Pre-combustion Carbon Dioxide Capture Materials

Qiang Wang, Qiang Wang

• Publisher: Royal Society of Chemistry
• Year: 2018
• ISBN:
  9781788014922
• Edition: 1
• Topic: Technik & Maschinenbau
• Subtopic: Werkstoffwissenschaft

Using inorganic solid adsorbents/sorbents is a promising approach for carbon dioxide (CO 2 ) capture and is attracting intense attention from both academic and industrial fields.

Pre-combustion Carbon Dioxide Capture Materials presents a range of the different inorganic materials that can be used as pre-combustion CO 2 adsorbents/sorbents with specific emphasis on their design, synthesis, characterization, performance, and mechanism. Dedicated chapters cover layered double hydroxide (LDH) derived adsorbents, MgO-based adsorbents, CaO-based sorbents and alkali ceramics based sorbents.

Edited and written by world-renowned scientists in each class of CO 2 capture material, this book will provide a comprehensive introduction for advanced undergraduates, postgraduates and researchers wishing to learn about the topic.

CHAPTER 1

Layered Double Hydroxides-derived Intermediate-temperature CO₂ Adsorbents

Junya Wang^a,b, Yu Zhang^b, Naveed Altaf^b, Dermot O'Hare^c, Qiang Wang^*b

^aFaculty of Environmental Science and Engineering, Kunming University of Science and Technology, Kunming, 650500, Yunnan, P. R. China

^bCollege of Environmental Science and Engineering, Beijing Forestry University, 35 Qinghua East Road, Haidian District, Beijing 100083, P. R. China

^cChemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford OX1 3TA, UK
^*E-mail: [email protected]; [email protected]

CO₂ capture, storage and utilization (CSU) have become worldwide concerns due to an increasing awareness of the link between CO₂ accumulation in the atmosphere and global warming. Layered double hydroxide (LDH)-derived compounds (LDOs) are recognized as important intermediate-temperature (200–400 °C) CO₂ adsorbents for pre-combustion CO₂ capture, particularly for the sorption enhanced water gas shift (SEWGS) and sorption enhanced steam reforming (SESR) processes. LDOs have been investigated for decades as CO₂ adsorbents and great efforts have been devoted to improving their CO₂ capture capacities and long-term stability. In this chapter, the research progress on the performance of LDH-derived CO₂ adsorbents will be critically reviewed, including influence of the chemical composition of LDHs, synthetic conditions and methods, LDH-based composites, doping with alkali metals, other co-existing gases, the adsorption mechanism and kinetics, and techno-economic assessment. In addition, new research directions for further study will be proposed. We hope this critical chapter will not only summarize the main research activities in this area, but also shed light on future developments and possible links between fundamental studies and industrial applications, as well as give suggestions for future research efforts.

1.1Introduction

Carbon dioxide (CO₂) is a major greenhouse gas that has triggered global warming and climate change.^1–3 Over the past two centuries, its concentration in the atmosphere has rapidly increased, mainly because of human activities such as fossil fuel burning.^4–9 However, it is predicted that this trend of increasing atmospheric CO₂ concentration with not be altered within the next several decades, because fossil fuels will still be the dominant energy source. Moreover, the energy demand will increase further by 53% by 2030.¹⁰ So development of technologies for CO₂ capture and storage will become increasingly important.¹¹

Concerns about the increasing concentration of greenhouse gases in the atmosphere have stimulated the study of CO₂ capture by using solid adsorbents.^12,13 LDHs-derived mixed oxides are considered to be one of the most promising adsorbents for CO₂ capture at an intermediate-temperature range (200–400 °C), which require less energy in regeneration and show superior multicycle stability.^14,15 In addition, they show fast adsorption/desorption kinetics and good performance in the presence of water,^16–18 making them very attractive not only for pre-combustion CO₂ capture but also for applications involving CO₂ equilibria such as sorption enhanced water gas shift (SEWGS) and sorption enhanced steam reforming (SESR).^19–22

LDHs, also known as hydrotalcite-like compounds or anionic clay, are composed of stacked positively-charged brucite-like layers with interlayer spaces containing charge-compensating anions and water molecules. The metal cations occupy the centers of octahedra whose vertexes contain hydroxide ions. The octahedra are connected by edge sharing to form an infinite sheet.²³ It has the composition [M_1−x²⁺M_x³⁺(OH)₂][Aⁿ⁻]_x/n·ZH₂O, where M²⁺ and M³⁺ are divalent and trivalent cations, respectively, and Aⁿ⁻ is the anion that is intercalated in the interlayer for charge compensation.^24–28 The general structure of LDHs is shown in Figure 1.1. Because the chemical composition of both the inorganic layers and the interlayer gallery anions can be precisely controlled, LDHs possess highly tunable properties and potentially can be used in a wide range of applications, such as for catalysts, fire retardant additives, polymer–LDH nanocomposites, CO₂ capture, luminescent materials, and magnetic materials.^29–35 LDHs have been investigated for decades as adsorbents as well.^36–38 Owing to their high surface area and abundant basic sites at the surface, LDHs are considered to be favorable for adsorbing acidic CO₂.^10,39 Fresh LDHs themselves do not possess any basic sites. However, upon thermal treatment, a LDH gradually loses interlayer water; with the temperature increasing, it dehydroxylates and decarbonates to a large extent, leading to the formation of a mixed oxide with a 3D network, with a larger surface area and good stability at high temperature.^18,40 Therefore, LDHs are significantly more active for CO₂ removal after thermal decomposition, being transformed into basic mixed oxides (LDOs).¹¹

Figure 1.1Schematic structure of LDHs. In this diagram, M²⁺ and M³⁺ represent di- and tri-valent cations, which, with the –OH molecules, form the layered structure of the LDHs. The interlayer spacing is occupied with charge-compensating anions (Aⁿ⁻) and water molecules. Reproduced from Adsorption, High temperature adsorption of CO₂ on various hydrotalcite-like compounds, 14, 2008, 781–789, N. D. Hutson and B. C. Attwood, © Springer Science + Business Media, LLC 2008, with permission of Springer.

Starting from the natural mineral (MgAl–CO₃), a lot of work has been done on LDHs-derived CO₂ adsorbents, which includes (1) influence of the chemical composition of LDHs, (2) influence of the synthetic conditions and method, (3) LDH-based composites, (4) influence of doping alkali metals, (5) influence of other co-existing gases, (6) adsorption mechanism and kinetics study, and (7) techno-economic assessment etc. Although several recent review papers have provided prolific insights into the progress in this area, most previous reviews have only discussed LDHs-derived CO₂ adsorbents as a part of the papers. A detailed review focusing only on LDHs-derived compounds as CO₂ adsorbents, addressing their pros and cons, and potential applications in industry is still needed.

In this regard, the objective of this chapter is to review the currently available literature on adsorption of CO₂ on LDHs-derived compounds, focusing on the aforementioned seven parts. In addition, based on the overview, the closing section will suggest future research efforts.

1.2Influence of the Chemical Composition of LDHs

As mentioned in the introduction, LDHs are composed of stacked positively-charged brucite-like layers with interlayer spaces containing charge-compensating anions and water molecules.^41,42 They are also very open to physicochemical manipulation, numerous combinations of structural cations (Mg²⁺, Co²⁺, Cu²⁺, Ca²⁺, Fe³⁺, Al³⁺ etc.) and interlayer charge-compensating anions (Cl⁻, NO₃⁻, CO₃²⁻, HCO₃⁻, SO₄²⁻ etc.).⁴³ With a proper understanding of their composition–structure–property relationships, LDHs may conceivably be synthesized and tailored as effective high temperature adsorbents for CO₂ separation and capture. Plenty of work has been done to study how substitution of cations and interlayer charge-compensating anions affects the CO₂ adsorptive capacity of LDHs.^43,44 Yong et al.⁴⁵ first investigated the effect of Al content in commercial LDHs on their CO₂ capture capacity. The adsorption capacities of three kinds of commercial LDHs from CONDEA Chemie Gmbh company (PURAL MG30 (70% Al₂O₃), MG50 (50% Al₂O₃), and MG70 (30% Al₂O₃)) with different aluminium contents were tested at 300 °C and 1 bar. The results showed that the amounts of adsorbed CO₂ increased with a ...