The hotspots of life cycle assessment for bioenergy: A review by social network analysis.

The purpose of this paper is to provide an up-to-date bibliometric view about the current life cycle assessment (LCA) for bioenergy. The social network analysis (SNA) method was applied to study total 2367 publications in this field. The results showed the high frequency keywords related with the "LCA" for bioenergy included three categories: (1) Bioenergy production, such as "Biodiesel", "Bioethanol", "Biogas" and "Biorefinery"; (2) Environmental problems, such as "Greenhouse gas" (GHG), "Environmental impact", "Climate change"; (3) Environmental target: "Sustainability". This means that LCA methods have been widely used in assessing the environmental impact from various types of bioenergy production process. Specially, the "GHG" attracted more attention in this research area. According to the temporal trend of the high frequency keywords, "bioethanol" is the most significant hotspot keyword of implication LCA. However, it has become colder since 2011. The environmental performance of "biogas" and "land use" began to receive attention since 2015.The evolutionary co-words network showed that the boundary of hotspots became overlapped. We also found four clusters were identified from keywords networks, i.e. the biggest cluster Cluster (I) (central cluster node linkage was "Bioethanol-GHG"), followed by Cluster (II) (central cluster node linkage was "Biodiesel-Algae"), Cluster (III) (central cluster node linkage was "Biorefinery-Sustainability") and Cluster (IV) (central cluster node linkage was "Biogas-Anaerobic digestion"). This cluster analysis also showed that the implication of LCA for the relationship between "bioethanol" and "GHG" is the most important hotspot research field. Although "biogas" is the smallest cluster now, it could be the next important hotspot of implication LCA for bioenergy. This study provides an effective approach to obtain a general knowledge of the LCA for bioenergy and supports a deeper understanding of research directions in the future.