SYNTHESIS AND CHARACTERIZATION OF
PHOSPHORYLATED CHITOSAN MEMBRANES OBTAINED
FROM SHRIMP SHELL WASTE AS AN ELECTROLYTE FOR
FUEL CELL
THESIS
As a pre-requisite to achieve Master Degree from Institut Teknologi Bandung
By
Widya Febrina
20506050
CHEMISTRY STUDY PROGRAM
INSTITUT TEKNOLOGI BANDUNG
2007
ABSTRACT
SYNTHESIS AND CHARACTERIZATION OF
PHOSPHORYLATED CHITOSAN MEMBRANES OBTAINED
FROM SHRIMP SHELL WASTE AS AN ELECTROLYTE FOR
FUEL CELL
By
Widya Febrina
NIM : 20506050
In fuel cell proton exchange membrane (PEM) serves to separate the reactant gases, provides the electrolyte for energy-generating electrochemistry, and facilitates the selective transport of protons from the anode to the cathode. The state-of-the-art proton exchange membrane is a polymer commercially called Nafion® which has almost all the necessary properties for a good fuel-cell membrane. The most significant drawbacks are the relatively high cost, the dependence on water for conduction, and instability at temperatures above 100 oC. The last mentioned is particularly unfortunate because membranes that allow stable, high-performance operation at elevated temperature should lead to substantial improvements in fuel-cell performance.
As a natural polymer, chitosan is one of the promising membrane materials which has been widely studied. Chitosan is the N-deacetylated derivative of chitin, which is a naturally abundant polysaccharide and the supporting material of crabs, shrimp shells, fungal mycelia, insects, etc. Chitosan can be obtained through deproteination, demineralization and deacetylation of chitin by using alkali treatment dan higher temperature. The presence of hydroxyl and amino groups on the backbone of chitosan provide chitosan with a high hydrophilicity, which is known to be quite beneficial for fuel cell operation. However in its actual state, a chitosan film has very low electrical conductivity. Although the structure of a chitosan monomer has three hydrogen atoms, they are strongly bonded to the
structure and cannot be mobilized under the action of an electric field to give a proton conductor. It has been found, however, that if chitosan is dissolved in acetic acid and the resulting solution is cast into a thin film, then the H+ or H
3O+ and CH3COO− ions in the acetylated chitosan film will be dispersed in the immobilized chitosan solvent and these ions can be mobilized under the influence of an electric field. If H+ or H3O+ ions are more mobile than the CH3COO− ions the film becomes a proton conductor. Chitosan in an acidic medium can become a polyelectrolyte through the protonation of the –NH2 groups. Due to the crystalline nature of chitosan, highly crystalline portions in the chitosan membranes obviously render resistance to water uptake and in turn hinder hydroxide ion transport in the membranes.
In order to increase the ionic conductivity, the chitosan membranes was phosphorylated. The phosphorylated chitosan membranes were prepared from the reaction of orthophosporic acid and urea on the surface of chitosan membranes in N,N-dimethylformamide. The reactions were carried out at varied temperatures, namely 60 ºC, 70 ºC, 80 ºC and 90 ºC. At each temperature the reaction time was also varied with the variable time were 30 minutes, 60 minutes, 90 minutes and 120 minutes. Compared to the unmodified chitosan membrane, it was found that hydrated phosphorylated chitosan membranes with an appropriate phosphorus content showed an increase of ionic conductivity of about one order of magnitude, from 2.89 x 10-4 S.cm-1 to 3.23 x 10-3 S.cm-1. Increasing the temperature and time of phosphorylation reaction resulted in increasing the phosphorus content on membrane, but the swelling index and ionic conductivity were changed pronouncedly because of the cross linked formation. It was also observed that the tensile strength and thermal stability of the phosphorylated chitosan membranes do not change significantly compared with the unmodified chitosan membranes. Optimum phosphorylation condition was obtained at temperature 80 oC for 30 minutes reaction.
Keywords: Chitosan, phosphorylated chitosan membranes, fuel cell.
ABSTRAK
SINTESIS DAN KARAKTERISASI MEMBRAN KITOSAN
TERFOSFORILASI YANG DIPEROLEH DARI LIMBAH
KULIT UDANG SEBAGAI ELEKTROLIT UNTUK SEL
BAHAN BAKAR
Oleh
WIDYA FEBRINA
NIM : 20506050
Dalam sel bahan bakar, material membran penukar proton (PEM) berfungsi sebagai pemisah gas-gas pereaksi dan sebagai elektrolit penghasil energi secara elektrokimia, serta sebagai fasilitator transpor selektif proton dari anoda ke katoda. Membran penukar proton yang sering dipergunakan adalah Nafion® yang memiliki hampir semua karakteristik yang sesuai sebagai membran elektrolit sel bahan bakar. Namun membran ini berharga mahal dan sangat bergantung pada air untuk proses konduksi, serta tidak stabil pada temperatur diatas 100 oC. Faktor-faktor tersebut kurang mendukung peningkatan kinerja sel bahan bakar. Sebagai elektrolit sel bahan bakar, membran elektrolit diharapkan bersifat stabil dan dapat dipergunakan pada temperatur yang lebih tinggi sehingga arus listrik yang dihasilkan sel bahan bakar juga cukup besar.
Kitosan merupakan polimer alamiah yang telah dipelajari secara luas dan cukup menjanjikan sebagai material elektrolit sel bahan bakar. Kitosan merupakan turunan N-deasetilasi dari kitin. Kitin adalah polisakarida alamiah yang melimpah dan menjadi material pendukung pada cangkang kepiting, kulit udang, miselia jamur, serangga, dll. Kitosan dapat diperoleh melalui serangkaian proses deproteinasi, demineralisasi, dan deasetilasi kitin menggunakan alkali dan temperatur yang tinggi. Keberadaan gugus hidroksil dan amino pada kerangka kitosan menyebabkan kitosan memiliki hidrofilisitas yang cukup tinggi, yang bermanfaat pada pengoperasian sel bahan bakar. Namun dalam keadaan
normalnya, film kitosan hanya memiliki konduktivitas listrik yang rendah. Meskipun struktur monomer kitosan memiliki tiga atom hidrogen, namun atom hidrogen tersebut terikat kuat pada kerangka kitosan dan tidak dapat digerakkan dibawah medan listrik, sehingga film kitosan tidak dapat dijadikan suatu konduktor proton. Akan tetapi, jika kitosan tersebut dilarutkan di dalam asam asetat dan kemudian dicetak sebagai membran (film tipis), maka ion H+ atau H3O+ dan CH3COO− pada sistem film kitosan terasetilasi akan tersebar pada kerangka kitosan. Ion-ion ini dapat digerakkan dibawah pengaruh medan listrik. Jika ion H+ atau H3O+ lebih mudah bergerak dibandingkan ion CH3COO−, maka film kitosan akan menjadi suatu konduktor proton. Kitosan dalam media asam juga dapat menjadi polielektrolit melalui protonasi gugus –NH2. Oleh karena sifat kristalin kitosan, bagian kristalin pada kitosan akan menghalangi molekul air untuk masuk ke dalam membran kitosan, sehingga menghambat transpor ion hidroksida di dalam membran.
Untuk meningkatkan konduktivitas ioniknya, membran kitosan difosforilasi. Fosforilasi membran kitosan dilakukan dengan mereaksikan asam orto-fosfat dan urea pada permukaan membran kitosan dalam pelarut N,N-dimetilformamid (DMF). Reaksi dilakukan pada beberapa temperatur yakni 60 oC, 70 oC, 80 oC, dan 90 oC. Pada masing-masing temperatur reaksi tersebut juga dilakukan variasi waktu reaksi yaitu 30 menit, 60 menit, 90 menit, dan 120 menit. Membran kitosan terfosforilasi dalam keadaan hidrat dengan kandungan fosfat tertentu menunjukkan konduktivitas ionik yang lebih tinggi sebesar satu orde magnitud bila dibandingkan dengan membran kitosan tanpa modifikasi, yakni dari 2,89 x 10-4 S.cm-1 ke 3,23 x 10-3 S.cm-1. Peningkatan temperatur dan waktu reaksi fosforilasi mengakibatkan naiknya kandungan fosfat pada membran, akan tetapi nilai derajat penggembungan dan konduktivitas ionik berubah akibat terbentuknya ikatan silang pada membran. Penelitian ini juga menunjukkan bahwa kekuatan mekanik dan stabilitas termal membran kitosan terfosforilasi tidak berubah secara signifikan terhadap membran kitosan yang tidak dimodifikasi. Kondisi reaksi fosforilasi yang optimum dicapai pada temperatur reaksi 80 oC dengan waktu reaksi selama 30 menit.
Kata kunci: Kitosan, membran kitosan terfosforilasi, sel bahan bakar.
SYNTHESIS AND CHARACTERIZATION OF
PHOSPHORYLATED CHITOSAN MEMBRANES OBTAINED
FROM SHRIMP SHELL WASTE AS AN ELECTROLYTE FOR
FUEL CELL
By
WIDYA FEBRINA
NIM : 20506050
CHEMISTRY STUDY PROGRAM
INSTITUT TEKNOLOGI BANDUNG
As a pre-requisite to achieve Master Degree from Institut Teknologi Bandung
Date ………
Supervisors,
GUIDELINE FOR USING THIS THESIS
This master thesis that is not published is registered and available at library of Institut Teknologi Bandung and open for public. The writer has the copyright of this thesis which is protected by HaKI law of Institut Teknologi Bandung. To cite this thesis, the citer must have the writer´s permission and has to be done in a way that is common in scientific community.
Copying and publishing some or all part of the thesis has to be under permission of Director of Post Graduate of Institut Teknologi Bandung.
ACKNOWLEDGEMENT
I would like to thank my supervisor, Dr. Ing Cynthia Linaya Radiman (ITB), Dr. Veinardi Suendo (ITB) and Dr. Katja U. Loos (RUG) for supervision, support and guidance through this research and thesis.
Thanks to DIKTI INDONESIA for the scholarship that i have got, and Dr. Fida Madayanti and Honors program administrator who always help me finishing this research.
The member of polymer research group, Joop, Harry, and Geert in Rijks Universiteit Groningen (RUG) are thanked for technical guidance and friendship during the collaboration research of ITB and RUG. Thanks to Nandang Mufti for assistance in impedance measurements in solid state laboratorium RUG.
Lastly and perhaps the most influencial, my family and some one that very special to me, Reynaldi Lee are thanked for making me happy and smiling always.
Bandung, September 12th, 2007
TABLES OF CONTENT
Abstract ... ii
Abstrak ... iv
Guideline for using this thesis ... vii
Aknowledgement ... viii
Tables of content ... ix
List of figures ... xi
List of tables ... xiii
Chapter I. Introduction ... 1
Chapter II. Literature Study ... 3
II.1 Fuel cell ... 3
II.1.1 Fuel cell history ... 3
II.1.2 Fuel cell definition ... 5
II.1.3 Types of fuel cell ... 6
II.1.4 Fuel cell components ... 12
II.1.5 Fuel cell benefits ... 15
II.2 Membrane ... 17
II.2.1 Membrane definition ... 17
II.2.2 Proton-conducting polymer electrolyte membranes ... 19
II.3 Chitin and Chitosan ... 24
Chapter III. Experimental ... 28
III.1 Materials and apparatus ... 28
III.2 Methodology ... 29
III.2.1 Isolation of chitosan from shrimp shells ... 29
III.2.2 Formation of chitosan membranes ... 30
III.2.3 Phosphorylation of chitosan membranes ... 30
III.3 Characterizations ... 32
III.3.1 FTIR analysis ... 32
III.3.2 Swelling index ... 32
III.3.3 Determination of chitosan molecular weight ... 32
III.3.4 Determination of phosphorus content ... 33
III.3.5 Ionic conductivity ... 34
III.3.6 Tensile strength ... 35
III.3.7 Thermal gravimetry analysis ... 35
III.3.8 Differential scanning calorymetry ... 35
Chapter IV. Results and Discussion ... 36
IV.1 Chitosan characterization ... 36
IV.2 Phosphorylation of chitosan membrane ... 38
IV.3 Characterization of chitosan and phosphorylated chitosan Membranes ... 40
IV.3.1 Phosphorus content ... 40
IV.3.2 Swelling index ... 42
IV.3.3 Thermal gravimetry analysis ... 44
IV.3.4 Differential scanning calorymetry ... 45
IV.3.5 Ionic conductivity ... 47
IV.3.6 Mechanical properties ... 51
Chapter V. Conclusions ... 54
Refererences ... 55
LIST OF FIGURES
Figure II.1 PEM Fuel Cell schematic ... 7
Figure II.2 PAFC Fuel Cell schematic ... 7
Figure II.3 Alkalien fuel cell schematic ... 9
Figure II.4 Molten carbonate fuel cell schematic ... 9
Figure II.5 Electrochemical reaction of fuel cell types ... 12
Figure II.6 PMFC fuel cell schematic ... 13
Figure II.7 Chemical structure of perfluoronated polymer electrolyte membranes ... 20
Figure II.8 Chemical structure of polymer electrolyte membranes based on hydrocarbon polymers... 21
Figure II.9 Chitin and chitosan monomer ... 25
Figure III.1 Flow chart of overall experiment ... 31
Figure IV.1 Chitin ATR-FTIR spectra ... 37
Figure IV.2 Chitosan ATR-FTIR spectra ... 38
Figure IV.3 Possible reaction mechanism for preparation of phosphorylated chitosan membranes ... 39
Figure IV.4 Phosphorylated chitosan membrane ATR-FTIR spectra ... 40
Figure IV.5 Effect of phosphorylation reaction in chitosan membranes ... 41
Figure IV.6 Effect of phosphorylation reaction on the chitosan membranes swelling index ... 44
Figure IV.7 TGA thermograms of chitosan and phosphorylated chitosan (reaction time=30 min) ... 45
Figure IV.8 DSC thermogram of: a. Chitosan membrane; b. PCM 60; c. PCM 70; d. PCM 80; e. PCM 90, with phosphorylation reaction time of 30 minutes ... 47 Figure IV.9 Impedance spectra of chitosan and phosphorylated chitosan
membrane with temperature reaction of 90°C after 1 h
hydration at room temperature ... 48 Figure IV.10 Impedance spectra of unhydrated chitosan and
phosphorylated chitosan membrane with temperature reaction of 90°C ... 48 Figure IV.11. Effect of phosphorylation reaction time and temperature on the tensile strength of dried phosphorylated chitosan
membranes ... 53 Figure IV.12. Effect of phosphorylation reaction time and temperature on breaking elongation of dried phosphorylated chitosan
membranes ... 53 Figure A.1 Calibration curve for chitosan molecular weight determination.. 60 Figure A.2 Calibration curve for stock solution using Friske and Subbarow method ... 61
LIST OF TABLES
Table II.1 Comparisons of fuel cell types ... 11
Table III.1 Fiske and Subbarow Callibration ... 34
Table IV.1 Yield of chitosan isolated from shrimp shell waste ... 36
Table IV.2 Characteristics peak of chitin and chitosan ... 37
Table IV. 3 Phosphorus content in phosphorylated chitosan membrane ... 41
Table IV.4 Swelling index of chitosan and phosphorylated chitosan membranes ... 43
Table IV.5 Variances in ionic conductivities of hydrated chitosan and phosphorylated chitosan membranes ... 49
Table IV.6 Tensile properties of chitosan and phosphorelated chitosan membranes in dry state ... 52
Table A.1 Flow time of chitosan solution in Oswaltd viscometer ... 60
Table A.2 Absorbance value of stock solution ... 61
Table A.3 Phosphorus content on chitosan membranes ... 62
Table A.4 Tensile strength and breaking elongation of chitosan and phosphorylated chitosan membranes ... 62
