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  • REA DEPARTAMENTAL DE ENGENHARIA QUMICA

    Syngas production by water electrolysis: preliminary

    tests on methane production

    SIRIA ROSSI (Graduated in Chemical Engineering)

    Master thesis to obtain the Master degree in Chemical Engineering Branch Chemical

    Processes

    Supervisors:

    Joo Carlos Moura Bordado, PhD

    Joo Fernando Pereira Gomes, PhD

    Jury:

    President: Rita Isabel Dias Pacheco, PhD

    Members:

    Jaime Filipe Borges Puna, PhD

    Joo Fernando Pereira Gomes, PhD

    February 2016

  • REA DEPARTAMENTAL DE ENGENHARIA QUMICA

    Syngas production by water electrolysis: preliminary

    tests on methane production

    SIRIA ROSSI (Graduated in Chemical Engineering)

    Master thesis to obtain the Master degree in Chemical Engineering Branch Chemical

    Processes

    Supervisors:

    Joo Carlos Moura Bordado, PhD

    Joo Fernando Pereira Gomes, PhD

    Jury:

    President: Rita Isabel Dias Pacheco, PhD

    Members:

    Jaime Filipe Borges Puna, PhD

    Joo Fernando Pereira Gomes, PhD

    February 2016

  • i

    Acknowledgements

    When I thought for the first time about writing the acknowledgements on my

    master thesis, I thought you didnt write them in your bachelor, but you need to, now,

    for people around you: they deserve it! It wont be difficult!, and I really believed in

    my words. But then, here I am, and I find it more difficult than expected, not because I

    dont know what to write, but because I have so many people to thank and so many

    things to say that I find it difficult to properly organize my thoughts.

    Firstly, I need to thank my supervisors, professor Joo Bordado and professor Joo

    Gomes, for this nice and very special experience they allowed me to do, with a

    particular thank to professor Joo Gomes, for being so helpful, patient and reassuring in

    every step of this work, and for his total availability.

    A special thank to Engineer Campos Rodrigues, first of all for having invented the

    innovative process objective of this work, which is an important step for the future of

    the environment and allowed me to join this interesting work and experience a

    formative activity in a research laboratory, but also for his niceness, his help and his

    patience, for his dedication to work, which has been an inspiration to do better.

    Thank to my family, from the bottom of my heart, for the total support in every step

    of this work (as in every step of my life), from the decision to develop the thesis away

    from home to the emotional support during the stay.

    Thank to my boyfriend, Matteo Eresia, for his unconditional support, in this

    experience as in whatever choice I make. Thanks for being patient, caring, reassuring,

    and I could continue indefinitely, but, simply, thank you for being the way you are, your

    presence in my life is more than precious.

    Thank to my friends, the ones that are in Italy and with whom I have continued to

    share despite the distance. Thank you for your presence in my life, and thanks for being

    such good friends. However, I need also to thank my new important friends from

    Lisbon, without whom I could not say I experienced one of the best experiences of my

    life. Thank you Beatriz Terra, Adriana Sousa, Marilia Gagliardi, Marta Ramos, Andr

    Gregrio, Marta Mendes, Tnia Santos, and Lus Guerra, for sharing with me these

    amazing five months, for our laughs, our tragedies, your help, your kind presence.

  • ii

    A special thank goes to Lus Guerra, a key figure in this work, patient, totally

    available, reliable, kind. The person who taught me how to move in a laboratory, the

    person with which I spent most of my days in Lisbon, but, above all, a special friend.

    Thank you for supporting and standing me, from the bottom of my heart.

    I would like to thank more people, to tell better, to everyone, how important is

    his/her presence in my life and in this wonderful experience. Alone we are nothing, and,

    alone, I could not have achieved all of this.

    Thank you very much, to everyone.

  • iii

    ABSTRACT

    Since the Second Industrial Revolution, the world energy demand has been always

    increasing, leading humanity to gradually focus on the sustainability of its activities.

    This trend is proved by the increased primary energy sources consumption registered in

    the last decades, combined with an interesting increase in the renewable energy

    consumption.

    This work consists, as a first step, in the synthesis gas (syngas) production and

    optimization through a one step innovative 1 kW prototype of alkaline water

    electrolysis (patented), using graphite electrodes and without separation of gases

    (containing CO, CO2, H2 and small amounts of O2). Thanks to the state-of-the-art

    achieved before this work, the electrolyte used is sodium hydroxide (NaOH), with a

    composition equal to 0.4 M. The behavior of the syngas composition and flow rate has

    been studied and optimized, changing operational parameters such as temperature,

    pressure and current intensity, and testing two different stacks. Afterwards, the best

    syngas composition has been sent into a catalytic reactor (filled with a Ni/CaO-Al2O3

    catalyst) for the second aim of this work: preliminary tests on the methane production,

    at 1 bar and different temperatures.

    The best results were obtained, in the so called stack 1, at 90 C, 35 V, 3 bar. In

    these conditions, the results obtained are a CO2 and O2 yield of 24.4 % and 4.9 %,

    respectively, and a flow rate and current intensity equal to 103.5 L/h and 17.1 A. In

    stack 2, the best results were obtained at 75 C, 10 A and 1 bar. In these conditions,

    the results obtained are a CO2 and O2 yield of 21 % and 10.6 % respectively, and a flow

    rate equal to 27.6 L/h. Regarding the catalytic reactor, the best results were at 125 C. In

    this condition, the results obtained are a CH4 yield of 25.51 %, a CO2 conversion of

    44.2 % and a CH4 selectivity of 96.5 %.

    Keywords: Alkaline water electrolysis; Synthesis gas; Graphite electrodes; Methane.

  • iv

  • v

    RESUMO

    Desde a Segunda Revoluo Industrial, a procura mundial de energia tem vindo

    sempre a aumentar, levando a humanidade a concentrar-se gradualmente na

    sustentabilidade das suas atividades. Esta tendncia comprovada pelo aumento do

    consumo das fontes de energia primria registado nas ltimas dcadas, combinado a um

    aumento interessante no consumo de energias renovveis.

    Numa primeira fase, o presente trabalho consiste na otimizao da produo de gs de

    sntese (syngas) numa nica etapa, num processo inovador e patenteado de eletrlise

    alcalina da gua, num eletrolisador de 1 kW, utilizando eletrodos de grafite e sem

    separao de gases (contendo CO, CO2, H2 e pequenas quantidades de O2). Graas ao

    estado da arte alcanado antes da realizao deste trabalho, utilizou-se como electrlito

    hidrxido de sdio (NaOH), com uma concentrao de 0,4 M. A evoluo do caudal de

    gs de sntese e a sua composio foram estudados e optimizados, variando os

    parmetros operacionais, nomeadamente a temperatura, presso e intensidade de

    corrente. Os testes foram realizados com dois diferentes stacks, denominados stack

    1 e stack 2.

    Posteriormente, o gs de sntese com a melhor composio obtida foi enviado para um

    reator cataltico (cheio com um catalisador de Ni/CaO-Al2O3) para o segundo objetivo

    deste trabalho: realizao de testes preliminares de produo de metano, a 1 bar e a

    diferentes temperaturas.

    Os melhores resultados foram obtidos, no stack 1, a 90 C, 35 V, e 3 bar. Nestas

    condies, obteve-se um teor em CO2 e O2 de 24,4 % e 4,9 %, respetivamente, e um

    caudal e intensidade de corrente iguais a 103,5 L/h e 17,1 A. Os resultados mais

    favorveis foram obtidos, no stack 2, a 75 C, 10 A, e 1 bar. Nestas condies,

    obteve-se um teor em CO2 e O2 de 21 % e 10.6 %, respetivamente, e um caudal igual a

    27.6 L/h. No que respeita ao reactor cataltico, os melhores resultados foram obtidos a

    125 C. Nesta condio, obteve-se um teor em CH4 de 25.51 %, uma converso em CO2

    de 44.2 % e uma selectividade em CH4 de 96.5 %.

    Palavras-chave: Eletrlise alcalina da gua; Gs de sntese; Eletrodos de grafite;

    Metano.

  • vi

  • vii

    TABLE OF CONTENTS

    1. INTRODUCTION ........................................................................................... 1

    2. LITERATURE REVIEW................................................................................ 5

    2.1 The world energy production and demand General overview ....................... 5

    2.2 Water electrolysis ............................................................................................ 15

    2.2.1 Historical background ........................................................................................... 15

    2.2.2 The importance of water electrolysis and hydrogen .............................................. 16

    2.2.3 Theory of water electrolysis and todays technologies.......................................... 17

    Alkaline water electrolysis ........................................................................................................... 18

    PEM electrolysis .............................................................................................