Fuel Additives E-Book

Robert D. Tack

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 657

Veröffentlichungsjahr: 2022

Beschreibung

FUEL ADDITIVES Explore a complete and insightful review of fuel additives In Fuel Additives: Chemistry and Technology, petroleum industry chemist R. D. Tack delivers a comprehensive and practical exploration of various types of fuel additives, the problems they're meant to address, what they do, their chemistries and preparations, and a discussion of how they work. The book introduces and summarizes refinery operations to an extent that discussions of fuels in the following chapters become easier to understand. Then follow detailed descriptions of problems that occur for reasons of the ways in which liquid petroleum fuels are transported, stored, and used. In these discussions, their applications to jet fuel, heating oils, gasoline, diesel fuels, and bunker fuels are covered. Fuel Additives: Chemistry and Technology also includes: * A thorough overview of fuels, including discussions of refinery operations and processes and the application of fuel additives * Aids to the transportation and storage of liquid petroleum fuels: practical discussions of stabilizers against oxidative degradation, drag reducers, static dissipators, anti-foamants, demulsifiers, de-icers, and biocides * Comprehensive explorations of fuel detergents, including their chemistries and proposals to their mechanisms of action * In-depth examinations of cold flow improvers, with detailed descriptions of the waxing problems that they solve * Combustion improvers that improve the efficiencies of fuel combustion in engines, burners, and particulate filters--while also reducing emissions * Additives that protect metal surfaces against wear, by providing lubricity, and corrosion Perfect for chemists working in the petroleum industry, Fuel Additives: Chemistry and Technology will also earn a place in the libraries of professionals working in related areas and seeking a quick understanding of topics such as oxidative stability, corrosion, or wax crystallization since 1974.

Leseprobe

Fuel Additives

Chemistry and Technology

Robert D. Tack

London, UK

This edition first published 2022

© 2022 John Wiley & Sons Inc.

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Contents

Cover

Title page

Copyright

Acknowledgements

Preface

Abbreviations

1 Fuels and Fuel Additives – Overview

1.1 Introduction

1.2 Refinery Operations and Processes

1.2.1 Distillation

1.2.2 Balancing Production to the Demand Barrel

1.2.3 Catalytic Conversions

1.2.4 Alkylation

1.2.5 Coking

1.3 Finished Fuels

1.3.1 Gasoline

1.3.2 Middle Distillates

1.3.2.1 Jet Fuel

1.3.2.2 Diesel Fuel

1.3.2.3 Heating Oils

1.3.2.4 Marine Diesel Fuels and Power Generation

1.3.4 Coal, Gas or Biomass to Liquids

1.3.5 Biofuels

1.4 Fuel Additives – Value and Need

1.4.1 Value

1.4.2 Need

1.5 The Application of Fuel Additives

1.6 Fuel Quality, Taxation, Dyes and Markers

1.6.1 The Need for Quality and Brand Recognition

1.6.2 The Introduction and Growth of Fuel Taxation

1.6.3 The Use and Chemistries of Fuel Dyes

1.6.4 Invisible Fuel Markers

1.7 Future Need for Fuel Additives

2 Fuel Stabilisers: Antioxidants and Metal Deactivators

2.1 Introduction

2.2 Detailed Problems

2.2.1 Oxidative Stability of Jet Fuels

2.2.2 Oxidative Stability of Gasoline

2.2.3 Oxidative Stability of Diesel Fuel

2.3 Tests of Oxidative Stability

2.3.1 Jet Fuel Stability Tests

2.3.2 Gasoline Stability Tests

2.3.3 Diesel Fuel Stability Tests

2.4 Stability Additives: Antioxidants and Metal Deactivators

2.4.1 Antioxidants

2.4.2 Metal Deactivators (Mdas)

2.4.3 Thermal Stability Additives

2.5 Mechanisms

2.5.1 Hydrogen Atom Abstraction from Hydrocarbon Molecules

2.5.2 Initiation

2.5.3 Propagation

2.5.4 Termination

2.5.5 Formation of Difunctional Molecules during Autoxidation

2.5.6 Mechanisms of Antioxidant Action

3 Fuel Detergents

3.1 Introduction

3.2 Detailed Problems

3.2.1 Gasoline Engines

3.2.2 Fuel Injector Deposits in Diesel Engines

3.2.3 Heating Oils

3.2.4 Jet Engines

3.3 What Detergents Do

3.4 The Chemistries of Fuel Detergents

3.4.1 General Background

3.4.2 Detail

3.4.2a Poly-IsoButylene, PIB

3.4.2b PIBSA

3.4.2c PIBSA-PAM

3.4.2d PIB-Amine

3.4.2e Mannich Detergent

3.4.2f Imidazoline

3.4.2g PIBSA/Polyols

3.4.2h Polyether Amines

3.4.2i Quaternised Detergents

3.4.2j Carrier Fluid

3.4.2k Jet Fuel Detergent

3.5 Mechanism of Detergency Action

3.5.1 Chemical Identities of Deposits

3.5.1a Oxygenated Hydrocarbons

3.5.1b Zinc Deposits

3.5.2 The Action of Detergents

3.5.3 Stabilisation of Dispersed Deposit or Particulate Material by Fuel Detergents in Gasoline and Middle Distillates

3.5.4 Chemical Reactions of Dispersants with Deposits

4 Cold Flow Improvers

4.1 Introduction

4.2 Detailed Problems and What Cold Flow Improvers Do

4.2.1 Diesel Vehicle Fuel Systems and Operability

4.2.2 Cloud Point Limitation

4.2.3 Pour Point Limitation

4.2.4 Diesel Vehicle Operability and the Cold Filter Plugging Point

4.2.5 Cold Flow Improvement and Fuel Variations

4.2.6 Cloud Point Depression

4.2.7 Wax Anti-Settling

4.3 The Organic Chemistry of Wax Crystal Modifying Cold Flow Improvers

4.3.1 Linear Ethylene Copolymers

4.3.2 The Free Radical Polymerisation Process

4.3.3 Comb Polymers

4.3.3a Free Radical Comb Polymers

4.3.3b Poly-1-Alkenes

4.3.4 Polar Nitrogen Compounds – Long Chain Alkyl-Amine Derivatives

4.3.5 Nucleators

4.3.6 Alkylphenol-Formaldehyde Condensates (Apfcs)

4.4 Mechanism of Wax Crystallization and Modification

4.4.1 Wax Crystal Compositions and Structures

4.4.1a Compositions

4.4.1b Structures

4.4.2 The Crystallisation Process

4.4.3 n-Alkane-Wax Nucleation

4.4.4 Effects of Additives on Nucleation

4.4.4a EVAC Nucleator

4.4.4b Nucleator Additives with Crystallinity, PEG Esters and PEPEP

4.4.5 n-Alkane-Wax Crystal Growth

4.4.5a Comparison of Untreated and WCM Treated Wax Crystals

4.4.5b Mechanism of Crystal Growth

4.4.5c Effects of Additives on Crystal Growth

4.4.5d Very Small Wax Crystals and Wax Anti-Settling

4.4.5e Cloud Point Depression

4.4.5f Rapid Growth of Wax Crystals in Narrow Boiling Distillates

4.6 Cold Flow Tests

5 Protection of Metal Surfaces in Fuel Systems: Lubricity Improvers and Corrosion Inhibitors

5.1 Lubricity: Introduction

5.2 Detailed Lubricity Problems

5.2.1 Jet Fuel

5.2.2 Gasoline

5.2.3 Diesel

5.3 Chemistries of Lubricity Improvers

5.3.1 Carboxylic Acids as Lubricity Improvers

5.3.2 Carboxylic Esters and Amides as Lubricity Improvers

5.4 Understanding of Boundary Friction and Lubricity

5.5 Introduction: Corrosion in Fuel Systems

5.6 Corrosion Issues in Various Fuels

5.6.1 Automotive Gasoline and Diesel Fuels

5.6.2 Jet Fuels

5.6.3 Heating Oils

5.6.4 Distillate Marine Fuels and Off-Road Fuels

5.6.5 Heavy (Residual) Fuels

5.7 Chemistries of Fuel Corrosion Inhibitors

5.7.1 Corrosion by Water/Oxygen and by Carboxylic Acids

5.7.2 Corrosion by Sulphur

5.7.3 Corrosion by Vanadium Pentoxide

5.8 Mechanisms of Corrosion and Its Inhibition

5.8.1 Corrosion by Water/Oxygen and by Carboxylic Acids

5.8.2 Corrosion by Sulphur

5.8.3 Corrosion by Vanadium Pentoxide

6 Combustion Improvers

6.1 The Need for Combustion Improvers

6.2 Combustion Improver Specific Problems

6.2.1 Gasoline Engine Knock and Octane Boosters

6.2.2 Diesel Knock and Cetane Improvers

6.2.3 Combustion Improvers for Heating Oils and Heavy Fuels

6.2.4 Combustion Improvers for Particulates in Diesel Engine Exhausts

6.3 Mechanisms of Soot Formation and Its Removal

6.3.1 The Formation of Soot

7 Additives to Treat Problems during the Movement and Storage of Fuels

7.1 Introduction

7.2 Drag Reducing Agents

7.2.1 The Pipeline Problem

7.2.2 Chemistries of DRAs

7.2.3 The Process of Drag Reduction

7.3 Static Dissipaters

7.3.1 The Problem of Static Electricity in Fuels

7.3.2 Chemistries of Static Dissipaters

7.3.3 Understanding Static Dissipaters

7.4 Antifoam Additives

7.4.1 The Problem of Foaming

7.4.2 What Antifoams Do and Their Chemistries

7.4.3 Syntheses of Silicone Antifoams

7.4.4 How Antifoam Additives Work

7.5 Demulsifiers and Dehazers

7.5.1 The Problem of Water-in-Fuel Emulsions or Haze

7.5.2 The Chemistry of Demulsifiers

7.5.3 The Process of Demulsification

7.6 Anti-Icing

7.6.1 The Problem of Icing

7.6.2 The Gasoline Icing Problem

7.6.3 The Jet Fuel Icing Problem

7.6.4 Jet Fuel Anti-Icing Additives

7.7 Biocides

7.7.1 Problems

7.7.2 Chemistries of Biocides Used in Fuels

Index

End User License Agreement

List of Figures

Chapter 1

Figure 1.1 Refinery Operations.

Figure 1.2 Straight-Run Yields...

Figure 1.3 Distribution of End...

Figure 1.4 Distribution of Liquid...

Figure 1.5 Distribution of Liquid...

Figure 1.6 EU-28 Imports of Diesel...

Figure 1.7 Distribution of Fuel...

Figure 1.8 Diagrammatic Inverse...

Figure 1.9 Solvent Yellow.

Figure 1.10 Sudan Red G.

Figure 1.11 Sudan Reds, Solvent...

Figure 1.12 Quinizarin and...

Figure 1.13 Solvent Blue.

Figure 1.14 Solvent Green.

Figure 1.15 Solvent Yellow.

Figure 1.16 Hydrolysed Protonated...

Figure 1.17 Some Markers in the Dow...

Chapter 2

Figure 2.1 A Commercial Synthesis...

Figure 2.2 Production of BHT.

Figure 2.3 Preparation of...

Figure 2.4 The Preparation of N,N'...

Figure 2.5 Free Radical Autoxidation...

Figure 2.6 Free Radical Autoxidation...

Figure 2.7 Two Peroxy Decomposition...

Figure 2.8 Formation of Difunctional...

Figure 2.9 Process of Radical...

Figure 2.10 Some BHT Antioxidant...

Figure 2.11 Initial Reactions...

Chapter 3

Figure 3.1 Port Fuel Injector.

Figure 3.2 Direct and Indirect...

Figure 3.3 Diesel Injector...

Figure 3.4 Typical Gasoline...

Figure 3.5 Typical Deposit Levels...

Figure 3.6 Cationic Polymerization...

Figure 3.7 Ene Reaction of...

Figure 3.8 Reaction of PIBSA...

Figure 3.9 DETA with Two...

Figure 3.10 PIBSA Reacted...

Figure 3.11 Possible PIBSA-Hydrazine...

Figure 3.12 Formation of Chloro-PIB...

Figure 3.13 PIB-Amine vis the...

Figure 3.14 Mannich Detergent...

Figure 3.15 2-Imidazoline Formation.

Figure 3.16 Formation of a Polyether...

Figure 3.17 Alternative Route...

Figure 3.18 Mannich Detergent...

Figure 3.19 Quaternized PIBSA-DMAP...

Figure 3.20 Polyester, Dimer-Intermediate.

Figure 3.21 Aldol Condensation.

Figure 3.22 Formation of Poly Ketals...

Figure 3.23 Particle Stabilisation...

Figure 3.24 Schiff Base Formation.

Figure 3.25 Condensation of sec-Diamine...

Figure 3.26 Formation of 4-Imidazolines.

Chapter 4

Figure 4.1 Wax Crystals...

Figure 4.2 Diesel Engine...

Figure 4.3 Use of Cloud Point...

Figure 4.4 Standard Distillation...

Figure 4.5 Middle Distillate...

Figure 4.6 2018 WDFQS Fuels...

Figure 4.7 2018 WDFQS Fuels...

Figure 4.8 2018 WDFQS Fuels...

Figure 4.9 Fuel Take-off as Tank...

Figure 4.10 Wax Settling Test...

Figure 4.11 Schematic Wax Crystal...

Figure 4.12 A Typical Section...

Figure 4.13 The Most Available...

Figure 4.14 Dibenzoyl Peroxide...

Figure 4.15 Initiator Radical...

Figure 4.16 Propagation.

Figure 4.17 Chain Transfer.

Figure 4.18 Backbiting Mechanism...

Figure 4.19 Poly (Hexadecyl Acrylate).

Figure 4.20 Conversion of Olive...

Figure 4.21 WASA Formed from...

Figure 4.22 Anionic Polymerisation...

Figure 4.23 Alkylphenol/Formaldehyde...

Figure 4.24 Diesel Fuel ...

Figure 4.25 N-Alkanes in...

Figure 4.26 n-Alkanes in a Diesel...

Figure 4.27 Nucleation Kinetic...

Figure 4.28 PEG Di-behen...

Figure 4.29 Untreated...

Figure 4.30 n-Alkane...

Figure 4.32 Adsorption...

Figure 4.33 MDFI Treated...

Figure 4.34 WASA Treated...

Figure 4.35 Wax Crystals...

Figure 4.36 Wax Crystals...

Chapter 5

Figure 5.1 Glycerol Monoo...

Figure 5.2 The HFRR Equip...

Figure 5.6 DDSA and TPSA....

Figure 5.7 Rearrangement ...

Figure 5.3 Alkyl Salicylid...

Figure 5.4 N,N-bis(2-hydrhyl...

Figure 5.8 Corrosion Inhis...

Figure 5.9 N-Acyl-Sarcosid...

Figure 5.10 Heterocyclesich ...

Figure 5.11 Triazole

Figure 5.12 Synthesis

Figure 5.13 Imidazoline

Figure 5.14 Formation of...

Chapter 6

Figure 6.1 The Four Strokes...

Figure 6.2 The Four Stokes...

Figure 6.3 The Thermal...

Figure 6.4 The Thermal...

Figure 6.5 Copper Complex...

Figure 6.6 Soot Formation...

Figure 6.7 Formation...

Figure 6.8 Formation...

Figure 6.9 Formation...

Figure 6.10 Growth of Large...

Chapter 7

Figure 7.1 Poly-1-Decene.

Figure 7.2a Fuel in Turbulent...

Figure 7.2b Fuel Containing...

Figure 7.3 Calcium-AOT...

Figure 7.4 The Preparation...

Figure 7.5 1-Decene Sulphone.

Figure 7.6 Formation of Methyl...

Figure 7.7 Reaction of...

Figure 7.8 Cyclic Silicones.

Figure 7.9 Ring Opening Polymerisation...

Figure 7.10 Adding a Polyol...

Figure 7.11 Schematic Representation...

Figure 7.12 Base Catalysed Formation...

Figure 7.13 Propoxylation of an...

Figure 7.14 Alkylphenol with Block...

Figure 7.15 Demulsifier Derived...

Figure 7.16 DIEGME Di-Ethylene ...

Figure 7.17 The Preparation of MBT.

Figure 7.18 The Preparation of TCMBT.

Figure 7.19 The Preparation of...

Figure 7.20 Preparation of KATHON...

List of Tables

Chapter 1

Table 1.1 Side-streams...

Table 1.2 Petroleum...

Table 1.3a EN 228, European...

Table 1.3b ASTM D4814...

Table 1.4 The refinery...

Table 1.5 Selected...

Table 1.6 Fuel additives...

Table 1.7 Dye absorption...

Chapter 2

Table 2.1 C–H Bond Dissociation...

Chapter 3

Table 3.1 Inlet Valve Deposits...

Table 3.2 Peugeot XUD-9 Loss...

Table 3.3 Temperatures...

Table 3.4 Loss of Engine...

Table 3.5 CSPIT Results...

Chapter 4

Table 4.1 Depressions (°C)...

Table 4.2 Winter Diesel Fuel...

Table 4.3 Wax Settling...

Table 4.4 Highest n-Alkane...

Table 4.5 n-Alkane and...

Chapter 5

Table 5.1 Comparison...

Chapter 6

Table 6.1 Leaded Aviation...

Chapter 7

Table 7.1 Conductivities...

Table 7.2 1-Decene Polysulphone...

Table 7.3 Effect on Conductivity...

Table 7.4 Fuel Conductivities...

Table 7.5 Chemical Demulsifiers...

Guide

Cover

Title page

Copyright

Table of Contents

Acknowledgements

Preface

Abbreviations

Begin Reading

Index

End User License Agreement

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Acknowledgements

I owe a great deal to my friend and colleague Graham Jackson for his encouragement and for his painstaking reviewing and editing of every sentence in this book. Many thanks also to Dhanesh Goberdhan for his careful reading and many useful suggestions. Several diagrams and pictures come with the Chevron copyright; I thank Dan Foscalina and his colleagues at Chevron Media Relations for gaining my permission to use them.

Robert D. Tack

Preface

It is not only chemists who realise the ubiquitous nature of chemical technology in our modern environment, though it may be that only chemical technologists fully appreciate just how wide ranging are the products of the chemical industry. The scope of the chemical technology can be thought of, broadly, as the applications – such the dyes, pharmaceuticals, and textiles – and within each application and subdivision, there is a whole technology specific to that application. One broad application is chemicals in the oil industry, which includes a few subdivisions: those for exploration and recovery, those in refineries and those for the finished products of oils and fuels.

Additives for lubricating oils have been well covered in the available literature while fuel additives have been covered in much less detail and provide an area of expertise whose existence is largely unknown to the public. This book is concerned with the problems addressed by fuel additives, their chemistries, and scientific insights into their actions.

In this book, chapters on the individual additive types generally follow a discussion of the problem that they address, what they do to alleviate the problem, their chemistries – including their preparations – and some understanding of how they work. Many fuel additives are derived from existing areas of technology in other applications; degradation by corrosion and autoxidation, for example, are wide ranging problems that have spawned studies to understand them and additives to overcome them. Some additives started life in other parts of the petroleum industry such as fuel detergents, that are derived from lubricating oil dispersants, and demulsifiers, that are heavily used in crude oil recovery. As a result of this wide relationship with other applications, the sources drawn on for each chapter are also wide ranging in technical area and in literature type.

There are some publications that provide useful summaries of fuel additives and their use. In particular, the booklets provided by the Technical Committee of Petroleum Additive Manufacturers in Europe (ATC) provide a paragraph on each additive/fuel combination. The Automotive Fuels Reference Book provides extensive coverage of the production, distribution and use of fuels along with details of internal combustion engines, along with few chapters on gasoline and diesel fuel additives. Books on refining are plentiful, but they usually pay little or no attention to fuel additives. However, to understand fuels and the roles of and incentives for the use of fuel additives, it is necessary to know something about refineries. So, the first chapter summarises refinery operations to an extent that discussions of fuels in the following chapters is understandable. This first chapter is an attempt to cover problems other than those occurring from of the way in which fuels are transported and used, so it also includes such items as the proportions of different fuels used at different times and places – the demand barrel; it also introduces the range of fuels and additives, and the influence of taxation.

Degradation of fuels resulting from autoxidation is widespread and is the source of deposits that interfere with the uses of fuels. Direct treatment of such problems is needed from the moment a fuel is blended in the refinery, so the problem of stabilisers is dealt with first. The use of detergents is needed to treat the deposits that escape stabiliser treatment, so this follows on directly.

There is no obvious further natural progression for the remaining problems that appear to be independent of each other in the end use. They are, however, often linked by the way the refiner has to operate to meet production of the demand barrel, or to meet the conflicting needs of various legal specifications. Cold flow improvers enable fuels to flow without problem when they precipitate wax in winter; this a valuable aid to refiners meeting the demands for different fuels in the most cost-effective way. Wear through physical contact and corrosion both cause gradual loss of metal in fuel systems that can lead to failure and leakage; lubricity and corrosion inhibitors are similar compounds designed to prevent these problems. Combustion improvers are concerned with flame chemistry in the different environments of engines and burners. Finally. There are several problems that arise during the movement and storage of fuels that are dealt with in the final chapter.

Sources for this book have ranged from newspaper articles to academic journals. Specialist technical journals, such as Infineum’s Insight magazine, and biannual reviews, such as BP’s review of World Energy and the Infineum Worldwide Winter Diesel Fuel Quality Surveys, provide valuable, wide ranging views of the business, changing specifications and fuel qualities. Academic journals are generally specialised such those on Energy & Fuels, Tribology, and Colloids. Websites of additive suppliers, oil companies and those set up by government agencies, such as the European CONCAWE1 and the International Energy Agency, are sources of wide-ranging relevant information.

For details of specific chemical additives, what they do and how they are made, there is no better source than patents. Details of the problem being addressed, tests used, the structures of commercial and proposed additives and how they are made, may be found in patents. A little more patent searching can also reveal a history of additive developments. While many materials may, in patents, be claimed to be effective solutions to the problem under discussion, the author has tried to keep to those that to have been or are commercial additives. Sometimes the exact structure of a commercial additive may not be easily accessible, but patent literature and company sponsored academic papers, combined with the suppliers’ broad descriptions, often identify structure type sufficiently to aid an understanding of its activity. If I have deduced an incorrect assumption from these sources, I offer my apologies and ask forgiveness.

For the organic chemist, the author has used much of the pre-IUPAC nomenclature for the alkenes (olefins). While ethene, propene and butene are the names used in the academic and some industrial occupations, the oil industry is mostly familiar with the older names ethylene, propylene, and butylene. Products such as poly-ethylene and poly-iso-butylene (PIB) are too well established to be replaced by poly-ethene and poly-(2-methyl-propene). However, the word ‘olefins’ is not specific enough when discussing the position of a double bond so the word ‘alkene’ is then used in preference.

The author hopes that this book has a wider utility than in the petroleum industry alone. Chapter subjects are mostly applicable in other spheres of industry; as such, the general aspects of their topics may be of use to those looking for quick understanding of, for example, oxidative stability or corrosion or crystallization. Finally, I hope that the chemistry is described in sufficient detail to provide examples that chemists in further education might use to answer student questions along the lines of ‘So, what is the use of this chemistry (or compound)?’.

Notes

1

 CONservation of Clean Air and Water in Europe, the European oil industry body that monitors health and safety of petroleum products.

Abbreviations

ACEA

European Automobile Manufacturers Association

AcOH

Acetic Acid

AKI

Anti-Knock Index (average of RON and MON)

APFC

Alkyl-Phenol-Formaldehyde Condensate

ARES

Atmospheric Residual fuel

ASA

Alkyl Salicylic Acid

ASTM

American Society for Testing and Materials

ATC

Additive Technical Committee

ATRP

Atom Transfer Radical Polymerization

Avgas

Aviation Gasoline

AWCD

All Weather Chassis Dynamometer

B10

Biodiesel, 10% FAME and 90% Petroleum Diesel

BBD

Broad Boiling Distillate

BCF

Burton, Cabrera and Franck

BHT

Butylated Hydroxy Toluene

BOCL

Ball-On-Cylinder Lubricity Evaluator

BS

British Standard

BTL

Biomass To Liquids

CAFE

Corporate Average Fuel Economy

cc

cubic centimetre

CCCD

Cold Climate Chassis Dynamometer

CCD

Combustion Chamber Deposits

CCT

Catalytic Chain Transfer

CEC

Confédération Européenne des Cadres

CEIC

Cision European Institutional Investor Company

CFPP

Cold Filter Plugging Point

CI

Cetane Index

CN

Cetane Number

COPD

Chronic Obstructive Pulmonary Disease

CP

Cloud Point

CPD

Cloud Point Depressant

CSPIT

Cold Spark Plug Immersion Test

CTL

Coal To Liquids

DDSA

DoDecenyl-Succinic Acid or Anhydride

DETA

Di-Ethylene-Tri-Amine

DI

Direct Injection

DIEGME

DiEthylene Glycol Monomethyl Ether

DMAPA

3-DimethylAminoPropylAmine

DPF

Diesel Particulate Filter

DRA

Drag Reducing Agent

DSC

Differential Scanning Calorimetry

DTBHQ

Di-Tert-ButylHydroquinone

DTBP

Di-Tertiary Butyl Peroxide

E30

Gasohol, gasoline with 30% ethanol

ECA

Emission Control Area

EDA

1,2-Ethylene-DiAmine

EDTA

Ethylene Diamine Tetra-acetic Acid

EGR

Exhaust Gas Recycle

EHN

2-EthylHexyl-Nitrate

EI

Energy Institute

EN

European Norms (standards)

EU

European Union

EV2-EH

Ethylene Vinyl-2-EthylHexanoate copolymer

EVA, EVAC

Ethylene Vinyl Acetate Copolymer

EVEC

Ethylene Vinyl Ester Copolymer

FAME

Fatty Acid Methyl Ester

FBC

Fuel Born Catalyst

FBP

Final Boiling Point

FCC

Fluid Catalytic Cracker

FO

Fuel Oil

FT

Fischer-Tropsch

FVAC

Fumarate Vinyl-Acetate Copolymer

GDI

Gasoline Direct Injection

GLC

Gas Liquid Chromatogram or Chromatography

GTL

Gas To Liquids

GC-MS

Gas Chromatography - Mass Spectroscopy

HAGO

Heavy Atmospheric Gas Oil

HCGO

HydroCracked Gas Oil

HFO

Heavy Fuel Oil

HFRR

High-Frequency Reciprocating Rig

HGO

Heavy Gas Oil

HGV

Heavy Goods Vehicle

HLB

Hydrophile Lipophile Balance

HSR

Heavy Straight Run

HT

Hydrogenated Tallow

HVO

Hydrogenated Vegetable Oil

IATA

International Air Transport Association

IBP

Initial Boiling Point

ICE

Internal Combustion Engine

IDI

InDirect Injection

IP

“Institute of Petroleum, merged with the Institute of Energy to form the Energy Institute”

IVD

Intake Valve Deposits

JFTOT

Jet Fuel Thermal Oxidation Tester

JP-8

Jet Propellant 8 or Jet Propulsion fuel 8

kg/m3

Kilograms per cubic metre

kJ

Kilo Joule

Km

Kilometre

KPa

Kilo Pascals

LGO

Light Gas Oil

LPG

Liquefied Petroleum Gas

LSP

Low Speed Pre-ignition

LSR

Light Straight Run

LTFT

Low Temperature Flow Test

MBT

Methylene Bis (Thiocyanate)

MD

Middle Distillate

MDA

Metal Deactivating Additive

MDFI

Middle Distillate Flow Improver

mEq

Milli-Equivalent

mg/kg

milligrams per kilogram (also ppm by weight)

MGO

Medium Gas Oil

ml

millilitre

mm

millimetre

MMT

Methylcyclopendadienyl Manganese Tricarbonyl

Mn

Number average molecular weight

MON

Motor Octane Number

MPa

Mega Pascal

MSDS

Material Safety Data Sheet

MT

Million Tonnes

MTBE

Methyl t-Butyl Ether

Mtoe

million toe

MW

Mega Watt

Mol.Wt.

Molecular Weight

NBD

Narrow Boiling Distillate

NBP

Normalised Boiling Point

nm

nanometre

NMP

Nitroxide Mediated Polymerization

NOx

Nitrogen Oxides

OMA

Olefin/Maleic Anhydride

ORI

Octane Requirement Increase

pa

per annum

PAA

Poly-Alkyl-Acrylate

PAH

Poly-Aromatic Hydrocarbon

PAM

Poly Amine (usually poly-ethylene diamine)

PAMA

Poly-Alkyl-MethAcrylate

PAO

Poly Alpha Olefin

PBO

Poly-Butylene-Oxide

PBTPA

PIB-ThioPhosphonic Acid

PDA

Para-phenylene DiAmine additives

PDMS

Poly-Di-Methyl Siloxane

PE

PolyEthylene

PEG

Poly-Ethylene-Glycol

PEO

Poly-Ethylene-Oxide

PEPEB

Poly-Ethylene/Poly-Ethylene-Butylene diblock

PEPEP

Poly-Ethylene/Poly-Ethylene-Propylene diblock

PFI

Port Fuel Injectors

PFT

Programmed Fluidity Test

PIB

Poly Iso Butylene

PIBSA

Poly Iso Butylene Succinic Anhydride (or acid)

PPD

Pour Point Depressant

ppm

parts per million

PPO

Poly-Propylene-Oxide

pS

PicoSiemens

RAFT

Reversible Addition-Fragmentation chain Transfer

RON

Research Octane Number

ROP

Ring Opening Polymerization

rpm

revolutions per minute

SEM

Scanning Electron Microscopy

TAPs

Trans-Alaska-Pipeline-systems

TCMBT

2-(ThioCyanoMethylthio)BenzoThiazole

TDC

Top Dead Centre

TEL

Tetra Ethyl Lead

TEM

Transmission Electron Microscopy

TEPA

Tetra-Ethylene-PentAmine

TETA

Tri-Ethylene-Tetra-Amine

TEU

Twenty-foot Equivalent Unit (shipping container)

toe

tonnes oil equivalent

TOFA

Tall Oil Fatty Acids

TPSA

Tetra-Propenyl Succinic Acid

UK

United Kingdom

ULSD

Ultra Low Sulphur Diesel

USA

United States of America

USAF

United States Air Force

V/V

Volume per Volume (as % V/V)

VAT

Value Added Tax

VisRES

Visbreaker Residual fuel

VRES

Vacuum Residual fuel

WAFI

Wax Anti-settling Flow Improver

WASA

Wax Anti-Settling Additive

WAXD

Waxy Distillate

WCM

Wax Crystal Modifier (or Modifying)

WDFQS

World Winter Diesel Fuel Quality Survey

WSD

Wear Scar Diameter

ZDDP

Zinc Dialkyl-Dithio-Phosphate

1 Fuels and Fuel Additives – Overview

1.1 Introduction

The fuels under consideration here are the liquid fuels obtained from crude oil by fractional distillation and other refinery processes, together with biofuels and synthetic Gas to Liquid (GTL) and related fuels. The gases methane, ethane, propane and butane are not covered as they generally need few, if any, additives other than odorants.

Coal is not considered here either. Most coal is burned in fluidised beds in electricity power stations, which provided about 38% of the world’s electricity (22% in Europe) in 2017 [1]; overall, coal provided 28% of the world’s energy and oil provided 34%, in 2017. Coal additives are added to reduce soot, fly-ash, bottom-ash, slag and clinker in power stations, but a European Commission research document concludes that only the use of lime or limestone effectively reduces deposits, fly-ash and sulfur oxides [2,3]. Magnesium additives are used in furnaces burning heavy fuel but are not effective in coal, so links with the additives used for petroleum derived fuels are almost non-existent.

This chapter will give a condensed explanation of the refinery operations that convert crude oil into fuels and compositions of the different fuels. Also, in this chapter are presented some of the statistics of quantities of various refinery products and global variations. The author’s intention is to provide sufficient understanding of refining to support the discussions of the applications of fuel additives. Much has been written about refineries, specifications and internal combustion engines, so the reader is guided to some of the relevant literature for more detailed explanations – for an example of the engineers’ perspective see the Automotive Fuels Reference Book [4].

Finished fuels are put together from the refinery components to provide the properties that they need to have and to meet fuel specifications. However, many of the properties that a fuel should have are difficult to achieve by blending refinery output streams. Fuel additives provide the additional necessary properties – usually in the most economical way and sometimes the use of additives is the only way for the different fuels to meet their specifications. This chapter introduces the reader to the range of fuel additives used in the different fuels.

When fuels reach the market and are sold, not surprisingly there is a whole tax regime, particularly for motor fuels. And, as in other areas of taxation, there are some concessions of low taxation on fuels for particular applications which carry the potential for criminal diversion of low-tax fuels into high-tax applications. So, it is here that we are first introduced a discussion of fuel additives: dyes and markers that are used to identify low-tax fuels.

While petroleum fuels and their production form a worldwide industry, most of the data referred to is from Europe and the USA because information of these markets is that which is most widely available. The oil industry started in the USA, followed closely by Europe [5] – the industry in other parts of the world followed in the footsteps of these two regions and still set specifications which are closely related to those in the USA and in Europe.

1.2 Refinery Operations and Processes

There is much literature on refineries, and useful, easy-to-follow descriptions and diagrams are provided in oil company websites [6–12]. A schematic of refinery operations helps to visualise how the different fuel components arise and how they are combined into the finished fuels (Figure 1.1) [8]; this will help in understanding the discussions of how particular fuel problems arise and the refinery limitations which lead to additives providing the best solutions.

Figure 1.1 Refinery Operations. © 2019 Chevron. All rights reserved.

1.2.1 Distillation

Crude oil coming into the refinery is preheated in the heat exchangers that, at the same time, cool the exiting refinery product streams. Steam is then injected into the crude which moves into a furnace (at about 500°C to 550°C) where it is heated to almost 400°C. The furnace is at the bottom of the atmospheric (pressure) distillation tower – more commonly known as the atmospheric pipestill or topping unit. Here, the more volatile fractions rapidly vaporise, and the hot vapours pass up the tower through a series of perforated metal trays – the perforations are holes with a collar and a supported cap known as a bubble cap. As the vapours cool to the lower temperatures higher in the tower, the less volatile components condense into liquids that collect on the trays and pass down the column. During this process, the bubble caps force the rising vapours to bubble through the condensing liquids, thus improving the efficiency of the fractional distillation: the cooler liquid condenses more of the less volatile liquids from the vapour and the vapour takes out the more volatile components from the liquid. Every few trays, the condensed liquids are continuously removed as a ‘side-stream’ or ‘cut’. These side-streams are collected and blended for use as the distillate fuels gasoline, jet, kerosene, diesel fuel and gas oil or are transferred to various conversion processes (Figure 1.1).

A steady, falling temperature gradient is established in the distillation tower. The most volatile components pass over at the top of the tower while the non-volatile material, known as atmospheric residual fuel, collects at the bottom of the pipestill, after removal of more volatile fractions with the help of a current of steam. Boiling temperatures of the side-streams are highest at the bottom of the tower – for example heavy gas oil (up to 380°C) – and lowest at the top (below 100°C) – such as the gasoline component light naphtha (up to 70°C). Exact boiling ranges of the side-streams and their degree of overlap (efficiency of separation) depend upon the exact details of operations at each refinery but the variations are not huge.

The proportions of side-streams, hence products, vary with type of crude oil. ‘Light crudes’ and ‘heavy crudes’, meaning low and high density, contain different proportions of lower and higher boiling material. West Texas Intermediate is a light crude which contains a relatively high proportion of the valuable low-boiling gasoline fractions and a low proportion of high-boiling residual fuel; in contrast, Arabian heavy crude has low proportions of the valuable light products and a large (about 60%) of low-value high-boiling material (‘other’ in Figure 1.2), of which half is vacuum distillable leaving half as an undistillable vacuum residual fuel [13]. More importantly, the distributions of products possible from both crudes after atmospheric distillation, known as ‘straight-run’, and blending do not match that of the average refinery output. A region’s average refinery output is designed to meet customers’ needs (such as the EU-28 [14,15] in Figure 1.2), which is termed the demand barrel.

Figure 1.2 Straight-Run Yields (Wt.% of Total) of a Range of Crude Oils, Compared with European Union-28 Refinery Output 2017.

Table 1.1  Side-streams in a typical modern refinery from Kuwait export crude.

Cut Number

Product Name

Cut Vol% of Whole

Distillation

3

End Point

Average NBP

Average Mol. Wt.

1

Gases

1.3

10

2.5

56

2

Light naphtha

7.3

70

44

71

3

Naphtha

16.6

180

132

112

4

Kerosene

10.1

240

210

160

5

Light diesel

7.8

290

264

200

6

Heavy diesel

7.0

340

314

244

7

Atmospheric gas oil

3.8

370

355

285

8

Vacuum gas oil

2.4

390

380

313

9

Vacuum distillate

18.3

550

467

435

10

Vacuum residue

26.7

–

689

1150

1.2.2 Balancing Production to the Demand Barrel

Distillate fuels are needed in larger proportions than are naturally present in crude oil. In Europe, this is particularly true for the middle distillates gas oil and diesel, while the USA needs more gasoline. The problem lies in the high proportions of atmospheric residual fuels, such as 32% to 54% of the crude oil (‘other’ in Figure 1.2), which outstrips demand for this fuel. Clearly, this excess cannot be treated as waste; the quantities are huge – the reality of refining is that all that comes into a refinery as crude oil must go out as products. For example, the Fawley refinery supplies 14% of the UK’s oil products; it processed around 22 million tonnes of crude oil in 2019 (60 thousand tonnes per day1) [11]. If one-third of this came out as atmospheric residual fuel, that would pose an enormous problem of disposal.

Most refineries, then, have more complex operations than those providing only straight-run, atmospheric distillation. Through the second half of the twentieth century, almost all simple, straight-run only refineries (also known as ‘hydro-skimming’ refineries) in Europe and North America have closed and the more complex refineries have expanded to meet demand. Atmospheric residual fuel is further refined first by being vacuum distilled up to a temperature equivalent2 of 550°C. This takes place in a vacuum distillation pipestill, which has the same arrangement as for the atmospheric pipestill but with the addition of a partial vacuum (reduced pressure), provided by steam injectors. From this pipestill, a range of vacuum-distilled fractions (known as ‘vacuum gas oils’) are produced; some of these are converted into lubricating oils but most is used as feed for the crackers (section 1.2.3). Finally, left behind at the bottom of the vacuum pipestill is a certain proportion of a high-boiling, undistillable vacuum residue. Some of the vacuum residue is converted to bitumen or heavy lubricating oil, some is blended with low-value distillates into residual fuels and some is processed further to produce lighter products in cokers (section 1.2.5). Residual fuels are used in heavy marine diesel fuels, in refinery furnaces and in some power stations.

After the atmospheric and vacuum distillations, the refinery products are typically those shown in Table 1.1 [6] from a heavy Middle Eastern crude. For this Kuwait crude oil distillation, the proportion of vacuum residue is 26.7% while an assay of Kuwait export crude put the proportion of atmospheric residue at 54.5% (Figure 1.2) [13], i.e. ‘fairly heavy’.

Refinery fuel products from complex European refineries are made up of higher proportions of non-residual, higher-value products than are possible by blending the straight-run distillation cuts of either the Kuwait or Arabian crudes (Figure 1.24, cf. Table 1.2 [15]). The difference between total refinery output (638.5 Mtoe5) and the use as liquid fuel (transport plus heating, 508 Mtoe) is made up of other petroleum product applications such as heavy (marine) fuel, industrial use (many varied sectors), liquefied petroleum gases, lubricating oils, waxes and chemicals (Figure 1.3 [16]). Many refineries produce items such as solvents that contain aliphatic and aromatic hydrocarbons, ketones and alcohols; raw materials for the chemical and plastics industries such as ethylene, propylene and butylene, and higher alkenes, such as tetrapropylene, are other refinery products. These other products are made from both the liquid fractions and the gases. Diesel is also used for non-transportation engines such as generators. Import/export balances can confuse the quantities, and the counting of residual fuel may be short because sales are often private.

Figure 1.3 Distribution of End Uses for Petroleum Products in the EU-28, 2016.

Table 1.2  Petroleum refinery products in Europe 2018.

Product

Refiney Output, Mtoe

Refinery Output, % of Total

Total output:

638.5

100

LPG

30.3

2.8

Naphtha

42.2

7.0

Gasoline

80.1

18.5

Kerosene + Jet

62.8

8.6

Gas oil /Diesel oil

292.6

39.4

Fuel oil

49.3

11.7

Other products

53.1

12.1

Refinery use/losses

27.7

–

(Quantities in million tonnes oil equivalent (Mtoe) are close to actual tonnes as the factors for conversion of quantities, by weight, to tonnes oil equivalent are close to 1.0:1.01 for diesel and 1.105 for gasoline; residual fuel oil is 0.955.)

Imbalances between the supply and demand barrels vary between regions, seasonally and over years with macroeconomic changes, such as the adoption of fuel-efficient diesel in Europe and heating oil being replaced by natural gas. They are corrected, in part, by refinery conversion facilities such as crackers (section 1.2.3). Such facilities raise costs and prices but enable global refining to meet the global balance in demand. Regional imbalance is corrected by trade that reflects different regional needs. As a result, excess of a fuel in one region may be exported to a region that has a shortage of that fuel. The import/export effect is illustrated by the European and USA markets. A comparison between the two illustrates the differences between the USA and the European petroleum fuel markets. These differences in fuel consumption explain the differences in emphasis on additives that have developed in these two markets.

Transportation fuels, road, aviation and shipping, take up the major part of fuel consumption (Figure 1.3, in Europe [16]) so dominate refinery operations and trade. Europe and the USA have quite different distributions of transport fuel consumption – European transport relies heavily upon diesel while gasoline dominates in the USA [17] (Figure 1.4). In a worldwide comparison, while Europe depends upon middle distillates and the USA upon gasoline, the Asia-Pacific region depends somewhat evenly upon these two (Figure 1.5 [18]).

Figure 1.4 Distribution of Liquid Transport Fuels in the USA and Euro 28 Countries, 2018.

Figure 1.5 Distribution of Liquid Fuel Use by Type in Main Economic Blocs, 2018 [18]6.

As might be expected, import/export figures for these fuels show that Europe imports substantial quantities of middle distillates, while exporting similar quantities of gasoline [15] (Figure 1.6). Historically, the USA imported more gasoline than it exported, for example 25 Mtoe in 2011 [19]; however, since the recent resurgence of oil production in the USA, it has become a net exporter of both diesel (58 million tonnes ULSD in 2017) and gasoline (31 million tonnes) [17]. Europe’s major supplier of diesel is now Russia, and the Middle East is its major supplier of jet fuel [15].

Figure 1.6 EU-28 Imports of Diesel/Gas Oil and Exports of Gasoline, Million Tonnes in 2017.

In the world of petroleum and petroleum products, such changes are not surprising given the background that over the ten years from 2008 to 2018, the total consumption of oil has changed little in North America (from 1105 to 1113 Mtoe) while falling in the European Union (731 to 647 Mtoe) and growing strongly in Asia Pacific (1250 to 1695 MT pa) [18].

Worldwide, the 4,474 million tonnes of petroleum products consumed in 2018 had a distribution of petroleum cuts [18] (Figure 1.7) most like that in the Asia Pacific. It is perhaps worth reminding the reader that diesel engines are used to propel buses, HGVs/trucks, ships and smaller boats, tractors, construction vehicles and back-up electricity generators as well as passenger cars and light vans. By reason of the greater fuel efficiency of diesel over gasoline engines (and the rising cost of oil), the growth in the demand for diesel was outstripping that for gasoline in the noughties, such that in 2012, 51% of new cars were diesel in the UK and 56% in Europe [20] – except in America. In fact, the USA had been dubbed ‘Refiner to the World’ because the high demand for diesel outside the USA was providing USA refineries with profitable production and sales of diesel for export [21].

Figure 1.7 Distribution of Fuel Consumption by Refinery Description, Worldwide, 2018.

Light distillate: aviation and motor gasoline with light distillate feedstock. Middle distillates: jet, heating kerosene, gas oils and diesel fuel, including some marine bunkers.7 Fuel oil: marine bunkers (heavy fuel) and crude oil used as fuel. Others: refinery gas, LPG, solvents, bitumen, lubricants and other refinery products and losses.

Looking to the future, in a 2011 survey for the UK department of energy [19], the projection to 2030 was for a fall in the gasoline share of demand (to 10% of total petroleum products) and a corresponding rise in diesel fuel demand (to 40%), an increase in jet fuel consumption and continued fall in the demand for heavy fuels. The last two did occur but the continued rise in diesel demand was being limited by worries about its contributions to city pollution, inroads of biodiesel and decreasing energy intensity8 as the new Asia Pacific economies mature.

In 2017, however, a break in the trend was underway, resulting from a combination of rising air pollution in cities, due to petroleum-driven motor transport, in particular diesel vehicles (particulates and NOx worries), and the rapid rise in electric vehicle technology. ACEA reported that of the new passenger cars sold in Western Europe, in 2016, 49.5% were diesel and 45.8 were petrol engine powered (2.1% hybrid electric, 1.5% rechargeable electric, 1.2% LPG) [22]. In June 2017, diesel passenger cars took only 39% of sales in Germany, and it was predicted that this could soon fall to 30% [23]; new passenger cars in Europe in 2018 showed a complete reversal to 36% diesel and 57% gasoline (electric rechargeable and hybrid 6%) [24]. As Yogi Berra said, ‘It is difficult to make predictions, especially about the future’.

1.2.3 Catalytic Conversions

As already discussed, there is not sufficient distillate fuel after straight-run, atmospheric distillation to meet customer demand. This mismatch between what is in crude oil, that may be separated by distillation, and the needs of the market for transportation is resolved by cracking the molecules in the higher boiling fractions – so converting the low-value high-boiling gas oil into valuable gasoline and diesel. Vacuum distillates are hydrotreated to remove the sulphur that would poison the catalysts, fed into the crackers, and redistilled to give the lower boiling cuts needed for automotive fuels.

There are two main types of cracker [6]. In one, the Fluid Catalytic Cracker (FCC), hydrotreated, liquid vacuum gas oils are passed through a bed of zeolite catalyst at about 500°C, under low pressure (1 to 5 bar). The FCC produces hydrocarbons with a high degree of unsaturation (alkenes and aromatics) as well as branched lower alkanes and hydrogen (which is used in the hydro-treaters). The product is then distilled to produce streams that are valuable, high octane blend components for gasoline, which is the primary purpose of the FCC. In addition, there are smaller amounts of aromatic-rich kerosene and middle distillate fractions.

The other is the hydrocracker, in which vacuum gas oils are cracked at 350°C to 450°C in the presence of hydrogen. There are degrees of hydrocracking: mild hydrocracking uses hydrogen at a pressure of 35 to 70 bar and a nickel-molybdenum catalyst to remove sulphur, nitrogen, and destabilising olefin unsaturation. Conventional hydrocracking uses hydrogen at 85 to 140 bar and a nickel-molybdenum on silica-alumina-zeolite catalyst to remove most of the sulphur and most of the aromatics; at the same time, hydrocracking9 and hydroisomerising occur to produce distillation streams that have high cetane numbers, so are suitable for ultra-low sulphur diesel fuel [6].

For light distillates, there is a further catalytic process. Catalytic reforming is used to convert low octane naphtha into gasoline components that are rich in iso-alkanes and aromatics, which have high octane numbers. Catalytic reforming is carried out by passing the naphtha over a platinum-based catalyst, under moderate pressure (5 to 25 bar) at 500°C [6].

1.2.4 Alkylation

Alkylates are the products of the sulphuric acid-catalysed reactions of short chain alkenes, usually butylene or propylene, with isobutene10. Alkylates are highly branched and so have high octane numbers ‒ for example, the isobutylene/isobutane product is iso-octane which has a 100 octane number [6].

1.2.5 Coking

Finally, there are the atmospheric and vacuum distillation residues. These may be converted to distillable liquids by ‘coking’ whereby the distillation residues are heated at a high temperature so that carbon is extruded, as coke, from the high molecular weight, carbon-rich molecules leaving liquid products of lower molecular weight that contain more hydrogen. The process also leaves much of the sulphur and metals in the coke. The chemistry of the process is thought to be that as the already high molecular weight molecules condense together into poly-aromatic structures, low molecular weight alkanes, alkenes and aromatics are split off. Eventually, the poly-aromatics have graphite-like structures and contain low proportions of hydrogen. The product liquids are distilled into a full range of products: gases such as methane and alkenes such as ethylene, propylene and butylene (valuable chemical intermediates); aromatic-rich (hence high octane) gasoline components; aromatic-rich kerosene and gas oils that need hydro-treatment to be useful as jet and diesel blend components [6].

In delayed coking, the residue is heated to about 500°C, at several bar pressure in a furnace. It is then kept in a ‘(heat) soak drum’ at about 450°C to 480°C until about 20% to 30% of the residual fuel is converted to coke plus lower boiling liquids, which are then redistilled. In a flexicoker, the residual fuel is passed through a fluidised bed, at about 520°C and low pressure (under 1 bar), with a flow of steam; in this process, the extruded carbon is burned off (only 2% left behind) providing the heat needed for the endothermic coking process. Visbreaking is a similar but milder process in which 15% to 25% of the residue is converted to lower molecular weight components that lower the viscosity, which is often necessary in heavy fuel blending. In the visbreaker, the residue is passed over heat-exchange tubes at 425°C to 450°C, depending upon the severity of cracking required; for example, at 450°C, 75% may be cracked to lower boiling materials [6,7]. Alternatively, the heated residue may be kept in a soaker drum for some time (as in delayed coking but at a lower temperature and shorter time).

1.3 Finished Fuels

As the boiling point range of the fuel is raised, the molecular weights and densities of the fuel components also increase giving rise to the terms ‘light’ and ‘heavy’, which refer to lower and higher boiling fractions, respectively. Finished fuels from a refinery are usually made up by blending a range of distillate streams (plus residual fuel for heavy fuels) – a range that can be several streams in a complex refinery (Figure 1.1). Blending enables all of a refinery’s production to be used. The process is guided by the need to meet a range of specifications for the products. Specifications are set by various industry and government bodies to ensure that fuels meet a minimum quality to provide the performance needed by the customer and minimise environmental pollution.

1.3.1 Gasoline

Several refinery streams may be combined to produce gasoline that meets the local specifications – the most important two are octane number and volatility. Octane number is the gasoline quality that indicates whether the fuel will work effectively in the engine; it is specified either as a Research Octane Number (RON) of at least 95 or a Motor Octane Number (MON) of at least 8511 (EN228 specifications) [25,26]. A minimum octane rating is necessary to ensure that gasoline used in an engine with standard compression12 does not cause the engine to knock. Such knocking is caused by auto-ignition of the gasoline/air mixture lower down the engine cylinder as the flame front moves through the cylinder. This causes an out-of-time spike in pressure accompanied by a sharp sound (knock or ping) that can lead to engine damage (section 6.2.1). Auto-ignition is a free radical process which is inhibited by compounds that form relatively stable radicals, such as highly branched alkanes as 2,2,4-trimethylpentane13 and alkyl aromatics such as toluene (see Chapter 6).

In order that gasoline burns evenly and completely in the combustion chamber, it must vaporise readily – the volatility of a gasoline should also be sufficient to ensure easy starting. Volatility is specified, for example in Europe and the USA (Table 1.3 [9,26]), and it depends upon the distillation properties of a gasoline, so the specifications are met by blending streams of different distillation ranges. Laboratory distillations of refinery products (by a standardised distillation procedure, ASTM D86) provide the cumulated weight percentage collected at each distillation temperature (see section 4.2.5). For the European EN 228 gasoline specification, distillation is presented as the amount evaporated (same as collected distillate) at 70°C, 100°C and 150°C or 180°C, and at the final boiling point (Table 1.3a)14. In the USA, ASTM gasoline specification D4814 distillation requirements are presented as the distillation temperature at which 10%, 50% and 90% of the distillate is collected, together with the end point – the temperature at which the last of the distillate is collected, the final boiling point (Table 1.3b). In general, the carbon numbers of the hydrocarbons that make up gasoline are mostly C4 to C11, with small amounts of C3 and C12 [9].

Table 1.3a  EN 228, European volatility class gasoline specifications (the first, fourth and sixth of the six classes have been selected).

Volatility/Distillation

Unit

Class A

Class B

Class C

Class D

Class E

Vapour pressure

KPa at 38°C

45–60

45–70

50–80

60–90

65–95

Ambient temperature

°C

>15

5 to 15

−5 to + 5

−15 to −5

<−15

% Evaporated at 70 °C

Vol %

20–48

20–48

22–50

22–50

22–50

% Evaporated at 100 °C

Vol %

46–71

46–71

46–71

46–71

46–71

% Evaporated at 150 °C

Vol % maximum

75

75

75

75

75

Final boiling point

°C, maximum

210

210

210

210

210

MON/RON

85/95

85/95

85/95

85/95

85/95

Table 1.3b  ASTM D4814, American volatility class gasoline specifications (the first, fourth and sixth of the six classes have been selected).

Volatility/Distillation

Unit

Class AA

Class C

Class E

Vapour pressure

Max. Kpa at 38°C

54

79

103

Temperature for 10% evaporated

°C, maximum

70

60

50

Temperature for 50% evaporated

°C, maximum

77–121

77–116

77–110

Temperature for 90% evaporated

°C, maximum

190

185

185

End point

°C, maximum

225

225

225

Anti-Knock Index, (MON + RON)/2

Regular 87

Mid-range 89

Premium 91–94

Different classes of volatility are set to allow for climatic variations owing to region and season. Vapour pressure is a balance between the need to avoid vapour lock (vapour bubbles in the fuel lines, inhibiting the pumping of the fuel in hot weather) and to provide easy starting in the cold (which needs the lower boiling material). Since the vapour pressure is measured at a fixed temperature, this figure rises along the series of fuel classes to reflect the lower temperatures at which these classes of fuels are used; class E fuels would be used when the ambient temperature is low (winter) and class A when it is high (summer) (Table 1.3). The variation in the distillation temperatures of the lowest boiling 10% (USA data) shows that the higher vapour pressure is a result of including more lower boiling material in the gasoline. The same higher boiling blend components are used in all grades so the amounts of distillate at higher test temperatures vary little across the class series.

To meet both the requirements of octane and volatility, a refiner blends together a range of components that depend upon their availability in his refinery. The range of components that may be used have varied octane numbers and volatilities (Table 1.4). Gasoline fractions are known either as light and heavy gasoline or as light and heavy naphtha. These are mostly volatile enough to be fed into the engine as a vapour mixed with air after passage through the carburettor. Modern gasoline engines now use fuel injection which provides much better, electronic control of the fuel/air mixture; however, when the gasoline enters the combustion chamber, it has been almost completely vaporised in the inlet port. The light and heavy gasolines make up the bulk of the final blend but, when straight run, these have relatively low RONs [6] (Table 1.4). However, in a complex refinery there are other gasoline blend components that have the similar boiling ranges but higher RONs; such components come from distillations of FCC and hydrocracker products, and from the reformer and alkylation (sections 1.2.3 and 1.2.4).

Table 1.4  The refinery components (Streams) that may be blended into the gasoline.

Component

Vapour Pressure, Kpa at 38°C

RON

Butanes, iso/normal

483/354

93/93

Pentanes, iso/normal

132/100

93/72

Light straight run (LSR) gasoline

76

66

Heavy straight run (HSR) gasoline

7

62

Light hydrocracker gasoline

88

83

Heavy hydrocracker gasoline

7

68

Coker gasoline

24

67

FCC light gasoline

95

92

FCC heavy gasoline

10

83

Reformate 94 RON

19

94

Reformate 98 RON

15

98

Alkylate C3’

39

91

Alkylate C4’

31

97

Alkylate C5’

7

90

Volatile alkanes ‒ butanes and isopentane ‒ help raise the RON of the blend towards the specification minimum of 95 but their use is limited by their volatility. Using the calculation for vapour pressure contributions to a gasoline blend [6], just 1.0 volume % of iso-butane increases the vapour pressure by 23 kPa, so it must be used sparingly.

Clearly, with this range of components, given the limitations of availability in a refinery, achieving a 95 RON may be quite difficult. There are, however, several alternative blend components with significantly higher RONs that can provide a boost to the RON of the blend. For example, methyl-tert-butyl ether (MTBE) was a much-favoured blend component having a RON of 115; a textbook example [6] shows that 7% of MTBE raises the RON from 88 to 95. Other components that can be used are short chain alkylated benzenes, such as toluene and xylene (RONs of 120 and 118), isopropanol and ethanol (RONs 118 and 109) – ethanol is a favoured component as it is readily made in large quantities from natural, renewable resources and, for example, blending 30% ethanol with gasoline (RON of 91) gives E30 which has a RON of 101 [27].