📄 chemistry

Preparation-dependent pyrolysis kinetics of rosehip seed, skin, and whole fruit: Multirate TG–DTG analysis and DAEM adequacy assessment

This study demonstrates that rosehip seed, skin, and whole fruit exhibit distinct, non-interchangeable thermal response architectures during pyrolysis, necessitating preparation-specific interpretations of their kinetic behaviors and activation energy trajectories.

Original authors: Ahsanullah Soomro, Anıl Tevfik Koçer, Iqra panhwar, Zafar Ali Siyal, Mahdi Hassan, Hamid Rehman, Tasawar Ali Chandio, Didem Balkanlı

Published 2026-08-24

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Ahsanullah Soomro, Anıl Tevfik Koçer, Iqra panhwar, Zafar Ali Siyal, Mahdi Hassan, Hamid Rehman, Tasawar Ali Chandio, Didem Balkanlı

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

When plant matter is heated without oxygen, it does not simply melt or burn; it breaks down in a complex, layered process called pyrolysis. This transformation turns solid biomass into useful gases, liquids, and a carbon-rich solid residue, a mechanism that underpins efforts to turn agricultural waste into energy. Because different parts of a plant contain different chemical structures, they often break apart at different temperatures and speeds. Scientists use a technique called thermogravimetric analysis to watch this process unfold in real time. By heating a tiny sample while carefully measuring how much mass it loses, researchers can map out exactly when the material starts to decompose, how fast it happens, and how much solid remains at the end. Understanding these patterns is crucial for designing efficient reactors, but it requires knowing whether different parts of the same plant behave as a single unit or as distinct materials with their own unique thermal personalities.

A team of researchers set out to answer this specific question using the rosehip, the fruit of the wild rose plant. They took a single batch of dried rosehips and separated them into three distinct preparations: the seeds, the outer skin, and the whole fruit ground up exactly as it was found, containing seeds, skin, and flesh all mixed together. The goal was to determine if these three forms shared a common thermal response or if they required completely different interpretations. The team heated each sample in a nitrogen atmosphere at four different speeds, ranging from a slow 5 degrees Celsius per minute to a faster 20 degrees Celsius per minute. By comparing how the seeds, skins, and whole fruits reacted to these heating rates, they could see if the way the material was prepared changed the fundamental way it broke down.

The results revealed that the three preparations are not interchangeable; each possesses a distinct thermal architecture. The seeds were the most resistant to heat, showing the latest start to decomposition. They held their mass until temperatures reached between 180.3 and 228.0 degrees Celsius before beginning to lose weight significantly. Once the seeds started to break down, they did so in a concentrated burst within a specific high-temperature zone, with their main decomposition event occurring between 332 and 360 degrees Celsius. In contrast, the skin began to break down much earlier, starting its mass loss between 141.8 and 175.1 degrees Celsius. However, the skin did not simply finish its job quickly; it decomposed in two distinct stages, with one wave of breakdown happening at lower temperatures and another at higher temperatures. The whole fruit, which contained both seeds and skin mixed together, showed the earliest onset of all, starting to lose mass as low as 116.0 degrees Celsius. Yet, despite this early start, the whole fruit maintained a strong, dominant decomposition event at higher temperatures, similar to the seeds, rather than behaving like a simple average of its parts.

The researchers also looked at how much energy was required to drive these reactions at different stages of the process. For the seeds, the energy needed to break the material down increased as the process went on, rising from about 99 kilojoules per mole at the start to roughly 147 kilojoules per mole in the middle of the reaction. The skin showed the most dramatic change, where the energy required dropped sharply from a high of 277 kilojoules per mole down to 152 kilojoules per mole as the reaction progressed. The whole fruit followed a path similar to the seeds, with the energy requirement climbing from 115 to 139 kilojoules per mole. These differences in energy demand confirm that the chemical changes happening inside the seeds, the skins, and the whole fruit are fundamentally different, not just variations of the same process.

To test if these complex behaviors could be simplified into a single mathematical model, the team tried to fit the data to a standard type of equation often used to describe biomass breakdown. They found that while these models could be tweaked to match the curves on a graph, they often failed to capture the true shape of the reaction or predict how the material would behave under new conditions. For the seeds, a model with two distinct reaction zones offered a reasonable description, but for the skin, even the most complex models failed to reproduce the real, multi-stage nature of the decomposition. The whole fruit was best described by a model with three zones, but this model had not been tested against unseen data. The study concludes that relying on a single, simplified equation to describe these materials is risky. Instead, the most accurate way to understand rosehip waste is to treat the seeds, the skins, and the whole fruit as three separate materials, each with its own unique timing, energy needs, and decomposition pattern. This finding suggests that future efforts to convert rosehip waste into energy must be tailored specifically to the part of the fruit being used, rather than treating the entire harvest as a uniform fuel source.

Technical Summary: Preparation-Dependent Pyrolysis Kinetics of Rosehip Seed, Skin, and Whole Fruit

Problem Statement
The increasing volume of fruit-processing residues has intensified interest in thermochemical conversion routes for energy recovery. While rosehip residues (seeds, skins, and whole fruit) are recognized as potential biomass feedstocks, existing literature lacks a matched-batch comparison to determine whether these distinct preparations share a common thermal response or require preparation-specific interpretation. Furthermore, kinetic interpretations based on single global activation energy values often obscure conversion-dependent changes in the reacting population. This study addresses the question of whether rosehip seed, an operationally defined skin fraction, and whole-fruit material can be represented by a common thermal and kinetic response or if they necessitate distinct analytical frameworks under an identical multirate protocol.

Methodology
The study employed a rigorous, multi-faceted analytical approach using rosehip materials from a single matched batch:

Feedstock Preparation: Dried rosehip fruits were processed via two routes: (1) manual separation into seeds and an outer skin/peel fraction, followed by independent grinding; and (2) direct grinding of whole fruits without separation.
Thermogravimetric Analysis (TGA): Dynamic non-isothermal measurements were conducted under nitrogen at heating rates of 5, 10, 15, and 20 °C min⁻¹ over a temperature range of ambient to 700 °C.
Data Processing: The analysis utilized characteristic mass-loss temperatures ( $T_{5\%}$ , $T_{10\%}$ , $T_{50\%}$ ), fixed-interval mass losses (Stage I: <150 °C, Stage II: 150–400 °C, Stage III: 400–700 °C), and recurring DTG domain identification.
Kinetic Analysis: Apparent activation energies ( $E_a(\alpha)$ ) were estimated using four isoconversional methods (Friedman, Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa, and Starink). A critical "analytical-support screening" was applied, evaluating temperature ordering, regression quality, inter-method agreement, and profile continuity to identify reliable conversion intervals.
Modeling: Gaussian Distributed Activation Energy Models (DAEM) with 1 to 3 reactivity domains were fitted to the data. Model adequacy was assessed not merely by calibration error (RMSE) but also by parameter stability, residual structure, derivative-shape fidelity, and cross-rate prediction capability (using a leave-one-heating-rate-out approach for seed and skin).

Key Results
The study established that the three preparations possess distinct, non-interchangeable thermal-response architectures:

Rosehip Seed: Exhibited the most delayed low-conversion response ( $T_{5\%}$ : 180.3–228.0 °C) and a concentrated higher-temperature conversion zone. It displayed a single recurring DTG domain (332–360 °C). The apparent activation energy ( $E_a$ ) increased from 99.25 to 147.16 kJ mol⁻¹ over the conversion range $\alpha = 0.10–0.70$ , indicating a transition to a uniform effective-energy regime. A two-domain ( $K=2$ ) DAEM provided a parsimonious description with partial cross-condition transfer, though it could not fully reproduce all derivative features.
Rosehip Skin: Converted earlier ( $T_{5\%}$ : 141.8–175.1 °C) but retained the highest terminal mass ( $R_{700}$ : 29.97%) and the latest $T_{50\%}$ (372.3 °C) among the samples. It featured two recurring DTG domains (173–223 °C and 310–336 °C). Crucially, skin showed the strongest conversion dependence, with $E_a$ decreasing sharply from 277.22 to 152.21 kJ mol⁻¹ over $\alpha = 0.40–0.60$ . Increasing DAEM complexity reduced calibration error but failed to yield stable parameters or reproduce the measured multistage derivative topology; thus, the measured TG–DTG and isoconversional profiles were deemed more informative than the DAEM candidates.
Whole Fruit: Showed the earliest low-conversion response ( $T_{5\%}$ : 116.0–136.9 °C) and the lowest terminal mass ( $R_{700}$ : 20.93%). Despite early onset, it maintained a dominant higher-temperature domain (333–352 °C). Its $E_a$ trajectory increased from 115.02 to 139.04 kJ mol⁻¹ over $\alpha = 0.30–0.60$ . A three-domain ( $K=3$ ) DAEM closely fitted the calibration curves but lacked independent predictive validation against an unseen heating rate.

Model Adequacy and Endpoint Sensitivity
Endpoint sensitivity analysis (varying the terminal temperature from 600 to 700 °C) confirmed that while absolute $E_a$ magnitudes are dependent on the conversion coordinate definition, the preparation-specific trajectory directions (increasing for seed and whole fruit, decreasing for skin) and the shared-window ordering ( $E_a$ : Skin > Seed > Whole Fruit) remained robust. The study demonstrated that low calibration error in DAEM fitting does not guarantee stable parameters, predictive transferability, or faithful reproduction of the measured DTG architecture.

Significance and Claims
The paper claims to provide the first matched-batch comparison of rosehip seed, skin, and whole fruit that integrates multirate TG–DTG architecture, analytical-support-screened isoconversional kinetics, and distributed-reactivity model-adequacy testing within a single evidence framework.

The primary contribution is the establishment of three non-interchangeable thermal-response architectures, supporting the conclusion that preparation-specific thermal screening is necessary for reactor-study design. The study emphasizes that:

Whole-fruit behavior cannot be inferred through simple additive reconstruction of separated fractions.
Low calibration error alone is insufficient to establish a stable, transferable, or derivative-faithful kinetic representation.
A quantitative basis for thermal screening must rely on the specific combination of conversion timing, domain structure, apparent-energy trajectory, and final mass retention unique to each preparation.

These findings provide a quantitative foundation for designing subsequent reactor studies that directly evaluate product yields and operating conditions based on the distinct conversion behaviors of specific rosehip preparations.

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