Preparation of Activated Carbon: Forest residues activated with Phosphoric Acid and Zinc Sulfate MSc. thesis Daniella Birbas Department of Chemical Engineering Royal Institute of Technology (KTH) Stockholm, Sweden April 2011 Preparation of Activated Carbon: Forest residues activated with Phosphoric Acid and Zinc Sulfate MSc. thesis Daniella Birbas Supervisors Rolando Zanzi Vigouroux Department of Chemical Engineering Royal Institute of Technology (KTH) Stockholm, Sweden Francisco Márquez Montesino Facultad de Forestal y Agronomia Departamento de Química Universidad de Pinar del Río ¨Hermanos Saiz Montes de Oca¨ Pinar del Río, Cuba Examiner Joaquín Martínez Department of Chemical Engineering Royal Institute of Technology (KTH) Stockholm, Sweden April 2011 2 ABSTRACT Activated carbon is a highly adsorbing material and has various scopes of uses depending on needs. It is used in many industries and applications e.g. to clean industrial wastewater, in medicine, discolor sugar and so on. What makes AC such a good adsorbent is its porous structure which gives it a high surface area. This report consists of three parts; general information about Activated Carbon (AC) and its characteristics, to give the reader a sufficient background about AC for continuous understanding throughout the report, an experimental investigation in chemical activation of carbon with phosphoric acid as the chemical reagent and sawdust from both Cuban and Swedish Pine tree as precursors, and a second experimental investigation in chemical activation of carbon with Zinc Sulfate as the chemical reagent and sawdust from Cuban Pine tree as the precursor. For the first experimental part as well as for the second the objective is how to best combine the three parameters; acid concentration, impregnation ratio and activation temperature in order to get the best adsorption performance when preparing activated carbon with different precursor specimens and chemical reagents. The experiments with phosphoric acid activation show that treatment with 40% acid concentration at 400 °C produce an activated carbon with good properties for ammonia adsorption and good iodine number. If a 30% phosphoric acid is used for activation, an activation temperature of 500 °C is recommended. With an impregnation ratio of 1, good adsorption was obtained in the activated carbon produced from Swedish pine while using Cuban pine a higher adsorption was obtained with an impregnation ratio of 2. The experiments with Zinc Sulfate activation show that influence of the sulfate concentration (between 10 % and 40 %) and temperature (between 400 °C and 500°C) on the properties for ammonia adsorption in the produced activated carbon was considerable for low impregnation ratio (0.5 and 1). In general, activation conditions of 20% zinc sulfate concentration, 400 °C and impregnation ratio: 1 are enough to produce an activated carbon with good properties for ammonia adsorption. The adsorption of carbon tetrachloride was lower. Activated carbons produced with 10 % zinc sulfate concentration, 0.5 impregnation ratio and 400 °C activation temperature (the mildest studied conditions) show already good iodine number and BET surface area. The main conclusion from the thesis work is that the optimal conditions vary widely with wanted results. Therefore a suggestion for future work is to narrow the research to fewer variables and more repetition of the samples. 3 SAMMANFATTNING Aktivt kol är ett mycket absorberande material och har många olika användningsområden beroende på behov. Det används i olika industrier och applikationer, t.ex. för att rena industriellt vatten, inom medicin, avfärga socker osv. Det som gör aktivt kol till en så bra absorbent är dess porösa struktur vilket ger det en stor ytarea. Den här rapporten består av tre delar; generell information om aktivt kol och dess egenskaper för att ge läsaren tillräckligt med bakgrund och förståelse genom hela rapporten, en experimentell undersökning i kemisk aktivering av kol med fosforsyra som reagens och sågspån från både kubansk och svensk tall som grundsubstanser, samt en undersökning i kemisk aktivering av kol med zinksulfat som kemisk reagens och kubansk tall som grundsubstans. För den första experimentella delen, såsom för den andra, så är syftet att undersöka hur man bäst kombinerar de tre parametrarna syrakoncentration, impregneringsförhållande och aktiveringstemperatur, för att få bästa möjliga prestanda vid preparering av aktivt kol med olika grundsubstanser och kemiska reagenser. Experimenten med aktivering med fosforsyra visar på att impregnering med 40-procentig syra och en temperatur på 400 °C genererar ett aktivt kol med goda egenskaper för adsorbering av ammoniak samt ett högt jodnummer. Vid användning av 30-procentig fosforsyra genererar 500 °C bäst resultat. Med impregneringsförhållandet 1 fås goda adsorberingsegenskaper för svensk tall men för kubansk tall erhålls högre adsorptionsförmåga vid impregneringsförhållandet 2. Experimenten gjorda med zinksulfat som kemisk reagens visar stora variationer i ammoniakadsorption vid låga impregneringsförhållanden (0,5-1) när sulfatkoncentrationen (10-40%) och temperatur (400-500°C) varieras. Generellt så räcker det med vid 20- procentig sulfat och 400 °C aktiveringstemperatur för en bra ammoniakadsorption. Adsorption av tetraklorid är dock lägre. Redan vid de mest milda omständigheterna (10% och 400 °C) så erhölls goda värden på jodnummer och BET ytarea. Den överhängande slutsatsen av undersökningarna är dock att optimala omständigheter varierar vitt med omständigheter och analysmetod. Därför ges också förslaget att för kommande undersökningar begränsa experimenten till färre variabler och fler repetitioner av proven. 4 ACKNOWLEDGEMENT I wish to express my sincere gratitude to my supervisor Prof. Rolando A Zanzi Vigouroux for his constant support, general guidance and 100 percent availability when I needed him. I also would like to thank Frank Marquez for administrative and organizational support as well as supervision while at The University of Pinar del Rio. Special thanks go to Frank Marquez son, also named Frank, for welcoming me at the university in Pinar and for his support throughout this project helping me with numerous things, everything from speaking Spanish to finding the fruitmarket. Of course I wish to send a huge thanks to all my newly found friends at the university who talked to me when I understood nothing, understood me when I couldn't speak and helped me with my everyday life in the fantastic country Cuba, which is so different from what I'm use to. Last but not least I would like to thank Maria Molander, who worked with me on the first experimental part of this project, for an efficient, constructive and motivating working atmosphere. 5 Contents ABSTRACT 2 SAMMANFATTNING 3 ACKNOWLEDGEMENT 4 1. INTRODUCTION 8 1.1 Objective 8 2. BACKGROUND INFORMATION 8 2.1 Activated Carbon 9 2.1.1Physical Activation 9 2.1.2Chemical Activation 9 2.1.3Structure of AC 10 2.2 Specific Reagent &Precursor 11 2.2.1Chemical Reagents 11 2.2.2Precursors 11 3. EXPERIMENTAL 12 3.1 Activation using phosphoric acid 12 3.1.1Production of AC 12 3.1.2Analysis of AC 14 3.2 Activation using zinc suphate 15 3.2.1Analysis of sawdust composition 15 3.2.2Production of AC 16 3.2.3Analysis of AC 18 4. RESULTS AND DISCUSSION 19 4.1 Activation using phosphoric acid 19 4.1.1Gas Adsorption 19 4.1.2Iodine Number 20 4.1.3Discussion 21 4.1.4Iodine Number 24 4.2 Activation using zinc sulphate 28 4.2.1Sawdust Composition 28 4.2.2Yield 28 4.2.3Gas Adsorption 29 4.2.4Iodine Number 31 4.2.5BET-Analysis 32 4.2.6Discussion . 33 5. CONCLUSIONS 43 6. CONTINUED WORK 46 6 7. REFERENCES 47 Table 1: Conditions for the experiment ...................................................................................... 13 Table 2: Preparation of the Phosphoric Acid Solution ................................................................ 13 Table 3: Calculation of amount of acid used for each impregnation ratio ................................... 14 Table 4 : Conditions for the experiment……………………………………………………………….17 Table 5 : Adsorption, Sample Set 1, 500 °C …………………………………………………………19 Table 6 : Adsorption, Sample Set 2, 400 °C …………………………………………………………19 Table 7 : Iodine number, Sample Set 1, 500 °C ……………………………………………………..20 Table 8 : Iodine number, Sample Set 2, 400 °C ……………………………………………………..20 Table 9 : Sawdust composition …………………………………………………………………….….28 Table 10 : Results from yield calculation.................................................................................... 28 Table 11 : Adsorption of ammonia during 24 hrs ……………………………………………………29 Table 12 : Difference between measurements ………………………………………………………30 Table 13 : Adsorption of CCl4 during 24 hrs …………………………………………………………30 Table 14 : Differences between measurements, 24 hrs t……………………………………………31 Table 15 : Adsorption of CCl4 after more than 24 hrs ………………………………………………31 Table 16 : Iodine number ………………………………………………………………………………32 Table 17: BET-analysis ............................................................................................................. 32 Table 18: Methods Optimizing the Activated Carbon Adsorption Capacity…………………….....43 Table 19: Highest and lowest values obtained through the experiment …………………………..45 Figure 1: Structure of graphite crystal ........................................................................................ 10 Figure 2: Structure of AC ..........................................................................................................