UNIVERSIT DEGLI STUDI DI MILANO

Scuola di Dottorato in Scienze e Tecnologie Chimiche Dipartimento di Chimica

XXVI Ciclo Dottorato in Chimica Industriale

Biomass to Liquid Process: new kind of cobalt and iron based catalysts for the

Fischer-Tropsch Synthesis (Settori Scientifico Disciplinari: ING-IND/25; CHIM/04)

Antonieta Di Fronzo (Matricola R09037)

Tutor: Prof. Claudia L. Bianchi Co-Tutor: Prof. Carlo Pirola Coordinatore del Dottorato: Prof. Dominique Roberto

A.A. 2012/2013

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TABLE OF CONTENTS

General abstract ................................................................................................... 5 Chapter 1. General Introduction ........................................................................ 27 Chapter 2 Chemistry of Fischer-Tropsch Synthesis ............................................ 57

2.1 FT Thermodynamics ................................................................................. 58 2.2 FT Reaction Mechanism ........................................................................... 59 2.3 FT Products Selectivity ............................................................................. 65 2.4 FT kinetics ................................................................................................. 68 2.5 Influence of FT process conditions ........................................................... 71

Chapter 3. Catalysts for Fischer Tropsch Synthesis ............................................ 76 3.1 Iron and Cobalt industrial FT catalysts ..................................................... 80

i) Iron catalysts: .......................................................................................... 80 ii) Cobalt catalysts: ..................................................................................... 81

3.2 Chemical State of active phase ................................................................ 82 3.3 Size of active phase .................................................................................. 83

Chapter 4. Experimental: FT plant and analytical methods ............................... 86 4.1 FT Laboratory plant .................................................................................. 88

a) First FTS unit (Unit 1): ............................................................................. 88 4.1a Main parts of the plant ....................................................................... 90 4.2a Analytical instruments ........................................................................ 94 4.3a Analytical instruments calibration ..................................................... 98 4.4a Experimental procedure ................................................................... 109 b) Second FTS unit (Unit 2): ...................................................................... 114 4.1b Main parts of the plant .................................................................... 116 4.2b Analytical instruments ..................................................................... 119 4.3b Experimental procedure .................................................................. 121

4.2 Experimental data elaboration .............................................................. 124 a)First FTS unit (Unit 1) ............................................................................. 124 4.2.5 Hydrogen ......................................................................................... 137 4.2.7 Oxygen Balance ............................................................................... 139 b)Seconf FTS unit (Unit 2) ......................................................................... 140

4.3 Novelties on the FT plant made in this PhD work .................................. 142 Chapter 5. Catalysts preparation and characterization ................................... 143

5.1 Catalysts preparation ............................................................................. 146 5.1.1 Catalyst preparation procedure ...................................................... 146

5.2 Catalysts characterization: ..................................................................... 155 5.2.1 Catalysis characterization: introduction and theory ....................... 155

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5.2.1.1 BET analysis .................................................................................. 157 5.2.2 Catalysts characterization: results .................................................. 174

Chapter 6. High Fe Loaded Supported Catalysts for Biosyngas Fischer Tropsch Conversion: experimental and simulation results ........................................... 197

6. Development of the kinetic model .......................................................... 197 6.1 Regression of kinetic constants .......................................................... 197 6.2 Mass Balance ...................................................................................... 199 6.3 Energy Balance ................................................................................... 200 6.4 Pressure variation............................................................................... 201 6.5 Catalyst Efficiency ............................................................................... 202

Chapter 7. Fischer Tropsch runs results and discussion .................................. 204 Chapter 8. Final remarks and Conclusions ....................................................... 216 List of publications ........................................................................................... 219 Publications in Conference Proceedings (peer reviewed) ............................... 219 Communications at congress ........................................................................... 220

General abstract

1. Introduction

Nowadays it is imperative to develop economical and energy-efficient

processes for the sustainable production of fuels and chemicals alternative to

the ones deriving from petroleum. Climate change and air quality are major

environmental concerns because they directly affect the way we live and

breath. In order to meet the present and future threats generated by emissions

to the atmosphere, environmental agencies around the world have issued

more stringent regulations. One of them is the control of residual sulfur in

diesel fuel and emission standards for particulates from diesel vehicles. All

these facts have recently aroused renewed interest in the FischerTropsch

Synthesis because it can produce super clean diesel oil fraction with high

cetane number (typically above 70) without any sulfur and aromatic

compounds, using syngas (mixture of H2, CO, CO2) from natural gas, CH4, coal

or, as a new tendency, from biomass. [1, 2]. The essential target of FTS is to

produce paraffins and olefins with different molecular weight and to limit the

maximum formation of methane and CO2 [3].

The main reactions involved in FTS are reported in the following scheme [4-8]:

Irreversible reactions:

1) n CO + 2n H2 CnH2n + n H2O for olefins

2) n CO + (1+2n) H2 CnH(2n+2) + n H2O for paraffins

3) 2n CO + n H2 CnH2n + n CO2 for olefins

4) n CO + 2n H2 CnH(2n+1)OH + (n-1) H2O for alcohols

Equilibrium:

5) CO + H2O CO2 + H2 Water-gas-shift reaction (WGS)

General Abstract

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6) CO + H2 C + H2O Carbon deposition

7) 2 CO C + CO2 Boudouard equilibrium

The whole reaction gives an energetic contribution strongly exothermic (about

150 kJ/mol CO reacted). FTS is a particularly complex system, in which a

number of different reactions are combined to a unique mechanism:

irreversible Fischer Tropsch (FT) reactions produce hydrocarbons and some

equilibrium reactions between CO, CO2, CH4 and C, such as the WGS reaction

and the Boudouard equilibrium, are present too. Nevertheless, it is possible to

suppose that FTS can be simplified as a combination of the FT reactions and the

WGS reaction [7]. According this hypothesis, hydrocarbons are primary

products of FT reaction, and CO2 can only be produced by WGS reaction, a

reversible parallel-consecutive reaction with respect to CO [9].

FTS usually requires catalysts based on cobalt or iron. Co-based catalysts have

been more largely used due to their high selectivity to heavy hydrocarbons and

low activity in the water-gas shift reaction, so limiting the CO2 formation.

Moreover Co-based catalysts have shown longer life-time and higher CO

conversion compared to the Fe-based ones [10]. Iron based catalysts are,

recently, highly investigated for FTS. Compared to cobalt systems, iron-based

catalysts are cheaper but less resistant to deactivation due to the oxidizing

effect of water, despite activating Water Gas Shift reaction (CO + H2O CO2 +

H2) well [5, 9]. Moreover they are flexible to changes in temperature, pressure

and they can work at different H2/CO feed ratios (for iron based catalysts this

ratio can be between 0.5 and 2.5) [11, 12].

2. Aims of the work

Considering very recent research results [13-15] the aim of the PhDs research

was addressed toward the development of three particular kind of catalysts:

General Abstract

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The first group of catalysts tested were the Co-based hydrotalcites (HTlc) with

different amount of Co in two different pilot plants. HTlc-based materials have

been recently reported as good catalysts for several pro