Permeability and Stability of Hydrophobic Tubular Ceramic Membrane Contactor for CO2 Desorption from MEA Solution

Ceramic membrane contactors hold great promise for CO2 desorption due to their high mass transfer area as well as the favorable characteristics of ceramic materials to resist harsh operating conditions. In this work, a hydrophobic tubular asymmetric alpha-alumina (α-Al2O3) membrane was prepared by grafting a hexadecyltrimethoxysilane ethanol solution. The hydrophobicity and permeability of the membrane were evaluated in terms of water contact angle and nitrogen (N2) flux. The hydrophobic membrane had a water contact angle of ~132° and N2 flux of 0.967 × 10−5 mol/(m2∙s∙Pa). CO2 desorption from the aqueous monoethanolamine (MEA) solution was conducted through the hydrophobic tubular ceramic membrane contactor. The effects of operating conditions, such as CO2 loading, liquid flow rate, liquid temperature and permeate side pressure, on CO2 desorption flux were investigated. Moreover, the stability of the membrane was evaluated after the immersion of the ceramic membrane in an MEA solution at 373 K for 30 days. It was found that the hydrophobic α-Al2O3 membrane had good stability for CO2 desorption from the MEA solution, resulting in a <10% reduction of N2 flux compared to the membrane without MEA immersion.

Analysis of Preferred Mechanisms of CO Oxidation with Atomically Dispersed Pt1/TiO2 Using the Energetic Span Model

This work examines the mechanisms of low-temperature CO oxidation with atomically dispersed Pt on rutile TiO2 (110) using density functional theory and the energetic span model (ESM). Of the 13 distinct pathways spanning Eley-Rideal (ER), termolecular ER (TER), Langmuir-Hinshelwood(LH), Mars-Van Krevelen (MvK) mechanisms as well as their combinations, TER with CO-assisted CO2 desorption yields the highest turnover frequency (TOF). However, this pathway is ruled out because Pt is dynamically unstable in an intermediate state in the TER cycle, determined in a prior ab initio molecular dynamics study by our group. We instead find that a previously neglected pathway – the ER mechanism – is the most plausible CO oxidation route based on agreement with experimental TOFs and turnover-determining states. The preferred mechanism is sensitive to temperature, with LH becoming more favorable than ER and TER above 750 K. By comparing TOFs for Pt1/TiO2 with prior mechanistic studies of various oxide-supported atomically dispersed catalysts in the literature, we also attempt to identify the most viable metal and support materials for CO oxidation.

Selective Electrochemical Regeneration of Aqueous Amine Solutions to Capture CO2 and to Convert H2S into Hydrogen and Solid Sulfur

Removing CO2 from natural gas or biogas in the presence of H2S is technically challenging and expensive as it often requires separation of both acid gases from the gas, typically using an aqueous amine solution, followed by separation of CO2 from H2S and conversion of H2S into solid S. In this work, the proof of concept of electrochemical, instead of thermal, regeneration of an aqueous amine solution is developed. This invention might be a very promising technology and has several advantages. It has H2S versus CO2 selectivity of 100%, can directly convert H2S into S and H2, and is economically competitive with CO2 desorption energy around 100 kJmol−1 and H2S conversion around 200 kJmol−1. If renewable energy is used for electrochemical regeneration, CO2 emissions due to the CO2 capture process can be significantly reduced.

Efficient nickel-based catalysts for amine regeneration of CO2 capture: From experimental to calculations verifications

High heat duty is an urgent challenge for industrial applications of amine-based CO2 capture. In this work, we report a novel, stable, efficient, and inexpensive Ni-HZSM-5 catalyst to reduce the heat duty. The density functional theory (DFT) calculations successfully explain the catalytic performance. The catalytic activity associates with the combined properties of MSA × B/L × Ni2+. The 7.85-Ni-HZ catalyst presents an excellent catalytic activity for the CO2 desorption: it increases the amount of desorbed CO2 up to 36%, reduces the heat duty by 27.07% compared with the blank run, and possesses high stability during five cyclic tests. A possible catalytic mechanism for the Ni-HZSM-5 catalysts through assisting carbamate breakdown and promoting CO2 desorption is proposed based on experimental results and theoretical calculations. Therefore, the results present that the 7.85-Ni-HZ catalyst significantly accelerates the protons transfer in CO2 desorption and can potentially apply in industrial CO2 capture.

CO2 Self-Poisoning and Its Mitigation in CuO Catalyzed CO Oxidation: Determining and Speeding up the Rate-Determining Step

Cu-based catalysts are promising for CO oxidation applications with catalyst deactivation being a major barrier. We start with a CuO/Al2O3 catalyst and find that while the CO conversion decreases, CO2 accumulates and the average Cu chemical state stays the same. It suggests CO2 self-poisoning, i.e., CO2 desorption is the rate-determining step. Subsequently, experiments are performed to prove this hypothesis by showing (1) CO2 adsorption inhibits O2 adsorption, (2) complete desorption of CO2 regenerate the catalyst, (3) pre-adsorbed CO2 quenches catalyst activity which recovers during the reaction and (4) the apparent activation energy is consistent with CO2 desorption. It is further evidenced by using a stronger CO2 adsorbing support CeO2 to speed up CO2 desorption from the CuO sites resulting in a superior CuO/CeO2 catalyst. It provides an example for experimentally deciding and speeding up the rate-determining step in a catalytic reaction.