452121 Synthesis of Immobilized Amine Sorbent Pellets from Poly (chloroprene) and Fly Ash Binders for Post-Combustion CO2 Capture

Monday, November 14, 2016
Grand Ballroom B (Hilton San Francisco Union Square)
Walter C. Wilfong1,2, McMahan L. Gray3, Brian W. Kail4,5, Bret H. Howard3, Thiago F DeAquino6 and Sabrina Estevam6, (1)National Energy and Technology Laboratory, Pittsburgh, PA, (2)Oakridge National Laboratory, Oakridge, TN, (3)U.S. Department of Energy, National Energy Technology Laboratory, Pittsburgh, PA, (4)National Energy Technology Laboratory, Pittsburgh, PA, (5)AECOM, Pittsburgh, PA, (6)Beneficent Association of the Santa Catarina Coal Association (SATC), Santa Catarina, Brazil

Synthesis of Immobilized Amine Sorbent Pellets from Poly (chloroprene) and Fly Ash Binders for Post-Combustion CO2 Capture

Walter Christopher Wilfong1, McMahan L. Gray2, Brian W. Kail3, Thiago F. De Aquino4, Bret H. Howard2, Sabrina T. Estevam4

 

1National Energy Technology Laboratory (NETL), USA, Pittsburgh, PA; Oak Ridge National Laboratory, Oak Ridge, TN

2National Energy Technology Laboratory (NETL), USA, Pittsburgh, PA

3National Energy Technology Laboratory (NETL), USA, Pittsburgh, PA; AECOM, Pittsburgh, PA

4Beneficent Association of the Santa Catarina Coal Association (SATC), Brazil, Criciúma, Santa Catarina.

            Post-combustion CO2 emissions primarily from coal-fired power plants constitute 31% of total CO2 greenhouse gas emissions, where CO2 represents 82.7% of all emitted greenhouse gases.[1] With the predicted use of coal as an energy source to continue for decades to come, it is paramount to remove these CO2 emissions in parallel with the current development of cleaner energy sources. Basic Immobilized amine sorbent (BIAS) processes are a promising technology to solve this CO2 problem. However, problems such as both the large pressure drops across tall sorbent beds and the failure of mechanical valves and conveyors due to particle agglomeration require pelletization of sorbents into larger millimeter-sized materials for practical application. Pelletization of these immobilized amine sorbents has been achieved by different methods [2, 3], including combining the sorbents with an inorganic strength additive, such as fly ash, and bonding the dry mixture with different polymer binders, namely poly (vinyl chloride) (PVC).[4] High crush strength of the FA/PVC/BIAS pellets in the study resulted from chemical interactions of a PVC polymer network with the BIAS and FA particles, where the smaller FA particles interlocked the larger BIAS particles.

            Although PVC with -Cl functional groups produced the strongest pellet of all polymers tested, these pellets degraded during semi-long (intermediate) term testing from reactions between PVC and BIAS. Therefore, an alternative chlorinated polymer is needed to produce strong and stable CO2 capture pellets. In this work immobilized amine sorbents were pelletized with a fly ash additive and poly (chloroprene) (PC, chlorinated rubber) polymer binder, which produced pellets with high attrition resistance and stable CO2 capture capacity during adsorption-desorption cycling under humid conditions.

            Pelletization of a dry mixture of FA/[ground 50 wt% ethylenimine E100 (Huntsman)/silica]-20/80 with a poly (chloroprene) polymer binder (PC) (Sigma-Aldrich, Mooney viscosity=40) was accomplished in four steps. Step 1 was preparing multiple batches of polymer binder solutions containing 10-13 wt% PC dissolved in 1,4-dioxane at 105 oC for 20-90 min. In step 2, 1.1 g of each PC solution was mixed with 1.0 g of the FA/sorbent dry mixture to form a putty-like paste, which was extruded into ropes in step 3. In step 4, the ropes were dried at room temperature for 1 hr then dried at 105oC for 1 hr. The final 1.5 to 2.5 mm diameter pellets contained 17-18 wt% FA, 10-13 wt% PC, and the balance of BIAS. CO2 adsorption of the pre-treated pellets (105oC, N2, 10 min) was performed in a thermogravimetric analyzer (TGA) with a 60 mL/min flow of 14 vol% CO2/N2 at 55oC. Figure 1 shows that slightly increasing the PC content of the pellet from 10.9 to 12.6 wt% diminished the relative CO2 uptake kinetics (normalized TGA weight profiles) and overall CO2 capture capacities from 3.20 (particle sorbent) to 1.46 mmol CO2/g (12.6 wt% PC), respectively. This reduction is attributed to pore blockage by PC. Here, PC likely interacted with the hydroxyl and amine groups of both the FA and BIAS inside the pore on the external particle surface, which imparted CO2 diffusion limitations within the pellet and blocked previously accessible amine sites of the initial particle sorbent.[4] The procedure yielding the optimum combination of strength, relatively minimal structural flaws, and good CO2 adsorption behavior (1.56 mmol CO2/g) for the 12.2 wt% PC pellet was further improved upon to give a strong pellet, FA/E100-S_(20/80)_12.2PC, with a higher CO2 capture of 1.76 mmol CO2/g capture capacity.

Figure 1: Normalized TGA weight profiles during CO2 adsorption over PC/FA/BIAS pellets containing 17-18 wt% FA and different amounts of PC. The numbers in parenthesis indicate the total CO2 capture capacity of the sorbents.

            Figure 2 (a) shows the scanning electron microscope (SEM) cross-section of the optimized FA/E100-S_(20/80)_12.2 wt% PC pellet along with energy-dispersive X-ray spectroscopy (EDS) elemental maps. These images and maps reveal that the attrition resistance/strength of the pellet is attributed to the interactions among a well-dispersed poly (chloroprene) network (Cl), and the FA (Ca, Fe, Al) and sorbent (Si) particles. The flexibility of this robust PC (chlorinated rubber)/FA/sorbent network, in contrast to the rigidity of the commercial pellets, could allow our pellets to absorb and dissipate the impact force experienced during attrition testing.

Figure 2: (a) SEM image of the FA/E100-S_(20/80)_12.2PC pellet cross section along with EDS elemental mapping of key sorbent, FA, and PC components.

            Attrition resistance of FA/E100-S (20/80)_12.2PC pellets was ascertained from 24 hour attrition testing of 2.0 g of the pellets in an in-house constructed ball mill, utilizing a 39 rpm rotating jar (D=7 cm, Vol=230 mL) affixed with a 0.5” Al baffle and filled with 46, 3/16” steel ball bearings. A <0.5 wt% attrition for our pellets was significantly smaller than attrition of two commercial silica pellets (14.5-80.0%, 1 hour) and one commercial brand zeolite 13x pellet (36.6%, 24 hour). These results suggest that flexibility of our pellets, imparted by the PC network, facilitated their high attrition resistance. Both the good CO2 capture stability of our pellets under practical conditions in the fixed-bed system and the high pellet attrition resistance make PC/FA/BIAS materials a promising candidate for larger-scale CO2 capture processes.

Figure 3: Fixed-bed reactor system loaded with the FA/E100-S_(20/80)_12.2PC pellets, along with a typical dry CO2 adsorption-desorption cycle.

            To assess the pellet performance under practical humid CO2 adsorption-desorption cycling conditions, the pellets were placed into a fixed bed reactor system illustrated in Figure 3 and were first pre-treated at 105oC in flowing N2 then cooled. In a typical cycle, CO2 was adsorbed by the pellets at 55oC from a 10% CO2/He flow for 20 min, where the adsorbed species were subsequently desorbed by flowing He at 55oC for 15 min (pressure swing desorption) and then by heating at 105oC in He for 20 min (temperature swing desorption). Two dry cycles (D1, D2) were followed by two wet cycles (~5 vol% H2O), and finally two dry cycles (D3, D4); total testing time was 13 hrs (6 hrs humid). Results of the CO2 capture tests, shown in Table 1, reveal the stability of the pellets during CO2 adsorption-desorption cycling in the presence of steam.

Table 1: Results of the fixed-bed (FB) reactor system tests on FA/E100-S (20/80)_12.2PC pellet. PCR values were calculated from the CO2 MS profiles (1 g system) and weight change (TGA) methods.

Cycle

CO2 ads.

(mmol CO2/g)

(cycle 1)

Percentage of CO2 capture retained /PCR* (%,from two-cycle averages)

Dry 1 (fresh, FB)

1.74

 

Dry 2 (fresh, FB)

1.74

Dry 3 (steam-treated, FB)

1.69

96

Dry 4 (steam-treated, FB)

1.65

Fresh/before Dry 1 (TGA)

1.78

 

Steam-treated/after Dry 4 (TGA)

1.58

88

* Calculated as, PCR=CO2 capture,steam-treated/CO2 capture,fresh x 100%.

Excellent agreement between the fresh CO2 capture of the pellets as determined from the CO2 MS profiles (fixed-bed, 1.74 mmol CO2/g) and from the TGA (1.78 mmol CO2/g) methods highlight the reliability of calculating CO2 capture capacity from the MS gas profiles. The high CO2 capture capacity of the pellets after testing (~1.67 mmol CO2/g) along with no change in the gray color of the pellet confirms the stability of the PC/FA/BIAS pellets under practical adsorption-desorption conditions. The low 8 percentage point difference in these FA/PC/BIAS pellets PCR values calculated by the CO2 MS profiles (96%) and TGA (88%) further highlights reasonably good agreement between the two CO2 capture capacity analysis methods. Overall the pellets exhibited excellent stability after 13 hrs of adsorption-desorption cycling, where exposure of the pellets to a humid environment was about 6 hrs.

References

1.         US. Environmental Protection Agency, U.S. Greenhouse Gas Inventory Report: 1990-2014. 2014.

2.         Knowles, G.P., Z. Liang, and A.L. Chaffee, Shaped polyethyleneimine sorbents for CO2 capture. Microporous and Mesoporous Materials, 2016.

3.         Rezaei, F., et al., Shaping amine-based solid CO2 adsorbents: Effects of pelletization pressure on the physical and chemical properties. Microporous and Mesoporous Materials, 2015. 204(0): p. 34-42.

4.         Wilfong, W.C., et al., Pelletization of Immobilized Amine Carbon Dioxide Sorbents with Fly Ash and Poly(vinyl chloride). Energy Technology, 2016, DOI: 10.1002/ente.201500419


Extended Abstract: File Not Uploaded
See more of this Session: Poster Session: Environmental Division
See more of this Group/Topical: Environmental Division