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TABLE OF CONTENTS

1 Overview and History of Synfuels .................................................................................................. 1

2 Synthetic Gas Production ................................................................................................................ 3

3 Fischer-Tropsch Reaction ............................................................................................................... 4

4 Sasol Reactor Technology .............................................................................................................. 6

4.1 Step 1: Natural Gas Reforming ............................................................................................... 6

4.2 Step 2: Sasols Proprietary Conversion Process ..................................................................... 6

4.3 Step 3: Product Separation and Upgrade ................................................................................ 6

5 GTL and CTL Technology ............................................................................................................. 7

5.1 GTL Technology ..................................................................................................................... 7

5.2 CTL Technology ..................................................................................................................... 8

6 OCM Technology ......................................................................................................................... 10

7 References ..................................................................................................................................... 12

LIST OF TABLES

Table 1 - Reactions depecting the reactions for different functional groups of the Fischer-Tropsch

process .................................................................................................................................................... 4

LIST OF FIGURES

Figure 1 - Syngas production scheme ..................................................................................................... 3

Figure 2 - Illustration of Fischer-Tropsch process .................................................................................. 5

Figure 3 - GTL process used at Sasol ..................................................................................................... 6

Figure 4 - Illustaration of gas-to-liquid process ...................................................................................... 7

Figure 5 - Direct coal conversion of coal-to-liquids process .................................................................. 8

Figure 6 - Indirect coal conversion of coal-to-liquid process ................................................................. 9

Figure 7 - Illustration for the proposed Siluria OCM process .............................................................. 11

Figure 8 - Illustration for the OCmol OCM process ............................................................................. 11

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1 OVERVIEW AND HISTORY OF SYNFUELS

Fossil fuelscoal, petroleum (oil), and natural gas are concentrated organic compounds found in

the Earths crust. They are created from the remains of plants and animals that lived millions of years

ago in the form of concentrated biomass. Prior to petroleum fractions, coal was the leading source of

fuel. With the advent of the gasoline and diesel oil engines, as well as the industrial revolution, the

demand for fuel had increased as well as the need for a fuel to offer a high source of energy. However,

many countries which do not have crude oil reservoirs had to develop alternate methods to produce fuel.

This need for an alternate fuel led to the development of synthetic fuels (Fossil Fuels, 2015).

Germany, having no petroleum reservoirs, had no problems prior to the twentieth century as Germany

possessed abundant coal reserves. Coal provided for commercial and home heating; it also fulfilled the

needs of industry and the military, particularly the navy. In the opening decade of the twentieth century,

Germanys fuel requirements began to change. Two reasons were especially important. First, Germany

became increasingly dependent on gasoline and diesel oil engines. The appearance of automobiles,

trucks, and then airplanes demanded a plentiful supply of gasoline. Moreover, oceangoing ships

increasingly used diesel oil rather than coal as their energy source. Second, Germanys continuing

industrialization and urbanization led to the replacement of coal with smokeless liquid fuels that not

only had a higher energy content but were cleaner burning and easier to handle (Lesch, 2000).

Petroleum was clearly the fuel of the future, and to insure that Germany would never lack a plentiful

supply, German scientists and engineers invented and developed two processes that enabled them to

synthesize petroleum from their countrys abundant coal supplies and to establish the worlds first

technologically successful synthetic liquid fuel industry.

Friedrich Bergius began the German drive for energy independence with his invention and early

development of high-pressure coal hydrogenation or liquefaction. Bergius results had been published

as a patent 1913, which lead to the industrialization of the process and was assisted by Karl

Goldschmidt. The process is known as the Bergius process and is the direct method for the production

of liquefied fuel from coal. Production began in 1919. A decade after Bergius began his work Franz

Fischer and Hans Tropsch invented a second process for the synthesis of liquid fuel from coal. This is

known as the Fischer-Tropsch (FT) process and is the indirect method for the production of liquefied

fuel from coal. Several breakthroughs contributed to the success of coal hydrogenation, the most

significant of which were the sulphur resistant catalysts and the two stage liquid-vapor phase

hydrogenation that Matthias Pier developed in 1920. For the FT synthesis, the cobalt catalysts that

Fischer and his co-workers prepared in the 1920-30 were crucial to its success (Stranges, 2001).

Another direct method is the Kohleoel process, which was also developed in Germany. In this process

coal is mixed with a recycle solvent and iron catalyst, which is then preheated and pressurized followed

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by adding hydrogen. The process takes place within a tubular reactor at a temperature and pressure of

470 C and 300 bar, respectively. This process was also explored by SASOL in South Africa.

Solvent refined coal processes were implemented as pilot plants in the United States. Hydrogenation

processes, patented in 1976, involved mixing dried, pulverised coal with roughly 1% molybdenum

catalyst at high temperatures and pressures to produce Naphtha, a synthetic crude product. The 1980s

saw Japanese companies develop the NEDOL process (Lesch, 2000).

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2 SYNTHETIC GAS PRODUCTION

Synthesis gas or briefly, syngas, is a mixture of carbon monoxide (CO), carbon dioxide (CO2) and

hydrogen (H2). Syngas can be produced from many sources, including natural gas, coal, biomass, or

virtually any hydrocarbon feedstock, by reaction with oxygen or steam. Syngas is a crucial intermediate

resource for production of hydrogen, ammonia, methanol, and synthetic hydrocarbon fuels

(Syngaschem, 2012).

Depending on the feedstock either gasification or steam reforming is undertaken. For coal and biomass

feedstock gasification is typically used. Gasification is achieved by reacting the feedstock at high

temperatures, typically above 700 C, without combustion, with a controlled amount of oxygen and/or

steam. In a gasification reactor the feedstock is transformed into a syngas, a mixture of H2, CO and CO2,

which opens up to making a variety of downstream energy carriers. The carbon in the coal combines

with oxygen in the water to create carbon monoxide, while the leftover hydrogen atoms create hydrogen

gas. The syngas could be used as a fuel at this stage or further processing can develop diesel and

kerosene (Blesl & Bruchof, 2010).

For a natural gas feedstock, typically steam reforming in used. The formation of syngas is strongly

endothermic and requires high temperatures. Steam reforming of natural gas proceeds in tubular

reactors that are heated externally. The natural gas, mainly methane (CH4) and steam react at high

temperatures (700 1100 C), in the presence of the nickel catalyst forming CO and H2. The process

uses a nickel catalyst on a special support that is resistant against the harsh process conditions.

Additional hydrogen can be recovered by a lower-temperature gas-shift reaction with the carbon

monoxide produced. The following two reactions summarize the process:

CH4+H2O CO+3H2 (1)

CO+H2O CO2+H2O (2)

Reaction (1) is highly endothermic and reaction (2) is moderately exothermic. Figure (1) summarizes a

typical syngas production scheme.

Figure 1 - Syngas production scheme

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3 FISCHER-TROPSCH REACTION

The Fischer-Tropsch Synthesis converts syngas into hydrocarbons which form the basis for gasoline,

diesel, jet fuel, and chemicals such as olefins and waxes. It forms the heart of the Gas-to-Liquids (GTL)

and Coal-to-Liquids (CTL) plants in South Africa, Qatar, Malaysia and China. The product distribution

is broader than liquids hydrocarbons alone, and includes methane and alkanes, CnH2n+2 (with n from 1

100), alkenes or olefins (CnH2n; n 2), and to a lesser extent oxygenated products such as alcohols.

Catalysts for the Fischer-Tropsch Synthesis are either based on cobalt or the much cheaper iron. In fact,

the iron-based catalyst is an iron carbide under reaction conditions, whereas cobalt works in the metallic

state (Syngaschem, 2012).

The synthetic gas produced from gasification is passed through reactors maintained at high temperatures

and pressures over a catalyst which speeds up the reaction of the gases together to form products useful

in daily life. Iron is the preferred catalyst to use in the Fischer-Tropsch process as it is not susceptible

to catalyst poisoning. Amongst the many products from the reaction chamber, the most useful are the

long chained alkanes consisting of hydrogen and carbon atoms. The lightest fuel is methane, having the

smallest chain, while longer heavier chains are responsible for products such as gasoline and kerosene.

Paraffins and waxes are derived from the much larger alkane chains. The medium chains are most

favoured and therefore, the reaction conditions are controlled to produce these intermediate chains.

Finally, the products are separated, cleaned and may be processed further to increase yields of desirable

products (Fischer-Tropsch Process, 2014).

The feedstock to FT are either coal, natural gas or biomass. The overall reaction equations are

depicted below:

Table 1 - Reactions depecting the reactions for different functional groups of the Fischer-Tropsch process

FISCHER-TROPSCH FUNCTIONAL GROUP REACTIONS

Alkanes nCO+(2n+1)H2CnH2n+2+nH2O (3)

Alkenes nCO+(2n)H2CnH2n+nH2O (4)

Alcohol nCO+(2n)H2CnH2n+1+(n-1)H2O (5)

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The reactions are exothermic and dealing with the heat is an important issue in the reactor design.

Reaction conditions include temperatures of 200 350 C and pressures of 20 - 50 bar. The FT process

conditions are chosen such that the formation of hydrocarbon liquid fuels having higher molecular

weight is maximized. The process also involves some other side reactions of which the water-gas-shift

reaction is dominant.

CO+H2O H2+CO2 (6)

The most commonly used reactors for Fischer-Tropsch Synthesis is the fixed bed reactor, the fluidised

bed reactor and the slurry reactor. These vessels are favoured due to their excellent heat transfer

characteristics, resulting in stable reactor conditions. No diffusion limitations and possibility of

continuous refreshment of catalyst particles (Boerrigter & Van der Drift, 2004). The slurry reactor is

used to carry out the reaction at the lower temperatures between 220 - 250 C. The reactor uses lower

temperature for the production of heavier components (greater than C20), forming the basis of wax and

paraffins production for FT synthesis. The fluidized bed reactor is used for high temperature FT

synthesis between 320 350 C. This type forms the basis of petroleum chemicals due to the production

for lighter components of between C1 C20.

Figure 2 - Illustration of Fischer-Tropsch process

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4 SASOL REACTOR TECHNOLOGY SASOL, South Africa uses a Gas to liquid (GTL) technology for the production of synthetic fuels. GTL

technology converts natural gas into high quality liquid petroleum product which includes naphtha and

diesel. Raw natural gas is purified in a hydrogenation reactor and a washing system. The purified feed

gas is then pre-treated by saturation with process waster and preheating (SASOL LTD., 2010). Once

pre-treated, the GTL conversion process consists of three main steps:

4.1 STEP 1: NATURAL GAS REFORMING Synthetic gas for the GTL process can be produced through various technologies that require mostly

steam and air or oxygen. During this process, hydrogen atoms are stripped from hydrocarbon molecules

present in the natural gas and the carbon atoms are used to react with oxygen (which is introduced as

steam, air or a pure gas) to produce carbon monoxide molecules. Synthetic gas, which consists of

hydrogen, carbon monoxide and carbon dioxide, is the resulting product of this step in the production

process (SASOL LTD., 2010).

4.2 STEP 2: SASOLS PROPRIETARY CONVERSION PROCESS The purified synthetic gas produced by step 1 is sent to a slurry phase synthetic reactor, and depending

on the temperature, pressure and type of catalyst used, either light synfuels or waxy synfuels are

produced. Hydrogen and carbon monoxide yield linear hydrocarbons, oxygenated hydrocarbons and

reaction water through a catalytic chemical process under heat and pressure with the aid of a catalyst

(either cobalt or iron based). The liquefied synthesis reactor is then employed and the products from

this reactor are cooled successively in a product recovery plant until most components become liquefied

(SASOL LTD., 2010).

4.3 STEP 3: PRODUCT SEPARATION AND UPGRADE Liquid products are separated in the final upgrading unity which makes use of mild hydrocracking to

convert higher molecular weight waxes and lubes into everyday products such as naphtha, diesel and

liquefied petroleum gas. The resulting diesel is clear and burns more easily compared to conventional

fuels as the diesel has been purified of sulphur and other impurities before the synthesis of the liquid

fuel (SASOL LTD., 2010).

Figure 3 - GTL process used at Sasol

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5 GTL AND CTL TECHNOLOGY

5.1 GTL TECHNOLOGY The gas-to-liquids (GTL) process involves two main operations: the conversion of natural gas into a

mixture of carbon monoxide and hydrogen, which is syngas, via processes such as steam methane

reforming (SMR) or autothermal reforming (ATR), followed by the Fischer-Tropsch (FT) process to

convert the syngas into paraffinic hydrocarbons. The products of the FT process can be blended with

naturally occurring crude oil to provide an economic route to market, or upgraded to produce a wide

range of high quality finished products including ultra-clean diesel, kerosene (jet fuel), naphtha, bases

for synthetic lubricants and waxes. Products of the FT process offer significantly better performance

than their petroleum-based equivalents (Gas-to-liquids, 2015).

Figure 4 - Illustaration of gas-to-liquid process

Natural gas is one of the most abundant energy sources available globally. The conversion of natural

gas is liquid fuels attracts wider markets due to easier handling and transportation. With the expected

rise in demand for diesel fuels, GTL technology provides an additional option to provide cleaner, more

environmentally fuels to meet global demands (Gas-to-Liquids, 2013).

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5.2 CTL TECHNOLOGY

The technology used for the conversion of Coal to Liquids (CTL) is referred to as coal liquefaction as

it allows for the transformation of coal into an alternative oil or fuel source. Clean petroleum and diesel,

synthetic waxes, lubricants, chemical feedstocks and alternative liquid fuels such as methanol are the

resulting products achieved from the process. CTL is particularly suited for countries that have large

coal reserves and currently depend on oil imports (Coal to Liquids, 2013).Two methods are currently

used for CTL technology:

1. Direct Liquefaction: coal is dissolved in a solvent at a high temperature and pressure. This

process is highly efficient, however, the liquid products require further refining to achieve high

grade fuel characteristics.

2. Indirect Liquefaction: this method calls for the gasification of coal to form a syngas. The syngas

is then condensed over a catalyst in a process like that of the FisherTropsch, to produce high

quality and clean products (Coal to Liquids, 2013).

Figure 5 - Direct coal conversion of coal-to-liquids process

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Figure 6 - Indirect coal conversion of coal-to-liquid process

Advantages of CTL process:

Coal is affordable and there is an abundant supply globally. This would prevent the drilling of

crude reservoirs and eliminate the import of oil.

Fuels derived from coal are sulphur free and low in nitrogen oxides.

Uses of coal liquids include transport, cooking, power generation and industrial application.

CTL process provides ultra clean cooking fuels hence the coal liquid fuels reduce the health

risks of indoor air pollution. (Coal to Liquids, 2013).

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6 OCM TECHNOLOGY

The oxidative coupling of methane (OCM) is a type of chemical reaction discovered in the 1980s for

the direct conversion of natural gas, primarily consisting of metharne, into value-added chemicals.

Methane, being the predominant component of natural gas, provides the perfect example of attractive

feedstock as a result of its enormous supply, low cost and global availability. Oxidative Coupling of

Methane (OCM) technology refers to the coupling of methane to form valuable products such as ethane,

ethylene and other such C2 hydrocarbons. The principle product of OCM is ethylene, the worlds largest

commodity chemical and the chemical industry's fundamental building block. While converting

methane to ethylene would offer enormous economic benefits, it is a major scientific challenge. The

use of ethylene in industry is limited for use in higher-value commodity processes and chemicals due

to its high cost. Enabling the production of ethylene will result in the deduction of the costs associated

with ethylene derived chemicals and liquid fuels. The steam cracking route to ethylene is the most used

in present times. Ethylene production by steam cracking consumes large amounts of energy, uses

valuable oil fractions, such as naphtha and is the largest contributor to Greenhouse gas emissions in the

chemical industry. The OCM reaction takes place at high temperatures of between 600 and 800 C, but

produces low C2 yields which is the main reason that it has not yet been commercialized despite its

potentially high profitability (Tullo, 2014).

CH4+O2Over Catalyst (Oxides) C2 Products (C2H6 and C2H4) (7)

More specifically, the oxidative coupling of methane to ethylene is:

2CH4+O2C2H4+2H2O (8)

The reaction is exothermic. The ethane subsequently undergoes dehydrogenation to form ethylene.

Hundreds of catalysts have been tested, and several promising candidates were extensively studied.

Researchers were unable to achieve the required chemoselectivity for economic operation. Instead of

producing ethylene, the majority of methane was non-selectively oxidized to carbon dioxide .

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Extensive research and funding has been generated for the development of the OCM process. Figures

(7) and (8) illustrates two processes displaying the advancement in the OCM process.

Figure 7 - Illustration for the proposed Siluria OCM process

Figure 8 - Illustration for the OCmol OCM process

Figure (7) is the process proposed by Siluria. Siluria are the leading researchers in OCM. Figure (8)

shows the OCmol proposed OCM method which includes oligoerization.

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7 REFERENCES

Blesl, M., & Bruchof, D. (2010, May 2). Syngas Production from Coal . Retrieved from Energy

Technology Systems Analysis Program: http://www.iea-etsap.org/web/e-techds/pdf/s01-

coal%20gasification-gs-gct.pdf

Coal to Liquids. (2013). Retrieved 04 30, 2014, from World Coal Association:

http://www.worldcoal.org/coal/uses-of-coal/coal-to-liquids/

Fischer-Tropsch Process. (2014). Retrieved May 05, 2014, from Hub Pages:

http://flyingvet.hubpages.com/hub/Fischer-Tropsch-process

Gas-to-Liquids. (2013, June). Retrieved April 30, 2014, from Chevron: Human Energy:

http://www.chevron.com/deliveringenergy/gastoliquids/

Gas-to-liquids. (2015, February 18). Retrieved from Velocys:

http://www.velocys.com/our_products_applications_gtl.php

Lesch, J. E. (2000). The German Chemical Industry in th eTwentieth century. Dordrecht: Kluwer

Academic publishers.

SASOL LTD. (2010). GTL Technology. Alberta.

Syngaschem. (2012, February 15). Synthesis Gas Chemistry and Synthetic Fuels. Retrieved from

Syngaschem: http://www.syngaschem.com/syngaschem

Tullo, A. H. (2014, July 7). Silurias Oxidative Coupling Nears Reality. Retrieved from C&EN:

http://cen.acs.org/articles/92/i27/Silurias-Oxidative-Coupling-Nears-

Reality.html?h=567597735