Optimization of CO2 Sorption onto Spent Shale with Diethylenetriamine (DETA) and Ethylenediamine (EDA)

Abstract

A novel technique was employed to optimize the CO₂ sorption performance of spent shale at elevated pressure-temperature (PT) conditions. Four samples of spent shale prepared from the pyrolysis of oil shale under an anoxic condition were further modified with diethylenetriamine (DETA) and ethylenediamine (EDA) through the impregnation technique to investigate the variations in their physicochemical characteristics and sorption performance. The textural and structural properties of the DETA- and EDA- modified samples revealed a decrease in the surface area from tens of m²/g to a unit of m²/g due to the amine group dispersing into the available pores, but the pore sizes drastically increased to macropores and led to the creation of micropores. The N-H and C-N bonds of amine noticed on the modified samples exhibit remarkable affinity for CO₂ sequestration and are confirmed to be thermally stable at higher temperatures by thermogravimetric (TG) analysis. Furthermore, the maximum sorption capacity of the spent shale increased by about 100% with the DETA modification, and the equilibrium isotherm analyses confirmed the sorption performance to support heterogenous sorption in conjunction with both monolayer and multilayer coverage since they agreed with the Sips, Toth, Langmuir, and Freundlich models. The sorption kinetics confirm that the sorption process is not limited to diffusion, and both physisorption and chemisorption have also occurred. Furthermore, the heat of enthalpy reveals an endothermic reaction observed between the CO₂ and amine-modified samples as a result of the chemical bond, which will require more energy to break down. This investigation reveals that optimization of spent shale with amine functional groups can enhance its sorption behavior and the amine-modified spent shale can be a promising sorbent for CO₂ sequestration from impure steams of the natural gas.

Keywords: amine modification; chemisorption; empirical model; enhanced sorption; physisorption; spent shale.

Figure 1

A schematic diagram of the volumetric sorption measurement setup.

Figure 2

Impact of pyrolysis on the mineralogical content of the shale samples. L–R (USQ 06, USM 3, USM 05, and US 6), Cl = clay, Q = quartz, F = feldspar, P = pyrite, and C = carbonate minerals.

Figure 3

Impact of various treatments on the N₂ Isotherm curves of Raw shale (a–d), Spent shale (e–h), DETA-modified spent shale (i–l), and EDA-modified spent shale (m–p).

Figure 4

Changes in microfabric of shale after treatments. Raw shale (a–d), Spent shale (e–h), DETA-modified spent shale (i–l), and EDA-modified spent shale (m–p) at 200 nm resolution and 30 kx magnification.

Figure 5

Appearance of new functional groups after the pyrolysis and amine treatments of samples (a) USQ 06, (b) USM 03, (c) USM 5, and (d) US 6.

Figure 6

CO₂ desorption sites at maximum temperature observed on Raw shale (a–d), spent shale (e–h), DETA-modified spent shale (i–l), and EDA-modified spent shale (m–p).

Figure 7

The thermal stabilities of Raw shale (a–d), spent shale (e–h), DETA-modified spent shale (i–l), and EDA-modified spent shale (m–p) at up to 900 °C.

Figure 8

Amount of CO₂ sorbed relative to the pyrolysis and amine treatments at temperatures 30 °C (a–d), 50 °C (e–h), 70 °C (i–l), and up to 8 MPa pressure.

Figure 9

Changes in the CO₂ sorption capacity of each sample after various treatments.

Figure 10

Prediction of the sorption behavior of USQ 06 variants with Isotherm models at temperatures 30 °C (a–d), 50 °C (e–h), 70 °C (i–l), and up to 8 MPa pressure.

Figure 11

Prediction of the sorption behavior of USM 3 variants with Isotherm models at temperatures 30 °C (a–d), 50 °C (e–h), 70 °C (i–l), and up to 8 MPa pressure.

Figure 12

Prediction of the sorption behavior of USM 05 variants with Isotherm models at temperatures 30 °C (a–d), 50 °C (e–h), 70 °C (i–l), and up to 8 MPa pressure.

Figure 13

Prediction of the sorption behavior of US 6 variants with Isotherm models at temperatures 30 °C (a–d), 50 °C (e–h), 70 °C (i–l), and up to 8 MPa pressure.

Figure 14

The prediction of sorption rate mechanism on USQ 06 variants at 30 °C (a–d), 50 °C (e–h), and 70 °C (i–l).

Figure 15

The prediction of sorption rate mechanism on USM 3 variants at 30 °C (a–d), 50 °C (e–h), and 70 °C (i–l).

Figure 16

The prediction of sorption rate mechanism on USM 05 variants at 30 °C (a–d), 50 °C (e–h), and 70 °C (i–l).

Figure 17

The prediction of sorption rate mechanism on US 6 variants at 30 °C (a–d), 50 °C (e–h), 70 °C (i–l), and up to 8 MPa pressure.

Figure 18

Van ‘t Hoff plots based on the CO₂ sorbed on Raw shale (a–d), Spent shale (e–h), DETA-modified spent shale (i–l), and EDA-modified spent shale (m–p).