The preparation of activated carbon discs from tar pitch and coal powder for adsorption of CO 2 , CH 4 and N 2

Abstract

We used a pitch foaming process to prepare high surface area activated carbon discs ACD with a relatively high mechanical strength (4.3 MPa) from mixtures of tar pitch and coal powders, with potassium hydroxide as a chemical activator. The two primary parameters investigated in this study were the amount of nitric acid used in the pitch pre-treatment and the size of the coal particles (0 -53 µm, 150 -250 µm, and 355 -550 µm). The pre-treatment of the pitch was observed to be critical in the production of the carbon discs and in this study the preferred ratio of 15 M nitric acid to pitch in weight was 17/100. The coal size of 0 -53 µm produced the activated carbon discs with the highest gas adsorption capacity, which we attribute to the stabilization of the pitch foaming process. Equilibrium adsorption capacities of CO 2 , N 2 , and CH 4 on the carbons were measured by a gravimetric sorption method at pressures up to 3500 kPa. At 298 K the adsorption capacities of carbon foam disc prepared with coal particle size of 0 -53 µm and pitch pre-treated with 18 ml HNO 3 per 100 g pitch were 3.08 mol/kg N 2 , 5.48 mol/kg CH 4 and 8.88 mol/kg CO 2 at about 3500 kPa.

Effect of rheological properties of mesophase pitch and coal mixtures on pore development in activated carbon discs with high compressive strength

“…These stress-stain measurements show that although mesophase pitch to coal ratio did not have a significant effect on the density or total porosity of the KOH activated ACDs (refer to Table 2), the amount of coal added did have a strong influence on compressive strength of the discs with the compressive strength of ACDMP1C2 (56 ± 3 MPa) prepared with the highest concentration of coal particles more than twice the strengths measured for ACDMP1C1 (27 ± 1 MPa) and ACDMP2C1 (24 ± 2 MPa). In fact, as shown in Table 3 all three KOH activated MP + coal ACDs produced in this study exhibited much greater compressive strengths than similar foambased discs reported in the literature including carbon foams derived from tar pitch [28,45], mesophase pitch [27], PAA resin [26] as well as a mixture of mesophase pitch and mesocarbon microbeads [34]. To our knowledge the measured strength of 56 ± 3 MPa for ACDMP1C2 places this carbon foam among the strongest pitch or resin derived carbon foams reported in the literature, and ACDMP1C2 has a very high strength to density ratio (62 MPa·g -1 cm 3 ).…”

“…In these experiments, changing the MP : coal ratio from 1:2 to 2:1 did not have a significant effect on the skeletal density or total porosity of the ACDs. The skeletal density of each of these ACDs is within the measurement uncertainty of the skeletal densities of coal particles activated with KOH at the same furnace conditions (1.92 ± 0.24 g·cm 3 ) [43] . The bulk densities of the ACDs shown in Table 2 ) [44].…”

“…To our knowledge the measured strength of 56 ± 3 MPa for ACDMP1C2 places this carbon foam among the strongest pitch or resin derived carbon foams reported in the literature, and ACDMP1C2 has a very high strength to density ratio (62 MPa·g -1 cm 3 ). As shown in our previous study [28], introducing modifiers can be an effective method to control the carbon foam production and morphology of the resultant carbon foams. Figure 5a shows ACDMP1C2, ACDMP1C1, and ACDMP2C1 all mostly exhibit Type I features in the sorption isotherms for N2 measured at 77 K. This isotherm shape indicates these…”

“…The yields of the MP-derived ACDs were in the ranged 74.4 % to 77.1 %, and these results confirm that higher carbon yields can be obtained with MP than tar pitch. For example, in our previous studies with tar pitch and coal filler particles we obtained yields of less than 50 % in most experiments [43], with only two ACDs produced at higher yields of 59.7 % and 67.6 %. The higher yields using MP are due to the lower concentration of volatiles in MP than in tar pitch [36][37][38].…”

“…Among these precursors, several studies have shown precursors that lead to high yields of carbon foams also produce strong carbons compared to low yield precursors. [25] For example, Liu et al [26] produced carbon foams at a carbon yield of more than 80 wt% with compressive strength of In the second common approach to improve carbon foam strength, particles such as coal [28], CNTs [29][30][31], carbon nanofibers [32], clays [33], and mesocarbon microbeads [34] have been reported as foam modifiers. Kim et al [35] added fluorinated CNTs to isotropic pitch and improved the compressive strength of their foams up to 2.42±0.…”