17], [18], metal organic framework [19], functionalized porous carbons [20], [21] and mesoporous silica materials [22], [23], [24]. But for most of these cases the reaction needs high temperature and pressure due to low concentrations of the catalytically active sites.

On the other hand, porous organic polymers bearing suitable functional groups at the pore surface are very demanding. These materials are potential candidates for a wide range of application areas such as gas adsorption [25], [26], [27], catalysis of various important organic transformations [28], [29], [30], [31], [32], [33], [34], drug delivery vehicle [35], sensing [35], [36] and so on. Due to high specific surface area and pore volume the target molecule can interact more easily with the required functional group present at the surface compared to non-porous materials. Intense research has being carried out on the designing of appropriate porous organic polymers for catalytic applications. Porous polymers rich in acidic functionality are thus highly demanding for the synthesis of biodiesels via esterification/transesterification reactions. In our present work, we report the synthesis of a new solid acid catalyst containing single bondSO3H group in the porous organic polymer network with high surface acidity for the synthesis of biodiesel products. The catalyst is thoroughly characterized using various instrumental techniques to investigate its BET surface area/porosity, framework-bondings, chemical environment, thermal stability and surface acidity. Various long chain fatty acids are used for the catalytic reactions and we have measured the recycling efficiency of the catalyst.

Section snippets

Materials

Divinylbenzene (DVB, monomer) and triallylamine (TAA, monomer) were obtained from Sigma–Aldrich. Azobisisobutyronitrile (AIBN, radical initiator) was obtained from SRL and recrystallized from hot ethanol prior to use. Chlorosulfonic acid was purchased from Spectrochem, India. All other chemicals used in the experiments were of analytical grade produced by E-Merk.

Instrumentation

A PerkinElmer Spectrum 100 was used to record the FT IR spectra of the PDVTA-1 and PDVTA-SO3H. A UV 2401PC with an integrating sphere

Nitrogen adsorption/desorption analysis

In Fig. 1 nitrogen adsorption/desorption isotherms of them porous organic polymers are shown. As seen from this figure that PDVTA-1 gave a type IV isotherm with a significant hysteresis loop in the high pressure region, indicating the presence of mesopores in the framework [37]. Moreover, a large amount of nitrogen uptake is observed in the low pressure region (below 0.1 bar). This result suggests the presence of sufficient amount of micropores in PDVTA-1. BET surface area and pore volume of the

Conclusions

A new sulfonic acid functionalized porous organic polymer has been synthesized via post-synthetic sulfonation of the porous polymer poly-divinylbenzene-co-triallylamine. The materials showed high BET surface area, presence of a wide range of pores in nanoscale dimensions and high Brønsted acidity. It showed excellent catalytic efficiency for the production of biodiesel products via esterification of long-chain free fatty acids at room temperature. High catalytic efficiency for the sulfonated

Acknowledgements

RG and PB thanks CSIR, New Delhi for respective senior and junior research fellowships, respectively. AB wishes to thank DST, New Delhi for instrumental facilities through DST Unit on Nanoscience and DST-SERB project grants.

References (40)

  • H.J. Berchmans et al.

    Bioresour. Technol.

    (2008)
  • L.T.H. Nam et al.

    Fuel

    (2011)
  • P. Hidalgo et al.

    Fuel

    (2015)
  • Y. Kuwahara et al.

    Appl. Catal. A: Gen.

    (2014)
  • J. Fu et al.

    Fuel

    (2015)
  • E.E. Macias et al.

    Catal. Commun.

    (2011)
  • H.Q. Yang et al.

    J. Mol. Catal. A: Chem.

    (2014)
  • F.G. Cirujano et al.

    Chem. Eng. Sci.

    (2015)
  • L.J. Konwar et al.

    J. Mol. Catal. A: Chem.

    (2014)
  • H. Wan et al.

    J. Mol. Catal. A: Chem.

    (2015)
  • A. Modak et al.

    Appl. Catal. A: Gen.

    (2013)
  • J. Mondal et al.

    J. Mol. Catal. A: Chem.

    (2012)
  • P. Borah et al.

    J. Catal.

    (2015)
  • R. Gomes et al.

    J. Solid State Chem.

    (2015)
  • L. Peng et al.

    Catal. Today

    (2010)
  • H. Baumann et al.

    Angew. Chem. Int. Ed. Engl.

    (1988)
  • L. Soh et al.

    Green Chem.

    (2011)
  • D. Elhamifar et al.

    Chem. Plus Chem.

    (2014)
  • F. Su et al.

    Green Chem.

    (2014)
  • C. Poonjarernsilpa et al.

    Appl. Catal. A: Gen.

    (2015)
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