A BIBLIOMETRIC ANALYSIS OF DEA CONTRIBUTIONS TO ENERGY EFFICIENCY IN THE PULP AND PAPER INDUSTRY

Objective: This article aims to analyze energy efficiency in the pulp and paper sector using Data Envelopment Analysis (DEA). Theoretical framework: The concern for sustainability has been a topic of discussion across the planet. Compliance with the Sustainable Development Goals (SDGs) stipulated by the 2030 Agenda has been a goal for organizations. In this sense, the pulp and paper industries stand out, as they stand out for their considerable participation in the impact on the environment. Methodology: As a methodology, bibliometric research was used to determine the number of publications, citations, authors and countries involved in energy efficiency research. Results and conclusion: The results showed that China leads the field with the highest number of publications and citations, followed by the United States. In addition, the authors with the most significant impact factor are of Chinese origin, with the Journal of Cleaner Production being the main source of publication of these critical studies. Research implications: These findings demonstrate the growing interest in energy efficiency research, highlighting the need to meet the planet's energy needs as quickly as possible. Originality/value: The results of this bibliometric analysis provided valuable insight into the current state of research and publications related to Energy Efficiency measured with DEA in the pulp and paper industries worldwide. Further exploratory analyzes and content analyzes are suggested to identify areas of research that have been neglected and provide new insights for future research.


INTRODUCTION
China stands out in investment in research and development to improve domestic energy efficiency in the pulp and paper sector, due to its intense consumption of energy and also due to the energy challenges generated by the exponential growth of its economy in recent decades (Hu & Wang, 2006;Wang, Wei, & Zhang, 2012Zhao at. al. 2019.).By using a wide range of energy sources, including fossil fuels, biofuels, and renewable energy, China is also a reference in clean technologies and renewable energy in the pulp and paper sector (Shi et al., 2010;Fang et. Al. 2011;Li et. al. 2012;Blomberg et al., 2012;Shi et al., 2014;Chang et al., 2013;Zang et al., 2013;Xiong et al. 2017Fernández et al., 2018;Haider et al., 2019).Data Envelopment Analysis (DEA) is a valuable tool for evaluating energy efficiency in the pulp and paper sector and is widely used in scientific studies on the subject worldwide (Seiford, 2005;Mardani, et al. 2017Emrouznejad & Yang, 2018Susaeta & Rossato, 2021).
As the pulp and paper industries are overly complex and involve several steps, including paper production, drying and pulp preparation (Harlaftis, Tenold, & Valdaliso, 2012;Ojala et al. 2013, Brolund et. Al 2017;Rossato, 2019), identifying opportunities for improving energy efficiency in all processes is a challenge.Data Envelopment Analysis (DEA) is a data analysis technique that allows evaluating the relative efficiency of different production units, based on a series of inputs (production factors) and outputs (final products) (koopmans, 1951;Farrell, 1957;Charnes, Cooper, & Rhodes, 1978), enabling more in-depth analysis for the sector.
Professor Abraham Charnes played a crucial role in the introduction of Data Envelopment Analysis, but other authors consolidated their procedures through theoretical issues raised by later reviews such as Førsund andSarafoglou (2002), Seiford (2005), and Emrouznejad and Yang (2018).Although when it comes to research using DEA to study energy efficiency in industries, Chinese studies are the most relevant (based on citations and H-index).Zhou, Ang, and Poh (2008) developed linear programming models to measure the performance of energy efficiency across the economy.Shi et al. (2010) evaluated the energy efficiency of industries based on a DEA model of fixing non-energy inputs.Chang et al. (2013) analyzed the environmental efficiency of a transport system through a non-radial DEA approach.Zhang et al. (2013) studied the relationship between energy efficiency, CO2 emission performance, and highlighting technological gaps in fossil fuel electricity generation through an analysis of the meta-frontier non-radial directional distance function.
The pulp and paper sector has been working to improve energy efficiency through improvements in technology, investments in renewable energy sources, and the promotion of more energy-efficient production practices (Rossato, 2019).Still, the sector faces challenges due to the need to provide steam and electricity for drying operations, refining, and other energy-intensive processes (Harlaftis, Tenold, & Valdaliso, 2012).Many mills are old and not designed with energy efficiency, producing large amounts of waste (paper and wood) that requires efficient and economical recycling (Boyd & Pang, 2000;Zhang et al., 2011).The industry also faces increasing competition from synthetic materials such as plastics, which are easier to produce and often cheaper (Boyd & Pang, 2000;Hu et al., 2007).Moreover, there are barriers related to climate change, such as greenhouse gas (GHG) emissions or the impact that adverse weather conditions have on the availability of raw materials (Zhang et al., 2013).
Thus, Bibliographical research on energy efficiency opportunities in the pulp and paper sector is essential to identify ways to reduce emissions, understand the most advanced and successful technologies in use in China, and provide insights to other countries seeking to improve energy efficiency in this sector.Ultimately, these efforts can help to reduce emissions and create a more sustainable future.

METHODS
The bibliometric review was made by searching for articles, conference proceedings papers, reviews, and early access, on the Web of Science Core Collection database (published by Clarivate AnalyticsTM), with the time limitation of publications in the last 20 years (timelapse: 2000 to 2020).Considering these terms, the search algorithm was built as follows: "Energy efficiency") AND TOPIC: (industry OR industries OR "pulp industries" OR "pulp industry" OR "paper industries" OR "paper industry") AND TOPIC: ("data envelopment analysis" OR "DEA") resulted in 437 documents, which were organized in EndNote® reference management software.After this stage, a search filter was developed, using a temporal filter (last 20 years) and then a filter in relation to the document filter, resulting in 435 articles at the end of the process.
These documents were analyzed descriptively to identify: the number of publications per year; the number of citations per year; authors with higher impact, measured by the -index; the most cited authors with the most significant amount of publications over the years; influential journals and countries; most relevant field of knowledge; relationship of authors, countries, and keywords.To facilitate the results presented, analytical visualizations tools such as bibliophagy (Aria & Cuccurullo, 2017), a bibliometric analysis package available in R Studio® software, and Microsoft Excel® were used.

FINDINGS OF THE STUDY
In this section, the reviewed studies are classified according to the following characteristics: (i) number of publications (per year and per countries) and citations (per year and per author); (ii) author impact measure; (iii) most relevant sources and knowledge fields; (iv) relationship of authors, countries, and keywords, as shown in Figure 1.The choice for the Web of Science repository was made due its outstanding reputation in the academic community.Besides presenting the evaluation of these three concepts is motivated by the fact that DEA and the impact of its supporters in the many theoretical fields of knowledge and sectors of economic activity.For this purpose, timeline-based and distancebased clusters are provided in the following sections.

Publications Per Years
The choice for the Web of Science repository was made do its outstanding reputation in the academic community.Besides presenting the evaluation of these three concepts is motivated by the fact that DEA and the impact of its supporters in the many theoretical fields of knowledge and sectors of economic activity.For this purpose, timeline-based and distance-based clusters are provided in the following sections.The Figure 2 show Number of publications in a 20-year period.

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During the periods of 2001,[2004][2005][2006], no documents related to the terms were published.In the years 2000, 2002, and 2003, only 1 (0.23%) article was published, which was considered a "dark time".After the last negative variation, specifically the 2015 period (20 documents), representing 4.60%, the graph shows that publications have increased.Over the past twenty years, the bibliographic production of documents on the subject has grown starting from 2016 as seen in Figure 2. 2018 and 2019 had the most notable number of published papers, with 73 and 84 documents, respectively, representing 36.09%.As of the time of the research, 69 (15.86%) articles have been published in 2020.
Overall, the trend of increasing bibliographic production on the terms shows that there is an increasing interest in the topics.This can be attributed to the development of new technologies and the need for new research to explore the possibilities of the terms.It is expected that this trend will continue in the years to come.

Citations Per Years
In the period studied, the bibliographic citation of documents related to the terms searched has grown, as shown in Figure 3  The authors Zhou, Ang & Poh (2008) developed three alternative energy efficiency performance indexes using Environmental DEA Technology.The purpose of this paper was to evaluate energy efficiency within a joint production framework of both desirable and undesirable outputs, by providing DEA-type linear programming models for measuring economy-wide energy efficiency performance.This paper has been the most cited since 2008, followed by the work of Hu, et al (2007) which published the Efficient energy-saving targets for APEC economies and Shi, et al (2010) with their research Chinese regional industrial energy efficiency evaluation based on a DEA model of fixing non-energy inputs.These studies also provide valuable insight into the potential for improving energy efficiency in various regions and industries.

Publications Per Countries
Figure 4 shows that out of all 435 articles filtered, 286 (53.66%) were published in China, more than the sum of publications from all other countries.The United States came in second with 36 (6.75%) publications, followed by Germany with 23 (4.29%), the United Kingdom with 18 (3.31%)and Brazil with 10 (1.88%) articles.2011), the pulp and paper industry has become a dominant activity in China, and studies have been conducted to maximize energy efficiency.As a result, Chinese companies have prioritized environmental issues, as the industry requires natural resources as raw materials.Lin and Zheng (2017) also point out that the conservation of natural resources (energy) and the reduction of pollution from industries have become the goal of sustainable development in China.Consequently, studies and analysis on energy efficiency have become increasingly common, aiming to bring advances in the production of pulp and paper, as well as to minimize environmental impacts.Despite Brazil occupying the first place in the export of cellulose, research and publications are still nascent, due to the movement of new productive plants with energy production capacity since 2009 (Rossato, 2019).The country has been investing in the development of new technologies in the pulp and paper sector, in order to increase competitiveness and promote sustainability.Therefore, Brazil has the potential to increase its presence in the international market and to reduce its environmental impacts.

Citations Per Authors
This section is devoted to the most relevant publications, journals, and contributors, ranked according to the methodology of bibliometric core publications.Though citation score 7 cannot measure the overall relative importance of a publication, it may mislead the research impact for specific subject areas of analysis, as some high-cited articles may cite a seminal work as a matter of curiosity, without a clear contribution to the field.The methodology of core publications (Seidman 1983;Van Eck & Waltman 2014a) grants the possibility to account for rank misplacements of high-cited works that are weakly related or completely unrelated to the subject field.
For a more in-depth analysis, we see an increase in the number of citations over the years, as evidenced in Figure 2, with the years in order, following the title of the lower axis (2010 -2020).All papers have a total of 2009 citations, 305 citations in 2019, and 272 citations in 2020 at the time of the research.The three most cited publications (Figure 4) were Linear programming models for measuring economy-wide energy efficiency performance (Zhou;Ang;Poh, 2008) with 278 citations, followed by Chinese regional industrial energy efficiency evaluation based on a DEA model of fixing non-energy inputs (Shi, et al., 2010) with 247 citations, and finally efficient energy-saving targets for APEC economies (Hu, Jin-Li;Kao, Chih-Hung, 2007) with 240 citations, representing 13.84%, 12.29% and 11.95% respectively for the entire analysis period.
Figure 5 shows author citations over the years.With regards to the percentage of evolution over these ten years, it appears that for these most cited articles, in 2010 the percentage was (1.19%) and as of 2014 (6.87%) none of the articles had been cited yet, with the article "Does environmental regulation affect energy efficiency in China's thermal power generation?Empirical evidence from a slacks-based DEA model" (Bi, Gong-Bing;Song, Wen;Zhou et al. 2014) being the only one.In 2018 there was a drop in the number of citations (13.74%), but for the subsequent period there was a recovery (15.18%).8 provide insight into which works are the most influential within a given field.This methodology can help researchers identify the most important works in their field of study and provide a more accurate picture of a field's research impact.

Author Impact Measured
By analyzing these publications over the years (Figure 5), it is observed that most of the published studies have been relatively recent, with the majority being from 2013 onwards.According to Bornmann and Daniel (2007), the h-index (Figura 6) quantifies the scientific production (documents) of research as a criterion.Therefore, when considering the hindex, which calculates the impact factor between the authors, the same order remains: Han YM (18), Lin BQ (17) and Geng ZQ (16).
Traditionally, the first author position in collaborative research is attributed to the individual who made the greatest contributions in terms of analysis and writing the scientific work (Riesenberg & Lundberg, 1990;Hunt, 1991;Gaeta, 1999;Yank & Rennie, 1999;Verhagen et al., 2003;Tscharntke et al., 2007).It is generally accepted that the first author in collaborative research should be the individual who made the greatest contributions in terms of analysis and writing the scientific work.This is to ensure that credit is given to the individual for their hard work and dedication to the project.

Journals
The concept of core journals and core authors refers to the inner outlets and researchers that compose the base for the propagation of Data Envelopment Analysis, Energy efficiency and Pulp and paper industries.A core journal is defined as any outlet that includes at least one core publication with a positive citation score (i.e., a score greater than zero).Regarding the number of publications, the Journal of Cleaner Production is the number one outlet, with 21.62% of all publications, followed by Energy Policy (9.80%) and Energy and Sustainability (9.46%), as shown in Figure 7.The methodological contributions are classified into 25 main areas of knowledge.With the three main categories of knowledge (Figure 8), the documents present 25 categories, with Environmental Sciences Ecology (23.4%),Engineering (17.3%), and Energy Fuels (17.1%) standing out the most, and the other categories making up the remaining 36.2%.China has produced the most consistent amount of literature regarding Circular Economy, an expected finding given the political steering towards the concept exercised by the government in recent years (Amato et. al, 2017).Studies have been more focused on environmental issues, such as the article by Blomberg, Henriksson and Lundmark (2012) and Alfredsson et al. (2016), which deals with environmental issues in Sweden.It points out that future energy efficiency projects could be more explicitly aligned to evolve aspects of information, relevant information and predetermine failures.

Relationship
The concept of core publication refers to a publication that has presented a certain minimum number of incoming or outgoing citation relations with another core publication (VAN ECK; WALTMAN, 2014a).This threshold is defined by the analyst and allows for maintaining the relevant contributions to the field in the core of a citation network, regardless of their citation scores.Thus, in the network of these publications, Figure 8 presents the authors on the left, the journal in which the publications were made in the center, and the keywords used in their publications on the right.This observation shows that such keywords have been used frequently in the production of Pulp and Paper in China studies.The results presented here suggest that China, in addition to being a leader in production of pulp and paper, also has a monopoly on the issue of studies in this sector.As they seek to analyze production with Data Envelopment Analysis tools, they aim to maximize the efficiency of production processes and thus there is an evolution of industries.
This suggests that China has a strong research focus on this topic, aiming to maximize production efficiency and drive the industry's evolution.Additionally, the other frequent keywords such as China and Resource allocation can be inferred to be important topics of research in this field.

CONCLUSIONS
The discussion provides some insightful comments on what has been warmly studied and what has been overlooked, as well as some good prospects for additional research.This article presented the results of a bibliometric analysis carried out to explore and describe the growth of interest and research with publications of articles related to Energy Efficiency measured with DEA in the pulp and paper industries around the world.The result of the bibliometric analysis shows that China is the country with the largest number of publications with 286 articles.There is a trend in these numbers, as well as in the number of citations, where The authors with the most significant impact factor are of Chinese origin, and have recent publications, dating from 2013 onwards.With 278 citations in total, the author of the most cited article also has one of the most significant impact factors, considering the search period.In the United States (second country with the most publications), there is a concentration of published studies, and the Journal of Cleaner Production is the main source of publication for this critical research.
For the next steps, we suggest further exploratory analysis based on these preliminary results and a description of the content analysis.For example, it is possible to perform a factor analysis (Principal Component Analysis, PCA) and clusters (k-means) for co-citations, a network of historical direct citations and other analyzes of coupling, collaboration, and coword.In this way, it is possible to identify areas of research that have been overlooked and provide new insights for future research.

Figure 3 -
Figure 3 -Number of citations in a 20-year period.Sources: Elaborated by authors (2023)

Figure 5 -
Figure 5 -Author with more citations in a 20-year period.Sources: Elaborated by authors (2023)

Figure 8 -
Figure 8 -Relationship between authors, journals, and keywords.Sources: Elaborated by authors (2023) ___________________________________________________________________________ Rev. Gest.Soc.Ambient.| Miami | v.17.n.10 | p.1-14 | e03251 | 2023.11 in this year of 2020 until the time of the research it was with 2297 citations, in relation to the previous years it is the biggest peak.