The world-wide consumption of natural gas (NG) and other fossil fuels (e.g., coal and crude oil) is ever increasing. However, most CO 2 resulting from either NG combustion or other processes is released into the atmosphere without capture. Chemical looping combustion (CLC) is a two-step combustion technology for power and heat generation with inherent CO 2 capture, using either gaseous fuels or solid and liquid fuels. A previous review focused on CLC of solid fuels or CLC of all types of fuels but did not give an in-depth and specific discussion of gaseous fuel CLC systems. China is one of the largest consumers of NG, coal, and crude oil in the world, and it is essential to develop an alternative technology to take the place of gaseous fuel (e.g., NG) combustion. This Review summarizes recent research and development work on CLC using gaseous fuels, including a technological and economic assessment, types of oxygen carriers (OCs), reactor types, coke formation and OCs poisoning, efficiency and exergy analyses, and model development based on a literature survey. The plant efficiency of NG-CLC can be up to 52−60% (LHV), including CO 2 compression, based on calculations and simulations, which is about 3−5% more efficient than a NG combined cycle with CO 2 capture. Ni-based materials have been widely developed and applied for NG-CLC because of its fast kinetics for methane conversion. CuO−Cu 2 O/Cu, Mn 3 O 4 −MnO, and Fe 2 O 3 −Fe 3 O 4 are typical OCs with high selectivity toward CO 2 and H 2 O. The operating conditions are closely dependent on reactor configurations, hydrodynamics, mass and heat balances, and characteristics of the OCs in the system. CLC and other CO 2 capture technologies are also compared in the present Review, which has rarely been investigated previously. From simulation and process analysis, a conceptual design of a NG-CLC power plant of thermal input 655 MW th is conducted to clarify its technological advantages and economic benefits compared to other power generation processes. The air reactor, fuel reactor, and OCs do not impose significant economic barriers for scale-up and commercialization of CLC.

Transesterification of waste cooking oil with high acid value and high water contents using heteropolyacid H3PW12O40 x 6H2O (PW12) as catalyst was investigated. The hexahydrate form of PW(12) was found to be the most promising catalyst which exhibited highest ester yield 87% for transesterification of waste cooking oil and ester yield 97% for esterification of long-chain palmitic acid, respectively. The PW12 acid catalyst shows higher activity under the optimized reaction conditions compared with conventional homogeneous catalyst sulfuric acid, and can easily be separated from the products by distillation of the excess methanol and can be reused more times. The most important feature of this catalyst is that the catalytic activity is not affected by the content of free fatty acids (FFAs) and the content of water in the waste cooking oil and the transesterification can occur at a lower temperature (65 degrees C), a lower methanol oil ratio (70:1) and be finished within a shorter time. The results illustrate that PW12 acid is an excellent water-tolerant and environmentally benign acid catalyst for production of biodiesel from waste cooking oil.

A new surface-ion-imprinted amino-functionalized silica gel sorbent was prepared by the surface imprinting technique with As(V) as the template, 3-(2-aminoethylamino)propyltrimethoxysilane as the functional monomer, silica gel as the support, and epichlorohydrin as the cross-linking agent and was characterized by FTIR, SEM, nitrogen adsorption, and the static adsorption–desorption experiment method. The results showed that the maximum static adsorption capacity of the imprinted silica gel sorbent was 16.1 mg·g–1, the adsorption equilibrium could be reached in 20 min, there was no influence of pH values on adsorption capacity of the imprinted silica gel sorbent in the range of 3.7–9.2, and the imprinted silica gel sorbent could be used repeatedly and indicated high selectivity even in the presence of the other metal ions. The Langmuir adsorption model was more favorable than the Freundlich adsorption model. Kinetic studies indicated that the adsorption followed a pseudosecond-order model. Various thermodynamic parameters such as ΔG o, ΔH o, and ΔS o were evaluated with results indicating that this system was a spontaneous and endothermic process.