Research Trends of Thermogravimetric Pyrolysis of Carnauba (Copernicia prunifera) and Thermokinetic Models Based on a Brief Bibliometric Investigation

Abstract

This study presents a brief bibliometric investigation of thermogravimetric pyrolysis of carnauba biomass (Copernicia prunifera), a palm tree native to northeastern Brazil belonging to the Arecaceae family. The objective was to analyze the scientific production and methods used to evaluate the kinetic parameters of biomass pyrolysis. An analysis was conducted using the Scopus, ScienceDirect, and Web of Science databases, and VOSviewer and Bibliometrix software. The methodology allows the generation of clusters and tables of scientific production, including authors, co-authors, affiliations, institutions, journals, and keywords. The search yielded 1983 articles, and after the application of exclusion criteria, 919 articles were retained, forming the basis for the bibliometric analysis. It provided an overview of thermogravimetric pyrolysis of carnauba research and identified areas that require further study. It also identified which universities and researchers have devoted the most effort to this area of research, the key findings, and areas that require further investment to complement existing research. Additionally, the study indicated the suitability of the Friedman method for determining kinetic parameters in biomass pyrolysis.

1. Introduction

Thermogravimetric pyrolysis is a technique that combines thermal analysis with pyrolysis. It permits the investigation of the thermal decomposition of complex organic and inorganic materials without oxygen, such as biomass conversion into products including coal, gas, and liquid [1]. For thermal study and to obtain thermodynamic data and kinetic parameters of the decomposition process, thermogravimetric analysis can be applied (TG curves) [2].

To determine the kinetic parameters associated with biomass pyrolysis, including the apparent activation energy, reaction constants, pre-exponential factor, and thermodynamic parameters such as enthalpy variations, entropy, and Gibbs free energy, thermogravimetric analysis has been employed extensively as a research tool [1]. These specifications are essential to determining the rate at which biomasses undergo thermal decomposition and allow the identification of the required temperature and residence time to achieve the optimal conversion into the desired products (bio-oil, biochar, and gases) [2,3,4].

Bongomin et al. 2024 [5] analyzed five biomass wastes using thermogravimetric analysis. The experiments were conducted under an inert atmosphere (N₂) with a heating rate of 20 °C/min and a temperature range of 25 °C to 950 °C. The results identified three pyrolysis stages (drying, devolatilization, and char formation) and the macadamia nutshell as having the highest thermal reactivity and efficient devolatilization characteristics (lowest initial devolatilization temperature (175 °C) and the highest peak temperature (380 °C)). Furthermore, the macadamia nutshell demonstrated high Gibbs free energy change (ΔG = 163.24 kJ/mol) and moderate enthalpy change (ΔH = 32.44 kJ/mol), indicating outstanding resistance to spontaneous decomposition. The coffee husk showed the highest activation energy (Ea = 60.59 kJ/mol), suggesting a complex thermal degradation behavior, and the rice husk had the lowest reactivity. The study emphasizes the importance of kinetic and thermodynamic analyses for understanding pyrolysis processes and optimizing biomass conversion for bioenergy production. Additionally, it highlights the necessity to investigate diverse biomass sources for future applications of the co-pyrolysis technique, including varied biomass mixtures and kinetic modeling to augment energy yields.

Nawaz et al. 2021 [6] investigated the pyrolysis performance and kinetic study of Lagerstroemia speciosa seed hull (waste biomass) in a thermogravimetric analyzer under an inert atmosphere. The kinetic study was conducted using isoconversional models, including the Ozawa–Flynn–Wall (OFW), Kissinger–Akahira–Sunose (KAS), Vyazovkin (VZM), Tang method (TM), and Starink method (STM). The results demonstrated the bioenergy potential of the biomass and average activation energies of 164 (OFW), 154.35 (KAS), 154.63 (TM), 154.61 (STM), and 141.93 kJ/mol (VZM). Additionally, the thermodynamic study showed that pyrolysis involves a complex reaction mechanism.

Among the biomasses with the potential for bioenergy production, lignocellulosic waste, including forestry and agriculture, can be subjected to several conversion technologies for further utilization on both small and large scales. In addition to pyrolysis, gasification, torrefaction, cogeneration (electricity and heat), recovery of energy from solid urban waste and landfill gas, and biofuels such as ethanol and biodiesel, they are among the options for processes and products [7,8,9,10]. Furthermore, bio-oil, fuel gas, and biochar may also be employed as chemical feedstocks in many industrial sectors [11,12,13].

According to the National Energy Balance (BEN) 2024, the proportion of renewable resources in the Brazilian energy matrix is 49.1%, influenced by an increase in the domestic supply of biomass (8.0%), wind (13.2%), and solar energy (7.0%) [14]. In particular, biomass represented the most significant contribution, accounting for 16.9% of the total bioenergy supply. Thus, to identify new biomasses and strategies for bioenergy production, it is essential to evaluate different species, including palm trees such as the carnauba (Copernicia prunifera (Miller) H. E. Moore) as a case study.

Carnauba is also known as the Tree of Life due to its resilience to rain and drought [15]. It is native to the northeast of Brazil, and its exploitation is mainly based on the extraction of ceriferous powder from the straw [16], in addition to the processing of the leaves, stems, fiber, fruit, and roots to manufacture craft and industrial products [17]. Each ton of carnauba wax results in 15,900 t of straw and 7650 t of stalk, representing a considerable quantity of biomass waste [18]. Therefore, these organic residues can contribute to the growth of bioenergy production. Figure 1 shows the carnauba palm tree.

The species belongs to the Arecaceae family, with geographical distribution in the Brazilian states of Ceará, Piauí, and Rio Grande do Norte (Caatinga biome) [19]. It is an arboreal plant with a stipe-like stem that can reach a height of 10 to 15 m and a diameter of 15 to 25 cm. The plant’s upper portion is characterized by fan-shaped leaves with a light green hue and a diameter of 0.6 to 1.0 m. The petioles measure between 1.0 and 1.5 m in length [20].

Carnauba’s growth rate is approximately 30 cm per year, and the first flowering occurs between 12 and 15 years of age. Its fruits are 1.5 to 3.0 cm long, and the tree has many applications in the manufacturing and chemical industries [21,22].

The extraction of carnauba has contributed to the income generation and occupation of a portion of the rural population in the Northeast of Brazil, particularly in the valleys of the Jaguaribe and Acaraú rivers (Ceará), Parnaíba (Piauí), and Apodi (Rio Grande do Norte) [23]. Figure 2 presents Brazil’s geographical distribution of carnauba powder and wax production. Piauí and Ceará are the principal producers of the tree byproducts, indicating the species as a source of employment and income.

The carnauba tree is entirely usable. The leaves, in addition to the ceriferous powder extraction, can be used in handicraft production [24,25]. The bagana (straw without ceriferous powder, Figure 3a), a byproduct derived from wax extraction, is also used to protect, cool, and maintain soil moisture, primarily in regions where the wax is produced [26]. The stalk (Figure 3b) can serve in handicraft production, toys, furniture, roofing material for homes, and other applications [27].

Thus, given the considerable quantity of biomass waste generated in carnauba wax production and the growing importance of bioenergy worldwide, this paper presents a brief bibliometric investigation [28,29] of the thermogravimetric pyrolysis of the carnauba (Copernicia prunifera) for the first time. Additionally, it shows an overview of the mathematical models frequently employed in kinetic and thermodynamic parameter determination. The analysis made it possible to delineate the research advancement and identify principal areas, outstanding authors, and interinstitutional and international collaborations.

2. Materials and Methods

2.1. Database, Descriptors, and Time Range

The research used the Scopus, ScienceDirect, and Web of Science databases. The following terms were employed: “Pyrolysis AND Carnauba OR Copernicia prunifera”; “Thermal AND degradation AND Carnauba OR Copernicia prunifera”; “Pyrolysis AND Thermogravimetric AND Carnauba OR Copernicia prunifera”; “Thermal analysis AND Carnauba OR Copernicia prunifera”; “Kinetic AND Study AND Thermogravimetric AND Differential Scanning Calorimetry AND Carnauba OR Copernicia prunifera”; “Friedman AND Ozawa-Flynn-Wall AND Kissinger-Akahira-Sunose AND Biomass”; and “Carnauba And Straw And Stalk”. In total, 174 articles were identified using a time range of January 2008 to May 2024.

2.2. Exclusion and Inclusion Criteria

The inclusion criteria were [A] articles containing descriptors in the title, abstract, or keywords; [B] articles with thermogravimetric pyrolysis data of the carnauba; and [C] complete articles of in vivo and in vitro studies in English. The exclusion criteria were [A] works outside the category of original research, including cover letters, prefaces, comments, editorials, and reviews; [B] case reports, review articles, books, book chapters, theses, and dissertations; and [C] repeated studies.

2.3. Document Selection Procedure

The data analysis was conducted using VOSviewer (version 1.6.19) and Bibliometrix (version 4.0.0) software. The flowchart shown in Figure 4 outlines the bibliometric investigation procedure.

The scientific production was demonstrated by clusters and tables.

3. Results and Discussion

A total of 1983 articles addressing the thermogravimetric pyrolysis of carnauba were identified. After applying the inclusion and exclusion criteria, 919 articles remained. Figure 5 shows 786 publications on pyrolysis, thermogravimetric analysis, and carnauba (Copernicia prunifera) from January 2008 to May 2024. The year 2023 recorded the highest number of scientific works, with 2022 and 2024 recording high rates.

3.1. Quantitative Analysis of Frequent Keywords

The keywords used in the documents are essential to understanding the evolution of a field of research. These provide invaluable insights into the subject, including applications, trends, relevance, discussions, and other general research issues. Applying the exclusion of articles written in Portuguese, conference papers, and early access papers, 786 documents were obtained.

Table 1. Quantitative analysis of the 30 most frequently used keywords in research investigations on pyrolysis, carnauba, and thermogravimetric analysis.

Rank	Keywords	Frequency	TLS *	Rank	Keywords	Frequency	TLS *
1	carnauba wax	56	15	16	thermal analysis	9	23
2	wax	27	9	17	degradation	9	14
3	cellulose	23	49	18	DSC	9	14
4	carnauba	21	16	19	thermal stability	9	13
5	Copernicia prunifera	21	5	20	biodegradable	9	5
6	mechanical properties	20	11	21	Fourier transform infrared spectroscopy	8	37
7	fibers	16	38	22	Differential Scanning Calorimetry	8	23
8	scanning electron microscopy	15	31	23	extraction	8	10
9	biomass	12	15	24	pyrolysis	8	5
10	kinetics	12	9	25	Caatinga	8	1
11	Brazil	11	2	26	thermal properties	6	9
12	composites	10	16	27	thermogravimetry	6	10
13	lignin	10	16	28	isotherm	5	8
14	physical properties	10	7	29	carnauba straw	5	3
15	thermogravimetric analysis	9	36	30	lignocellulosic residues	5	10

* TLS: total link strength.

shows the ranking and total link strength (TLS) of the 30 main keywords, representing the most pertinent issues in this field of research over the past 16 years. The keywords “carnauba wax”, “wax”, and “cellulose” are particularly prominent.

Figure 6 shows a word cloud generated by the VOSviewer software, comprising clusters of different colors. The keywords of the 786 articles were analyzed, resulting in 3695 words, of which the 30 cited at least five times were selected for use. The larger circles represent words with more significant connections between clusters. The more visibility of the connections, the stronger the link.

The titles of the 786 articles were analyzed using the Mendeley tool and the filter “Pyrolysis”, “Thermogravimetric”, “Carnauba”, and “Copernicia prunifera”, which resulted in one article with the title ‘Thermogravimetric pyrolysis of residual biomasses obtained post-extraction of carnauba wax: Determination of kinetic parameters using Friedman’s isoconversional method’. The analysis of the keyword co-citation identified 26 words and their connections (Figure 7). The red color for all connections indicates that all terms are part of the same study area.

The Bibliometrix software was used to create a keyword cloud (Figure 8). The size of the words represents their relevance. The most common keywords were pyrolysis, activation energy, and cellulose. Other relevant keywords were thermogravimetric pyrolysis, kinetics parameter, isoconversional method, carnauba stalk, and carnauba straw.

3.2. Publications by Countries and Institutions

The analysis utilized the information provided by the authors in the fields of affiliation, country, and institution of origin. The 10 countries with the highest scientific production represent 89.60% of the total publications (

Table 2. Countries’ major bibliometric performance indicators associated with research on pyrolysis, carnauba, and thermogravimetric analysis.

Rank	Countries	Nº of Papers	Rank	Countries	Nº of Papers	Rank	Countries	Nº of Papers
1	Brazil	402	12	Germany	6	23	France	2
2	China	34	13	Republic of Korea	6	24	Ghana	2
3	India	25	14	Belgium	5	25	Sweden	2
4	Turkey	19	15	Ukraine	5	26	Austria	1
5	Italy	18	16	Bangladesh	4	27	Cameroon	1
6	Portugal	17	17	Czech Republic	4	28	Chile	1
7	Spain	15	18	Canada	3	29	Costa Rica	1
8	USA	14	19	Mexico	3	30	Libya	1
9	Iran	8	20	South Africa	3	31	Norway	1
10	Malaysia	8	21	Sudan	3	32	Russia	1
11	Serbia	7	22	Australia	2	33	UK	1

). The publications are mainly concentrated in Brazil (402 publications: 64.32%), China (34 publications: 5.44%), and India (25 publications: 4%).

Figure 9 presents the distribution of publications by country, categorized by period and research area. The analysis focuses on countries that produced at least one publication. Brazil has the highest number of publications in the field, probably attributed to the importance of the carnauba wax industry.

Figure 10a shows a density map of the countries with published articles on the research issue. Brazil’s intensity of color indicates its higher contribution. Figure 10b presents a map of the collaborative links between the scientific groups. Brazil, the USA, and China collaborate the most in this field.

The documents from the Web of Science (WoS) database were analyzed. Of the 220 institutions, 10 contribute 51.72% of the total articles (

Table 3. Top 10 institutions with publications on pyrolysis, carnauba, and thermogravimetric analysis.

Rank	Organizations	Documents	TLS *
1	Universidade Federal do Piauí	19	42
2	Universidade Federal do Ceará	18	33
3	Universidade Estadual do Ceará	10	14
4	Universidade Federal de Campina Grande	5	11
5	Universidade de São Paulo	5	17
6	Universidade Estadual de Campinas	4	15
7	Universidade Federal de Lavras	4	7
8	Universidade Federal do Rio Grande do Norte	4	7
9	Embrapa Agroindústria Tropical	3	4
10	Universidade Federal do Maranhão	3	4

* TLS: total link strength.

). The Federal University of Piauí (19 publications), the Federal University of Ceará (18 publications), and the State University of Ceará (10 publications), all located in Brazil’s northeast, concentrate the highest number of articles. This can probably be attributed to the production of carnauba wax, which represents one of the economic bases for the region’s farmers [30].

Figure 11 shows a network map that allows the observation of interinstitutional collaboration. Applying the restriction of at least one publication per institution, 220 occurrences were obtained. A total of 70 institutions demonstrated a correlation, with the most relevant being the Federal University of Piauí, the Federal University of Ceará (linked to Embrapa Agroindústria Tropical), and the State University of Ceará.

3.3. Scientific Journals with Publications in the Field

We used the Bibliometrix software and the criterion of at least one publication per journal to obtain scientific journals with articles in the field. The analysis returned 303 journals and an average of 2.6 articles per journal. The result suggests interest in the subject, but the number of relevant publications is still reduced.

Table 4. Top 15 scientific journals with the most publications related to pyrolysis, carnauba, and thermogravimetric analysis.

Rank	Journals	Number of Publications	IF	PC
1	Food Chemistry	37	8.80	4.71%
2	International Journal of Biological Macromolecules	26	8.20	3.31%
3	Powder Technology	23	5.20	2.93%
4	Industrial Crops and Products	20	5.90	2.54%
5	LWT	20	6.00	2.54%
6	Food Hydrocolloids	19	10.70	2.42%
7	Food Research International	17	8.10	2.16%
8	Progress in Organic Coatings	16	6.60	2.04%
9	Chemical Engineering Journal	15	15.10	1.91%
10	International Journal of Pharmaceutics	15	5.80	1.91%
11	Carbohydrate Polymers	14	11.20	1.78%
12	Polymers	14	4.60	1.78%
13	Food Bioscience	10	5.20	1.27%
14	Journal of Food Engineering	10	5.50	1.27%
15	Colloids And Surfaces A: Physicochemical and Engineering Aspects	9	5.20	1.15%

Note: IF: impact factor; PC: percentage of the total articles per journal.

shows the 15 most relevant scientific journals in thermogravimetric pyrolysis, classified according to the number of publications and impact factor. These journals represent 33.72% of the total publications of the 303 journals.

As observed, the journals with the highest number of articles in the field are related to the food industry, including Food Chemistry (37 publications), Food Hydrocolloids (19 publications), and Food Research International (17 publications).

3.4. The Most Cited Researchers and Articles

The number of citations is an indicator frequently used to assess the publication’s relevance [31].

Table 5. The ten most cited documents related to pyrolysis, carnauba, and thermogravimetric analysis.

Rank	Documents	Authors	Citations	Years
1	Rhodamine b removal with activated carbons obtained from lignocellulosic waste [32]	Da Silva Lacerda, V.	171	2015
2	Effect of beeswax and carnauba wax addition on properties of gelatin films: A comparative study [33]	Zhang, Y.	106	2018
3	Hydroxystilbenes are monomers in palm fruit endocarp lignins [34]	Del Río, J.C.	72	2017
4	Optimization studies on cellulase and xylanase production by Rhizopus oryzae uc2 using raw oil palm frond leaves as substrate under solid state fermentation [35]	Ezeilo, U.R.	63	2020
5	Aqueous choline chloride: a novel solvent for switchgrass fractionation and subsequent hemicellulose conversion into furfural [36]	Chen, Z.	58	2018
6	Mechanical, thermal and ballistic performance of epoxy composites reinforced with Cannabis sativa hemp fabric [37]	Ribeiro, M.P.	46	2021
7	Antioxidant and antifungal activity of carnauba wax powder extracts [38]	Da Silva Andrade, L.B.	29	2018
8	Analysis of mechanical and wettability properties of natural fiber-reinforced epoxy hybrid composites [39]	Atmakuri, A.	28	2020
9	Hexavalent chromium removal from water: adsorption properties of in natura and magnetic nanomodified sugarcane bagasse [40]	Abilio, T.E.	25	2021
10	Copernicia prunifera leaf fiber: A promising new reinforcement for epoxy composites [41]	Junio, R.F.P.	19	2020

presents the most cited articles obtained from the Scopus base. The results revealed that the works of Da Silva Lacerda et al. (2015) [32], Zhang et al. (2018) [33], Del Río et al. (2017) [34], and Ezeilo et al. (2020) [35] are significant contributors to the field, with papers with over 60 citations.

The authors with the most publications in the area were obtained from the Web of Science, ScienceDirect, and Scopus databases. The search returned 3921 authors. After applying the criteria of a minimum of three documents per author, the number was reduced to 125.

Table 6. Top ten authors with the most publications in the area.

Rank	Authors	Number of Publications	TLS *	Year
1	Monteiro, S. N.	13	7	2022
2	Guedes, M. I. F.	9	18	2019
3	Bezerra, L. R.	7	16	2021
4	Nascimento, L. F. C.	7	7	2022
5	Bezerra, A. M. E.	6	20	2015
6	Correa-Guimaraes, A.	6	41	2016
7	Da Silva, A. L.	6	16	2020
8	Hernández-Navarro, S.	6	41	2016
9	López-Sotelo, J. B.	6	41	2016
10	Martín-Gil, J.	6	41	2016

* TLS: total link strength.

presents the ten authors with the highest productivity, representing 14%. The number of authors indicates a notable interest in pyrolysis, carnauba, and thermogravimetric analysis issues.

Figure 12 shows a map of the authors’ network collaborations, comprising 42 clusters, with the largest in red, green, blue, and yellow. Guedes, M. I. F., Correa-Guimaraes, A., Bezerra, L. R., and Monteiro, S. N., are in the most representative clusters. These researchers have several publications in the area (Table 6). Researchers with many citations, such as Monteiro, S. N. and Ribeiro, M. P., present a collaborative network (Table 5).

The analysis of the articles returned one document with the keywords “pyrolysis”, “thermogravimetric analysis”, and “carnauba (Copernicia prunifera)”. The title is “Thermogravimetric pyrolysis of residual biomasses obtained post-extraction of carnauba wax: Determination of kinetic parameters using Friedman’s isoconversional method” [42]. The article was published by Carvalho et al., 2023 [42], Federal University of Ceará, in the Renewable Energy journal. The aim was to study the thermogravimetric pyrolysis of carnauba straw and stalk. The experiments were conducted at four heating rates, and kinetic parameters were calculated using three isoconversional methods: Friedman (differential), KAS (integral), and OFW (integral). Currently, the article has six citations.

A single article with the keywords “pyrolysis”, “thermogravimetric analysis”, and “carnauba (Copernicia prunifera)” in the title does not indicate a lack of interest in the field, as 786 articles on the topic were found in 303 journals by 220 institutions.

3.5. Residual Carnauba (Copernicia prunifera) Biomass

The residual biomasses (bagana and stalk) are derived from ceriferous powder extraction. However, other parts of the palm can be commercialized, such as the straw for handicrafts and the stalk for bioenergy [43]. The research was conducted in the Scopus database to identify relevant literature on the carnauba stalk and straw. A total of 43 articles were identified.

Table 7. The nineteen keywords frequently used in carnauba, straw, and stalk’s research investigations.

Rank	Keywords	Frequency	TLS *
1	cellulose	12	29
2	lignin	10	26
3	biomass	9	21
4	scanning electron microscopy	9	28
5	Fourier transform infrared spectroscopy	8	29
6	thermogravimetric analysis	6	17
7	biodegradable polymers	3	3
8	degradation	3	10
9	lignocellulosic biomass	3	11
10	mechanical properties	3	4
11	straw	3	9
12	thermal properties	3	4
13	activation energy	2	7
14	biochar	2	3
15	bioconversion	2	4
16	kinetics	2	3
17	pyrolysis	2	9
18	thermodynamics	2	5
19	thermogravimetry	2	10

* TLS: total link strength.

shows the classification and total link strength of the 19 main keywords.

Figure 13 presents a word cloud of the principal keywords from the 43 articles. The Scopus database yielded 795 words, including words cited at least five times in different documents. The biggest circles represent the words with the most occurrences: green, “cellulose”, “lignin”, and “biomass”; red, “scanning electron microscopy”, “Fourier transform infrared spectroscopy”, and “thermogravimetric analysis”; blue, “pyrolysis” and “thermogravimetry”; and yellow, “kinetics” and “thermodynamics”. These words are directly related to the area under discussion.

The 43 articles were analyzed for the number of citations.

Table 8. Top ten cited documents in research studies related to carnauba, straw, and stalk.

Rank	Documents	Authors	Citations	Years
1	Effects of chitin nano-whiskers on the antibacterial and physicochemical properties of maize starch films [44]	Qin, Y.; Zhang, S.	137	2016
2	Removal of copper ions from aqueous solution using low temperature biochar derived from the pyrolysis of municipal solid waste [45]	Hoslett, J.; Ghazal, H.	81	2019
3	Hygrothermal properties of bio-insulation building materials based on bamboo fibers and bio-glues [46]	Nguyen, D.M.; Grillet, A	70	2017
4	Ethanol production from sugarcane bagasse: Use of different fermentation strategies to enhance an environmental-friendly process [47]	De Araujo Guilherme, A.	60	2019
5	Effect of maleated pla on the properties of rotomolded pla-agave fiber biocomposites [48]	González-López, M.E.	56	2019
6	Rice straw pretreatment with koh/urea for enhancing sugar yield and ethanol production at low temperature [49]	Zahoor; Wang, W.	44	2021
7	Biochemical characterization of cellulase from bacillus subtilis strain and its effect on digestibility and structural modifications of lignocellulose rich biomass [50]	Malik, W.A.; Javed, S.	42	2021
8	Co-fermentation of immobilized yeasts boosted bioethanol production from pretreated cotton stalk lignocellulosic biomass: long-term investigation [51]	Malik, K.; Salama E.-S.	35	2021
9	Copper removal using carnauba straw powder: equilibrium, kinetics, and thermodynamic studies [52]	Ferreira da Silva, A.J.	17	2018
10	Valorization of carnauba straw and cashew leaf as bioadsorbents to remove copper (ii) ions from aqueous solution [53]	Pereira, J.E.S.	11	2021

presents the ten most cited. The articles published by Qin Y. et al. (2016) [44], Hoslett J. et al. (2019) [45], and Nguyen D. M. et al. (2017) [46] received the highest number of citations.

Among the ten most cited articles, two stand out: (i) “Copper removal using carnauba straw powder: Equilibrium, kinetics, and thermodynamic studies” (17 citations) and “Valorization of carnauba straw and cashew leaf as bioadsorbents to remove copper (ii) ions from aqueous solution” (11 citations).

3.6. Research Areas

From 786 documents, 30 research areas related to pyrolysis, carnauba, and thermogravimetric analysis were identified. The most prominent fields were agriculture and biological sciences (27.07% of occurrences), materials science (14.59%), and chemistry (12.35%) (Figure 14).

3.7. Methods for Determining Kinetic Parameters

The International Confederation for Thermal Analysis and Calorimetry (ICTAC) recommends applying isoconversional methods to determine the kinetic parameters of biomass pyrolysis using thermogravimetry data [54,55]. Isoconversional models, also known as Model-free kinetics, allow kinetic parameters of solid-state reactions to be determined without knowledge of the reaction mechanism for a wide range of temperatures [5,56]. Non-isothermal models can be divided into two main categories: differential and integral methods [55]. Friedman (FRI)—differential, Ozawa–Flynn–Wall (OFW)—integral, and Kissinger–Akahira–Sunose (KAS)—integral were selected for the analysis.

The Friedman method (FRI) is based on the hypothesis that the reaction model is independent of the heating program. According to this method, for a series of experiments carried out at different heating rates, it is possible to determine the value of the activation energy (E_a) for each mass conversion fraction (α) by linearly fitting the curve of ln(dα/dt) or ln(βdα/dT) as a function of 1/T only for experiments with dynamic analyses (non-isothermal), i.e., linear heating. In both analysis conditions, the slope of the curve is equal to −E_a/R, as described in Equation (1) [57].

$$\mathrm{l}\mathrm{n}\left({\displaystyle \frac{\mathrm{d}\mathsf{\alpha }}{\mathrm{d}\mathrm{t}}}\right)=\mathrm{l}\mathrm{n}\left(\mathsf{\beta }{\displaystyle \frac{\mathrm{d}\mathsf{\alpha }}{\mathrm{d}\mathrm{T}}}\right)=\mathrm{l}\mathrm{n}\left[\mathrm{A}\mathrm{f}\left(\mathsf{\alpha }\right)\right]-{\displaystyle \frac{{\mathrm{E}}_{\mathrm{a}}}{\mathrm{R}\mathrm{T}}}$$

(1)

where α = mass conversion fraction (f(α)); β = heating rate (dT/dt); T = absolute temperature (K); t = time (s); A = pre-exponential factor (1/s); E_a = activation energy (kJ/mol); and R = universal ideal gas constant (8.314 J/K mol).

The Ozawa–Flynn–Wall method (OFW) is a kinetic analysis that calculates the dependence of the activation energy, E_a(α), with the degree of conversion, α, for dynamic experiments with different constant heating rates, β, as shown in Equation (2) [58].

$$\mathrm{l}\mathrm{n}\mathsf{\beta }=\mathrm{l}\mathrm{n}\left({\displaystyle \frac{\mathrm{A}\mathrm{E}}{\mathrm{R}\mathrm{g}\left(\mathsf{\alpha }\right)}}\right)-5.331-1.052{\displaystyle \frac{{\mathrm{E}}_{\mathrm{a}}}{\mathrm{R}\mathrm{T}}}$$

(2)

where g(α) = integral form of the reaction; T = absolute temperature (K); A = pre-exponential factor (1/s); E_a = activation energy (kJ/mol); and R = universal ideal gas constant (8.314 J/K mol).

The Kissinger–Akahira–Sunose method (KAS) assumes that the temperature of the maximum reaction rate point is equal to the temperature of the maximum inflection point of the thermal analysis curve. It is a method for calculating the activation energy of a reaction from thermal analysis curves at different heating rates. In the case of f(α) = 1 − α, the Kissinger equation, derived according to the maximum reaction rate condition, is represented by Equation (3) [54].

$$\mathrm{l}\mathrm{n}\left({\displaystyle \frac{\mathsf{\beta }}{{\mathrm{T}}_{\mathrm{P}}^2}}\right)=-{\displaystyle \frac{{\mathrm{E}}_{\mathrm{a}}}{\mathrm{R}}}\left({\displaystyle \frac{1}{{\mathrm{T}}_{\mathrm{P}}}}\right)+\mathrm{l}\mathrm{n}\left({\displaystyle \frac{\mathrm{R}\mathrm{A}}{\mathrm{E}}}\right)$$

(3)

where A = pre-exponential factor (1/s); E_a = activation energy (kJ/mol); β = heating rate (dT/dt); T_p = absolute temperature (K); and R = universal ideal gas constant (8.314 J/K mol).

Bibliometric analysis for publications on kinetic parameters and their isoconversional models in the Scopus database was conducted using VOSviewer and Bibliometrix software. A filter identified 90 articles about the Friedman, Ozawa–Flynn–Wall, and Kissinger–Akahira–Sunose models. Figure 15 illustrates a word cloud generated by the VOSviewer software comprising clusters of different colors. The co-citation of keywords in the 90 selected articles was subjected to analysis. A total of 976 words were identified, of which 30 were cited at least eight times. The most prominent words were activation energy (74 occurrences), kinetics (59), pyrolysis (58), thermogravimetric analysis (58), and kinetic parameters (23).

Figure 16 was generated from the 90 articles selected from the Scopus database. The bibliometric analysis was conducted using the most frequent words in the abstracts. A total of 2000 words were used to determine the most frequently utilized model for determining pyrolysis parameters associated with carnauba biomass. The Friedman model was identified as the most used, followed by OFW and KAS [59].

The differential Friedman model is the most prominent thermokinetic method, probably due to its simplicity, which allows for the more straightforward determination of activation energy (E_a) and the pre-exponential factor (A) [60,61].

4. Conclusions

A literature review was conducted on thermogravimetric pyrolysis of carnauba biomass (Copernicia prunifera). The analysis included an examination of established trends within the field and a detailed investigation into the methodologies employed for evaluating the thermokinetic parameters of biomass pyrolysis. The study assessed 919 articles published between January 2008 and May 2024 in the Scopus, ScienceDirect, and Web of Science databases using three tools: VOSviewer, Bibliometrix, and Microsoft Excel. The database allowed the creation of network maps (clusters) and tables related to scientific production, thus facilitating the comprehension of research trends in this field; for example, valuable insights into thermogravimetric pyrolysis. According to the results, the following points are highlighted:

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The countries with the highest number of publications were Brazil, China, and India;

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The kinetic parameters of biomass pyrolysis were highlighted in this article, with Friedman’s isoconversional method being the most recommended by researchers;

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The research topics were identified through keyword analysis, and the following themes emerged: carnauba wax, cellulose, biomass, activation energy, kinetics, pyrolysis, thermogravimetric analysis, and kinetic parameters;

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The Federal University of Piauí (Brazil) is the core institution in a network of 220 organizations involved in research on pyrolysis, carnauba, and thermogravimetric analysis. It has produced the highest number of publications in this field, followed by the Federal University of Ceará (Brazil).

The number of journals on this topic shows significant interest from several academic fields. However, the number of relevant publications remains low. Lignocellulosic waste has many potential applications, including energy and biochar production. This charcoal is made using thermoconversion technology, namely pyrolysis, and can be used in soil to reduce greenhouse gas emissions. Given this, it is clear that an in-depth study of thermoconversion technologies is necessary to enhance the potential of renewable energies by effectively harnessing biomass and thus reducing dependence on fossil fuels.