Energy Saving Approach to Chemical Processing of Lignocellulosic Feedstock into Sorptive Materials

load 120 Wt . min/(g . mL) is 1085 m 2 /g. Total pore volume reaches almost 0,7 cm 3 /g. Pore size distributions indicates that carbons consists of micropores (0.9–1.1 nm) and mesopores with size 4 nm. Obtained carbons have high adsorption capacity towards copper ions from aqueous solutions at pH (cid:5) 4. The results proved that this process is rapid, power-efficient and economic. Bibl. 10, Fig. 3, Tab. 1.

bon yield) improved when these parameters were enhanced up to their optimum points, and then these properties decreased when these parameters were increased beyond their optimum values.
Current study was focused on the processing of lignocellulosic feedstock -dogwood stone into sorptive materials using microwave-assisted phosphoric acid activation.
Dogwood stone was grounded and sieved to obtain particle size 1.0-2.0 mm. 5 g of dried dogwood stone was impregnated with 50 mL of phosphoric acid solution with concentration adjusted to obtain desired impregnation ratio and stayed during 30 min. The microwave-induced activation treatments were conducted in a multi-mode type microwave furnace Zelmer 29Z023. Total microwave energy delivered to sample (microwave load) was 74 % of maximum power and time of irradiation was 1, 2, 3 and 5 min. After the treatment, the residual phosphoric acid was eliminated from carbon by extensive washing with hot water in Soxhlet extractor until neutral pH of wash water.
Information on carbons pore structure was derived from nitrogen adsorption isotherms obtained at -196°C on a NOVA 2200 apparatus (Quantachrome, USA). The pore size and pore size distribution were calculated by the BJH model using desorption isotherm branch. The adsorption isotherms were determined in a conventional high accuracy volumetric adsorption rig. Prior to the measurement the samples were outgassed at 180°C under vacuum for 2 h. Activated carbons were obtained under microwave irradiation using different amount of phosphoric acid which is presented as ra-

Energy Saving Approach to Chemical Processing of Lignocellulosic Feedstock into Sorptive Materials
High porous activated carbons were prepared by microwave-induced phosphoric acid activation of lignocellulosic raw material. It was established that the parameters of porous structure of carbons obtained are increased with increasing of treatment duration and reach maximum under 3-5 min staying. Maximum BET surface area achieved during the microwave treatment with energy load 120 Wt . min/(g . mL) is 1085 m 2 /g. Total pore volume reaches almost 0,7 cm 3 /g. Pore size distributions indicates that carbons consists of micropores (0.9-1.1 nm) and mesopores with size 4 nm. Obtained carbons have high adsorption capacity towards copper ions from aqueous solutions at pH £ 4. The results proved that this process is rapid, power-efficient and economic. Bibl. 10, Fig. 3, Tab. 1. Key words: microwave-induced energy, phosphoric acid activation, lignocellulosic feedstock, surface area.
tio of introduced acid to sample weight. Two impregnation ratio (IR) were applied: 0.9 and 1.7. Threshold of microwave effect on development of porosity is about 40 W . min/(g . mL) for all experiments with phosphoric acid. Maximum BET surface area is achieved at 120 W . min/(g . mL) with slight decrease at higher energy delivered to the sample. Increasing impregnation ratio from 0.9 to 1.7 increases BET surface area by about 100-150 m 2 /g. Maximum BET surface area is achieved during 3-5 min of microwave treatment at 74 % of maximum power provided by microwave furnace. While the value of BET surface area of microwave-activated carbons (1085 m 2 /g) is less than that for conventionally heated carbon (2070 m 2 /g) [9], microwave-assisted activation is much faster and needs less energy than conventional heating.
Carbon obtained by microwave-assisted phosphoric acid activation with treatment duration of 1 min does not show any significant nitrogen adsorption in entire relative pressure region that indicates negligible development of porous structure (Fig.1).
Under increasing of treatment duration up to 2 min nitrogen adsorption firstly sharply increases. Under following increasing up to 3, 5 min it almost doesn't vary. Nitrogen adsorption isotherms obtained with treatment duration of 2, 3, 5 min belong to a mixed type of IUPAC classification [10]. The initial part of the isotherms is of type I with significant uptake at low relative pressures, which corresponds to adsorption in micropores. At intermediate and high relative pressures the isotherms are of type IV with a hysteresis loop of type H4 associated with monolayer-multilayer adsorption followed by capillary condensation in narrow slit-like pores. The parameters of porous structure of carbons obtained by microwave-assisted phosphoric acid activation (Table) are increased with increasing of treatment duration and reach maximum under 3min staying -1085 m 2 /g. Total pore volume reaches almost 0,7 cm 3 /g. The results proved that this process is rapid, efficient and economic. Porous structure of microwave-activated carbons is presented of micropores (0.9-1.1 nm) and mesopores of with size 4 nm (Fig.2).

The parameters of porous structure of carbons obtained with microwave-induced phosphoric acid activation
Increasing impregnation ratio from 0.9 to 1.7 develops additional larger mesopores with size 5-11 nm. Porous structure of conventionally heated carbon is different in that main mesopore size is 2.3 nm.
Large amount of surface groups of acid character are responsible for adsorption properties towards copper ions from aqueous solutions. 0.1 g of carbon was shaken with 20 mL of 0.001 M   Carbons obtained with microwave-assisted phosphoric acid activation (Fig.3) demonstrate high adsorption capacity at pH £ 4 as compared to ion exchange resin with carboxylic groups (KB-4). With increasing microwave load copper adsorption increases. The highest adsorption shows conventionally heated carbon.

Conclusions
Large surface area activated carbons were prepared by microwave-assisted phosphoric acid activation. It was established that the parameters of porous structure of carbons obtained are increased with increasing of treatment duration and reach maximum under 3-5 min staying. Maximum BET surface area achieved during the microwave treatment with energy load 120 W . min/(g . mL) is 1085 m 2 /g. Total pore volume reaches almost 0,7 cm 3 /g. Pore size distributions indicates that carbons consists of micropores (0.9-1.1 nm) and mesopores with size 4 nm. Obtained carbons have high adsorption capacity towards copper ions from aqueous solutions at pH £ 4. The results proved that this process is rapid, efficient and economic.