Global Trends in the Research and Development of Petrochemical Waste Gas from 1981 to 2022

Abstract

As a highly energy-intensive and carbon-emitting industry with significant emissions of volatile organic compounds (VOCs), the petroleum and chemical industry is a major contributor to the global greenhouse effect and ozone layer destruction. Improper treatment of petrochemical waste gas (PWG) seriously harms human health and the natural environment. This study uses CiteSpace and VOSviewer to conduct a scientometric analysis of 1384 scholarly works on PWG and carbon sequestration published between 1981 and 2022, revealing the basic characteristics, knowledge base, research topic evolution, and research hotspots of the field. The results show the following: (1) In the early stages of the petrochemical industry, it was processed tail gas, plant leakage waste gas, and combustion flue gas that were investigated in PWG research. (2) Later, green environmental protection technology was widely studied in the field of PWG treatment, such as biotechnology, catalytic oxidation technology, membrane separation technology, etc., in order to achieve efficient, low energy consumption and low emissions of waste gas treatment, and the number of publications related to this topic has increased rapidly. In addition, researchers studied the internet of things and technology integration, such as the introduction of artificial intelligence, big data analysis, and other technologies, to improve the accuracy and efficiency of exhaust gas monitoring, control, and management. (3) The department has focused on how to reduce emissions by optimizing petrochemical process lines or improving energy efficiency. Emission reduction and low-carbon transition in the petrochemical industry will become the main trend in the future. Switching from renewable carbon to feedstock carbon derived from captured carbon dioxide, biomass, or recycled chemicals has become an attractive strategy to help curb emissions from the chemical industry. The results of our analysis can provide funding agencies and research groups with information to better understand the global trends and directions that have emerged in this field from 1981 to 2022 and serve as a reference for future research.

1. Introduction

The petrochemical industry is a primary sector that affects agriculture, energy, transportation, machinery, construction, and other aspects of production and life. The industry occupies an important position in the national economy of all countries in the world. Since the inception of the petrochemical industry in the late 1850s, the demand for oil and gas has grown exponentially, and oil and liquid fuel consumption is expected to grow by 34%, reaching 126 million barrels per day (mb/d) by 2050, compared to 94 mb/d in 2020 [1,2,3,4,5]. However, the booming petrochemical industry has caused serious air pollution, releasing a substantial amount of toxic and harmful gases (sulfur compounds, nitrogen compounds, carbon monoxide, etc.) into the environment and exerting adverse effects on human health [6]. Petrochemical industrial facilities are the main emitters of volatile organic compounds (VOCs) in the world [7]. A large amount of VOC emissions aggravates the greenhouse effect, leads to the destruction of the ozone layer, causes photochemical smog, and even leads to climate anomalies [8]. In addition, the improper handling of petrochemical waste gas (PWG) can lead to poisoning or even death through animal respiration, drinking water contamination, ingestion by herbivores, and other processes. Even within permissible limits, long-term exposure of the human body to VOCs has adverse effects on the respiratory tract, cardiovascular system, immune system, nervous system, et cetera [9,10].

In addition, the petrochemical production process is complex, and the overall process is long. The production process involves various kinds of raw materials and products, each with different characteristics [11]. Therefore, air pollution from petrochemical enterprises has many characteristics, posing serious harm to the atmosphere and making control and mitigation efforts challenging. The demand for chemicals and related products is expected to increase dramatically, and the dominance of petrochemicals as feedstocks across the chemical industry means that a focus on reducing their environmental footprint is particularly necessary [12]. Studying global PWG processing can promote transnational cooperation and experience sharing, accelerating technological innovation and experience accumulation through case studies and technical exchanges in different countries and regions.

For nearly half a century, the international community has been committed to mitigating the greenhouse effect. Especially in the past decade, many countries have introduced carbon emission reduction policies. China, the Marshall Islands, Mexico, and Singapore, for example, have pledged to reach the carbon peak by 2030. It is worth noting that the global chemical industry, as an important source of carbon emissions, has a large carbon footprint, contributing 124 million tons of carbon dioxide equivalent per year, accounting for approximately 10% of total global final energy consumption and 7% of industry-related greenhouse gas emissions [13]. The main source of emissions in the chemical sector is the use of fossil fuel energy. Other sources of emissions include chemical processes and indirect emissions. As a great part of emissions is related to the production of chemicals based on carbon feedstocks, energy electrification or the deployment of carbon capture and storage (CCS) will not completely stop the sector’s heavy reliance on fossil carbon as a feedstock [14,15,16]. Therefore, the study of PWG is gaining momentum among scholars worldwide. From 1981 to 2022, there has been a rapid growth in publications on PWG. The understanding of the hotspots and trends in PWG research as well as the contributions from research institutions and outstanding individuals is very important. Given the large number of published articles and reviews, new methods are needed to evaluate and analyze trends in the knowledge domain. Through the study of PWG treatment technology and experience on a global scale, it can promote the formulation and promotion of international standards and norms and promote the improvement in the management and supervision level of waste gas treatment in various countries. The strength of PWG treatment research is its ability to draw on the experiences and best practices of different countries and regions to promote sustainable development. This includes improving environmental quality, energy conservation and emission reduction, the efficient use of resources, and the development of a circular economy, to summarize emerging hotspots in PWG research, future directions in international research, and provide a scientific reference for the formulation of carbon emission reduction policies in the global petrochemical industry.

By employing bibliometric analysis of the petrochemical industry exhaust emissions, the collected papers can, to a certain extent, offer insights into trends in the scientific frontier and enable statistical analysis and content mining. Our main goal is to systematically describe how PWG research has evolved. The evolution of key research topics can be determined through an analysis of the co-cited reference network and the co-emerging keyword network. Emerging trends and transient patterns in the research frontier can also be detected to provide a comprehensive and in-depth analysis of the development of the PWG field. Our second goal is to provide researchers with measures of research networks (countries, institutions, authors, and journals) and to detect research richness, gaps, emerging trends, biases, and limitations.

2. Data Sources and Analysis Methods

2.1. Data Sources

Web of Science (WOS) is the most comprehensive database for bibliometric analysis. To ensure the quality of data, we searched the website of the WOS Core Collection (WOSCC). Our search criteria incorporated the keywords related to research on waste gas emissions in the petrochemical industry, specifically focusing on the terms “petrochemical industry” and “waste gas”. We used the following search strings: “(((((((((TI = (petrochemical)) OR TI = (petro-chemical)) OR TI = (synthetic fiber)) OR TI = (petroleum)) OR TI = (petroleum catalytic cracking)) OR TI = (crude oil)) OR TI = (refinery)) OR TI = (natural gas)) OR TI = (natgas)) OR TI = (LNG)” AND“((((((((((TI = (REDD)) OR TI = (carbon emission)) OR TI = (CO₂ emissions)) OR TI = (carbon dioxide release)) OR TI = (CO₂ release)) OR TI = (discharge of carbon)) OR TI = (discharge of CO₂)) OR TI = (carbon dioxide emission)) OR TI = (carbon output)) OR TI = (emission reduction technology)) OR TI = (CO₂)”. The search spanned from 1 January 1981 to 1 June 2022 and was limited to only “articles” or “reviews” without any language/time restrictions. Finally, 1384 records, comprising 1343 articles and 41 reviews, were analyzed using VOSviewer (1.6.18) and CiteSpace. 6.1.R3 (64-bit).

Firstly, a literature search was conducted to gather relevant data which were then analyzed to ensure the accuracy and the replicability of the research through the application of uniform retrieval criteria and filtering principles. Microsoft Excel 2019 was used to analyze and export documents that exhibited the highest citation counts or productivity based on factors such as authors, countries/regions, publications, journals, and institutions. Tables and graphic data were extracted from published articles using Origin (2018) software. Selected experiments were analyzed in detail and data were extracted for analysis.

2.2. Analysis Methods

First, the full record with the citation was extracted from WOSCC into a plain text file separated by a label. Before visual analysis, CiteSpace was used to eliminate duplicate content. Furthermore, CiteSpace was used to extract collaborative networks and perform co-reference and co-occurrence analyses. CiteSpace was also used to burst analyze keywords and remove time intervals to obtain optimized time slices and logical and intuitive visualizations. VOSviewer was used to obtain a network graph of the most frequently cited journals and a network of co-occurring author keywords.

The analysis encompassed annual publications, WOS citations of articles, author–institutional partnerships, countries or regions, source journals, foundation programs, and keywords. To highlight the variation in parameters over time, a segmented analysis of periods was conducted and all statistical data were converted into tables. The average number of citations (CPA) was calculated in each table, corresponding to the H-index of the classification interval. Bibliographic measurement results included numbers of citations, co-citations, and co-occurrences. The number of citations refers to the number of citations to a publication, and the number of co-citations refers to how often two published articles are jointly cited by subsequently published articles [17,18]. The total number of publications (TP), the total number of citations (TC), the CPA, and the H factor were used as judgment indexes to comprehensively evaluate the degree of academic influence. For the cooperative relationship, the total number of operations (TCN) and the centrality of CiteSpace (percentage) were selected as indicators.

Co-citation networks are particularly useful for systematic reviews because co-citation links can reveal how groupings evolve independently out of an original publication. On the other hand, a co-occurrence network is a graphical representation of the frequency in which variables occur together. The result of a system map is a network and a co-reference (or co-occurrence) cluster. The explanation of these clusters is reinforced by CiteSpace’s automated cluster labels and summaries [19].

3. Results and Discussion

3.1. Contributions of Top Producers

3.1.1. Global Research Situation

From 1981 to 2022, WOS published 1384 PWG-themed publications, comprising 1343 research articles (97.04%) and 41 reviews (2.96%) (Figure 1). These articles were cited 34,374 times, with an average of 24.78 citations per article. The number of publications on PWG shows an increasing annual trend (Figure 1). The number of studies published before 1994 was minute, with only 10 annual publications worldwide. Slow growth was experienced between 1994 and 2006 (6 to 15 publications, with an average annual growth rate of 8.32%). The last 15 years have seen a dramatic increase in the number of publications per year (more than 89% of all publications), reaching 134 in 2021, with the number expected to exceed 150 in 2022. Due to increasing concerns about climate change as well as carbon peaking and carbon neutrality goals, the number of citations of papers about petrochemical industry waste gas increased between 1981 and 2022, with two remarkable leaps in climate change and carbon sink research in 2005 and 2020. These trends reflect the increasing attention devoted to this area during the past decade [20,21,22].

As shown in

Table 1. Top 10 countries in the field of PWG (1981–2022).

No.	Country	TA	TCN	CPA	H-Index	Centrality	CA
1	Peoples R China	375	8464	23.35	50	0.15	7201
2	United States	225	8598	38.67	55	0.34	7426
3	Iran	108	1901	18.01	25	0.18	1659
4	Canada	90	3205	36.14	32	0.17	2820
5	England	71	2056	29.48	26	0.2	1844
6	South Korea	66	1359	20.79	23	0.02	1254
7	Malaysia	58	1343	24.03	22	0.08	1203
8	Italy	54	1304	24.85	22	0.07	1058
9	Norway	54	2165	40.96	27	0.04	1815
10	Brazil	45	581	13.4	15	0.02	525

and Figure 1, the top 10 countries published 1151 articles, comprising 83.16% of the total articles published. At the same time, according to the fitting curve in Figure 1, we find that 2005 is a time node, and the number of PWG publications has increased sharply since then. This year marks the beginning of the Kyoto Protocol, which for the first time in human history put in place legal limits on greenhouse gas emissions. In the same year, an explosion occurred at the 101biphenyl plant of Jilin Petrochemical Company in China, causing about 100 tons of chemicals to flow into the Songhua River and explode at a terminal oil depot in Hertfordshire, England. It can also be seen that the formulation and implementation of policies and the impact of very large-scale pollution events will lead to an increase in research on more powerful PWG emission control technologies. Among these countries, China has the highest output of PWG academic papers, with a total of 378 publications (27.31%; China has always ranked first in the number of papers published annually), which also confirms that the petrochemical industry is a pillar of China, accounting for one-fifth of the national economy [23]. The environmental impact of the petrochemical industry has attracted wide attention, especially since China made a goal of “achieving carbon peak by 2030 and carbon neutrality by 2060” in September 2020 [24]. Subsequently, the number of published articles has dramatically increased. China is followed by the United States (226 articles; 16.33%) and Iran (108 articles; 7.80%). Although the United States ranked second in the total number of articles (TA = 226; 16.33%) and average citations (38.67), it had the highest total number of citations (8598) and the highest H-index. A country’s H-index and total citations are important indicators of the country’s influence in a field [25]. These metrics show that the United States has been actively promoting PWG research in the environmental sector and has made large contributions to PWG research. This highlights the nature of the United States petrochemical industry, which is concentrated and developed, with a high level of management automation [26,27,28]. Considering the value of TC and CPA, the United States, China, Canada, and Norway are important contributors to the global PWG work, while Brazil has a relatively low TC and CPA, indicating relatively weak research on the relevant aspects. Overall, there has been a steady increase in research into PWG, reflecting the growing public interest in the subject.

3.1.2. Contribution of Institutions and Journals

The first paper on PWG was published in June 1981 by Acta Technica Academiae Scientiarum Hungaricae [29], 18 years before the first PWG study in China (The CO₂ Reforming of Natural Gas in a Pulsed Corona Discharge Reactor) [30]. Subsequently, countries began to focus on PWG research. The results of an institutional analysis show that a total of 200 institutions participated in the study of PWG. Institutions with a total of more than 17 publications are presented in Figure 2a (15 institutions in total;

Table 2. Top 10 journals in the field of PWG (1981–2022).

No.	Journal	TC	CPA	H-Index	Percentage(%)
1	Energy	2160	31.93	26	14.44
2	International Journal of Greenhouse Gas Control	2345	39.7	27	12.55
3	Energy Fuels	1735	30.34	22	12.13
4	Fuel	1061	19.49	19	15.51
5	Industrial Engineering Chemistry Research	1123	25.69	19	9.21
6	Energy Conversion and Management	1407	33.83	22	8.79
7	Applied Energy	1700	44.28	28	8.16
8	Journal of Natural Gas Science and Engineering	533	15.17	13	7.53
9	Energies	328	14.39	9	4.81
10	International Journal of Hydrogen Energy	690	34.7	13	4.18

shows detailed information on the top 10 institutions, and Southwest Petroleum University is in 10th place). There are three institutions from China, two from Iran, and one each from Norway and the United States. Since 2003, Norwegian institutions have had the third-highest number of publications and the highest quality of papers and research impact. The H-index of the institutions was 44.15, indicating that Norwegian researchers attach great importance to PWG research.

A WOS analysis shows that these publications come from 200 journals. Journals with more than 17 publications are summarized in Figure 2b (the details of the top 10 journals are summarized in Table 2). In terms of the number of articles, the top three journals were Energy (TA = 69, p = 14.44%, TC = 2160, CPA = 31.93, and H-index = 26), the International Journal of Greenhouse Gas Control (TA = 60, p = 12.55%, TC = 2345, CPA = 39.7, and H-index = 27), and Energy Fuels (TA = 58, p = 12.13%, TC = 1725, CPA = 30.34, and H-index = 22). It is worth noting that although Applied Energy (TA = 39, p = 8.16%, TC = 1700, CPA = 44.28, and H-index = 28) ranked seventh in the number of publications, its TC value exceeded 1700, similar to that of Energy Fuels. Moreover, the CPA (44.28) and H-index of Applied Energy ranked first, indicating that this journal played the most important role in PWG research. In addition, ENERGY has become the most important journal for PWG research in terms of publication volume in recent years, with more than five papers published annually since 2017. Although the number of papers published by Energy Conversion AND Management and the International Journal of Hydrogen Energy is no more than three per year, the impact of the published articles has consistently remained high. Considering the top 10 high-volume journals and taking PWG, energy fuels, and chemistry as the research object, energy fuels and chemistry accounted for 58% and 29% of the total published volumes, respectively, which was well ahead of environmental sciences ecology and meteorology atmospheric sciences.

3.2. Scientific Research Cooperation

3.2.1. Analysis of Cooperation Networks across Countries

Figure 3 shows the relationship between cooperation and co-citation of PWG among different countries and institutions around the world, providing insights into the distribution of their research capabilities and shedding light on the status of PWG development. This analysis enables tracking of the research trends of countries and institutions, which could guide the promotion of academic exchanges and the implementation of relevant research work.

Between 1981 and 2022, a total of 75 countries/regions participated in the publication of PWG thematic papers (Figure 3). The larger the node, the greater the number of publications in a region and the stronger the cooperation between countries. Global research was concentrated in the United States, Asia, and Europe. European countries are geographically adjacent, so if large-scale petrochemical exhaust pollution occurs, the cross-border pollution effect will inevitably affect the environment of the neighboring countries. Also, the establishment of the EU Environment Agency has provided a large data-sharing platform for its member states, which is conducive to scientific research cooperation among countries [31]. China and Iran are prominent in Asia. As shown in Table 1, China and Iran rank first and fifth, respectively, in the number of published articles. Iran has the third-largest oil reserves in the world and was one of the first countries to develop a petrochemical industry in the Middle East. Furthermore, Iran has the second-largest petrochemical industry in the Middle East. The country’s petrochemical industry has grown exponentially over the past 40 years, and this growth has led to an increased environmental burden. Scholars have conducted in-depth studies on environmental risk assessment, energy efficiency, and the emission reduction potential of the petrochemical industry in order to improve the environmental and economic benefits of Iran’s petrochemical industry [32,33,34].

Centrality refers to the frequency that a node serves as the shortest bridge between two other nodes. Table 1 shows the top three countries in the central position: the United States (0.34), the United Kingdom (0.2), and Iran (0.18). China ranked first in the number of publications but fifth in centrality. It indicates that the country attaches great importance to PWG and contributes a large number of papers to the literature every year, but it is relatively weak in international cooperation. Therefore, for the long-term development of the PWG research field, all countries need to strengthen mutual cooperation. In particular, China should strengthen its cooperation with other countries and jointly improve the scope of the PWG global research framework.

3.2.2. Analysis of Cooperation Networks across Institutions

In this study, 200 institutions participated in the publication of PWG papers. We created an institutional cooperation network (1981–2022), which produced significant modularity and contour scores (Q = 0.9485; S = 0.9368). Some research institutions are relatively concentrated, forming several major clusters of institutional cooperation. As shown in Figure 4, among these institutions, the top five according to the size of the nodes are CAS (0.06), CUP (0.05), NTNU (0.02), U of R (0.02), and UTP (0.01). The size of a node reflects a comprehensive consideration of the number of articles issued by an institution and the closeness of its cooperation with other institutions. Therefore, node size indicates the influence of the institution in the field of PWG research.

As shown in

Table 3. Top 10 institutions in the field of PWG (1981–2022).

No.	Institution	TA	TC	CPA	H-Index	Centrality
1	China University of Petroleum	63	1627	26.19	16	0.05
2	Chinese Academy of Sciences	41	1367	33.34	21	0.06
3	Norwegian University of Science Technology NTNU	33	1475	44.15	23	0.02
4	United States Department of Energy DOE	29	1300	44.83	20	0.00
5	Universiti Teknologi Petronas	29	622	21.45	15	0.01
6	University of Regina	25	747	29.88	14	0.02
7	Polytechnic University of Milan	24	808	33.67	16	0.00
8	Islamic Azad University	21	272	12.95	8	0.00
9	Sharif University of Technology	19	457	24.05	12	0.00
10	China National Petroleum Corporation	18	201	11.17	6	0.00

, the China University of Petroleum, the University of Chinese Academy of Sciences, the University of Norway, and the US Department of Energy were the top four institutions in terms of publication volume. The University of Chinese Academy of Sciences published the second largest number of articles but has the largest node and is in the center of Figure 4. This research institution works closely with other institutions (Politecnico Milano, Azad University, Sharif University, and the University of Regina), revealing its strong ability to cooperate with other institutions. The China University of Petroleum ranks first in the number of publications, and its research focuses are CO₂ emission material flow and spatial data analysis in the petrochemical industry [35], the analysis of the effect of natural gas and renewable energy replacing fossil energy on CO₂ emissions [36,37], the development of detection and remediation techniques for VOC leaks in the petroleum industry [38], and the conversion of CO₂ emissions from the petrochemical industry into methanol and other chemical industrial products to achieve emission reduction and resource utilization [39]. Recent papers reveal that China attaches great importance to the study of PWG, and the research is mainly focused on CO₂ recycling and utilization as well as the establishment of relevant models to evaluate petrochemical emissions, control their escape range, and reduce environmental hazards. The US Department of Energy has also conducted research on CO₂ emission assessment and recycling. The department has focused on how to reduce emissions by optimizing petrochemical process lines or improving energy efficiency [40,41,42]. The petrochemical industry is vital for the development of energy, processing materials, agriculture, and transportation, but it is also one of the main sources of greenhouse gas emissions. With the growing environmental awareness, emission reduction and low-carbon transformation in the petrochemical industry will become the main trend in the future. Switching from renewable carbon to feedstock carbon obtained from captured carbon dioxide, biomass, or recycled chemicals has become an attractive strategy to help curb emissions from the chemical sector, contribute to meeting the Paris climate goals, and, arguably, improve the sustainability of chemical products. The petrochemical industry occupies an irreplaceable position in economic development.

3.2.3. Analysis of Author Cooperation Networks

Research authors play a key role in reflecting research competence and evaluating developments in an academic field. Based on 1384 articles published by 195 authors, Figure 5 illustrates the collaborative network of authors in the PWG domain (Q = 0.9485; S = 0.9638), where each node represents an author, the size represents the closeness of the cooperation relationship between the author and other authors, the color corresponds to the year, and the lines between authors indicate the existence of a collaboration. Many authors tend to work with a small group of collaborators, resulting in several major groups of authors. As shown in

Table 4. Top 10 authors in the field of PWG (1981–2022).

No.	Authors	TA	TCN	TC	CPA	H-Index	Centrality	Country
1	Koros WJ	21	155	159	19.88	7	0.01	United States
2	Zhang ZH	18	141	142	17.75	6	0.01	China
3	Jin HG	17	347	356	39.56	7	0.01	Italy
4	Chiesa P	17	26	30	6	3	0.01	South Korea
5	Pourkashanian M	17	38	42	7	3	0.01	England
6	Bustam MA	16	275	380	54.29	6	0.02	Malaysia
7	Ahmad AL	14	40	40	6.67	3	0	Malaysia
8	Dai YP	14	219	229	32.71	3	0.01	China
9	Chavadej S	14	24	24	3.43	3	0	Italy
10	Gundersen T	13	148	149	29.8	4	0.01	Norway

, Koros WJ dominates the list of papers and is the most influential scientist with the most extensive cooperation with other authors. Other prolific authors are Zhang ZH and Jin HG. These three authors are from the United States, China, and Italy, respectively. This analysis also indirectly confirms the conclusion in 3.2.1: the United States and China work closely together. As shown in Table 4, although Bustam MA ranked sixth in the number of publications, their centrality (0.02) and average citation count (54.29) were the highest, indicating a major influence in the field of PWG research. Bustam MA studies the conversion of CO₂ into value-added chemicals and fuels in ionic liquids [43]. Koros WJ works on gas separation membranes, including carbon molecular sieves, polyimide hollow fiber membranes, and MOF molecular sieves for front-end natural gas desulfurization, waste gas membrane treatment, and CO₂ capture [44,45,46]. These three authors and their partners focus on the treatment of petrochemical exhaust emissions and have established relatively sound treatment measures from source to process and end [47,48]. It can be seen from the analysis in 3.2.2 and 3.2.3 that PWG studies mainly focus on the diffusion model establishment, capture, and resource utilization of waste gases, especially CO₂.

Most of the other authors with prominently published articles engaged in certain exchanges and cooperation are from domestic scientific research institutions. Consequently, they have limited scientific research exchanges with each other, leading to relatively independent research topics with robust regional characteristics. However, it is undeniable that these authors have made outstanding contributions to PWG research through their collaborations.

3.2.4. Document Co-Citation Analysis

References are an important part of domain knowledge, and their quality reflects the overall level of research within the field. Co-citation analysis of the literature can effectively determine and guide the development direction of the research field. As you can see from Figure 6, co-citation connections between references can be described by connections between nodes. The larger the size of the node, the more important the corresponding article. The color of the relationship between the nodes represents the morning and night connection between the articles. The node label marks the first author and the year of publication. The diagram illustrates interdisciplinary collaboration, multi-oriented research methods and models, and the interplay in PWG research. We found that 15 articles in the co-citation graph were cited more than 10 times. We list the 10 most frequently cited articles in

Table 5. Top 10 references in the field of PWG (1981–2022).

Rank	Author	Year	Title
1	Bui M	2018	Carbon capture and storage (CCS): the way forward. [51]
2	Song CF	2019	Cryogenic-based CO2 capture technologies: State-of-the-art developments and current challenges. [52]
3	Biliyok, Chet	2022	Performance of an amine-based CO2 capture pilot plant at the Fortum Oslo Varme Waste to Energy plant in Oslo, Norway. [3]
4	Kopyscinski J	2010	Production of synthetic natural gas (SNG) from coal and dry biomass—A technology review from 1950 to 2009. [50]
5	Zheng YF	2022	Interface-Enhanced Oxygen Vacancies of CoCuOx Catalysts In Situ Grown on Monolithic Cu Foam for VOC Catalytic Oxidation. [53]
6	Luo XB	2015	Modelling and process analysis of hybrid hydration–absorption column for ethylene recovery from refinery dry gas. [54]
7	Huang YZ	2022	Mobile monitoring of VOCs and source identification using two direct-inlet MSs in a large fine and petroleum chemical industrial park. [55]
8	Zhao Y	2008	Primary air pollutant emissions of coal-fired power plants in China: Current status and future prediction. [49]
9	Singh P	2017	Current and emerging trends in bioremediation of petrochemical waste: A review. [56]
10	Yuan ZH	2017	Smart Manufacturing for the Oil Refining and Petrochemical Industry. [57]

. Of the 10 most frequently cited articles, 40 percent were review articles, including personal views and ideas from multiple perspectives. These reviews summarize petrochemical exhaust emissions, including carbon dioxide, volatile organic compounds, ethylene, and other pollutants. These emissions can come from a variety of processes in the petrochemical industry, including combustion, refining, and chemical synthesis. For example, Zhao Y and Wang SX et al. analyzed the current and future emissions of coal-fired power plants in China [49]. Kopyscinski J et al.’s research on synthetic natural gas (SNG) production reviewed the history and latest processes for the production of SNG from coal and biomass [50].

Others describe treatment technologies for petrochemical exhaust gases: a range of treatment technologies exist, including CCS, low-temperature CO₂ capture, amine capture, bioremediation, and smart manufacturing technologies designed to optimize processes to reduce emissions. Bui M et al. explored the potential of CCS to mitigate climate change and discuss the challenges of its deployment [51]. Carbon dioxide capture mainly consists of five technologies: membrane, absorption, adsorption, cryogenic distillation, and chemical looping. Recently, many efforts have been made to optimize the carbon dioxide adsorption process, reduce energy consumption, thereby reducing operational costs, and develop sustainable adsorbents for carbon capture. Song CF et al. highlighted the latest developments in cryogenic CO₂ capture technology, including its challenges and future opportunities [52]. Biliyok, Chet demonstrated the effectiveness of amine-based CO₂ capture technology in waste-to-power plants [3]. Singh P et al. reviewed the biological treatment methods of petrochemical wastes, with emphasis on bacterial degradation [56]. Yuan ZH et al. discussed how smart manufacturing can change the petrochemical industry through enhanced connectivity and optimization [57]. Luo XB et al. proposed a more efficient way to recover ethylene from refinery dry gas [54]. In addition, VOCs as a key emission pollutant in the petrochemical industry have also been studied in depth. For example, Zheng YF et al. introduced a novel catalyst for the removal of volatile organic compounds (VOCs) from industrial emissions [53]. Huang YZ et al. used direct-access mass spectrometry to monitor and identify VOCs in chemical parks [55]. Most articles conclude that processing techniques are available, but challenges remain in scaling these solutions from laboratory settings to practical applications. Factors such as cost, efficiency, and adaptability to different types of emissions need to be addressed. Co-citation analysis is useful and relevant for identifying cited articles and important documents that make up the core knowledge system of a particular domain.

Future direction: There is a clear trend towards more sustainable and efficient practices in the petrochemical industry. This includes the adoption of intelligent manufacturing to optimize operations, and today it is common to combine traditional mechanistic approaches based on momentum transfer, energy transfer, mass transfer (TT), and reaction engineering (RG) (TT-RG) with data-driven AI approaches. Through the analysis of energy efficiency evaluation indicators, the use of combination methods to achieve production optimization and energy savings has gradually become an important part of complex petrochemical industry. Exploring new bioreaction strategies and improving CO₂ capture techniques, such as capturing CO₂ from industrial sources via microalgae, has been widely reported in the literature [58]. A CO₂ capture capacity of 102.13 tonnes/year per hectare was achieved by breeding the microalgae chlorella in a waterway pond [59]. Integration and collaboration: Successfully addressing petrochemical emissions may require integrated solutions that integrate multiple technologies and strategies. Collaboration between industry, researchers, and policymakers is essential to overcome barriers and implement effective solutions. In conclusion, the petrochemical industry faces significant challenges in managing its environmental footprint, but ongoing research and technological advances offer promising pathways to reduce emissions and improve sustainability. The integration of smart manufacturing, bioremediation, and advanced CO₂ capture technologies has the potential to move the industry towards a greener future.

3.3. Research Hotspots and Emerging Trends in PWG

3.3.1. Research Hotspots

Keywords can provide important information about the core content, which is of great significance to the understanding of the research model, the overall research focus direction, and the research gap [60]. Figure 7a shows a co-occurrence network diagram of keywords used in research articles related to PWG. Co-occurrence research on frequently used keywords is essential for people to read publications on current and past research issues. According to VOSviewer statistics, there were 473 keywords in 1384 articles over the past 42 years, with 10 keywords appearing more than 80 times. In this study, the minimum keyword frequency was set at 35, as shown in Figure 7a. To facilitate the identification of research clusters, the collected keywords from different authors were categorized into four color groups based on research field similarity. Connecting lines indicate a close relationship between two items, while a large-sized node indicates a high occurrence rate of an item. Keyword distance clustering, clustering, and density distribution are shown in Figure 6 and Figures S1–S3. We found that the keywords with the largest nodes, the highest density, and the highest frequency include “crude oil” (225), “VOCs” (165), “gas storage tank” (139), “circulation” (106), and “catalyst” (105). This finding is consistent with our research theme and shows that the source and treatment processes of PWG are the focus of water environment research. Other keywords such as “nitrogen oxides”, “carbon dioxide”, “phase”, “selectivity”, “structure”, and “exhaust gas” were in the cluster groups. Combined with cluster groups, PWG studies mainly include components of exhaust gas emitted by the petrochemical industry, petrochemical industry waste gas treatment methods, and the waste heat utilization of petrochemical industry waste gas. To some extent, these PWG studies reflect the diversity and complexity of PWG research.

The approach of analyzing academic fields through keyword analysis alone is inadequate to reflect the research trend in an academic field because it does not consider the influence of the timeline of the different kinds of literature. To overcome this shortcoming, we performed a cluster analysis via keywords, spreading them across the timeline to identify emerging trends and frontier areas in blockchain research. The scientometric process of cluster analysis enables a comprehensive examination of a field from different perspectives [61]. As can be seen from the timeline view and cluster view (Figure 7b and Figure S6), the most popular research area has shifted from crude oil (cluster #2), the raw material used in the petrochemical industry, to exhaust gas emission (cluster #9), the constituents of the emitted gases. Petrochemical industry waste gas comprises hydrocarbons, alcohols, aldehydes, acids, ketones, amines, butadiene, dichloromethane, and other organic and inorganic carbon dioxide waste gases [62]. In recent years, as a result of carbon peaking and carbon neutrality policies, the petrochemical industry has paid increasing attention to carbon emissions. It is only by actively adopting all cost-effective energy efficiency and carbon dioxide reduction technologies while actively shifting from fossil fuels to renewable and other non-fossil resources that nations can fulfill their intended nationally determined contribution commitments under the Paris Agreement [63].

Thermodynamic analysis (cluster #0) is the most popular field of PWG research. Thermodynamic analysis is popular because the conversion of VOCs by the catalytic reaction is restricted by reaction kinetics and reaction equilibrium. Consequently, catalytic combustion is an economically feasible (low energy consumption) treatment method for exhaust gas in the petrochemical industry [64]. Although the thermal incineration of VOC emissions has been successful, the problem of insufficient combustion still exists. Therefore, efficient catalysts, improvement in the efficiency of the catalytic combustion of PWG, and the elimination of pollutants are some of the most active research areas at present [65].

Carbon dioxide emission (Cluster #3), carbon dioxide ratio (cluster #5), and carbon dioxide synthetic natural gas (methane) (cluster #6) (Figure 7b and Figure 8) represent carbon emission modules on which PWG research is performed. These modules reflect the carbon peak and carbon-neutral policy background. One research hotspot is the carbon emissions of the petrochemical industry. The industry is a major consumer of energy and a significant contributor to greenhouse gas emissions in China [66]. In particular, heavy industries such as petroleum refining and coking and chemicals account for more than 60% of carbon dioxide emissions from all industries [67]. Carbon dioxide emissions from China’s petroleum refining and coking industry, which is highly energy-intensive, have put great pressure on China’s emission reduction targets [68]. Since most of the exhaust gases emitted by the petrochemical industry are also converted into carbon dioxide emissions after catalytic combustion treatment, managing carbon dioxide emissions becomes a crucial aspect of PWG treatment. The emission of greenhouse gases makes global temperatures rise, causing a series of ecological crises [69]. Although scholars have been working on carbon dioxide treatment for many years and have made many achievements, there is still ample room for progress in combating the greenhouse effect, which will be a long battle, especially in the context of the Paris Agreement. The raw materials used in the petrochemical industry are mostly oil and natural gas. It has been widely reported in recent years that the synthesis of natural gas from carbon dioxide (cluster #6) involves the conversion of carbon dioxide into methane, the main component of natural gas. There are several methods for converting carbon dioxide into methane, including carbon dioxide reforming and oxidation coupling to methane [70], microbial electrolysis conversion of carbon dioxide into methane [71], and catalytic hydrogenation of carbon dioxide to methane [72]. However, these methods are confined to laboratory settings. If they can be widely applicable, they will not only effectively reduce the greenhouse effect but also turn natural gas into renewable energy. The conversion of carbon dioxide to natural gas will be a hot area of research in the future.

3.3.2. Emerging Trends

For further analysis, we selected the top 25 most prominent keywords in the literature from 1993 to 2022 according to CiteSpace and also made a co-citation reference network with cluster visualization and hotspot outburst (Figure 8). This selection can help us to visually identify research hotspots in a neighborhood during a certain period, the duration of the research, the transition from one field to another, and the focus of research in recent years [73]. We sorted keywords by time (Figure 8) and by outbreak intensity (S8).

1.

Automatic supervisory control

Among these keywords, “data simulation”, “VOCs”, and “hydrocarbon” have been the focus of research for the longest duration in the past five years. These keywords have occurred at a high frequency in the research on the unorganized emission of waste gas in the petrochemical industry, such as the data simulation literature. Analysis of the retrieved literature from 1981 to 2020 indicates several studies on the unorganized emission of waste gas in the petrochemical industry [74,75]. Unorganized emission is one of the main sources of exhaust gas emission in the petrochemical industry [76]. Consequently, researchers are exploring unorganized emission detection (for example, through laser detection) [74] and building models to estimate unorganized emissions. Researchers should consider using big data analytics and artificial intelligence to optimize existing treatment processes or to predict the efficiencies of new treatments under different operational conditions. AI models can also help in simulating the environmental impact of petrochemical waste gases, designing more effective mitigation strategies [77,78], and controlling unorganized exhaust gas emissions by improving tank valves or process equipment [79].

2.

Improve process efficiency

The keywords “thermodynamics”, “heat transfer efficiency”, “combustion”, and others appear in the 2009–2020 literature, indicating the focus on combustion flue gas in the PWG field during this period. Combustion flue gas is one of the exhaust gas emissions in the petrochemical industry, accounting for approximately 60% of the total exhaust emissions. The heating furnace in the petrochemical industry mostly uses vacuum residuum as fuel, and the residuum contains approximately 0.2–3% sulfur [80]. The resulting exhaust gas containing sulfur dioxide, nitrogen oxide, and dust generated by combustion is discharged after dust removal. However, sulfur dioxide and nitrogen oxide are not treated and are generally discharged at high altitudes [81]. The primary research focus in this area is improving heat transfer efficiency through improved processes [82].

3.

Low-carbon sustainable development

According to the keyword breakout charts of the recent five years (S4 and S5), popular keywords include “VOCs”, “methane”, “carbon dioxide”, “carbon dioxide emission”, and “carbon dioxide capture”. This is also consistent with our results in Figure 7b: we identified 16 distinct clusters in the co-reference network, with references with significant modularity and architecture scores indicating highly reasonable clusters (Q = 0.9485; S = 0.9561). By looking at these clusters, we found that CO₂ was the most frequently used word. As with the analysis in 3.3.1, among the exhaust gas emissions from the petrochemical industry, the focus is mostly on carbon, especially in the context of double carbon goals. Almost every part of the petrochemical industry—from raw materials to process production and waste emissions—involves carbon [83,84,85]. Considering that the industry uses fossil energy as a raw material, promoting the green and low-carbon transformation of the petrochemical industry is a key step in achieving positive economic and social benefits, especially within the dual carbon framework [86]. Scientists are working to help this challenging industry achieve low-carbon sustainability by replacing fossil carbon feedstocks with carbon from biomass, captured carbon dioxide, and other recyclable sources [87].

In recent years, a significant amount of research has been conducted on chemical production by green or low-carbon methods. As an illustration, a major component of the petrochemical industry is the precursors of several fine and bulk chemical products, including ethylene, propylene, benzene, toluene, xylene, and methanol, all of which are produced directly by renewable carbon methods or through the use of “green” methanol as intermediates, namely, through the methanol-to-olefin and methanol-to-aromatics processes. These processes require a large amount of energy obtained from renewable sources, such as wind, solar, and CCS (including bioenergy with CCS) [24,88]. Furthermore, achieving a negative emission balance can be accomplished by permanently storing carbon dioxide in specific plastics or building materials [89]. In addition, different types of biomass resources, including energy crops and residues, can be used as bio-carbon feedstock for chemical conversion within the framework of bio-refining [90]. This approach can also be carbon-neutral by utilizing naturally captured carbon dioxide. Therefore, it can be seen why low-carbon transformation technology in the petrochemical industry has become the focus of research recently and why it will continue to be an area of focus for a long time to come. The formulation of policies and regulations will directly affect this transformation. Cooperation and joint exploration among scholars, government officials, and business leaders for new ways of emission reduction in the petrochemical industry has great social and economic value for the future development of the industry.

4.

Adsorption gas filtration technology

Chemical and petrochemical companies are increasingly realizing that their sustainability depends in large part on developing new and innovative processes to use materials and energy more efficiently. Since the entire separation/purification process accounts for 40–60% of capital and operating costs, their improvements can significantly reduce costs, energy use, and waste generation by increasing profits [91]. Adsorptive gas separation technology is a mature unit operation in the chemical and petrochemical industries because it can efficiently handle a variety of gas separations, including impurity removal, gas purification, and separation in circulating streams [92,93]. The technology is still far from mature, and there are high opportunities to expand its applicability and improve efficiency in the context of a better understanding of physical phenomena and technological advances in materials and engineering research. The main contribution of adsorption technology to gas separation innovation is the discovery of novel adsorbents with better separation properties, combined with the use of multi-objective and multi-domain numerical methods for process development and optimization.

4. Discussion and Conclusions

4.1. Future Research Directions

As can be seen in Figure 8 and the co-cited cluster (S8), carbon reduction is a hot topic in PWG research. In order to mitigate climate change, the international community has come together to identify ways to reduce energy consumption and greenhouse gas emissions from the petrochemical sector [94,95] and made efforts to estimate energy requirements for manufacturing petrochemicals. The International Energy Agency’s forecast study suggests that more than a third of the growth in global oil demand from 2021 to 2030 will come from chemicals, and this proportion will grow to over 50% by 2050 [96]. Thus, the shift in petroleum processing from “fuel production” to “chemical maximization” has become a consensus. This shift is considered essential for the refining industry to become “carbon neutral” by the middle of the century [97]. Most oil companies and research institutions have responded to this trend by deploying crude oil-to-chemical technologies [98]. The current global research focus is mainly on the development of oil refining and chemical integration technology aimed at directly converting crude oil into chemicals while bypassing conventional atmospheric pressure and vacuum refining equipment [71]. As a large user of petroleum products, the industry’s continued reliance on fossil fuels has made the petroleum sector a great emitter [99]. Therefore, adopting a life-cycle approach is essential to comprehend the full impact of greenhouse gas emissions and explore mitigation opportunities. Energy efficiency and process heating based on renewable energy, biomass feedstocks, circular economy concepts, the synthesis of hydrocarbons from green hydrogen and carbon dioxide, and proper accounting for CCS and biomass carbon will collectively play pivotal roles in significantly reducing carbon emissions [100].

4.2. Policy Recommendations

In the face of the future development of PWG, government departments are more concerned about emission reduction and low-carbon transition in the petrochemical industry. Governments, consumers, and relevant enterprises in the petrochemical industry want to promote a transition to a low-carbon regime in the chemical and petrochemical industry. This transition requires careful consideration of inter-enterprise competitiveness issues and carbon emissions [101]. The government will create an appropriate enabling environment to support petrochemical enterprises to carry out technological research and development and promote advanced low-carbon technologies, such as the adoption of clean energy, the development of carbon capture and utilization, and the promotion of and full evaluation of the possibility of promoting the long-term development of intelligent manufacturing, so as to achieve the required economies of scale and technology learning [102]. For example, creating market demand that is conducive to enterprise development, such as implementing mandatory quotas for green products, may require a certification of green supply chains [103]. Since exhaust gas treatment involves chemistry, engineering, environmental science, and even economics, fostering an interdisciplinary approach can provide comprehensive solutions.

4.3. Limitations

Our study has some limitations. For instance, our bibliometric analysis data were collected from WOSCC, which is considered to be the most suitable database for scientometric research. However, the retrieved publications may have defects in terms of the timeliness and completeness of the literature. In future studies, databases such as Scopus, Google Scholar, PubChem, and PubMed could be included for comparison to obtain comprehensive results. The initial data set included only the English literature, and future studies should also include the literature in other languages, such as Spanish and Russian, to obtain a more complete analysis of the data. Another important limitation of scientometric research is citation bias: the sole purpose of a citation is to emphasize the impact of an article. A citation may not truly reflect the quality or relevance of an article, resulting in an underutilization of the available data. Different parameters, such as TP, TC, H-index, and percentage centrality of CiteSpace, can also lead to citation bias. Finally, different expressions of keywords may also lead to different search results and picture clustering outcomes. In our study, synonymous words were included in the search for keywords as much as possible.

4.4. Conclusions

This study analyzed the intellectual landscape of research in the PWG field over the past 41 years, identifying 1384 scholarly works. CiteSpace and VOSviewer software are used to provide a quantitative and visual review and critique of research results and advances in the field. This comprehensive mapping helps to reveal fundamental characteristics of the field, such as research strength, knowledge base, and research topic evolution. First, we performed a quantitative analysis of basic information, such as the number of annual publications, authors, institutions, countries, and journals. PWG is a growing field, and publications related to PWG are increasing annually. The top 10 institutions and the top 10 authors are concentrated in the United States, Europe, and China. This indicates that core journal organizations in this field have been established, while research collaboration remains an area that requires improvement. Our analysis also shows that the field is relatively concentrated in its focus, yet there is a need for enhanced interdisciplinary cooperation. Second, we obtained the main research emphases and hotspots within PWG during this period by analyzing keywords and citations. The research focuses of this field are improving efficiency and reducing costs, mixed pollutant treatment, sustainability and life cycle analysis, emerging pollutants, etc. In petrochemical waste gas, people are paying increasing attention to CO₂ recycling and treatment from exhaust gases emitted by the petrochemical industry and replacing fossil energy with clean energy to reduce pollution originating from exhaust gas emissions. Another area of interest pertains to the PWG emissions of VOCs, characterized by challenges such as difficulty in monitoring unorganized emissions, complex components, and difficult recycling and treatment options. Take, for example, the convergence of iot and smart technologies: automated monitoring and control systems are being integrated to optimize the performance of processing units and reduce operating costs. Our study provides useful information for researchers to understand the progress of PWG research and serves as a valuable resource for researchers, grant applicants, funding agencies, and policymakers.