# Biomass-Based Chemical Looping Gasification: Overview and Recent Developments
## 1 Introduction  
The combustion of fossil fuels (coal, petroleum, and natural gas) contributes the largest share of greenhouse gas (GHG) emissions and currently, the mitigation of these emissions is one of the most challenging global issues. The Paris Agreement aims to limit the temperature increase to 1.5 \({}^{\circ}\)C above pre-industrial levels [1]. According to international energy outlook 2016 (IEO 2016), the total world energy consumption will predictably increase by 48% from 2012 to 2040 due to growth in non-OECD Asia (including China, India, Southeast Asia), the Middle East, parts of Africa, and America [2]. According to the IEO 2016 reference case, fossil fuels will present the greatest energy source in the world in 2040, accounting for 78% of total world energy consumption [2]. Although coal is the slowest-growing energy source with 0.6% annual growth, it still accounts for a large proportion of world energy consumption. This is due to the fact that coal is abundant and less expensive than natural gas or oil. However, the utilization of coal is related to the challenge of increasing the efficiency of thermal power plants and reducing emissions such as carbon dioxide that is the primary greenhouse gas and its increase in the atmosphere mainly causes global warming. Germany has set a key goal to achieve at least a 40% cut in GHG emissions by 2020 and 80-95% by 2050 compared to its 1990 levels [3]. To reach this target, the increased use of renewable energy will play a key role. By 2050, power generation in Germany must be almost entirely based on renewable energy sources. TheEuropean Union (EU) has planned to achieve a 20% share of renewable energy in total energy consumption across its members by 2020 [4]. Biomass has been considered one of the most important primary and renewable energy resources for a renewable and sustainable energy future due to its carbon-neutral renewable and abundant quantity, which can give more carbon credit for conversion technologies and consequently economic advantages. Additionally, biomass has higher reactivity and higher volatile content, which can promote its conversion reactions. Its low content of sulfur and mercury leads to lower SO\({}_{\text{x}}\) emissions and pollutants. Other benefits of biomass are low ash content, thereby reducing solid residue, handling, and processing costs overall [5]. Combined with the carbon capture and storage processes, the overall system could achieve carbon negative emissions [6; 7]. Biomass conversion pathways can typically be classified as biochemical and thermochemical processes. The biochemical conversion pathway consists of two main processes used, namely fermentation and anaerobic digestion [8]. Fermentation, a metabolic process, converts solid fuels into biofuels or chemicals through the action of enzymes, while anaerobic digestion is a conversion of organic material into biogas in the absence of oxygen. The biochemical processes have main disadvantages such as low energy efficiency, high water requirement, long conversion times, and stringent feedstock requirements [9]. The thermochemical conversion processes mainly include combustion, gasification, and pyrolysis. Biomass thermochemical conversion processes are characterized by low efficiency mainly due to biomass properties such as high moisture content and relatively low energy density. Biomass gasification, a thermochemical conversion approach, is to convert efficiently the solid fuels into a combustible gas mixture, mainly CO and H\({}_{2}\), which can be used as a feedstock in the production of chemicals or power generation. However, the drawback of conventional gasification technology is a demand for a large amount of heat supply for the production of high-quality syngas, making the process less attractive. Therefore, a new technology is required to be more economically feasible to produce enriched hydrogen syngas from biomass. [PERSON] et al.