Analysis Soot Formation During Asphaltene Gasification Biology Essay


Global demand for energy is expected to increase 47 by 2035 as economies in both developed and emerging countries continue to grow and standards of living improve (1). All sources of energy will be needed to meet growth in global demand. With conventional oil supply declining, the need for unconventional resources, like oil sands, will increase. Canada has the largest oil reserves in the world after Saudi Arabia and 97% of these reserves are in the oil sands. According to Canadian Association of Petroleum Producers (CAPP) report Canada has 174 billion barrels of oil that can be recovered economically with existing technology (2). Of that total oil, 169 billion barrels are located in the oil sands. Oil sands generally contain a mixture of sand, water, clay and bitumen. Bitumen is a component of oil that is too thick to flow or be pumped without being diluted or heated. Some bitumen is found within 200 feet from the surface but the majority is deeper underground.

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Canada's oil sands are found in three important basins - the Athabasca, Peace River and Cold Lake basins in Alberta. The two important methods used for oil sands recovery are surface mining and drilling (in situ). The method applicable depends on at what depth the reserves are deposited. 20% of the oil sands deposits are close enough to the surface, so that it can be mined using shovels and trucks. The balance 80% of oil sands deposits are too deep to be mined and are recovered using in situ technologies, by drilling wells. Drilling (in situ) methods reduce the impact of environmental concerns as they do not require tailings ponds. Advanced technology is used to inject steam or other sources of heat into the reservoir to heat the deposited bitumen so it can be pumped out to the surface through recovery wells. This technology is called Steam Assisted Gravity Drainage (SAGD) and natural gas was used for generating steam. Bitumen production by SAGD is more energy intensive with lower recovery and greater GHG emissions as compared to open pit mining. But SAGD requires less water and minimal direct land disturbances, featuring a lower capital cost per m3 of bitumen production. And also considering the large reserves available for bitumen production by in situ technology, it is important to find alternating energy source other than natural gas for further exploration of oil sands.

Canada's raw bitumen production from oil sands has been expected to increase from 1.74 million bpd in 2011 to 5.33 million bpd in 2030, according to Canadian Association of Petroleum Producers (CAPP) forecast report (4). The ore from Athabasca oil sands contains between 8 to 14% bitumen and rest is coarse sands and fine silts and clays which are impregnated with bitumen as shown in figure 1. Compared to conventional crude oil, crude bitumen has much lower hydrogen to carbon ratio, higher molecular weight, greater specific gravity, and higher sulphur, nitrogen and metal content. Crude bitumen must be upgraded before it can be refined to other petroleum products. OPTI and Nexen integrated the upgrading and SAGD to produce fully upgraded synthetic crude oil.

Figure 1. Characteristics of oil sands

Upgrading occurs in two stages, primary upgrading is the initial process and achieves most of the value improvement. Secondary upgrading is a refinery process that finalizes the quality and stabilizes the product. In an upgrading process integrated with SAGD carbon rejection is the preferred method to increase the hydrogen to carbon ratio because the rejected carbon stream can be used as the fuel for SAGD steam generation. Asphaltenes are formed during the primary upgrading process of bitumen as shown in figure 2. The vacuum residuum from the distillation column is sent to the solvent de-asphalting unit where a paraffinic solvent is used to remove the high carbon content asphaltenes from the vacuum tower bottoms. These asphaltenes, about one-third of the vacuum residuum, is liquid at operating temperatures but are very problematic in bitumen upgrading facilities (5). Asphaltene is highly aromatic and normally contain substantial quantities of coke precursors, metals, sulfur, and nitrogen. Considering the increasing rate of oil sand production in Alberta, handling asphaltenes would be a real challenge for oil sands industry. Considering these facts and an alternative to natural gas for SAGD operation gasification of asphaltenes can be a great option and it increases the usability of asphaltene.

Figure 2. Primary upgrading of bitumen (5)

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Gasification is a process that can convert organic or fossil based carbonaceous materials into gaseous products such as carbon monoxide, hydrogen and carbon dioxide with a usable heating value using O2/steam/CO2, in an oxygen deficient atmosphere (1). This is achieved by reacting the fossil material with steam at high temperatures (>700°C), at an oxygen deficient atmosphere. So it is a partial oxidation process. Complete combustion (oxidation) of any hydrocarbon fuel yields CO2 and H2O. However a partial oxidation will result in the production of CO and H2. This resulting gas mixture is called syngas (from synthesis gas or synthetic gas) or producer gas and is having calorific value. Gasification is a mature technology and has been successfully tried since 1800's over a variety of feedstocks like wood, biomass, coal, petroleum coke, liquid hydrocarbons, natural gas etc. Currently there are around 120 gasification plants with around 400 gasifiers.

Using gasification technology the efficiency will be improved and the environmental impacts and greenhouse gas emissions will be reduced significantly (2). Gasification is a reliable option which can produce various products such as syngas for power generation, hydrogen and reformable liquid fuels and other valuable products as shown in figure 3. Nowadays integrated gasification combined cycle (IGCC) is an ideal and suitable technology instead of coal-fired processes which utilize gasification instead of combustion which leads to higher efficiency and lower environmental impacts.

Figure 1.Gasification-based energy conversion options (1)

During gasification the metals in asphaltene get concentrated in gasifier and present in gasifier soot. Soot is a general term that refers to impure carbon particles resulting from the incomplete combustion of a hydrocarbon. It is the residual pyrolyzed fuel particles that may become airborne during pyrolysis. A study by Stanford University calculated that carbon dioxide was the number one cause of man-made global warming, accounting for 48 percent of the problem. Soot was second with 16 percent of the warming (6). The formation of soot depends strongly on the fuel composition.

Literature review

2.1 Types of gasification technologies

Gasification process can be performed in different reactor or gasifier depending on operating condition and required situation obligated by fuel properties. Three main groups of gasifier that are available for commercial use are: fixed bed gasifier, fluidized bed gasifier and entrained-flow gasifier.

2.1.1 Fixed bed gasifier

Figure 4. Fixed bed gasifier (8)

The flow of fuel and the gasification agent in fixed bed is usually counter current. Gases flow upward through a bed of feedstock with the typical particle size of 5-80mm. In this type of gasifier, the residence time is relatively long in range of 0.5-1 hour which is suitable for large particles. This kind doesn't have the temperature limitation of fluidized bed, so they can operate at low temperature and produce just dry ash or operate at high temperature as a slagging gasifier. In order to maintain permeability of the fixed bed in slagging fixed bed, physical strength and cocking behavior of coal particles are very important factors. They are principally used for the production of heat and also for small scale power generation (2).

2.1.2 Fluidized bed gasifier

Figure 5. Fluidized bed gasifier (8)

In fluidized bed gasifier feedstock fuel particles usually with size of 0.5-5mm are suspended in a bed of coal ash, sand and other material and the bed is fluidized by gas flow. This kind of gasifiers operates at low temperature in the range of 600-1000°C and the feedstock should be dry and crushed. Ash agglomeration in fluidized bed causes uneven bed fluidization so in order to avoid this matter the ash fusion temperature of fuel should be higher than operating temperature. They generally operate in the MWh range, and are generally of two types, i.e. bubbling fluidised bed (BFB) gasifiers and circulating fluidised bed (CFB) gasifiers (2).

2.1.3 Entrained flow gasifier

Fuel particles and gases flow concurrently from top to bottom in entrained-flow gasifier. Therefore due to this kind of flow configuration the residence time of fuel particles is very short in the gasification zone (usually in the range of 5-10s). Consequently due to this short residence time in entrained-flow gasifier in order to have high carbon conversion, the fuel should be pulverized and the system should be designed to operate at high temperatures. Due to intense reaction condition inside of this kind of gasifiers, entrained-flow gasifiers are capable of working with high throughput and can use a wide range of less reactive coals. Entrained-flow gasifier are also capable of working with dry or slurry feed depending on their design however dry-fed gasifier is more coal efficient and less oxygen consuming in comparison with slurry-fed, because slurry-fed system requires additional energy to evaporate water in slurry. These are generally larger units for power generation and operate at very high temperatures, in excess of 1200 C and for very short residence times. They are normally fired with fossil fuels (2).

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Generic characteristics of entrained flow gasifiers include:

• High-temperature slagging operation;

• Entrainment of some molten slag in the raw syngas;

• Relatively large oxidant requirements;

• Large amount of sensible heat in the raw syngas; and

• Ability to gasify all coal regardless of rank, caking characteristics or amount of fines.

Many IGCC plants utilize entrained bed gasifiers. Entrained bed gasifiers are available in much larger capacities (100 MWe) than other types, but these are more commonly used for fossil fuels like coal, refinery wastes, etc.

Figure 6. Entrained flow gasifier (8)

2.2 Gasification theory

Gasification can be summarized into two major steps (2):

- Pyrolysis (also called thermolysis): during pyrolysis organic substances are decomposed into solid residue (i.e. char) and volatiles when it is heated up in the absence of oxygen.

Organic matter + heat char + liquids + gases

- Gasification The reaction between the char (from pyrolysis) and gasifying agents including oxygen, CO2 or steam.

Char + gasifying agent + heat gases + ash

Moreover, gasification reactions can be summarized into these parallel reactions:

Partial Oxidation and complete combustion with

(∆H = -405.9 kJ/mol)

(∆H = -123.1 kJ/mol)

Partial oxidation and complete combustion with oxygen are exothermic reactions which provide required heat for proceeding gasification reactions by using much of the oxygen in the gasifier.

Reaction of CO2 with carbon (Boudouard's reaction)

(∆H = +159.7 kJ/mol)

The reaction is endothermic and proceeds very slowly at temperatures below 1000 K and is inhibited by its product.

Water gas reaction

(∆H = +118.9 kJ/mol)

This endothermic reaction is favoured by elevated temperature and reduced pressure, and in the absence of catalyst, occurs slowly at temperatures below 1200 K.

Hydrogasification reaction

(∆H = -87.4 kJ/mol)

Because of some thermodynamic and kinetic limitations hydrogasification reaction is always incomplete and it produces some char residues (2)

The following gas phase reactions are important for the final gas quality to influence H2/CO ratio. This ratio is important if the gas is for synthesis or hydrogen production.

Water gas shift reaction

(∆H = -40.9 kJ/mol)

Steam methane reforming reaction

Methanation reaction

(∆H = -206.3 kJ/mol)

Methanation reaction is very slow except at high pressure and increases the caloric value of the gas (2).


The name "asphaltene" was first used by J.B. Boussingault in 1837 when he observed that the distillation residue of crude oils had asphalt-like properties. Asphaltenes are insoluble in n- pentane (or n-heptane) and are soluble in toluene. Asphaltenes are the heaviest and most polar molecular component of any carbonaceous material such as crude oil, bitumen or coal. Asphaltenes consist of carbon, hydrogen, nitrogen, oxygen, and sulfur and trace amounts of vanadium and nickel. The H:C ratio is approximately 1:1.10 to 1.20, depending upon the asphaltene source and the solvent used for extraction.

Asphaltenes have been the subject of considerable discussion and controversy in the literature. Controversy and ambiguity arise largely because of the lack of chemical definition of asphaltene mixtures for which composition is dependent upon the source material and method of isolation. Asphaltenes are generally classified by the particular paraffin used to precipitate them from the benzene-soluble portion of the feed. Thus, there are pentane asphaltenes, hexane asphaltenes, heptane asphaltenes, and so on. However, the present tendency is to define the material precipitated by n-heptane as asphaltenes. The inter-relationship of polarity and molecular weight in terms of solubility behavior can be better understood and it becomes clear that there is not a specific chemical composition or a specific molecular weight description for asphaltenes. Rather, asphaltenes contain a wide distribution of polarities and molecular weights.


Petroleum Residuum







Deasphaltened Oil



Figure 7. Separation of asphaltenes from petroleum residuum

The classic definition of asphaltenes is based on the solution properties of petroleum residuum in various solvents. The asphaltene fraction of petroleum crude is defined according to Nellensteyn (9) as the fraction insoluble in low boiling point paraffin hydrocarbons but soluble in carbon tetrachloride and benzene. According to Pfeiffer (10), asphaltene is defined as the fraction insoluble in n-heptane but soluble in toluene.

The asphaltenes from different origins have specific properties. Table 1 shows the properties of asphaltenes from Fosterton and Neilburg in Saskatchewan and Athabasca in Alberta, Canada, San Fernando in Columbia and Orimulsion in Venezuela. Asphaltenes generally contain very low ash (mostly less than one percent), but are high in volatile matter and fixed carbon. The sulfur content of the asphaltenes varies based on the origin of asphaltenes. The H/C ratio is around one due to it is being composed of mostly aromatic components. The feedstock for this study is mainly asphaltene from the Athabasca basin.



Neilburg (13)

San Fernando





Proximate Analysis (wt.%)

Volatile matter






Fixed Carbon












Ultimate Analysis





































Table 1. Typical properties of asphaltenes from various origins (12)

2.4 Asphaltene/Heavy oil gasification

Watanabe et al (16) developed a numerical model for the design and performance evaluation of the extra heavy oil gasification in an entrained glow gasifier. Four reaction processes like atomization, pyrolysis, coke gasification and gaseous phase reaction were modeled. Heterogeneous phase reaction concept of this model is shown in figure 8. The particle transport is modeled with Lagrangian particle tracking approach. Comparison between the computational results and the experimental results on "Research Gasifier for Liquid Fuel" of CRIEPI shows that the results such as temperature distribution, the gas composition distribution, the heating value and the carbon conversion efficiency are matches well. Vaezi et al (17) also developed a numerical model for gasification of the same feed based on the experimental results of Ashizawa et al (15). This study did not consider heterogeneous char reactions.

Figure 8. Heterogeneous phase reaction model

Ashizawa et al. (15) investigated the gasification characteristics of extra heavy oil in a research-scale gasifier with a capacity of 2.4 ton/day. The feedstock for this study was Orimulsion, which is a bitumen-based fuel constituted by 70% bitumen and 30% water. The set up consisted of a pressurized (1.9 MPa) entrained flow type gasifier, a raw-gas cooler and, 15m3 feedstock storage tank along with a supply system. The gasifying agent used was oxygen with an oxygen ratio of 0.37 to 0.41. They found that increasing the oxygen ratio leads to increase of carbon conversion while it reduces the cold gas efficiency (CGE) and caloric value of products. The HHV wet values were in the range of 9.5-10.5 MJ/m3 and CGE was about 75-80% and carbon conversion was more than 97%. They collected char and gas samples at different levels of the gasifier and found that high carbon conversion efficiency was obtained at top 1/3 of the reactor. Also, gas analyses revealed that CH4, H2O and CO concentrations decreased along the gasifier while H2 and CO2 concentrations increased.

Moreno et al. (14) investigated gasification of Colombian asphaltenes from San Fernando crude oil with oxygen in a laboratory scale batch process. The objective of their work was to find the effect of temperature and gasifying agent flow rate on syngas composition. The asphaltenes sample (15 gr) was placed in a horizontal tubular oven and heated up to 1000 °C. The continuous flow of O2 diluted with Ar at 170 psi (11.6 atm) was supplied as the gasifying agent. The temperature of the gasification experiments were varied in the range of 900 to 1000 °C. They results indicated that increasing the temperature improved the syngas composition (i.e., CO and H2 content) and carbon conversion since gasification at higher temperatures decreases the amount of tar and other by-products. They varied the gasifying agent from 33% to 47% (of the amount of oxygen required for complete combustion) and it was established that the best results in terms of CO and H2 content is obtained at 40% of gasifying agent.

Nassar et al (18) studied the application of nanotechnology for gasification/cracking of asphaltene. The adsorption and gasification of asphaltenes were investigated using thermogravimetric analysis in the presence and absence of different metal oxide nanoparticles. They found that the activation energy and oxidation temperature of asphaltenes decreased significantly in the presence of nanoparticles.

Soot formation

Soot is a carbonaceous solid material with 10 mole % hydrogen formed during pyrolysis and flame combustion. Soot is usually formed when the process conditions are sufficiently fuel rich to allow condensation or polymerization reactions of the fuel (and its initial decomposition products) to compete with oxidation (19). According to Neves et al (20) polycyclic aromatic hydrocarbons (PAH) are products of primary pyrolysis and the pre cursors of the soot particles in a secondary pyrolysis process. Soot exists in the form of both individual particles and agglomerate comprised of several primary particles. The fundamental unit of soot agglomerates are the spherules (21). Spherule diameter varies from 10-50 nm. The figure 9 shows the shape of soot particle consisting of clusters (4000 spherules) or chains of spherules. Soot in combustion flames is very important because it significantly enhance the radiative heat transfer with its large surface area. The near-burner flame temperature could be lowered several hundred degrees due to the extra heat transfer to the surrounding walls due to the presence soot particles in addition to gas, char and ash. The low temperature at the burner will decrease the thermal NOx as well as fuel NOx formation.

Soot contributes to many serious problems in the industry. In addition to contributing to pollution, soot enhances the emission of other pollutants from flames (e.g., carbon monoxide). Soot has been suggested to be a major contributor to global warming: its effect in raising the global surface air temperature is double to that of carbon dioxide (22). Also, smaller soot particles are suspected to exhibit dangerous effects on human health as they penetrate easily into the respiratory tracts. Soot formation also affects the efficiency and maintenance of combustion device.

Figure 9. Micrograph of diesel soot (21)

Soot formation has been extensively studied in different experimental devices such as flames, shock wave reactors, flow reactors, using different hydrocarbon fuels. Chen (23) performed coal pyrolysis experiments in an inductively-heated radiant drop-tube furnace in an inert argon atmosphere. He found that the yields of tar/oils plus soot in the secondary pyrolysis experiments were constant and were equal to the tar-plus-oil yields obtained at the longest residence time in primary pyrolysis experiments. For a high-volatile bituminous coal at higher temperatures, more than 25% of the coal mass (daf) was converted to soot. The high soot yields reported by Nenniger, et al. (24), Wornat, et al. (25) and Chen (23) were probably due to the inert conditions, since no destruction occurred by oxygen-containing species. The profiles of soot yield versus temperature in these coal pyrolysis experiments were not bell-shaped; the soot yields increased with temperature monotonically. Table 2 summarizes their experimental results.

Frenklach et al (27) modeled the soot particle nucleation and growth in laminar premixed hydrocarbon flames. The simulation of soot particle formation included fuel pyrolysis, polycyclic aromatic hydrocarbon formation and its planar growth, coagulation into spherical particles and also the surface growth and oxidation of particles. Shurupov (28) concluded that the pyrolysis temperature, reactant residence time and the feeding concentration of the fuel are the main parameters that govern soot formation during pyrolysis of any fuel. The induction periods of nucleation of the soot particles for different hydrocarbons may be different.

Soot formation is approximated by four stages as follows (29, 30):

Nucleation of soot particle (inception and growth of PAHs)

Particle coagulation

Particle surface reactions ( Growth and surface oxidation)

Particle agglomeration




Table 2. A summary of coal pyrolysis experiments conducted by three investigators.(26)

The presumed pathways for soot formation from coal given by Chen et al (31) are shown in figure 10. They studied the gasification of coal biomass blend in an atmospheric fluidized bed. Their results showed decrease in concentration of soot along with the increase on O/C ratio.

Figure 10. The presumed pathways for soot formation (31)

The Long Lake facility, operated by NEXEN, is the first large-scale integration of oil-sands Steam Assisted Gravity Drainage and Upgrader with gasification (32). Asphaltene from the Upgrader OrCrude process is used as the feedstock, having viscosity of 300 cSt at 300°C. The gasification of the feedstock occurs by partial oxidation using pure oxygen. A small amount of carbon, along with all the non-hydrocarbon components in the feed, exits the gasifier as particulates with the syngas. These soot particles create erosion/corrosion issues at the downstream of the gasifier as the syngas is cooled down. The available literature gives little information about the characteristics of the soot formed during asphaltene gasification. So it is selected as the main objective for the current study. The results will help in rectifying the industrial problems related to erosion of tube walls in the downstream of the gasifier.

2.6 Important Findings from Literature

Entrained flow gasification is a proven technology commonly used for fossil fuels like coal and refinery wastes. Many entrained bed gasifiers are in operation at larger capacities than other types.

Asphaltene gasification experiment is conducted in a laboratory scale batch process in which the temperature is varied from 900 to 1000oC. It is much below the normal operating temperature of entrained bed gasifiers (>1300oC).

Gasification of extra heavy oil revealed that an increase in oxygen ratio will lead to increase in carbon conversion but reduces the cold gas efficiency and calorific value of products.

A decrease in concentration of soot is observed with the increase in O/C ratio during the atmospheric fluidized bed gasification of coal biomass blend.

When the temperature of the coal pyrolysis experiment is varied between 1130 to 2200oK, the tar yield decreases with temperature and soot yield increases with temperature.

Little information is available about the characteristics of soot during asphaltene gasification.


The main objective of this study is to develop fundamental understanding of the formation of soot particles during asphaltene pyrolysis and gasification in an entrained flow gasifier. The yield and properties of soot formed in inert atmosphere (pyrolysis) may be different from that formed in the presence of oxygen-containing species (gasification). An electrically heated drop tube furnace will be used for the gasification experiments. The main objectives are:

Find the effect of pyrolysis temperature on the soot yield by varying the temperature from 1200 to 1400oC with an interval of 50oC.

Find the optimum range of operating conditions of the gasifier with respect to the generated syngas and mineral deposits by varying the conditions close to the real industrial gasifier. The temperature will be varied from 1200 to 1400oC.

Analyze the soot formed during both gasification and pyrolysis in detail regarding the particle size distribution, chemical composition, structure, morphology etc.

Find the effect of syngas cooling temperature on the interaction of soot minerals and the mechanisms of mineral evaporation/re-condensation and deposit formation. The gasifier exit gas can be subjected to controlled cooling and soot collection can be done at specified temperatures. The soot collection temperature will be varied from 50 to 300 oC.

Investigate the role of soot particles on the erosion/corrosion of tubes in the downstream of gasifier.

Estimate reactivity of asphaltene char with respect to the important gasification reactions using thermogravimetric analyser(TGA).

CFD simulation of asphaltene gasification in an entrained flow gasifier using the kinetic data developed with TGA.


4.1 Experiments in an Entrained flow gasifier

In an entrained flow gasifier, an atomized liquid fuel/ pulverized solid fuel is gasified with oxygen/air and/or steam in co-current flow. The main characteristics of this type of gasifier are the high operating temperatures and high heating rates and short residence times which in turn result in high throughput of fuels compared to other conventional gasifiers such as fluidized bed and fixed bed. Knowing thermal behaviour of the fuel is a preliminary stage to study various processes such as fuel gasification or fuel combustion. Char oxidation is the rate-limiting step and determines the carbon conversion and the ash formation.

The experimental setup of the drop tube furnace (DTF) is shown schematically in Figure 11 (12). The reactor furnace consists of an electrically heated vertical core of Mullite tube (2.5'' ID, 60.875'' height). The temperature of the reactor is fixed along the tube length using three PID temperature controllers in three different zones. A feed nozzle in combination with a primary flow of N2 is used to entrain and feed the fluid particles into the reactor. For gasification Air and N2 are preheated on the preheating section of tube before reacting with samples. Pyrolysis products are collected through a water-cooled collection probe.

To prevent condensation of gaseous products on the inner shell of the collector probe, the probe is equipped with a sintered stainless steel inner shell through which gas (N2) is passed. Following the collection probe, the cooled stream is passed through a cyclone where char and ash samples are separated from flue gas and collected. Then, the flue gas is passed through a bag filter to trap sub-micron particles and a condenser to take out the remaining water vapor. The pressure in the gasifier is fixed in proximity of ambient via a vacuum pump.

The drop tube furnace will be used for the pyrolysis as well as gasification of asphaltene liquid. The soot particles will be collected in both the cases using a cascade impactor for further characterization. The cascade impactor is capable of collecting literally all the particles with respect to their particle size at different stages. The char particles of heavier size can be collected in the cyclone separator which is connected prior to the cascade impactor. This char prepared at different temperatures will be used for the reactivity studies using thermo gravimetric analyser. The kinetic data thus obtained will be used for the computational fluid dynamics (CFD) simulation of the asphaltene gasification. The effect soot properties formed in presence of oxygen containing species (gasification experiment) will be examined by characterizing the gasification soot. The evaporation and re-condensation of the soot minerals can be studied by controlling the temperature of the collection probe and tubes connecting to cascade impactor. The syngas quality during the gasification experiment can be monitored using the micro-GC connected to the system. Thus the variation of syngas properties can be estimated at different operating conditions.

Figure 11. Schematic diagram of entrained flow gasification system

4.2 Characterization of the resulting samples

4.2.1 Surface area

Char surface area can be measured by volumetric adsorption analysers and BET method. Total surface area of char will be measured using two techniques: N2 adsorption and CO2 adsorption. These two techniques are different in adsorption temperatures and the used gases. In the first technique, N2 is adsorbed at 77K and the isotherm will be interpreted further by BET equation. In this technique, the surface area of meso and macropores (greater than 20 A) will be measured while the surface area of micropores will be found by CO2 adsorption at 0°C (32, 33).

4.2.2 Microscopy

Scanning Electron Microscope (SEM) can be used to observe the morphological structure of char and to see how a coal particle is affected by different process conditions (32).

4.2.3 Proximate and ultimate analyses

Proximate and ultimate analysis will be carried out based on ASTM D 3172-89 standard. Also, it could be used to find the percentage of the minerals. These methods will be done according to the procedures reported in the literature.

4.2.4 Char density

Relative bulk packing density will be measured as the char density. This is an indicator of the nature of char and provides some understandings about the reaction of char with gases like CO2, O2 and H2O (32).

4.2.5 Particle size distribution (PSD)

Char and coal particle size distributions will be found by Malvern laser-scattering. In order to prevent char particles damages, first they will be dispersed in propanol and undergo a mild ultrasonic dispersion before analyzing for PSD.