Activated Carbons from Herbaceous Bioenergy Crops Oluwatosin Oginni and Kaushlendra Singh School of Natural Resources, West Virginia University Northeast Agricultural and Biological Engineers Conference Orono, Maine July 31 - August 3, 2016

Background

Activated carbon is an amorphous solid with large internal surface area/pore structure that absorbs molecules from both the liquid and gas phase. It is has been proven to be an effective adsorbent for the removal of a wide variety of organic and inorganic pollutants dissolved in aqueous media, or from gaseous environment, wastewater treatment and soil amendment. Biochar, a product of biomass pyrolysis due to its properties such as porosity, surface area, pore structure, volatile and carbon contents, has been identified as a precursor for activated carbon production. Activated carbon production involves activation process and it is classified into two types: Physical and Chemical Activation.

Physical Activation Chemical Activation Physical activation involves carbonization of the raw material in an inert atmosphere. Thereafter, the carbonized material is partially gasified with steam, CO2 or a mixture of both at temperatures in the range 800 – 1000 0C to form a complex array of micropores and mesopores. Chemical Activation The biochar is impregnated with chemical compounds such as KOH, H3PO4 or ZnCl2. The impregnated product is carbonized and then washed to remove the activating agent. Some possible advantages of chemical activation are: (a) simplicity, (b) good development of the porous structure and (c) easy recovery of some of the impregnated chemicals

MOTIVATION Recent studies had shown that conventional wastewater treatments are not effective to eliminate majority of the pharmaceutical active compounds. A residual quantities are found in the treated water and have been found to accumulate in drinking water. However, adsorption has become a well-established technique in removing pollutants and hence activated carbon finds an application in this area. With the abundant biomass resources available for conversion into liquid, the resulting biochars can serve as a low cost resource for production of activated carbon. In West Virginia, there are herbaceous bioenergy crops grown on reclaimed mining lands and the use of these resources for activated carbon can serve as a source of income for the plant growers

OBJECTIVE To investigate activated carbon production via chemical activation of biomass and biochar samples of two herbaceous bioenergy crops (switchgrass and miscanthus) harvested from a reclaimed mining land in West Virginia.

Batch Pyrolysis Reactor METHODOLOGY Two biomass samples (namely Switchgrass and Miscanthus) harvested from a reclaimed mining land in West Virginia were used in this study. The samples were dried and ground through a sieve of size 1.00 mm. About 50 g of the ground samples were impregnated with 200 ml of phosphoric acid (85% wt.) using a parr reactor at a temperature of 85 0C continuously stirred for 24 hours. Pyrolysis of the biomass samples were carried in a batch pyrolysis reactor at temperature of 500 0C for 30 minutes under constant flow of nitrogen. The biochar produced from the two samples were also subjected to similar impregnation. The impregnated samples were oven dried and thereafter heat-treated using thermogravimetric analyzer at 900 0C. The carbonized samples were washed using distilled water to remove the acid, oven dried for 24 hours at 103 0C and thereafter characterized. Batch Pyrolysis Reactor Parr Reactor System

Characterization of Biochar and Activated Carbon Properties Sulfur Porosity Hydrogen Nitrogen SEM Volatile Matter Proximate Analyzer Elemental surface composition (XPS) Characterization of Biochar and Activated Carbon CHNS/O Analyzer

RESULTS Fig 1: Carbon, Hydrogen, Nitrogen and Sulfur content of Biomass and Biochar Fig 2: Van Krevelen diagram of H/C and O/C atomic ratios for biomass, bio-oil and biochar The carbon content of the biochars in comparison to the parent feedstock is significantly high (p<0.05). The high carbon content of the biochars makes it a good precursor for activated carbon production (Fig 1). Biochars have a relatively low H/C and O/C ratio which depicts a high concentration of carbon which makes it a good candidate for carbon sequestration and activated carbon production.

Properties Switchgrass Miscanthus pH 7.57 + 0.18 8.44 + 0.16 Volatile (%) 16.82 + 0.64 16.69 + 1.62 Fixed Carbon 76.78 + 0.10 74.59 + 2.77 Atomic C/N 145.64 85.64 Atomic O/C 0.15 0.17 Atomic H/C 0.41 0.45 Porosity 0.83 0.85

XPS Elemental Surface Composition Carbon Oxygen Aluminum Silicon Phosphorus 74.14 18.75 1.83 1.26 4.03 % Fig 3: Activated Carbon from Impregnated Switchgrass Biochar

Carbon Oxygen Aluminum Silicon Phosphorus Iron 79.68 15.03 0.57 0.61 3.36 0.75 % Fig 4: Activated Carbon from Impregnated Switchgrass Biomass

Carbon Oxygen Silicon Phosphorus Iron 47.39 38.27 1.10 11.07 2.18 % Fig 5: Activated Carbon from Impregnated Miscanthus Biochar

Carbon Oxygen Aluminum Silicon Phosphorus 80.30 14.61 0.78 0.74 3.57 % Fig 6: Activated Carbon from Impregnated Miscanthus Biomass

SEM Micrograph of Biochar and Activated Carbons Fig 7a: SEM Micrograph of Switchgrass Biochar Fig 7b: SEM Micrograph of Activated Carbon from Impregnated Switchgrass Biochar

Fig 8a: SEM Micrograph of Miscanthus Biochar Fig 8b: SEM Micrograph of Activated Carbon from Impregnated Miscanthus Biochar

Ongoing Work Adsorption of two pharmaceutical compounds (Acetaminophen and Caffeine) using the produced activated carbons. Determination of surface area, pore size distribution, total pore volume, micropore and mesopore volume. Performance comparison of commercial activated carbon with carbon from herbaceous bioenergy crop. Techno-economic analysis of activated carbon production from herbaceous bioenergy crops harvested on reclaimed mining lands in West Virginia.

SUMMARY The low H/C and O/C ratio of the biochars compared favorably with reported lignite coal composition hence making it a good candidate for carbon sequestration and activated carbon production Impregnation and carbonization of the biomass samples yielded an activated carbon with high surface carbon, low oxygen and other minerals as compared to the activated carbons produced from the biochar. Activated carbon produced from impregnated Miscanthus biomass has the best surface elemental composition. The SEM micrographs of the activated carbons showed the amorphous nature of the carbons.

THANK YOU FOR YOUR TIME.