In recent years, the application of Lean models in manufacturing processes has received significant attention due to the successful implementation of relatively simple measures to eliminate or reduce waste. Similarly, Six Sigma has attracted the interest of the industry for reducing production costs through statistical methods and data analysis tools. The combination of both techniques constitutes a powerful management model known as Lean Six Sigma (LSS), whose application has been unevenly spread across the different services and industrial sectors. Despite the multiple studies conducted on the use of LSS methodologies in manufacturing processes, few studies have focused on its direct application in chemical manufacturing are less numerous. Consequently, many chemical companies still face major challenges in implementing the LSS model. This study explores the state of the art, current trends, and perspectives of Lean and Six Sigma integration in the chemical manufacturing sector. For this purpose, a bibliometric analysis was conducted covering topics from the implementation of the LSS on a global scale, i.e., non-manufacturing and manufacturing environments, to its application in the manufacturing of chemical products. The literature search was carried out in the Scopus and Web of Science databases using a different sequence of terms. The findings of this study revealed the most important contributions in terms of publications, authors, countries, and institutions over the past two decades. Additionally, avenues for future research are discussed.

In the pursuit of operational excellence and enhanced competitiveness, a wide range of industries have turned to methodologies such as Lean and Six Sigma; however, in the chemical sector, their application is very limited. This paper presents a Lean Six Sigma framework to identify and reduce sources of variability occurring in the final product composition of a Spanish SME fertilizer manufacturer. The company faced important challenges related to product variability, adversely affecting overall productivity. A real-life case of the Lean Six Sigma implementation was conducted over two years, and its applicability and ability to improve productivity performance were thoroughly assessed. The proposed framework successfully integrated Lean and Six Sigma methodologies, i.e., process mapping (value stream mapping), root cause analysis (Ishikawa cause–effect diagram), project management (SIPOC and DMAIC), and statistical process control, and demonstrated practical benefits for the case company by identifying the key variables affecting product variability and determining their optimal levels. A substantial 50% reduction in the variability of several products and a 42% reduction in material preparation time were achieved. These reductions resulted in a 40% reduction in costs associated with product losses and a 54% reduction in costs from raw material losses.