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CHAPTER ONE

General Introduction

1.0 Introduction

Energy is indispensable to the society. Virtually all human socio-economic activities involve

expending one form of energy or another. Energy has been found to assume the status of the next

basic need of mankind after food, clothing and shelter. It is a major dominating factor in the

development of human civilization. Energy consumption per head is one of the indices used for

measuring the standard of living. In order to increase standard of living of its citizens, a country has

to develop its own energy sources. As a result of increasing global population and increase in

average standard of living, the world energy consumption is on the rise [1-2].

At present, the world energy needs are largely being met by fossil fuels (natural gas, petroleum and

coal as natural sources of gaseous, liquid and solid fuels respectively). In particular, liquid fuels due

to their higher energy density, occupies a centre place in the present energy system. However, there

has been increasing awareness of diminishing world crude oil reserves. This accounts in part for the

renaissance of discussions on Fischer-Tropsch (FT) technology in recent times. In addition,

concerns about air pollution and global warming and the resulting climate change have led to more

stringent legislation on emission or flaring of associated natural gas from oil fields. Another reason

for the renewed interest in FT technology is the quest to diversify energy sources. For socio-

political and economic reasons, nations desire to attain some measure of independence in supply of

liquid fuels and FT technology provides viable options for conversion of natural gas, coal and other

carbonaceous resources to liquid hydrocarbons and other useful products [3-4].

1.1 Fischer-Tropsch Technology

Fischer-Tropsch technology can be briefly defined as the means of converting synthesis gas

containing hydrogen and carbon monoxide to hydrocarbon products. The hydrocarbon products are

mostly liquid at ambient conditions but some are gaseous and some may even be solid. For the

above definition the term 'hydrocarbons' includes oxygenated hydrocarbons such as alcohols.

However, the sole production of an oxygenated hydrocarbon such as methanol is excluded.

Depending on the starting carbon material, different conversion projects based on Fischer-Tropsch

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technology have been conceived to produce liquid hydrocarbons as substitute to petroleum (Fig:

1.1). These include: Coal to liquid (CTL), Gas to Liquid (GTL) and Biomass to Liquid (BTL) [5-7].

Hydrocarbons are produced from the carbonaceous feedstocks through synthesis gas (CO,H2

mixture) intermediate [8-9].

Figure 1.1: Schematic diagram of Fischer-Tropsch technology

Renewed interest in Fischer-Tropsch technology is due to recent improvements to the technology

and the realisation that it can be used to monetize stranded natural gas via GTL projects. i.e

remotely located natural gas can be converted to liquid hydrocarbon products that can be sold in

worldwide markets. Another approach to get value from remote natural gas is through the

deployment of conventional liquefaction technology that produces liquefied natural gas (LNG).

Although, LNG has the advantage of having been developed for the past 40 years and having an

excellent safety record. Technological improvement and compelling investment from the world’s

major oil companies suggest that the GTL industry is likely to expand rapidly over the next decade

and will develop into a significant commercial factor in world energy markets over the next few

years [10].

1.2 History of industrial Fischer-Tropsch processes

The history of commercial Fischer-Tropsch processes is closely connected with the price of crude

oil. Crude oil prices had varied considerably over the years (see figure 1.2). FT development has

also been influenced by political decisions to attain sufficiency in fuel supply. After its discovery in

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Germany by Franz Fischer and Hans Tropsch in the 1920s, Germany produced fuels from its coal

reserves by 1938 – 39 using FT technology during World War II. Although expansion of these

plants intended around 1940, but could not be implemented, existing plants were operated till the

end of the War. Japan also operated 3 F–T plants based on coal reserves in 1944.

Figure 1.2: Map of oil consumption per capita (in tonnes) in 2007 (source: BP)

http://www.bp.com/liveassets/bp_internet/globalbp/globalbp_uk_english/reports_and_publications/statistical_energy_re

view_2008/STAGING/local_assets/charts/oil_graph_crude_oil_prices_560.gif [accessed 25 October, 2010]

A FT plant was built in Brownsville (Texas, USA) in 1950; the plant was shut down due to the

sharp increase in the price of methane. The 1950s was marked with discovery of more oil fields in

the Middle East countries with attendant boom in petroleum production with a reduction in crude

price. This led to a general discontinued industrial interest in FT technology due to bad economic

for FT processes. An exception was South-Africa, which started making fuels and chemicals from

coal based on the F–T process since a half century ago due to embargoes initiated by the country’s

apartheid policies. Till today, South Africa’s Sasol (South African Coal, Oil and Gas Corporation,

Ltd.), which built its first commercial F–T plant in 1955, is known as a major player in this field. A

brief history of FT technology from 1902-1993 as compiled by Samuel [8] is presented in Table 1.1.

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1902 Methanation reaction with Syngas over Ni catalyst (Sabatier & Senderens).

1923 Franz Fischer & Hans Tropsch reported hydrocarbon synthesis at higher pressure

using Co, Fe Ru catalysts.

1936 4 FT Plants commissioned in Germany (total cap. 0.2 MMTA)

1944 Capacity of 9 plants (5 plants added) was increased to 0.7 MMTA. Although Fe

catalyst development continued, Co was not replaced until after World War II.

1950 Hydrocol plant operated for some time based on Fixed Fluidized Bed rector with

Fe-K catalyst, Cap. 5000 bpd at Brownsville, Texas.

1950-53 In Germany, Koelbel set up 1.5 m dia. slurry phase reactor at Rheinpreussen and

operated successfully

1950s: US Bureau of Mines operated a plant in Louisiana, Missouri with Fe catalyst (FB

Reactor).

Mid 1950s German plants were shut down after brief operation using petroleum residue.

Interest in FTS declined worldwide, when oil deposits were discovered in

abundance in the Middle East.

1955 However, in South Africa the first plant Sasol I was commissioned, based on Fe

catalyst in ARGE tubular fixed bed (TFB) and circulating fluidized bed-Synthol

(CFB) reactors. This was followed by Sasol II (1980) and Sasol III (1982) based on

Synthol-CFB. Later CFB has been replaced with Fixed Fluidized Bed (SAS

Reactor).

1970-80 Renewed interest in FTS due to increased oil prices and fear of oil shortage

1990s Further revival of FTS or GTL due to discoveries of huge stranded natural gas

reserves and requirement for clean fuels.

1992 First natural gas based plant (Mossgas) set up in S. Africa, based on Sasol’s Synthol

reactor.

1993 Shell Middle Distillate Synthesis (SMDS) plant (12,500 bpd) was set up in

Malaysia (natural gas based) using TFB reactor and Co catalyst

Table 1.1: Brief History of Commercial Fischer Tropsch Synthesis [8]

Current estimate of the liquid product cost of CTL without carbon capture and sequestration is

about $78/barrel [4]. Since the oil crisis of 1970s, the price of crude oil was well above this bench

mark. Although there was a dip in the oil price in 2008 due to global financial crisis (economic

recession), oil price is peaking again as nations are recovering and energy demand is on the

increase. Currently, the transportation sector is witnessing the fastest growth rate. The sector

depends on stored energy in the form of liquid fuels which are derived predominantly from

petroleum. Moreover, estimates of worldwide reserves and resources of fossil fuels indicated that

coal outpaces crude oil and natural gas both in regard to reserves and resources. Reserves of crude

oil and natural gas are in the same range, but the resources of gas are much larger than those of oil

(mainly due to unconventional resources of gas, which include tight gas, coal-bed methane, aquifer

gas and gas hydrates).

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Figure 1.3: Worldwide reserves and resources of fossil fuels at the end of 2007

Reserves or proved reserves are those portions of the total resources which are documented in detail

and can be recovered economically using current technologies. Resources are either proved but at

present not economically recoverable or only geologically indicated [6]

The above highlights account for the renaissance of FT technology and constructions of more GTL

plants in strategic gas reserves around the world (see Table 1.2). Sasol, the pioneer of commercial

FT processes is expanding its operations both in CTL and GTL around the globe (Fig 1.4). In

addition, the limited petroleum resources in the face of increasing demand for liquid hydrocarbon

have foster industrial and political decision for conversion of coal to liquid fuels.

Nations with abundant coal reserve are strongly pursuing the development and deployment of CTL

technologies which can reduce their dependence on crude oil imports [11-13]. Around eighteen

projects are located in the USA, a few of them are at the design stage. Several CTL projects are at

different stages of completion in China (with one plant already commissioned), two commercial

CTL projects are also in pipeline in India. Other projects exist in a number of other countries

including South Africa, Australia, the Philippines and Indonesia.

1.3 Fischer-Tropsch Process

1.3.1 Operation modes

Presently there are two modes of operations in commercial FTS processes [14]:

1. High-temperature FT (HTFT) mode: Here the reactor temperature is between 300 and 350

°C, gasoline and linear low molecular-mass olefins are selectively produced with Fe-based

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catalysts. Significant amounts of oxygenates are also produced. Diesel may be produced by

oligomerisation of the olefins.

2. Low-temperature mode (LTFT): The reactor temperature is usually between 200 and 240 °C

with either Fe or Co-based catalysts. This mode gives products with a high selectivity for

paraffins and high molecular-mass linear waxes. Besides the primary diesel cut,

hydrocracking of the waxes yields excellent diesel fuels. The primary gasoline cut here

needs further treatment to obtain a high octane rating fuel.

Country

Company or

Companies

Technology

Production

level (bpd) Start-up year

Qatar Sasol and Qatar

Petroleum, in alliance

with Chevron

Sasol’s slurry phase

Technology

34 000 2005 (2 other F–T

plants are

scheduled to

operate in the

coming years with

the second F–T

plant having a scale

of 65 000 bpd)

Nigeria Chevron Nigeria

(Sasol/Chevron

alliance) and Nigeria

National Petroleum

Company

Sasol’s slurry phase

Technology

34 000 2007

Qatar Shell and Qatar

Petroleum

Shell middle distillate

synthesis (SMDS)

fixed-bed technology

140 000 2009 (first train of

70 000 bpd)/2010

(second train of

70 000 bpd)

Qatar ExxonMobil and

Qatar Petroleum

Advanced gas

conversion for the

21th centure (AGC-

21) technology

154 000 2011

Table 1.2: Recent GTL plants locations and their production capacities

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Figure 1.4: Sasol's current global Fischer–Tropsch activities

Source: Brian Tait, Sasol’s Activities on Synthetic Fuels, 2nd International BtL Congress, 2006

1.3.2 Fischer-Tropsch Reactors

The main design consideration for Fischer-Tropsch reactor is the removal of the large exothermic

heat of reaction. The choice of reactor type for a commercial operation is largely dictated by the

desired product selectivity, which a function of market demand and potential product price

structure. Other factors include catalyst type, syngas feed composition and recycle ratio. In a typical

commercial plant about 55,000 to 60,000 kJ/kgmol of synthesis gas may be liberated which need to

be efficiently removed. There are four types of Fischer-Tropsch (FT) reactor in commercial use at

present. Three broad categories of catalyst are used in these reactors. The four types of reactor are:

• Circulating fluidized bed reactor (CFB)

• Fixed fluidized bed reactor (FFB)

• Multi-tubular fixed bed reactor (MTFB)

• Slurry phase reactor

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In HTFT operations, catalysts with alpha value (chain propagation probability factor) are usually

employed while LTFT directed at waxy distillate production the alpha of the catalyst is about 0.9.

The operation of HTFT reactors is such that no liquid phase is present outside the catalyst particles.

Formation of a liquid phase in the HTFT fluidized bed reactors leads to serious problems due to

particle agglomeration and loss of fluidization. However, heavy hydrocarbons in the form of liquid

wax are present in these reactors [16-19].

Figure 1.5: Schematic diagram of commercial Fischer-Tropsch reactors

The Fixed Fluidized bed reactor also known as Sasol Advanced Synthol (SAS) reactor was

developed to eliminate the disadvantages of the CFB operations. The disadvantages include [20-

22]:

Complex reactor configuration which needs complex operation system for circulating the

catalyst loads and operating temperature especially at the start up. This makes it expensive.

Large amount of catalyst circulation causes large pressure drop across the reactor system.

At any time only small portion of the catalyst in the system is used for the conversion

purposes.

The reactor systems are prone to erosion due to high gas velocities in the reactor which

operate in the transport bed mode.

The advantages and disadvantages of the Multi-tubular fixed bed reactor and Slurry phase reactor

are presented in Table 1.3, which reveals that neither of the two reactors is exclusive in their

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benefits. The choice of reactor type is a prerogative of a company and strategic goals. For instance,

for natural-gas-based Fischer-Tropsch distillate designs, Shell has selected the tubular fixed-bed for

their plant in Bintulu, Malaysia which commenced operation in 1991, whereas Statoil & partners

operates a semi-commercial plant using slurry reactor design at Mossel Bay, South Africa in 2006.

Multi-tubular fixed bed reactor Slurry phase reactor

Advantage Advantage

Simple to operate and can be used for

wide range of temperature in plug flow

concentration profile

Easy catalyst loading and unloading

without or with a short downtime

Easy in-situ activation and

regeneration of the catalyst

Efficient heat and mass transfer, low

tendency of hot spot formation in the

catalyst.

Product exit reactor leaving catalyst

behind

Reasonable pressure drop, good

distribution of reactants inside bed

resulting in better control of hydrocarbon

distribution at relatively high conversion

Only catalyst at the reactor inlet may

be easily deactivated by the presence

of poison (e.g H2S) in the syngas feed

Disadvantage Disadvantage

Poor heat and mass transfer, resulting

in high tendency of hot spot formation

in the catalyst bed

Difficulty in separation of the wax

product from catalyst.

Catalyst loading and unloading is

demanding and may be take long

duration of downtime.

Insitu catalyst activation or regeneration

is difficult

Relatively high capital cost for

fabrication of the reactor

Whole catalyst in the reactor inlet may be

easily deactivated by the presence of

poison (e.g H2S) in the syngas feed

High tendency of catalyst deactivation

due to carbon deposition

Foam formation inside bed

High pressure drop Catalyst attrition, settling or

agglomeration.

Table 1.3: Comparison of LTFT reactors

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In addition to the need to ensure very low ppm of H2S in the syngas feed for slurry reactor

operations, catalyst separation from the wax/heavy product constitute a significant portion of the

running cost. Magnetic separation of iron catalyst from wax has been reported to have potential of

reducing the reactor running cost [23]. The main concern in multi-tubular fixed bed reactor is the

need for small diameter tubes for high rate of heat transfer. Having multi-tubular fixed bed reactor

with small diameter tubes is associated with pressure drop challenges and high capital cost of

fabrication of the reactor. Recent reports have shown that the disadvantages of multi-tubular fixed

bed reactor system are partly or completely eliminated in micro-channel reactor technology.

Micro-channel reactor is a relatively new reactor technology, it is claimed to be ideally suitable for

highly exothermic reactions like FTS and highly endothermic reactions like steam reforming.

Successful pilot-scale FTS operation has been demonstrated using micro-channel reactor. The

reactor assemblies are generally smaller compared with conventional reactor technologies. From the

pilot-scale operation, it is stated that micro-channel reactor provides technical and economic

benefits when compared with multi-tubular fixed bed reactor [24-25]:

High efficient heat and mass transfer rate, this minimize tendency of hot spot formation and

allows maximizing catalyst activity and stability.

Micro-channel reactors can be fabricated in small modular forms. This allows speedy

construction and installation. The small reactor size also promotes the realization of

economic of scale at much smaller production capacity (500 bpd) than conventional reactor

technology.

Modular form of micro-channel reactor can also enhance easy loading and unloading of

catalyst.

In addition to small and modular form of micro-channel reactor, it has low profile (height).

This makes it suitable for mobile and off-shore installations.

Other reactor systems under evaluation for application in Fischer-Tropsch synthesis include

monolith reactor [26], use of near-critical & supercritical solvent as reaction media [27-28] and

reactive distillation reaction systems [29-31].

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Figure 1.6: Description of Micro-channel reactor [24]

1.3.3 Syngas feed

The composition of the components of raw syngas from the various feedstocks is shown in Table

1.2. Table 1.4 above reveals that syngas compositions from natural gas feedstock have high H2/CO

ratios and low % CO2 compared to those of coal, biomass and black oil feedstocks. Biomass gives

syngas feeds with low H2/CO ratio (range of 0.455–1.03). The Lurgi gasifier gives higher ratios but

along with high CO2 content. Thus, syngas feeds from coal and biomass sources are either H2-

deficient or CO2-rich and fall short of the stoichiometric ratio required for the most desired

reactions, 1 and 2 in Table 1.4. Part of the energy in these fuel feedstocks is used to provide the heat

needed in the endothermic steam-reforming reactions. It has been estimated that about 20% of C

(carbon) in natural gas is completely burned and converted to CO2 for this purpose, while the

estimate for coal is about 50% due to the much lower hydrogen content. The hydrogen content can

be enhanced when the feed gas is reconditioned by mixing with feed gas from steam reforming of

methane; but when used directly it implies much of the excess carbon in the feed gas must release

as CO2 via WGS.

1.3.4 Fischer-Tropsch Process Variable

Commercial FT process conditions are influence by the choice of reactor type. The process

conditions as well as the catalyst influence conversion and product selectivity. The effect of

temperature, pressures, syngas composition and space velocity will be discussed briefly. Table 1.5

shows the influence of the process variables on the selectivity. Increase in temperature increases the

Microchannel Reactor

Exothermic

Reaction

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rates of all reactions, the situation moves towards that predicted by thermodynamics. As the

temperature is increased, the system becomes more hydrogenating, the ratio of alkenes to alkanes

decreases. Irrespective of the type of metal catalyst increasing the FT operating temperature shifts

product selectivity to lower carbon number products. Desorption of growing surface species is one

of the main chain termination steps and since desorption is an endothermic process, higher

temperatures should increase the rate of desorption which would then result in a shift to lower

molecular mass products. Selectivity of the alcohols and of the acids decrease as the temperature is

raised. The degree of chain branching increases as the temperature is raised, as one would expect

from thermodynamics [32].

Feedstock Process Component (Vol.%)

H2 CO CO2 Others

Natural gas, steam SR 73.8 15.5 6.6 4.1

Natural gas, steam, CO2 CO2–SR 52.3 26.1 8.5 13.1

Natural gas, steam, CO2, O2 ATR 60.2 30.2 7.5 2.0

Coal/Heavy oil, steam Gasification 67.8 28.7 2.9 0.6

Coal, steam, O2 Texaco gasifier 35.1 51.8 10.6 2.5

Coal, steam, O2 Shell gasifier 30.1 66.1 2.5 1.3

Coal, steam, O2 Lurgi gasifier 39.1 18.9 29.7 12.3

Woody biomass Gasification 29.9 30.3 28.3 11.5

Black oil Gasification 39.2 38.1 19.1 3.6 SR = Steam Reforming, ATR = Autothermal Reforming

Table 1.4: Syngas composition from various feedstocks [14,15]

Studies have shown that product selectivity shifts to heavier products and to more oxygenates with

increasing total pressure. Increasing H2/CO ratio increases the partial pressure of H2 relative to that

of CO. Higher H2 partial pressure increases the rate of hydrogenation and chain termination step

which results in increase selectivity to methane, lighter hydrocarbons and a lower olefin content. In

contrast, lower H2/CO ratios translate into higher CO partial pressure relative to that of H2.

Process variable Conversion

(C – mol %)

Selectivity (C – mol %) O/(O+P)

in C2 – C4 HC CH4 CO2 C2 – C4 C5+ alcohols

Temperature ↑ ↓ ↑ ↑ ↑ ↓ ↓ ↓

Pressure ↑ ↑ ↓ ↓ ↓ ↑ ↑ ↓

H2/CO ↑ ↓ ↑ * ↓ ↓ * *

Space velocity ↓ ↑ ↓ ↓ ↓ ↓ ↑ ↑ ↑ and ↓ represent the increase and the decrease respectively, while * means complex behaviour

Table 1.5: Effect of operating conditions on conversion and product selectivity

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Higher CO partial pressure will increase CO coverage of the catalyst surface and monomer

formation which in turn will increase the probability of chain propagation step. Thus, higher CO

partial pressure increases selectivity to longer chain hydrocarbon and lower methane formation.

Space velocity of the synthesis gas (residence time) also influences the selectivity of FTS product.

Lower space velocity or longer residence time of the syngas gas in the reactor will increase the

extent of hydrogenation of the monomer. This promotes re-adsorption of olefins and increase chain

termination step thereby leading to increase saturation and lighter hydrocarbon products [33-34].

For iron-based catalysts, it has been indicated that CO2 appears to play an important role in the

product distribution. Increasing CO2 pressure is reported to result in a decrease of the methane

selectivity. It had also been pointed out that other factors such as difference between H2/CO feed

ratio and usage ratio of the catalyst, extent of water gas shift (WGS) reaction and the exit gas

recycle ratio may influence FTS product selectivity. These factors influence partial pressure of H2

and CO on the catalyst surface, thus, it implies that interplay of the process variables and the listed

factors determines FTS product selectivity in commercial FTS operations [32, 35-37].

1.4 Process Economy in Fischer-Tropsch Technology

A typical commercial Fischer–Tropsch process involves three main sections: synthesis gas (syngas)

production and purification; Fischer–Tropsch synthesis (FTS) and product up-grade. The syngas

production usually accounts for 60–70% of the total on-site capital cost of the process. The FTS

section consists of the reactors, recycles, compression of unconverted syngas, CO2 removal,

recovery of hydrogen and hydrocarbon, reforming of the methane produced and separation of the

products. The most important aspects of the development of commercial FTS reactors are the

management of the high reaction heat and large number of products with varying vapour pressures.

The FTS section normally accounts for about 22% of the total cost of the process. The product up-

grade usually starts with the removal of the light hydrocarbons and dissolved gases to make the

hydrocarbon suitable for atmospheric pressure storage. Olefins may be removed from the straight

run liquid products for use as chemical feedstocks. This is often achieved by means of fractionation

and extractive distillation. The conventional petroleum refinery processes can be used for the up-

grading of liquid products and waxes. The product up-grade/refining section of the Fischer–Tropsch

process accounts for about 12% of the total cost [38-39].

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From the above process cost information, it is evident that the process economy depends largely on

the syngas production and FTS sections. The syngas production depends on the choice of the carbon

feedstock and the gasification technology employed; these in turn determine the composition of the

syngas feed for the FTS section. In addition to the syngas composition, the other key variables in

FTS sections are the operating mode, type of catalyst used and the reactor design. These process

variables determine the syngas conversion efficiency as well as the product distribution of the feed

for the product up-grade section.

A low cost technology for monetisation of remote natural has been suggested. It involves partial

oxidation of the natural gas with air instead of pure oxygen to produce nitrogen-rich syngas which

can be used directly for hydrocarbon synthesis in the FT reactor. This process eliminates the need

for an air separation plant, and a process with nitrogen-rich syngas does not utilize a recycle loop

and a recycle compressor. In an FTS evaluation study with the nitrogen-rich syngas feed on iron

catalyst in MFB reactor, it is reported that nitrogen-rich syngas could have some technical and

economic benefits over nitrogen free syngas feed. These include: the nitrogen act as diluents which

enhances heat removal which affords using optimised tubes diameter of 1.6 times than nitrogen-free

syngas; the nitrogen-rich syngas gives about three times higher diesel oil and wax production rate

per tube than nitrogen-free syngas. Although this process is an alternative syngas production

technology with a lower investment cost, there is yet a commercial process that is based on it [40-

41].

1.5 Motivation and objectives of the thesis

Although the share of FTS section in the cost of fuels through Fischer-Tropsch technology is less

than that of the syngas gas production and purification section, it plays a central role in the process

economy of FT technology. Particularly, design of efficient catalyst is strategic for enhancing the

process economy. Despite an overwhelming number of reports on FT catalysts design in the ninety

years history of FT technology, there still seems room for further contributions in order to obtain

low cost and high efficiency catalysts for FTS operations.

1.5.1 Cobalt based catalyst

Generally, cobalt based catalysts is preferred for LTFT operation mode. Cobalt metal is about 25

times more expensive the iron. Hence, the design objective in cobalt based FTS catalyst is

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maximizing the product formation per unit amount of the metal. This is often pursued by dispersing

the cobalt metal precursor on high surface area supports. To this end, alumina is usually of choice

because it affords high dispersion of cobalt salt. However, this is at the expense of lower

reducibility of the resulting cobalt oxides due to strong metal support interaction (SMSI) between

the cobalt and the alumina support. Efforts at achieving higher reducibility of cobalt oxides on

alumina had focused majorly on use of reduction promoters (Pt, Ru, Re, Ir, etc).

The use low cost chemicals and non-complicated procedure for preparation of a catalyst are

incentives for easy scale-up and attractive process economy. This may account for why commercial

FT catalyst preparations are restricted to incipient wetness impregnation and precipitation

techniques. Several studies on development of FT catalysts involved the use of expensive

reagents/materials and complex procedures. Although the techniques resulted in improved catalysts,

they are less suitable for easy scale-up or commercial adoption. Therefore towards low cost cobalt

based FT catalyst this study seeks to investigate synergistic effects Ca and Cu as transition metal

promotion on alumina supported cobalt catalyst.

1.5.2 Iron based catalyst

Iron-based FT catalysts are reported to be less active in hydrocarbon formation than cobalt-based

counterparts. Since iron-based FT catalysts are less expensive, the design of iron-based FT catalysts

with comparable performance is desirable for enhanced process economy. Moreover, iron-based

catalysts are flexible in terms of H2/CO ratio of syngas feed. In addition, analysis of ease of refining

of different syncrudes to on-specification diesel fuels indicated that iron-based LTFT syncrude

possess less refining challenges compared with cobalt-based LTFT. Synergistic effect of Ca and Cu

as transition metal promotion on the performance of new iron catalysts (Fe-Zn-Cu-Ca) is also

studied for LTFT at H2/CO < 1.