Preparation of Activated Carbon from Caribbean Pine by Chemical Activation
Johanna Ahnemark Sandra Marques
Department of Chemical Engineering Royal Institute of Technology (KTH)
Stockholm, Sweden
September 2013
Preparation of Activated Carbon from Caribbean Pine by chemical activation
Johanna Ahnemark Sandra Marques
Supervisors
Rolando Zanzi Vigouroux
Department of Chemical Engineering and Technology Royal Institute of Technology (KTH)
Stockholm, Sweden
Francisco Márquez Montesino Facultad de Forestal y Argonomia
Departamento de Química
Universidad de Pinar del Río “Hermanos Saiz Montez Oca“
Pinar del Río, Cuba
Examiner
Henrik Kusar
Department of Chemical Engineering and Technology Royal Institute of Technology (KTH)
Stockholm, Sweden
Abstract
Activated carbon, AC, is a porous material derived from a feedstock containing carbon that has been activated to open up millions of small pores between the carbon atoms. The structure of the material enables the material to effectively adsorb both gaseous and liquid compounds. Examples of different kinds of raw materials are nutshells, wood, some polymers and coal. In this project the activated carbon will be produced from the tree Caribbean Pine, which is a very common plant on Cuba. The consumption of activated carbon is increasing worldwide and therefore is the importance of research is great. It is of interest to investigate from which renewable sources activated carbon can be produced.
In the first section of experiments the physical properties of the raw material, saw dust from the plant, were determined. The analyzed properties were humidity, ash content and volatile matter.
The activated carbon was then produced by chemical activation with phosphoric acid as an impregnation agent that was applied during varied time and heated at different temperatures.
The main purpose for this project was to, by varying the parameters temperature (400 ˚C and 500
˚C), acid concentration (10%, 25% and 40%), relative impregnation (0.75, 1.35 and 2.0) and impregnation time (1 h, 2 h and 3 h), evaluate which parameters that affect the product. Also, an investigation was made to determine the interaction of the different parameters. This was done by analysing the properties of the AC with gas adsorption of gasoline and ammonia. Liquid adsorption was analysed with iodine number and the yield of the AC was calculated with two different methods.
In general an increasing of the temperature and the impregnation time results in a higher iodine number and higher capacity to absorb gasoline in the produced activated carbon. When the conditions were too strong the iodine number and the capacity to absorb gasoline decreased. The pore structure of the activated carbon is destroyed by too strong conditions.
The results were also analysed with a computer program to establish statistical evidence of influence from the parameters indicating that temperature has strong effect on iodine number of the
produced activated carbon. If the AC from Caribbean Pine would be commercially produced the recommended design is to keep all parameters low. This is both cost effective and energy efficient.
Based on the experimental results it was determined that the AC from Caribbean Pine is better suited for adsorbing gasoline compared with ammonia. Furthermore, the adsorption of gasoline is
increasing with an increasing temperature. An industrial manufactured AC was compared with the AC produced from Caribbean Pine and it had a better liquid and gas adsorption showing that more research and optimization of AC from Caribbean Pine must be done before commercializing the product.
A suggestion for further research is to use the time in the oven as a parameter to be varied in the experimental setup. This could be valuable in order to determine the influence of the time in the oven both concerning the yield but also the adsorption ability of the AC.
Sammanfattning
Aktivt kol, AK, är ett poröst material som utvinns från ett råmaterial som innehåller kol som aktiveras för att öppna upp miljontals små porer mellan kolatomerna. Strukturen hos materialet gör det möjligt för materialet att effektivt adsorbera både gasformiga och flytande föreningar. Exempel på olika typer av råvaror är nötskal, trä, vissa polymerer och kol. I detta projekt kommer det aktiva kolet framställas från trädet karibisk tall, en mycket vanlig växt på Kuba. Förbrukningen av aktivt kol ökar i världen och därför är betydelsen av forskning stor. Det är också av intresse att undersöka från vilka förnybara källor aktivt kol kan produceras.
I de första experimenten bestämdes de fysikaliska egenskaperna hos råvaran, sågspån från karibisk tall. De analyserade egenskaperna var fukthalt, askhalt och andel flyktiga ämnen. Det aktiva kolet framställdes därefter genom kemisk aktivering, med fosforsyra som ett impregneringsmedel som tillsattes under en varierad tid och värmdes vid olika temperaturer.
Det huvudsakliga syftet med projektet var att, genom att variera parametrarna temperatur,
koncentrationen av syra, relativ impregnering och impregneringstid, utvärdera vilka parametrar som påverkar produkten. Dessutom gjordes en undersökning för att bestämma interaktionen av de olika parametrarna. Detta gjordes genom att analysera egenskaperna hos AK med gasadsorption av bensin och ammoniak. Adsorptionen av ämnena i vätskefas analyserades med jodtal och utbytet beräknades med två olika metoder.
Allmänt en ökande av temperaturen och impregneringstid resulterade i ett högre jodtal och högre kapacitet att absorbera bensin hos det producerade aktiva kolet. När förhållandena är alltför starka, minskar jodtalet och förmåga att absorbera bensin. Den porstrukturen hos det aktiva kolet förstörs av för starka förhållanden.
Resultaten analyserades med ett datorprogram för att fastställa statistiska bevis för påverkan från parametrarna. Resultaten visade att temperaturen har en stark effekt på jodtalet hos det
producerade aktiva kolet. Om AK från karibisk tall skulle tillverkas rekommenderas därför att alla parametrar hålls låga. Detta är bra både ur ett kostnads‐ och energi perspektiv.
Baserat på de experimentella resultaten fastställdes att det aktiva kolet är bättre lämpat för
adsorption av bensin än ammoniak. Vidare ökar adsorptionen av bensin med en ökande temperatur.
Ett industriellt tillverkat AK jämfördes med AK från karibisk tall och det hade en bättre vätske‐ och gasadsorption vilket visar att mer forsking och optimering måste göras innan AK från karibisk tall kan kommersialiseras.
Ett förslag för kommande forskning är att använda tiden i ugnen som en variabel. Detta kan vara värdefullt för att bestämma hur tiden i ugnen påverkar utbyte och adsorptionsförmågan.
Acknowledgement
This project had not been able to be accomplished without help from our supervisor at the Royal Institute of Technology, KTH, Rolando Zanzi Vigouroux. We would like to give a special thanks to our supervisor, who helped us with the scholarship to make the trip to Pinar del Río University on Cuba possible, who gave us information regarding flights, transfers, accommodation and visa. He also supplied us with all the necessary equipment we needed to finish our laboratory work at KTH in Stockholm. He has also been a support in that manner that he has always had time for us to exchange ideas, results and much more. Thanks also to our supervisors on Cuba; Leonardo Aguiar, Julián Triana Dopico and Boris who had patience with us during our experimentation time on Cuba.
Finally, thanks to the entire laboratory team that helped us with materials, equipment and chemicals.
Contents
1 Introduction ... 8
1.1 Aim and objective ... 8
1.2 Limitations ... 8
2 Background ... 9
2.1 Caribbean Pine ... 9
2.2 Activated carbon ... 9
2.2.1 Usage ... 9
2.2.2 Activated carbon on Cuba ... 9
2.3 Principle of activated carbon adsorption ... 10
2.4 Emissions which can be reduced with activated carbon ... 10
2.4.1 Nitrogen oxides, NOx ... 10
2.4.2 Sulphur oxides ... 10
2.5 Factors that influence the activated carbon ability to adsorb ... 11
2.6 Methods for production of activated carbon ... 11
2.6.1 Physical reactivation ... 11
2.6.2 Chemical activation ... 11
3 Methodology ... 12
3.1 Feed stock ... 12
3.2 Design computer program ... 12
3.3 Optimizing of parameters... 12
4 Experimental setup ... 13
4.1 Humidity ... 13
4.1.1 Calculations of humidity ... 13
4.2 Ash content ... 13
4.2.1 Calculations of ash content ... 13
4.3 Volatility ... 14
4.3.1 Calculations of volatility ... 14
4.4 Preparation of activated carbon ... 15
4.4.1 Phosphoric acid ... 15
4.4.2 Chemical activation ... 15
4.4.3 Parameters and influence ... 16
4.4.4 Preparations of the acids ... 16
5 Analysis ... 17
5.1 Adsorption ... 17
5.1.1 Gas phase adsorption ... 17
5.1.2 Liquid adsorption ... 20
5.2 Yield ... 21
5.2.1 Product yield ... 22
6 Results ... 24
6.1 Influence of temperature on gasoline adsorption ... 25
6.2 Influence of relative impregnation on gasoline adsorption ... 27
6.3 Influence of impregnation time on gasoline adsorption ... 29
6.4 Influence of acid concentration time on gasoline adsorption ... 31
6.5 Influence of temperature on iodine number ... 33
6.6 Influence of relative impregnation on iodine number ... 35
6.7 Influence of impregnation time on iodine number ... 37
6.8 Influence of acid concentration on iodine number ... 39
7 Discussion ... 41
7.1 Preparation of activated carbon ... 41
7.2 Yield ... 41
7.3 Gas adsorption ... 41
7.3.1 Adsorption of ammonia... 42
7.3.2 Adsorption of gasoline ... 42
7.4 Liquid adsorption ... 42
7.4.1 Iodine number ... 42
8 Conclusions ... 43
9 Bibliography ... 44
10 Appendix ... 46
10.1 Design Expert results for ammonia. ... 46
10.2 Design Expert results for the yield. ... 47
10.3 Design Expert results for the product yield. ... 48
10.4 Design Expert results for gasoline. ... 49
10.5 Design Expert results for iodine number. ... 50
1 Introduction
Activated carbon, AC, is a porous material derived from feedstock containing carbon. The structure of the material enables the material to effectively adsorb both gaseous and liquid compounds. Different raw material can be used to produce activated carbon such as coal, wood, lignite, shells from varying fruits and nuts and some polymers. (T. Vernersson, 2001) The consumption of activated carbon is increasing worldwide and therefor the importance of research is great. Also it is of interest to investigate from which renewable sources activated carbon can be produced. (Department of Agriculture, Fisheries and Forestry, 2010)
This project was dived in two parts. First different sets of activated carbon were prepared from Caribbean Pine at Universidad de Pinar del Río in Pinar del Río on Cuba. Analysis of the AC, adsorption of gasoline and ammonia, was also conducted on Cuba. The samples of AC were later analysed in Sweden at KTH, both adsorption of gasoline, ammonia and iodine number were performed.
This report contains a short description of activated carbon, its characteristics and applications, an explanation of the experimental setup and analysis of the results and conclusion.
1.1 Aim and objective
In this project the aim was to suggest how to design the parameter setup when producing activated carbon from the tree Caribbean Pine and determine if the raw material is suitable for production of AC. In order to meet this goal the objective was to prepare activated carbon with different
parameters and evaluate which parameters affect the product. Also the object was to investigate the interaction of the different parameters.
1.2 Limitations
For this study the feed stock to analyse was Caribbean Pine. The parameters investigated were temperature, acid concentration, impregnation time and relative impregnation and the values of these criteria were decided in a previous laboratory setup. Also, the only impregnation agent investigated was phosphoric acid. For analysis a computer program tool was suggested to be used.
However, additional manual analyses have been made comparing the parameters in graphs.
2 Background
To improve the understanding of the investigation of activated carbon is it important to have a general knowledge about the field. Therefore will the background section of the report contain information about the raw material, Caribbean Pine, its properties, which areas the AC is useful in, which compounds that could be reduced and further more.
2.1 Caribbean Pine
Caribbean Pine, Pinus Carribea, is distributed in Central America, Cuba and the Bahamas. It is also grown on plantations worldwide. One region on Cuba were it is native is in Pinar del Río, that is a province that is located in the west of Cuba. The Pine is around 20‐30 m tall, has a diameter about 0.6‐1.0 m and an average dried weight close to 625 kg/m3. (Department of Agriculture, Fisheries and Forestry, 2010) (Caribbean Pine, 2013) Cuba has a varied humidity during the different seasons.
During the period when the experiments were conducted was the relative humidity high; during March it was around 75%, compared with Sweden, Stockholm, when it is around 55‐65% during the same period. (Weather history, 2013) The two main sectors that the Caribbean Pine are used in are purification and within the construction sector. Caribbean Pine is a decorative wood and an
important timber tree that has many uses as a material for production and for construction.
Applications are in furniture’s, plywood, for frames, laminated beams, flooring and playground equipment. Other applications for Caribbean Pine are as scaffold planks, wood wool and paper products. (Department of Agriculture, Fisheries and Forestry, 2010) (Pinus caribaea (Caribbean pine))
2.2 Activated carbon
Activated carbon, AC, may also be called activated charcoal or activated coal. AC is a worldwide expanding product and the usage of it is likewise increasing. AC is created from a various numbers of carboneous materials that is treated with oxygen to open up millions of small pores between the carbon atoms. Examples of different kinds of raw materials are nutshells, wood, some polymers and coal. In this project will the activated coal be produced from the tree Caribbean Pine, a very common plant on Cuba. Factors that affects if the activated carbon is suitable manufacturing or not is a combination of factors such as; economy, AC capability and its characteristics. (Anne Marie Helmenstine)
2.2.1 Usage
The main reason why the usage of AC is expanding in the world is because of its complexness. AC is suitable to remove a variety of compounds in streams depending if the stream is in a gaseous or a liquid phase. The purpose for the material is to increase the surface area and to form a porous area were the adsorption and chemical reactions can occur. A higher amount of adsorbed compounds and a larger number of chemical reactions will achieve a higher purification and separation with the activated carbon which is highly desirable. (Ohlson)
2.2.2 Activated carbon on Cuba
In order to decrease the extensive import of activated carbon to Cuba a factory to produce AC opened in 1998. Still there is a large import to the country, around 600 ton every year for a cost of 8 million dollars (Ingenieros escoceses buscan la solución para una pesadilla cubana, 2012). The raw material used today is coconut because of its low ash content and high iodine number. The capacity of the plant is said to be 500 ton produced AC per year, but the limiting factor is access to raw
Activated carbon is an important product that is used in several areas on Cuba. The main industrial processes are medicine‐, sugar‐, and beverage production. It is also used within biotechnology and water treatment. (Baracao, 2010) In medicine it can be used to selectively remove/absorb toxic compounds. Another application is to use AC in waste water treatment as a cleaning step. (Anne Marie Helmenstine)
New research shows that AC also can be used in the production of batteries with high energy content at a low cost since the material conduct electricity. (Ingenieros escoceses buscan la solución para una pesadilla cubana, 2012; Lars Ivar Elding, 2013)
2.3 Principle of activated carbon adsorption
The separation occurs when the gas comes in contact with a solid porous phase, adsorbent, and the pollutants in the gas phase bind to the surface. Forces that enable the molecules in the gas phase to connect to the adsorbent can be physical, van der Waal, or chemical, ionic ‐ or covalent bond. The chemical force is stronger than the physical due to the properties of the bonds. The performance of the adsorption depends on the fluid‐solid equilibrium and mass transfer rates. (Anne Marie
Helmenstine)
There are several common adsorbents such as activated carbon, silica, aluminium oxide, zeolites and polymeric adsorbents. Which adsorbent that is applied depend on the components that is going to be separated. (Kan‐Carbon Private Limited, 2011)
2.4 Emissions which can be reduced with activated carbon
Pollutants that can be treated with AC are mainly nitrogen‐ and sulphur oxides. These have negative impact on different environmental systems. (Ohlson)
2.4.1 Nitrogen oxides, NOx
Nitrogen monoxide and nitrogen dioxide, out of the seven known nitrogen oxides, ΝΟ/ ΝΟ2/ ΝΟ3/ Ν2Ο/Ν2Ο3/ Ν2Ο4 / Ν2Ο5, are the two compounds that are significantly important for atmospheric pollution problems. For this reason is the name NOx commonly used. Nitrogen monoxide, NO, is a colourless and tasteless gas while nitrogen dioxide, ΝΟ2, has a red brown colour and is soluble in water, is a powerful oxidant and has a peculiar odour. NO and NO2 contributes to the formation of ground level ozone and acidic rain. Nitrogen compounds also contribute to the eutrophication.
(Hansson).
2.4.2 Sulphur oxides
Sulphur dioxide, SO2, is a colourless gas, odourless in low concentration but with an intense irritant odour in very high concentrations. It is know that SO2 has a bad influence on the health of people with respiratory problems either by itself or together with particular matter. The main sources of this pollutant in the atmosphere are energy producing plants, oil refineries, chemical plants and paper plants. It can cause alterations in vegetation and material, as well as decreases visibility and increases acidity in lakes and rivers. Sulphur dioxide is one of the elements that form acid rain. (Sabelström, 2013)
2.5 Factors that influence the activated carbon ability to adsorb
When activated carbon is going to be used it is important to consider factors that might influence the result. There are several factors that impact the effectiveness of the AC. The absorption of the AC depends on the pore size and distribution varies depending on the source of the carbon and the manufacturing process. General is larger organic molecules easier for the AC to absorb compared with smaller molecules. The adsorption capability tends to increase as the surrounding pH and temperature decrease. Contaminants are also removed more effectively if they are in contact with the activated carbon during longer time, which means that the flow rate through the carbon affects the filtration. (Anne Marie Helmenstine)
2.6 Methods for production of activated carbon
There are two different methods, physical ‐and chemical activation. The processes are described below.
2.6.1 Physical reactivation
The activated carbon is produced by carbonization and activation of the raw material using different gases. First the material is carbonized by pyrolysis at high temperatures, 500‐900°C, in absence of air.
The activating step also known as oxidation occurs when the material is exposed to an oxidizing surrounding, carbon dioxide, oxygen or steam, during high temperatures, 800‐100°C. (Mansooreh Soleimani, 2007) The first step, carbonization, is performed to remove non‐carbon‐elements from the raw material and in the activating stage the desired porosity of the material is developed. (Joana M. Dias, 2007)
2.6.2 Chemical activation
In the chemical activation the material is impregnated before carbonation with an acid or base. This is done to lowering the activation temperature and assists to create the porosity of the AC by dehydration and degradation. This is a one‐step method and these steps occur simultaneously.
(Joana M. Dias, 2007)
Advantages with this method compared to physical reactivation are higher yield and lower energy cost as a result of the lower activation temperatures. Furthermore the porosity increases and activation time decreases. (Joana M. Dias, 2007)
The main problems with this method are higher costs and residues of the chemical substance used can stay in the product, corrosiveness and a cleaning stage is necessary to remove the chemical agent. (Mansooreh Soleimani, 2007)
3 Methodology 3.1 Feed stock
The raw material that was used to produce the activated carbon is a common plant in Cuba named Caribbean Pine, in latin Pinus Caribaea. It grows easily and does not demand extensive amounts of care. These features are preferred if the purpose of the AC is to be commercialized. (Caribbean Pine)
3.2 Design computer program
The computer program that was used is called Design Expert Stat‐Ease and the software is developed in England, New Castle. It is a multifunctional program that preferably is applied in situations where a company wants to improve the quality in an experiment, develop efficient experiments, quickly solve manufacturing problems and make breakthroughs in processes. (History of Stat‐Ease)
Stat‐Ease is a program that uses statistical simulations methods. In this project it minimized the numbers of experiment that had to be performed to get a valid result. The purpose of the program was to generate a flow sheet for the analysis. It calculated the minimum respectively the maximum value of each of the four factors, temperature, concentration, impregnation time and relative impregnation that should be analysed. (History of Stat‐Ease)
3.3 Optimizing of parameters
The purpose of the project was to investigate how factors such as temperature, acid concentration, relative impregnation and the impregnation time affected the activated carbon ability to adsorb. For an overview of which parameters that were investigated and their values see Table 1.
Table 1: Overview of the factors investigated.
Sample No.
Temperature [˚C]
Acid concentration [%]
Relative impregnation [‐]
Impregnation time [h]
1 400 10.00 0.70 1.00
2 500 10.00 0.70 1.00
3 400 40.00 0.70 1.00
4 500 40.00 0.70 1.00
5 400 10.00 2.00 1.00
6 500 10.00 2.00 1.00
7 400 40.00 2.00 1.00
8 500 40.00 2.00 1.00
9 400 10.00 0.70 3.00
10 500 10.00 0.70 3.00
11 400 40.00 0.70 3.00
12 500 40.00 0.70 3.00
13 400 10.00 2.00 3.00
14 500 10.00 2.00 3.00
15 400 40.00 2.00 3.00
16 500 40.00 2.00 3.00
17 400 25.00 1.35 2.00
18 500 25.00 1.35 2.00
19 400 25.00 1.35 2.00
20 500 25.00 1.35 2.00
21 400 25.00 1.35 2.00
22 500 25.00 1.35 2.00
4 Experimental setup
The first stage was to determine the physical properties of the raw material, saw dust from the plant Caribbean Pine. The analyzed properties were humidity, ash content and volatile matter.
4.1 Humidity
Cuba is a country with a high ‐and a varied level of humidity in the air, therefore is it of importance that the humid is calibrated before each new experiment. The humidity, residual moisture, was calculated by following steps:
1. The oven was set to 107 ˚C, when the temperature was obeyed were the empty crucible placed in the oven during 8 min.
2. Then were it placed in a desiccator during 15 min and the empty crucible was weighed, mcrucible. 3. The raw material mass was placed in the crucible and measured, m before, and after that placed in
the oven again during one hour.
4. Finally the crucible with the heated mass weight, mafter, was weighed and the humidity residual moisture, R, could be calculated with Equation 1.
4.1.1 Calculations of humidity
mcrucible=22. 6332 [g] mbefore= 29. 8252 [g] mafter= 29. 2947 [g]
mdifference= mafter‐ mbefore= 29.8252 – 29.2947= 0.5305 [g]
100 29.8252 29.2947
100 7.376[%] 7.4[%]
29.8252 22.6332
before after before crucible
m m
R m m
R
= − ⋅
−
→ = − ⋅ = ≈
−
Equation 1
4.2 Ash content
1. The oven was installed to 107 ˚C were the two empty crucibles was reserved during 5 min.
2. Then was the crucibles kept in the desiccator during 15 min and then separately weight.
3. 2 g of the raw material was weight in each one of the crucibles.
4. Then were they putted in the oven in 580˚C during three hours and finally were the oven installed to 60C so that the crucibles that contain the mass were cooling down.
5. When they were at room temperature was they placed in the desiccator during 15 min again and lastly weight.
4.2.1 Calculations of ash content
See Equation 2 for the calculated ash content.
mcrucible1= 20. 4200 [g] mcrucibel2= 18. 6142 [g]
mbefore1= 1. 9809 [g] mbefore2= 1. 9867 [g]
mafter1= 20. 4317 [g] mafter2= 18. 6247 [g]
100[%]
after crucible before
m m
A m
= − ⋅ Equation 2
20.4317 20.4200
1 100 100 0.5906[%]
1.9809
after crucible before
m m
A m
− −
→ = ⋅ = ⋅ =
18.6247 18.6142
2 100 100 0.5286[%]
1.9867
after crucible before
m m
A m
− −
→ = ⋅ = ⋅ =
4.3 Volatility
1. The oven was set to 107 ˚C, when the temperature was obeyed were the empty crucible placed in the oven during 8 min.
2. Then were it placed in a desiccator during 15 min and the empty crucible was weigh, mcrucible. 3. The raw material mass was placed in the crucible and measured, m before, and after that placed in
the oven again at 900 ˚C during 7 min.
4. The crucible was then cooled on a metal tray and after that placed in the desiccator.
5. Finally were the crucible with the sample was weighed, mafter, and the volatile content could be calculated with Equation 3.
4.3.1 Calculations of volatility
Mcrucible= 33. 2452 [g] mbefore= 34. 2456 [g] mafter= 33. 3743 [g]
100( )
34.2456 33.3743
7.37625 79.4845[%]
34.2456 33.2452
before after before cruicble
m m
V R
m m
V
= − −
−
→ = − − =
−
Equation 3
The total composition of the raw material, saw dust from Caribbean Pine, is shown in Figure 1.
Figure 1: Summary of sawdust composition.
Volatiles [%]
79,5%
Ash [%]
0,6%
Moisture [%]
7,4%
Fixed carbon [%]
12,6%
Sawdust composition
4.4 Preparation of activated carbon
As written before the activated carbon was derived from the common tree on Cuba Caribbean Pine.
The wood had to be completely dried and thereafter grated finely in order to be used in the experiments.
4.4.1 Phosphoric acid
In this investigation was chemical activation used and the impregnation agent was phosphoric acid.
Earlier research shows that this method as well as using phosphoric acid is to prefer according to similar experimental setups. (Birbas, 2011)
Phosphoric acid, H3PO4, is a medium power colorless acid. In waters solution it is not as reactive as other acids. Not the acid or the salts derived from it are poisonous. (Lars Ivar Elding, 2013)
4.4.2 Chemical activation
In general, activated carbon is formed when the carbon rich raw material is treated with acid and then heated. This procedure creates the porous structure crucial for the activated carbon. In this case approximately 10 g of the saw dust were put in a crucible and the acid was added with the
concentration and relation according to the design scheme. Saw dust and acid is mixed and then impregnated for a period of time. The sample was then placed in the oven at 400°C or 500°C for 20 minutes. Formation of the active carbon is now realized. When the 20 minutes had passed the sample was cooled in room temperature for five minutes then placed in a desiccator for 15 minutes.
The samples are weighed and the yield is calculated. After is the AC is washed with distillated water until the pH reaches 6 or above. The samples are then dried in the oven at 60°C during 40 minutes and placed in closed containers to be analyzed later. The different samples are displayed in Figure 2.
Figure 2: Samples of activated carbon for analysis.
4.4.3 Parameters and influence
Four parameters were varied in order to show if an influence of the separated parameters could be displayed, temperature of the oven, acid concentration, impregnation relation and time of
impregnation. Also the interaction of the parameters was investigated. The highest and the lowest value were put into the design program and the middle value was calculated by the program. The temperature of the oven was set to 400°C respectively 500°C. The concentration of the phosphoric acid was set to 10%, 25% and 40%. The relative impregnation was set to 0.7, 1.35 and 2.0 which is a volume ratio of the acid and the raw material. The impregnation time was set to one hour, two hours and three hours.
4.4.4 Preparations of the acids
In order to vary the acid concentration in the samples three different solutions of the phosphoric acid were made. The concentrations were set at 10%, 25% and 40%. To vary the relative impregnation different amounts of the acids were mixed with the saw dust. This ratio was calculated using volume as a reference. 10 grams of sawdust corresponds to 35 ml acid. Therefor a ratio of 0.7 corresponds to 24.5 ml acid, 1.35 corresponds to 47.25 ml acid and 2.0 correspond to 70 ml acid.
5 Analysis
The activated carbon has the property to be an adsorbing agent in a gas –and a liquid phase. These two different scenarios have been investigated. See Figure 3 for a display of the samples during adsorption in a desiccator.
Figure 3: Adsorption in a desiccator.
5.1 Adsorption
5.1.1 Gas phase adsorption
When the AC ability to adsorb was in a gas phase was ammoniac 25 % and gasoline used. The procedure for the two different chemicals was the same. The experiment stared with that the crucible was weight when it was empty, mcrucible. After was the raw material weighed, approximately 0.1 g of the AC. The crucibles and the sample were put in the desiccator during 24 hours. When the time had passed was the weight finally measured and the values of the adsorption calculated with Equation 4. A commercial AC was also analysed in two samples, AC1 and AC2.
100[%]
before
Adsorption m m
= Δ ⋅ Equation 4
5.1.1.1 Gasoline adsorption
Gasoline is a liquid containing different mixtures of hydrocarbon. The liquid is volatile, flammable and viscous. Since the composition varies the boiling point differ from 30 to 190°C. Gasoline is the most important fuel for passenger vehicles. (Carlsson, 2013) The results of gasoline adsorption are shown in Table 2. And for and overview of the result with a comparison between the different temperatures are shown in Figure 4.
Table 2: Experiment results of gasoline adsorption.
Sample No.
mcrucible
[g]
mbefore
[g]
mafter
[g]
Δm [g]
Adsorption [%]
1 21.87 1.00 22.84 0.97 96.42
2 21.81 1.00 22.36 0.55 55.00
3 25.37 1.00 25.95 0.58 58.39
4 22.34 1.00 23.35 1.01 100.85
5 20.95 1.00 21.48 0.53 53.08
6 22.85 1.00 23.74 0.89 89.17
7 27.37 1.00 27.78 0.41 40.93
8 27.36 1.00 28.04 0.68 68.24
9 22.85 1.00 23.82 0.97 97.11
10 20.95 1.00 21.87 0.92 92.05
11 22.84 1.00 23.80 0.96 95.80
12 25.36 1.00 26.38 1.02 101.57
13 21.81 1.00 22.72 0.91 90.77
14 21.87 1.00 22.97 1.10 109.59
15 21.87 1.00 22.88 1.01 101.23
16 21.81 1.00 22.84 1.03 102.64
17 25.36 1.00 26.37 1.01 100.46
18 22.84 1.00 23.94 1.10 109.95
19 20.95 1.00 21.95 1.00 99.80
20 22.85 1.01 24.26 1.41 139.66
21 27.37 1.00 28.20 0.83 82.82
22 27.36 1.00 28.68 1.32 132.08
AC 1 27.36 1.00 28.70 1.34 134.24
AC 2 23.31 1.00 24.70 1.39 138.70
Figure 4: Gasoline adsorption, comparison between 400°C and 500°C.
0 20 40 60 80 100 120 140 160
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
Adsorption [%]
Sample No.
Gasoline adsorption
T= 400 °C
T= 500 °C
5.1.1.2 Ammonia adsorption
Ammonia, NH3, is a colorless gas in room temperature with a density lower than air. The odor is intense and at low concentration irritating for the eyes and respiratory system. At high concentration NH3 is dangerous and poisonous for the mucous membrane and respiratory system if inhaled. The gas is easily soluble in water releasing heat. Ammonia is one of the most produced chemical
components with the highest applications within fertilization, explosives and plastic industry. (Elding, 2013) The results of ammonia adsorption are shown in Table 3.
Table 3: Experiment results of ammonia adsorption.
Sample No.
mcrucible
[g]
mbefore
[g]
mafter
[g]
Δm [g]
Adsorption [%]
1 23.83 0.96 24.87 0.09 8.88
2 21.04 1.00 22.11 0.07 6.71
3 21.10 1.01 22.20 0.10 9.64
4 20.29 1.00 21.38 0.09 8.75
5 22.63 1.00 23.65 0.02 1.62
6 21.93 0.95 22.93 0.05 5.07
7 23.35 1.08 24.47 0.04 3.51
8 21.28 0.98 22.30 0.05 4.66
9 15.17 1.01 16.28 0.10 9.67
10 23.02 1.00 23.87 ‐0.15 ‐15.16
11 21.03 1.07 22.17 0.07 6.72
12 21.09 1.01 22.15 0.06 5.59
13 20.28 1.01 21.32 0.03 3.29
14 22.63 1.02 23.73 0.08 7.42
15 21.27 0.99 22.33 0.07 7.20
16 23.34 1.01 24.45 0.09 9.33
17 21.93 1.01 23.04 0.10 10.33
18 15.16 1.11 16.37 0.10 8.97
19 23.31 1.00 24.25 ‐0.06 ‐6.02
20 29.42 1.00 30.72 0.29 29.15
21 26.69 1.00 27.60 ‐0.09 ‐8.76
22 28.28 1.00 29.46 0.18 18.08
AC 1 21.27 1.00 22.50 0.22 22.11
AC 2 27.26 1.00 28.49 0.23 22.52
5.1.2 Liquid adsorption
To investigate the quality of the AC further liquid adsorption was tested.
5.1.2.1 Iodine number
In order to evaluate the liquid adsorption of the AC the DIN 53582 standard method for determining the iodine number was used. This number corresponds to the porosity and surface area of the AC.
The more iodide adsorbed the larger porosity and surface area. A 0.04N Na2S2O3 solution was titrated with 10 ml iodine mixture containing the AC sample. The iodine mixture was prepared by taking 25 ml 0.5 N of iodine solution mixing it with approximately 0.1 g AC and filtrating it before titration. The volume of Na2S2O3 required in the titration was noted and used in the calculations. For values and results see Table 4 and to calculate the Iodine number Equation 5 was used. The solutions used are displayed in Figure 5.
Figure 5: Solutions used to determine iodine number.
( 2 2 3)
25 12 0.05 126.9044 12
Na S O
sampleAC
v Iodine number
m
⎡ ⋅ − ⋅ ⋅ ⎤
⎣ ⎦
= ⋅ Equation 5
25 = ml iodine solution
12 = ml Na2S2O3 solution used for titration of 10 ml iodine solution as reference VNa2S2O3 = ml of thiosulfate solution used for titration of 10 ml iodine mixture.
msampleAC = weight of AC sample [g]
126.9044 = molar weight of iodine [g/mol]
0.05 = iodine concentration [N]
Table 4: Results of Iodine number analysis.
Sample No.
m sample [g]
vsol [ml]
Inumber [mg/g]
1 0.10 11.20 105.65
2 0.10 10.60 180.56
3 0.11 9.80 274.88
4 0.10 9.70 298.37
5 0.10 11.10 119.93
6 0.10 9.90 274.31
7 0.10 11.10 120.42
8 0.10 10.20 233.51
9 0.10 10.45 200.10
10 0.10 10.35 212.38
11 0.10 10.10 251.42
12 0.10 9.70 305.26
13 0.10 11.00 132.99
14 0.10 9.50 325.92
15 0.10 10.45 205.10
16 0.10 10.00 260.99
17 0.10 10.20 234.89
18 0.10 9.20 362.17
19 0.10 10.30 222.28
20 0.10 8.50 456.28
21 0.10 10.45 204.69
22 0.10 8.20 501.33
AC 1 0.10 7.60 580.48
AC 2 0.10 7.90 533.98
5.2 Yield
To determine the quantity of activated carbon that was produced the yield was calculated. The activated carbon was weighed before washing away the acid, therefor this number do not show the yield of the end product. See Equation 6 for the equation that was used to calculate the yield and Table 5 for the measured values.
100 [%]
sample crucible after crucible
m m
Yield
m m
= − ⋅
− Equation 6
Table 5: Values and results in yield calculations.
Sample No.
mcrucible
[g]
mbefore
[g]
mafter
[g]
Yield [%]
1 56.25 10.01 63.35 70.88 2 56.29 10.00 61.91 56.22 3 45.87 10.00 59.81 139.40 4 45.87 10.00 57.88 120.13 5 63.47 10.00 82.77 192.95 6 68.08 10.00 78.03 99.54 7 68.41 10.00 112.64 442.34 8 68.08 10.00 99.06 309.76 9 67.80 10.00 74.29 64.87 10 63.47 10.00 68.85 53.71 11 56.26 10.00 70.36 140.96 12 63.51 10.00 75.46 119.44 13 68.13 10.00 93.62 254.86 14 68.47 10.00 77.78 93.12 15 67.80 10.00 108.40 405.96 16 68.04 10.00 98.08 300.31 17 69.06 10.00 88.23 191.75 18 58.57 10.00 72.65 140.75 19 66.43 10.00 83.23 167.98 20 68.12 10.00 81.64 135.20 21 69.05 10.00 85.35 162.99 22 58.62 10.00 72.55 139.22
5.2.1 Product yield
To calculate the yield in another manner as mentioned above the product yield was used. This is to take away the uncertainties when it comes to impurities in the samples such as remains from the acid. This was done in order to investigate if the values shown are more useful.
The crucibles and samples were weighed and placed in an oven at 600°C during three hours then the oven were cooled to room temperature and the crucibles and samples were weighed again.
Equation 7 (Rolando Zanzi, 1996) was used to calculate the product yield with values from Table 6.
The equation is based on the assumption that the inlet ash content correspond to the outlet ash content. This means that the total ash amount correspond to the ash in the activated carbon. This is not true in reality since acid is added to the ash, therefore cannot the assumption be true but in this case is it a valid approximation.
Product yeild 100 100 [%]
1 100
biomass biomass AC
biomass
a a
a a
−
= ⋅
− Equation 7
