Synergistic conversion of bitumen and biomass into high performance carbon materials

Abstract

A method of forming activated carbon is provided wherein bitumen, biomass, and an activating agent are combined to form a mixture and then the mixture is heated under an inert atmosphere to form activated carbon. Activated carbon materials and uses thereof are also provided.

Description

SYNERGISTIC CONVERSION OF BITUMEN AND BIOMASS INTO HIGH PERFORMANCE CARBON MATERIALSCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This paragraph is left intentionally blank.FIELD

[0002] The present disclosure relates generally to high performance carbon materials. More particularly, the present disclosure relates to the co-processing of biomass and bitumen into activated carbon.BACKGROUND

[0003] The ever-increasing demand for electricity has drawn attention toward energy storage systems (ESS). Supercapacitors (SCs) are of great attention in this regard due to their excellent power density, fast charge-discharge capability, and great cycling stability, with broad applications in hybrid vehicles and portable electronic devices. It is predicted that demand for SCs will rise to $3.5 billion by 2025.

[0004] A crucial parameter to have SC with great performance is the selection of electrode material. A vast variety of substances have been used for this purpose, including metal oxides, conductive polymers, carbide, graphene, and carbon-based materials. However, the commercialization of these materials is limited due to their high cost. Furthermore, as Schutter et al. mentioned, regular carbonaceous materials need a mass loading of more than 10 mg / cm2for an electrode in SCs, which is too thick for an electrode and ends in reducing the capacitance values. Instead, activated carbon (AC), a carbonaceous material with high surface area and tunable surface chemistry, seems to be an ideal candidate for this purpose. AC has excellent power density, long cycling stability, suitable conductivity, and tunable surface chemistry, and more importantly, is a cost-effective material.

[0005] It is, therefore, desirable to provide activated carbon materials with desirable properties.SUMMARY

[0006] It is an object of the present disclosure to obviate or mitigate at least one disadvantage of previous high performance carbon materials.

[0007] In a first aspect, the present disclosure provides a method of forming activated carbon, the method comprising: combining bitumen, biomass, and an activating agent to form a mixture; and heating the mixture under an inert atmosphere to form activated carbon.

[0008] In further aspect, the present disclosure provides an activated carbon material derived from a combination of biomass and bitumen.

[0009] In one aspect there is provided a method of forming activated carbon, the method comprising: combining bitumen, biomass, and an activating agent to form a mixture; and heating the mixture under an inert atmosphere to form activated carbon.

[0010] In one example, the activating agent is alkaline.

[0011] In one example, the activating agent is KOH.

[0012] In one example, the step of heating the mixture comprises heating the mixture at an activation temperature of about 500 °C to about 1200 °C.

[0013] In one example, the step of heating the mixture comprises heating the mixture for about 30 minutes to about 4 hours, such as for about 2 hours.

[0014] In one example, the activating agent is steam or CO2.

[0015] In one example, the activating agent is steam.

[0016] In one example, the method further comprises: pretreating the bitumen and the biomass by heating at a carbonization temperature.

[0017] In one example, the carbonization temperature is between about 550 °C and about 650 °C.

[0018] In one example, the step of heating the mixture comprises steam activation at about 1200 °C.

[0019] In one example, the activating agent is CO2.

[0020] In one example, the step of heating the mixture comprises heating the mixture at an activation temperature of about 500 °C to about 1200 °C.

[0021] In one example, the activating agent is a salt.

[0022] In one example, the activating agent is selected from the group consisting ofZnCh, KCI, NaCI, K2CO3, Na2COs, and mixtures thereof.

[0023] In one example, the activating agent is ZnCh.

[0024] In one example, the step of heating the mixture comprises heating the mixture at an activation temperature of about 500 °C to about 1200 °C.

[0025] In one example, the method further comprises: washing the activated carbon.

[0026] In one example, washing the activated carbon comprises washing sequentially with dilute HCI, hot deionized water, and then cold deionized water.

[0027] In one example, the method further comprises: drying the activated carbon after the washing step.

[0028] In one aspect, there is provided activated carbon obtained by the method described herein.

[0029] In one aspect, there is provided use of the activated carbon as described herein as an electrode.

[0030] In one aspect, there is provided use of the activated carbon as described herein as an adsorbent.

[0031] In one aspect, there is provided an activated carbon material derived from a combination of biomass and bitumen.

[0032] Other aspects and features of the present disclosure will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Embodiments of the present disclosure will now be described, by way of example only, with reference to the attached Figures.

[0034] Fig. 1 is a flowchart of steam activation process for the production of activated carbon using woody biomass.

[0035] Fig. 2 is a graph showing the survey XPS spectra and quantification of carbon products (AC007) from bitumen.

[0036] Fig. 3 is a graph showing the survey XPS spectra and quantification of carbon products (AC0112) from asphaltene.

[0037] Fig. 4 is images of SEM images of carbon product (AC007) from bitumen with different resolutions.

[0038] Fig. 5 is images of SEM images of carbon product (AC008) from biochar with different resolutions.

[0039] Fig. 6 is images of SEM images of carbon product (AC006) from the mixture with different resolutions.

[0040] Fig. 7 is a graph showing the Raman spectra of carbon products (AC006- AC010).

[0041] Fig. 8 is a graph showing the XRD pattern of carbon products (AC007 and AC005).

[0042] Fig. 9 is a schematic illustration of AC preparation from co-processing of biomass and bitumen.DETAILED DESCRIPTION

[0043] Generally, the present disclosure provides a method of forming activated carbon.

[0044] The method may include combining bitumen, biomass, and an activating agent to form a mixture, and heating the mixture under an inert atmosphere to form activated carbon.

[0045] As used herein, the term “biomass” means matter from recently living organisms. The biomass may be any organic matter that can be used for fuel. For example, the biomass may be wood, or agricultural waste.

[0046] As used herein, the term “bitumen” means a black viscous mixture of hydrocarbons obtained naturally or as a residue from petroleum distillation. The term bitumen may include coal, and asphaltene.

[0047] The activating agent may be alkaline.

[0048] The activating agent may be KOH. The activating agent may be any suitable alkaline agent, such as KOH, or NaOH. If the activating agent is alkaline, the step of heating the mixture may comprise heating the mixture at an activation temperature of about 500 °C to about 1200 °C. The activation temperature may be about 500 °C, about 550 °C, about 600 °C, about 650 °C, about 700 °C, about 750 °C, about 800 °C, about 850 °C, about 900 °C, about 950 °C, about 1000 °C, about 1050 °C, about 1100 °C, about 1150 °C, or about 1200 °C. The activation temperature may be between about 500 °C and about 600 °C, or between about 500 °C and about 700 °C, or between about 500 °C and about 800 °C, or between about 500 °C and about 900 °C, or between about 500 °C and about 1000 °C, or between about 500 °C and about 1100 °C , or between about 600 °C and about 700 °C, or between about 600 °C and about 800 °C, or between about 600 °C and about 900 °C, or between about 600 °C and about 1000 °C, or between about 600 °C and about 1100 °C, or betweenabout 600 °C and about 1200 °C, or between about 700 °C and about 800 °C, or between about 700 °C and about 900 °C, or between about 700 °C and about 1000 °C, or between about 700 °C and about 1100 °C, or between about 700 °C and about 1200 °C, or between about 800 °C and about 900 °C, or between about 800 °C and about 1000 °C, or between about 800 °C and about 1100 °C, or between about 800 °C and about 1200 °C, or between about 900 °C and about 1000 °C, or between about 900 °C and about 1100 °C, or between about 900 °C and about 1200 °C, or between about 1000 °C and about 1100°C, or between about 1000 °C and about 1200 °C, or between about 1100 °C and about 1200 °C. The step of heating the mixture may comprise heating the mixture for about 30 minutes to about 4 hours, such as about 2 hours or any suitable length of time.

[0049] The activating agent may be steam or CO2.

[0050] The activating agent may be steam. The activating agent may be CO2. If the activating agent is steam or CO2 the method may further comprise pretreating the bitumen and the biomass by heating at a carbonization temperature. The carbonization temperature may be between about 550 °C and about 650 °C. If the activating agent is steam, the step of heating the mixture may comprise steam activation at about 1200 °C. If the activating agent is CC>2, the step of heating the mixture may comprise heating the mixture at an activation temperature of about 500 °C to about 1200 °C. The activation temperature may be about 500 °C, about 550 °C, about 600 °C, about 650 °C, about 700 °C, about 750 °C, about 800 °C, about 850 °C, about 900 °C, about 950 °C, about 1000 °C, about 1050 °C, about 1100 °C, about 1150 °C, or about 1200 °C. The activation temperature may be between about 500 °C and about 600 °C, or between about 500 °C and about 700 °C, or between about 500 °C and about 800 °C, or between about 500 °C and about 900 °C, or between about 500 °C and about 1000 °C, or between about 500 °C and about 1100 °C , or between about 600 °C and about 700 °C, or between about 600 °C and about 800 °C, or between about 600 °C and about 900 °C, or between about 600 °C and about 1000 °C, or between about 600 °C and about 1100 °C, or between about 600 °C and about 1200 °C, or between about 700 °C and about 800 °C, or between about 700 °C and about 900 °C, or between about 700 °C and about 1000 °C, or between about 700 °C and about 1100 °C, or between about 700 °C and about 1200 °C, or between about 800 °C and about 900 °C, or between about 800 °C and about 1000 °C, or between about 800 °C and about 1100 °C, or between about 800 °C and about 1200 °C, or between about 900 °C and about 1000 °C, or between about 900 °C and about 1100 °C, or between about 900 °C and about 1200 °C, or between about 1000 °C andabout 1100°C, or between about 1000 °C and about 1200 °C, or between about 1100 °C and about 1200 °C.

[0051] The activating agent may be a salt.

[0052] The activating agent may be ZnCI2. The activating agent may be selected from the group consisting of ZnCI2, KCI, NaCI, K2CO3, Na2CC>3, and mixtures thereof. Activated carbon materials and uses thereof are also provided. If the activating agent is a salt, the step of heating the mixture may comprise heating the mixture at an activation temperature of about 500 °C to about 1200 °C. The activation temperature may be about 500 °C, about 550 °C, about 600 °C, about 650 °C, about 700 °C, about 750 °C, about 800 °C, about 850 °C, about 900 °C, about 950 °C, about 1000 °C, about 1050 °C, about 1100 °C, about 1150 °C, or about 1200 °C. The activation temperature may be between about 500 °C and about 600 °C, or between about 500 °C and about 700 °C, or between about 500 °C and about 800 °C, or between about 500 °C and about 900 °C, or between about 500 °C and about 1000 °C, or between about 500 °C and about 1100 °C , or between about 600 °C and about 700 °C, or between about 600 °C and about 800 °C, or between about 600 °C and about 900 °C, or between about 600 °C and about 1000 °C, or between about 600 °C and about 1100 °C, or between about 600 °C and about 1200 °C, or between about 700 °C and about 800 °C, or between about 700 °C and about 900 °C, or between about 700 °C and about 1000 °C, or between about 700 °C and about 1100 °C, or between about 700 °C and about 1200 °C, or between about 800 °C and about 900 °C, or between about 800 °C and about 1000 °C, or between about 800 °C and about 1100 °C, or between about 800 °C and about 1200 °C, or between about 900 °C and about 1000 °C, or between about 900 °C and about 1100 °C, or between about 900 °C and about 1200 °C, or between about 1000 °C and about 1100°C, or between about 1000 °C and about 1200 °C, or between about 1100 °C and about 1200 °C. The method may further include washing the activated carbon. Washing the activated carbon may comprise washing sequentially with dilute HCI, hot deionized water, and then cold deionized water. Any suitable washing sequence may be carried out. The method may further comprise drying the activated carbon after the washing step.

[0053] Activated carbon materials and uses thereof.

[0054] Herein provided is activated carbon obtained by a method herein disclosed, or an activated carbon material derived from a combination of biomass and bitumen. The activated carbon may be used as an electrode. The activated carbon may be used as an adsorbent.EXAMPLES

[0055] Example 1 : Co-processing of bitumen and biomass via alkaline activation

[0056] Highlights:(a) An innovative approach that combines two different feedstocks (biomass and bitumen, both are cheap, abundant, and low value) to generate highly valuable carbon materials.(b) Taking advantage of the strengths of both feedstocks (biomass has porous structures in nature; bitumen contributes to the carbon content; the utilization of both feedstocks synergistically leads to the production of high-quality carbon materials with a high yield.)(c) The impressive specific capacitance which makes it hold promise for its use as an electrode material in supercapacitors.

[0057] 1. 1 1ntroduction

[0058] The ever-increasing demand for electricity has drawn attention toward energy storage systems (ESS). Supercapacitors (SCs) are of great attention in this regard due to their excellent power density, fast charge-discharge capability, and great cycling stability, with broad applications in hybrid vehicles and portable electronic devices. It is predicted that demand for SCs will rise to $3.5 billion by 2025.

[0059] A crucial parameter to have SC with great performance is the selection of electrode material. A vast variety of substances have been used for this purpose, including metal oxides, conductive polymers, carbide, graphene, and carbon-based materials. However, the commercialization of these materials is limited due to their high cost. Furthermore, as Schutter et al. mentioned, regular carbonaceous materials need a mass loading of more than 10 mg / cm2for an electrode in SCs, which is too thick for an electrode and ends in reducing the capacitance values. Instead, activated carbon (AC), a carbonaceous material with high surface area and tunable surface chemistry, seems to be an ideal candidate for this purpose. AC has excellent power density, long cycling stability, suitable conductivity, and tunable surface chemistry, and more importantly, is a cost-effective material.

[0060] Different preparation methods of AC are generally divided into two categories, namely physical activation and chemical one. In the former, the carbon source initially goes through carbonization and then the obtained char is activated in the presence of H2O or CO2. In the chemical method, on the other hand, the carbonization and activation steps usuallyoccur at the same time under an inert atmosphere using a chemical agent, such as alkali metal compounds. Some advantages of the chemical method over the physical one includes lower cost and energy demand, larger surface area and higher yield of the AC product. Various chemicals have been used as the activating agent for the preparation of AC namely, ZnCh, CaCOs, K2CO3, or even the mixture of different chemicals. High fluidity as a result of a relatively low melting point, and also high reactivity which improve the surface area and other properties of AC have made KOH a widely used activating agent.

[0061] To promote the feasibility of AC for SC application, aside from the preparation method, starting material is of great importance. The carbon precursor for AC production needs to have good accessibility, be cost-effective, and be renewable. Various carbon sources have been used for AC generation up to now. Recently, shifting to renewable carbon-rich sources, such as biomass, to prepare sustainable AC has emerged as an interesting idea. Biomass is an abundant, low-cost, and eco-friendly precursor for AC, that has been recently used for SC applications. Using AC as an electrode material for SCs, directly contributes to sustainable development goals. Liu et al. used Trichoderma bridges waste biomass to produce AC with high surface area with KOH activation. They fabricated SCs with the as-prepared ACs to evaluate their capacitance properties.

[0062] Nevertheless, the yield of the obtained AC using biomass as feedstock is usually low. Bitumen, on the other hand, is an abundant low-cost natural resource, particularly in Canada where 2.8m barrels of it are produced per day based on 2017 statistics. To the best of the authors’ knowledge, the co-processing of bitumen and biomass to produce high-valued AC has never been reported previously. In fact, both are low-cost, abundant sources and the mixing strategy could result in interesting synergy as the use of bitumen could improve the yield of the product, and biomass on the other hand, can make the process greener as it is a renewable carbon source. Besides, the porous structure of the biomass can enhance the surface area and porous structure of AC.

[0063] Herein, we co-processed bitumen and biomass to produce AC via KOH activation. Different parameters, including carbon source (biomass, bitumen, and mixture of biomass and bitumen), biomass to bitumen ratio, and impregnation ratio (KOH to carbon source), were evaluated in a fixed activation temperature (800 °C). The textural analysis of obtained ACs were carried out to determine AC with the best textural properties. The optimized AC was further employed as an electrode in SC to evaluate its capacitance ability. The impressive capacitance makes AC hold promise for its use as an electrode material inSCs. The findings in this study shed new light on the production of sustainable and inexpensive AC from the co-processing of low-value precursors for energy storage applications.

[0064] 7.2 Results and Discussion

[0065] 1.2.1 Alkaline activation

[0066] The co-processing of heavy oil / bitumen with biochar (derived from biomass carbonization) to produce valuable carbon materials are conducted at 600 or 800 °C under N2 atmosphere for 2 hours, and the results are listed in Table 1. Table 1. Carbon products from the co-processing of heavy oil / bitumen with biochar under different conditions

[0067] As shown in Table 1 , more KOH favors the formation of carbon products with higher surface area but decreases the product yield. Mixing biomass with bitumen as the feedstock benefits the generation of porous structures in the final carbon products (AC005, AC006) as seen by the higher surface area and iodine number compared to the counterpart using sole bitumen (AC007) or biochar (AC008). Low yield (21 wt.%) of carbon products frombitumen is due to the high content of volatiles in bitumen (> 60 wt.%) which are carried out by N2 flow during the process. Adding biochar in bitumen could potentially capture volatiles due to the porous structures of biochar, thus leading to higher yield of products. Therefore, the mixture of biochar and bitumen benefits the yield of carbon products with high surface area. Obviously, high temperature favors the formation of carbon products with high surface area. Under optimal conditions, the surface area of carbon products could reach up to 4245 m2 / g with a yield of 31 wt.% (AC011), even using asphaltene as the feedstock, the carbon products still display high surface area and a high yield (AC012).

[0068] This process is applied to coal as the feedstock for the production of carbon materials as shown in Table 2.Table 2. Carbon products using coal as the feedstock

[0069] Higher mass ratio of KOH to coal results in a lower yield while higher surface area. Alkaline usage and temperature are critical for the formation of carbon products with high yield and high surface area.

[0070] 7.2.2 Steam and CO2 activation

[0071] Besides KOH activation, steam and CO2 are also employed as the activation agent to produce carbon products. Compared to alkaline activation, steam or CO2 activation for carbon materials production is more environmentally friendly in terms of technology implementation at a large scale, such as wastewater treatment, severe alkali corrosion at high temperatures, and agent recycling. Figure 1 shows the production of carbon materials from woody biomass using steam activation agent. Basically, the raw woody biomass is subjected to carbonization at 550-650 °C under an anaerobic environment to form biochar, then grounded into fine particles. The fine particles undergo fast steam activation at around1200 °C for less than 30 min. The obtained carbon product is characterized, and the results are listed in Table 3.Table 3. The product specifications of activated carbon

[0072] Steam activation process is free of any chemical additives and the energy requirements are fulfilled by renewable energy. Therefore, this process is considered as a carbon neutral sustainable technology.

[0073] Table 4 shows the production of carbon materials via CO2 activation at 800 °C using the mixture of woody biomass and bitumen as the feedstock. Iodine number tests shows that carbon materials from pure bitumen as the feedstock displays relatively low absorption capability as seen by the low iodine number, while carbon products using woody biomass render strong absorption ability (695 mg iodine / g). CO2 flow rate has little effect on the iodine number of carbon products.Table 4. The production of carbon materials via CO2 activation at 800 °C

[0074] Higher activation temperature could improve the iodine number as shown in Table 5. The iodine number could reach up to 1036 mg / g after 1 h of CO2 activation at 900 °C. Blending bitumen with biomass significantly improves the product yield but decreases the iodine number and surface area.Table 5. The production of carbon materials via CO2 activation at 900 °C

[0075] 1.2.3 Electrochemical performance

[0076] High carbon content and rich polycyclic aromatic hydrocarbons in petroleum asphalt, when mixed with corn cobs to prepare activated carbon, can increase the yield of activated carbon, enhance graphitization, reduce internal resistance in the material, andpromote electron transfer. Corn cobs possess a natural three-dimensional structure (tubular, honeycomb, lamellar, and network), and when mixed with petroleum asphalt to produce activated carbon, they can inherit the excellent three-dimensional structure of biomass. This results in an increased surface area, which is favorable for ion transport.

[0077] Corn cobs and petroleum asphalt are separately crushed to a particle size of40 mesh. They are then mixed in specific mass ratios in a graded manner to create composite raw materials. Potassium hydroxide (KOH) is added in a graded manner according to specific mass ratios and thoroughly mixed. The mixture is then transferred to a tube furnace and activated in a nitrogen atmosphere at a controlled temperature gradient for 1 hour. The prepared activated carbon is mixed with acetylene black and polytetrafluoroethylene in a mass ratio of 8:1:1, with the addition of ethanol to form a slurry. The slurry is uniformly coated onto a nickel foam current collector and subsequently compressed using a press. The components are assembled in the following order: electrode plate - separator - electrode plate, to create a two-electrode system. Additionally, an electrode plate - Pt electrode - Hg / HgO electrode is assembled in this order to create a three- electrode system for testing electrochemical performance.Table 6. The electrochemical performance of carbon products under various conditions

[0078] As shown in Table 6, carbon products produced via KOH shows ultrahigh surface area (>3500 m2 / g) under optimal conditions (Activation temperature of 750-800°C, mass ratio of KOH / feedstock: 3-4, and mass ratio of biomass / bitumen: 1:1). However, the yield is low (~20 wt.%). The electrochemical performance evaluation of various carbon products revealed their excellent specific capacitance (>450 F / g), surpassing most reported values for AC used as electrode materials in supercapacitors. This suggests that our carbon products have the potential to be high-performance materials for energy storage applications.

[0079] 7.2.4 Characterizations

[0080] Various solid sample characterizations are performed including N2 physisorption for specific surface area and pore size distribution according to BET method,Raman and X-Ray Diffraction (XRD) for phase structures, Scanning Electron Microscopy (SEM) for morphology observation, and elemental analysis with X-ray Photoelectron Spectroscopy (XPS) for the chemical composition. Table 7 shows the elemental analysis of carbon products from different feedstocks via KOH activation. KOH activation under N2atmosphere gives the good quality of carbon products with less impurities (~ 94 C wt.%), while KOH activation under aerobic environment results in more impurities or oxygencontaining chemicals (< 60 C wt.%) in the final carbon products. There is trace S or N in carbon products from both activation processes.Table 7. Elemental analysis for carbon products under different conditions

[0081] The survey spectra and quantification by XPS are conducted for carbon products from bitumen (Figure 2) and asphaltene (Figure 3). Both show the high carbon content. Compared to elemental analysis, C content is underestimated by XPS because it is a surface sensitive technique (depth< 5 nm).

[0082] The morphology of carbon products is observed by SEM as shown in Figure 4 and Figure 5. SEM images clearly show that more amorphous structures are observed on carbon materials from bitumen (Figure 4) and more regular porous structures are observed on carbon materials from biochar (Figure 5). Mixing biochar with bitumen benefits the formation of more regular porous structures in the carbon products as seen by SEM images in Figure 6.

[0083] Raman and XRD analyses of carbon products are shown in Figure 7 and 8, respectively. As shown in Figure 7, more bitumen favors the production of carbon materialswith more amorphous carbon and defective sites. High temperature benefits the formation of carbon products with graphitic structure using biochar but leads to carbon products with more disordered or amorphous structure using bitumen. Undoubtedly, XRD (Figure 8) shows the amorphous nature of carbon material which is the major portion of carbon products.

[0084] 1.2.5 Comparison of carbon products with other competitors

[0085] The proposed process produces high performance carbon materials with BET surface area more than 4,000 m2 / g, pore volume up to 2.6 cm3 / g and trace impurity content. These highly impactful properties provide significantly higher performance when carbon products are used in various energy storage systems, and environmental, agricultural, and pharmaceutical applications. Table 8 shows how our carbon product stacks up against the competitors. Our carbon products have higher surface area and better gravimetric capacitance.Table 8. The comparison between our carbon products with competitorsFor competitors' products, the data are obtained from the website at Imps:in diisTries.com asac-teclmolosv (access date: 2022-04-19).

[0086] Example 2: Co-processing of bitumen and biomass via salt activation

[0087] Highlights:• Activated carbon with a high surface area was successfully obtained through co-processing of biomass and bitumen.• The source of raw material and process parameters played crucial roles in determining the textural properties of the activated carbon. • Among different process parameters, activation temperature and impregnation ratio were the most effective parameters affecting activated carbon characteristics.• When biomass is used as the sole feedstock, remarkable results were achieved, with a large surface area of 1854 m2 / g and a product yield of 30%.• When biomass is co-processed with bitumen, with the feedstock ratio of 4:1 (biomass to bitumen) and the impregnation ratio of 3:1 (ZnCh to carbon source), activated carbon with a high surface area of 1371 m2 / g and a total pore volume of 1.266 cm3 / g with the product yield of 46-50% was obtained.

[0088] 2. 1 1ntroduction

[0089] Activated carbon (AC) is a carbonaceous material with a large surface area, high porosity, and excellent surface reactivity that can be used as an adsorbent for liquid and gas purification. The most critical parameter for AC is the pore structure, namely the surface area and pore volume and size. AC with higher surface area and larger pore volume has an enhanced adsorption capacity. The textural and surface properties of ACs highly depend on the source of raw material and the activation method. Previously, AC was produced from coal due to its high availability. However, producing AC from coal is so costly. Nowadays, several low cost and abundant carbon sources with high carbon content are used to produce AC. The potential of different waste materials to produce low-cost AC have been studied recently. In this regard, biomass are potential sustainable precursors to produce AC.Biomass is rich in carbon and can be readily found at a low cost. It is waste material that has found new applications today. However, it is essential to note that the intended final use of activated carbon (AC) is crucial in determining the appropriate preparation method for AC.

[0090] Both physical and chemical methods are used to produce AC. In the physical activation method, raw materials are carbonized first, followed by the gasification of the resulting char. In the chemical activation method, both carbonization and activation steps are combined in a single stage. The chemical activation method takes priority as it operates at lower temperatures by introducing a chemical agent. Alkaline activation, typically using agents like KOH or NaOH, yields activated carbon (AC) with exceptionally high surface areas (>2000 m2 / g) but lower overall yields (<30%), making it suitable for applications prioritizing surface area and adsorption capacity. In contrast, salt activation with agents like ZnCh results in AC with a good surface area (<2000 m2 / g), though lower than alkaline activation, but offers higher product yields (>30%), making it a cost-effective choice for applications where a balance between surface area and yield is required. ZnCh is the most used salt agent in AC production because ZnCh can act as a Lewis acid and serves as a dehydration agent to remove hydrogen and oxygen from the biomass source, preventing the formation oftar and facilitating the development of a porous structure. Various biomasses, such as cherry stones, peach stone, paper mill sludge, kraft lignin, were used to produce AC with ZnCh. Besides, bitumen is considered as a cost-effective precursor for the production of AC. Bitumen is a viscous, adhesive, and involatile substance that is present either naturally (in oil sands and tar sands) or can be produced through crude oil refining as a residual of distillation process. According to Canada Energy Regulator report, this contaminant-heavy end of the crude oil scale and has the potential to create serious corrosion problems due to its corrosive nature.

[0091] Producing activated carbon (AC) from low-cost carbon sources like bitumen and biomass is an intriguing endeavor. To the best of our knowledge, there have been no previous studies conducted on this emerging topic. However, some research efforts have produced AC from asphaltene particles, oil sands bitumen and petroleum residues, Athabasca oilsands bitumen, oil sands coke, and bituminous coals. In this study, a mixture of bitumen and biomass was selected as precursors to produce AC. Various salts were utilized as the activation agent to enhance surface area and yield. Among these agents, ZnCh yielded the highest surface area. This work offers new insights into the co-processing of biomass and bitumen, enabling the production of AC with enhanced surface area and high yield.

[0092] 2.2 Activated carbon production

[0093] Bitumen and / or biomasses (Aspen, Hemp, Straw) were used as raw materials to produce AC. A schematic illustration of AC preparation is depicted in Figure 9.

[0094] In the typical process, bitumen and biomass with various mass ratios were thoroughly blended with ZnCh, and the resulting mixture was loaded into a stainless-steel reactor for activation. After purging the air from the reactor, the mixture was heated to the activation temperature (500, 600, 700, and 800°C) with a heating rate of 10°C / min under a nitrogen atmosphere flowing at a rate of 50 ml / min. Once the target temperature was reached, it was held for 2 hours. Subsequently, the mixture was cooled to room temperature and subjected to several rounds of washing, involving a sequence of dilute HCI, hot deionized water, and cold deionized water. Then, the samples were dried in an oven at 110°C overnight.

[0095] 2.3 Characterizations

[0096] The elemental analysis of bitumen and biomass was carried out to determine the content of C, H, N, S and O. The thermogravimetric analysis (TGA) was carried out tomeasure the ash content. The textural properties of samples were estimated by N2 adsorption / desorption analysis, and the BET (Brunauer, Emmett and Teller) theory, BJH method, and t-plot approach were employed to determine the surface area, the total pore volume, and macro pore volume, respectively, lodin number (IN) analysis was carried out according to standard ASTM D 4607 procedure. Briefly, a standard iodine solution was prepared by mixing 12.7g of iodine and 19.1g of potassium iodide (KI). DI water was added dropwise while continuously stirring until the total volume of 50 ml. The solution remained constant for 4 h to ensure all the crystals were dissolved and then DI water was added to reach the total solution volume of 1 L. The prepared solution should be stored in an amber bottle. A titration solution was also prepared by dissolving 24.820 g sodium thiosulfate in 75 DI water. Then, 0.1 g sodium carbonate is added to minimize the bacterial decomposition of thiosulfate solution. The solution was diluted with DI water to 1 L. For IN measurement, the obtained AC was well grinded. Then, 100 mg of powdered AC was mixed vigorously with prepared iodine solution for 30 s and filtered immediately. The filtrate was titrated with the as- prepared 0.1 N sodium thiosulfate solution until the color changes to pale yellow. 2 mL of starch indicator solution was added, and the titration was continued until obtaining a colorless solution. IN was calculated based on the used volume of sodium thiosulfate.

[0097] 2.4 Results and discussion

[0098] 2.4. 1 Effect of activation temperature

[0099] The effect of activation temperature on AC production were tested using pure bitumen, and the results are summarized in Table 9. The results indicate that activated carbons (ACs) derived from pure bitumen exhibit poor structural characteristics, featuring BET surface areas below 500 m2 / g and iodine numbers (IN) lower than 1000 mg / g. However, they demonstrate a high product yield, exceeding 40%. It is worth noting that raising the activation temperature from 500 to 600 °C resulted in an increase in the BET surface area from 390 to 486 m2 / g. This improvement in surface area can be attributed to the more effective removal of non-carbon components from the matrix structure at higher temperatures, consequently enhancing the material's overall porosity. Nevertheless, a further increase in activation temperature, going from 600 to 800 °C, negatively impacted the quality of the activated carbon (AC) products, particularly in terms of surface area and iodine number (IN). This adverse effect could be attributed to factors such as heat shrinkage and the swelling effect of ZnCh, which transforms micropores into mesopores. This transformation is evident in the reduced presence of micropores and total pore volume withincreasing temperature. Therefore, the activation temperature is optimized to be 600 °C for further investigations.Table 9. Effect of carbonization temperature on characteristics of activated carbon

[0100] 2.4.2 Effect of carbon source

[0101] The choice of an appropriate carbon source is another consideration in shaping the texture and porosity of the resulting carbon materials. Bitumen and three commonly used biomass (Straw, Hemp, and Aspen) are employed to prepare AC. The elemental analysis of these different carbon sources is provided in Table 10, showing that bitumen has a carbon content of 84.56%, nearly double that of biomass, while biomass has higher oxygen content, as expected.Table 10. Elemental composition of carbon source

[0102] As shown in Table 11, the yield of AC obtained from biomass was lower than that from bitumen, falling below 40%. The lower yield from biomass is attributed to the fact that biomass has a lower carbon content (<50%) compared to bitumen (>80%), as illustratedin Table 10. However, AC products derived from biomass display superior porous structures, characterized by their higher surface area (>1200 m2 / g) and IN (>1000 mg / g). The enhanced porous structure of biomass derived AC is attributed to the presence of rich oxygencontaining functional groups in biomass. Under the facilitation of ZnCh as the activation agent, ZnCh acts as dehydration agent and converts these oxygen-containing functional groups into water through deoxygenation reaction. The formed water reacts with the ZnCh to form hydroxy dichlorozincic acid (HDA) as indicated in reaction (1). HDA is corrosive and possesses an etching effect that promotes the formation of porous structures. Additionally, ZnCh can react with oxygen-containing functional groups (-OH) to form ZnO through the reaction (2). The produced ZnO particles remains in cavities, contributing to additional porosity in the internal structure when ZnO is removed.ZnCl + H;o -> H [ZnCl: (OH)] (1)ZnC12 + -OH ZnO + HC1 (2)Therefore, a combination of biomass and bitumen as the carbon source is employed to produce AC. This approach offers the advantage of benefiting from the high yield typically associated with bitumen and, simultaneously, taking advantage of the enhanced surface area resulting from the presence of oxygen functional groups in biomass. Aspen was chosen as the biomass carbon source because it exhibited both a high surface area and a good yield among the various biomass materials that were tested.Table 11. Effect of carbon source on characteristics of activated carbon

[0103] 2.4.3 Effect of activation agent

[0104] A variety of salts, including ZnCh, KHCO3, NaHCC , K2CO3, and a eutectic mixture of KCI and ZnCh with a molar ratio of 51 :49, were evaluated to assess the impact of the salt activation agent on AC production. As shown in Table 12, compared to ZnCh, using KHCO3 or K2CO3 as the chemical agent shows the similar performance on the generation of porous structures but with a lower product yield. This can be attributed to the decomposition of KHCO3 or K2CO3, leading to the formation of KOH, which exhibits a higher etching effect. On the other hand, NaHCOs produces AC with a lower surface area compared to KHCO3, likely due to the fact that KOH activation tends to create more micropore structures than NaOH (derived from NaHCOs decomposition) activation. Additionally, it's worth noting that, compared to carbonates or bicarbonates, ZnCh is easier to recycle and regenerate.Therefore, ZnCh is selected as the preferred activation agent due to its lower cost, reduced environmental impact, and ease of recycling and reuse.Table 12. Effect of chemical reagent on characteristics of activated carbon

[0105] 2.4.4 Effect of mass ratio of activation agent to carbon source

[0106] The mass ratio of the activation agent to the carbon source is a critical factor affecting the porosity and surface area of AC. As presented in Table 13, when using biomass (Aspen) as the sole carbon source for AC production, it is observed that increasing the mass ratio of ZnCh (the activation agent) to Aspen from 1 :1 to 2:1 leads to a significant enhancement in the BET surface area of AC. The BET surface area improves from 1245 to1854 m2 / g. This improvement can be attributed to the release of tar within the cross-linked framework of the activation agent at a higher impregnation ratio. However, further adding more ZnCh, leading to a higher mass ratio, results in a decrease in the surface area from 1854 to 1177 m2 / g. This phenomenon is likely due to the swelling effect induced by ZnCh, which subsequently reduces the formation of micropores. The optimized mass ratio of ZnCh to Aspen is determined to be 2:1. In the case of a mixture of bitumen and Aspen as the carbon source, achieving a high surface area necessitates a higher proportion of ZnCh to create porous structures from bitumen. Therefore, the optimal mass ratio of ZnCh to mixture in this scenario is 3:1.Table 13. Effect of salt to feedstock mass ratio on characteristics of activated carbon

[0107] 2.4.5 Effect of mass ratio of biomass to bitumen in carbon source

[0108] As discussed in Section 2.4.2, the presence of oxygen-functional groups in biomass is crucial for the production of AC with high surface area when using ZnCh as the chemical agent. The proportion of biomass in the mixed feedstock has a significant impact on both surface area and yield of AC. As shown in Table 14, a lower proportion of biomass in the mixture results in AC products with a reduced surface area but a higher yield.Conversely, due to the lower carbon content in biomass, a higher proportion of biomass in the mixture leads to AC products with a lower product yield but a higher surface area. Toattain both a high surface area and a good yield, the optimal mass ratio of biomass to bitumen is determined to be 4:1.Table 14. Effect of Biomass / Bitumen ratio on characteristics of activated carbon

[0109] 2.4.6 Effect of activation time

[0110] The impact of carbonization time was also investigated, as it is a crucial parameter influencing the energy consumption in the process. As demonstrated in Table 15, an activation duration of 30 min yielded the highest surface area (1371 m2 / g). Notably, by reducing the activation time from 120 min to 30 min, a significant increase in surface area (16.58%) and iodine number (IN) (9.19%) was achieved. This finding is consistent with prior research, where several studies have indicated that extending the activation time results in a decrease in AC surface area. This outcome is typically attributed to the cracking and collapse of pores due to prolonged heating.Table 15. Effect of reaction duration on characteristics of activated carbon

[0111] 2.5 Conclusion

[0112] In summary, the optimized activation conditions for co-processing bitumen and biomass to produce activated carbon (AC) are as follows: ZnCh as the activation agent, an activation temperature of 600 °C, a mass ratio of the activation agent to carbon source of 3:1 , a mass ratio of biomass to bitumen in the mixture as the carbon source of 4:1, and an activation time of 30 min. Repeated experiments, as shown in Table 16, demonstrate that AC products obtained from the co-processing of bitumen and biomass under these optimized conditions have a BET surface area of 1167 ± 82 m2 / g with a yield of 45 ± 3%, while AC products obtained from a sole biomass source have a BET surface area of 1608 ± 102 m2 / g with a yield of 31 ± 3%.Table 16. Repeated experiments under optimized conditions

[0113] The embodiments described herein are intended to be examples only.Alterations, modifications and variations can be effected to the particular embodiments by those of skill in the art. The scope of the claims should not be limited by the particular embodiments set forth herein, but should be construed in a manner consistent with the specification as a whole.

[0114] All publications, patents and patent applications mentioned in this Specification are indicative of the level of skill those skilled in the art to which this invention pertains and are herein incorporated by reference to the same extent as if each individual publication patent, or patent application was specifically and individually indicated to be incorporated by reference.

[0115] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modification as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. A method of forming activated carbon, the method comprising: combining bitumen, biomass, and an activating agent to form a mixture; and heating the mixture under an inert atmosphere to form activated carbon.

2. The method of claim 1 , wherein the activating agent is alkaline.

3. The method of claim 2, wherein the activating agent is KOH.

4. The method of claim 2 or 3, wherein the step of heating the mixture comprises heating the mixture at an activation temperature of about 500 °C to about 1200 °C.

5. The method of any one of claims 2 to 4, wherein the step of heating the mixture comprises heating the mixture for about 30 minutes to about 4 hours, such as for about 2 hours.

6. The method of claim 1 , wherein the activating agent is steam or CO2.

7. The method of claim 6, wherein the activating agent is steam.

8. The method of claim 7, wherein the method further comprises: pretreating the bitumen and the biomass by heating at a carbonization temperature.

9. The method of claim 8, wherein the carbonization temperature is between about 550 °C and about 650 °C.

10. The method of any one of claims 7 to 9, wherein the step of heating the mixture comprises steam activation at about 1200 °C.

11. The method of claim 6, wherein the activating agent is CO2.

12. The method of claim 11, wherein the step of heating the mixture comprises heating the mixture at an activation temperature of about 500 °C to about 1200 °C.

13. The method of claim 1 , wherein the activating agent is a salt.

14. The method of claim 13, wherein the activating agent is selected from the group consisting of ZnCh, KCI, NaCI, K2CO3, Na2COs, and mixtures thereof.

15. The method of claim 14, wherein the activating agent is ZnCh.

16. The method of any one of claims 13 to 15, wherein the step of heating the mixture comprises heating the mixture at an activation temperature of about 500 °C to about 1200 °C.

17. The method of any one of claims 13 to 16, wherein the method further comprises: washing the activated carbon.

18. The method of claim 17, wherein washing the activated carbon comprises washing sequentially with dilute HCI, hot deionized water, and then cold deionized water.

19. The method of claim 17 or 18, wherein the method further comprises: drying the activated carbon after the washing step.

20. Activated carbon obtained by the method according to any one of claims 1 to 18.

21. Use of the activated carbon according to claim 20 as an electrode.

22. Use of the activated carbon according to claim 20 as an adsorbent.

23. An activated carbon material derived from a combination of biomass and bitumen.

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