A thermogravimetric-infrared combined characterization method for analyzing lignin thermal decomposition products in situ

Abstract

The present application relates to a kind of lignin thermal decomposition product in situ analysis thermogravimetric-infrared combined characterization method, including cantilever baseline test, precursor loading, mass loss detection and infrared signal detection.All experiments of the present application are carried out on the cantilever chip of micro-nano scale, with excellent thermal response consistency, atmosphere control uniformity and optical detection repeatability, create same, controllable experimental benchmark for comparing the influence of different conditions.At the same time, can systematically only change single variable, and real-time detection how this variable changes functional group evolution path directionally.Therefore, can clearly, intuitively compare and summarize the different regulation of pyrolysis path under different conditions.This enables researchers to systematically elucidate how heating rate, reaction atmosphere, catalyst and other parameters synergistically or competitively affect the whole pyrolysis, and lays a foundation for building a complete process control theory system.

Description

Technical Field

[0001] This invention belongs to the field of materials analysis technology, and specifically relates to a thermogravimetric-infrared combined characterization method for in-situ analysis of lignin thermal decomposition products. Background Technology

[0002] Lignin is an abundant, renewable aromatic polymer found in nature, making it an ideal sustainable alternative to fossil resources in the production of fuels and high-value chemicals. Currently, lignin can be converted into fuels and chemicals through methods such as thermal decomposition, chemical decomposition, biochemical conversion, and mechanical processing. Among these, thermal decomposition is solvent-free and involves rapid reactions. Through process optimization, pyrolysis can efficiently depolymerize lignin macromolecules and convert them into bio-oils rich in phenols, hydrocarbons, and oxygen-containing compounds. However, the order of chemical bond breaking and key reaction pathways during lignin thermal decomposition remain unclear, making it difficult to establish a correlation between process conditions and product distribution, thus hindering the targeted optimization and control of the pyrolysis process.

[0003] Revealing the intrinsic laws governing the pyrolysis mechanism and product distribution of lignin is a prerequisite for achieving its directional transformation. Although existing thermogravimetric analysis (TGA) and infrared spectroscopy techniques can analyze the pyrolysis process of lignin in situ, their detection targets are limited to the gaseous products that escape during the reaction, making it difficult to directly capture the dynamic evolution of the chemical structure on the material surface. The fundamental reason is that the furnace structure and optical system of traditional TGA analyzers are spatially independent, making it impossible to obtain information on structural changes on the sample surface during the reaction.

[0004] Therefore, developing an in-situ characterization method that can simultaneously track changes in mass and the evolution of the chemical structure of the material surface is crucial for elucidating the pyrolysis mechanism of lignin. Summary of the Invention

[0005] This invention provides an in-situ thermogravimetric-infrared (TGA) characterization method for lignin pyrolysis products. This method addresses the limitations of existing lignin pyrolysis research methods, which cannot synchronously, in-situ, and in real-time correlate macroscopic mass loss, microscopic functional group evolution, and final product distribution during the pyrolysis process. Consequently, it is difficult to systematically reveal and precisely control the directional influence of key parameters such as heating rate, reaction atmosphere, and catalyst on the pyrolysis reaction pathway, thus restricting the optimization and development of lignin-directed pyrolysis processes.

[0006] This invention provides a thermogravimetric-infrared combined characterization method for in-situ analysis of lignin thermal decomposition products, comprising the following steps:

[0007] (1) Place the resonant cantilever chip into a cavity with an optically transparent window and connect it to an external circuit through an electrical adapter on the cavity; introduce gas into the cavity, program the temperature of the cantilever chip through the circuit, and record the curve of the cantilever chip resonant frequency changing with time / temperature.

[0008] (2) Remove the above cantilever beam chip from the cavity, and then coat the free end of the cantilever beam in the chip with lignin precursor material as a sample;

[0009] (3) The above cantilever beam chip is put back into the cavity and the electrical and gas circuits are connected. Under the same programmed temperature control and atmosphere conditions, the heating process of step (1) is repeated to detect mass loss and obtain the thermogravimetric curve and its differential curve.

[0010] While detecting mass loss, the infrared beam of the infrared spectrometer is incident on the surface of the cantilever beam sample through the optically transparent window on the cavity. The reflected infrared signal is collected by the spectrometer and transmitted to the detector to acquire the reflective infrared spectrum in real time.

[0011] Preferably, the heating temperature range of the resonant cantilever beam chip in step (1) is room temperature to 1000°C.

[0012] Preferably, the resonant cantilever beam chip in step (1) is the resonant cantilever beam chip disclosed in CN111362226B.

[0013] Preferably, the gas flow rate in step (1) is 1 mL / min to 1 L / min, and the gas concentration ranges from 0.01% to 100%.

[0014] Preferably, the temperature rise rate of the programmed temperature control in step (1) is 1℃ / min to 100℃ / min.

[0015] Preferably, the infrared spectrometer scanning range in step (3) is 400~4000 cm⁻¹. -1 .

[0016] Addressing the limitations of existing technologies in providing synchronous, in-situ, and real-time analysis, the cantilever beam chip is used in conjunction with a micro-heater, mass sensor, and infrared spectrometer. This enables the simultaneous acquisition of highly sensitive thermogravimetric (TG) curves and in-situ infrared spectra of the sample surface from the same micro-region under programmed heating and a controlled atmosphere. This hardware-based solution resolves the data asynchrony issue caused by spatial separation in traditional devices, allowing for a direct correlation between weightlessness and structural evolution.

[0017] Addressing the problem of existing technologies' "difficulty in systematically revealing the regulatory mechanisms," this invention can systematically alter and study the effects of single or multiple parameters (such as heating rate, atmosphere, and catalyst). By observing changes in functional groups under different conditions in real time, it directly infers the regulation of the pyrolysis pathway by different conditions at the chemical bond level, thereby systematically revealing its influence.

[0018] Addressing the issue of "difficulty in precise control" in existing technologies, traditional product sampling is often based on fixed temperatures or time intervals, lacking process-based data. This invention utilizes real-time chemical information provided by coupled technologies to locate sampling points at the "critical temperature" where the reaction pathway undergoes a key inflection point. This ensures that the collected products best represent the dominant pathway of primary pyrolysis, minimizing interference from secondary reactions. Based on this, by correlating critical temperatures under different conditions, functional group evolution patterns, and the final GC-MS product distribution, a clear logical chain is established from condition control to pathway guidance to product verification, providing direct evidence for precise control.

[0019] like Figure 1 As shown, this invention places a miniature reaction chamber equipped with a cantilever beam chip below the microscope lens of an infrared spectrometer, allowing the infrared beam to pass through a diamond window for incident and reflected light. A trace amount of lignin sample is loaded onto the free end of the cantilever beam used in the experiment. During the test, the circuit system can acquire the resonant frequency of the cantilever beam in real time and convert it into a mass change curve; simultaneously, the infrared spectrometer irradiates the same micro-region of the sample through the microscope lens and acquires the reflected signal, detecting the infrared changes on the sample surface in real time. This system, through an intelligent gas distribution system, enables simultaneous, in-situ analysis of sample mass loss and surface chemical structure changes under a controlled atmosphere, providing key technical support for revealing the regulatory mechanisms of heating rate, reaction atmosphere, and catalyst on the pyrolysis path and product distribution at the mechanistic level.

[0020] Beneficial effects

[0021] (1) This invention employs a cantilever beam chip as the core device integrating heating, weighing, and infrared detection, enabling the measurement of mass changes and surface chemical bond evolution in the same tiny sample region to be completely synchronized in time and absolutely co-located in space. Because the measurements are synchronous and co-located, the dynamic changes of specific functional groups at each weightlessness step can be precisely correlated. This fundamentally overcomes the information disconnect problem caused by traditional TG, FTIR, and GC-MS analyses, providing reliable in-situ experimental evidence for directly explaining macroscopic weightlessness phenomena from the perspective of chemical bond breaking and recombination.

[0022] (2) All experiments in this invention are conducted on cantilever chips at the micro-nano scale, exhibiting excellent thermal response consistency, atmosphere control uniformity, and optical detection repeatability, creating a consistent and controllable experimental benchmark for comparing the effects of different conditions. Simultaneously, it allows for the systematic modification of a single variable and real-time detection of how that variable directionally alters the functional group evolution path. Therefore, it enables a clear and intuitive comparison and summarization of the differentiated control laws governing the pyrolysis pathway under different conditions. This allows researchers to systematically elucidate how multiple parameters, such as heating rate, reaction atmosphere, and catalyst, synergistically or competitively influence the overall pyrolysis process, laying the foundation for constructing a complete theoretical system for process control. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the method of the present invention.

[0024] Figure 2 (a) TG-DTG test results at 30-800°C; (b) in-situ infrared results at 30-650°C.

[0025] Figure 3 (a) is the TG-DTG curve at 30°C / min, showing the difference in thermal weight loss of lignin after increasing the heating rate; (b) is the in-situ infrared image of the second stage of pyrolysis at 30°C / min.

[0026] Figure 4 (a) is the TG / DTG curve of pyrolysis at 30°C / min and 5% H2 / Ar atmosphere; (b) is the in-situ infrared spectral change process of CH, C=C bonds at the key temperature points under the corresponding conditions. Detailed Implementation

[0027] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0028] Example 1

[0029] Using alkaline lignin as a precursor, this embodiment provides an in-situ thermogravimetric-infrared (TGA) characterization method for lignin thermal decomposition products, comprising the following steps:

[0030] (1) Place the resonant cantilever chip into a cavity with an optically transparent window and connect it to an external circuit through an electrical adapter on the cavity; introduce argon gas (gas concentration of 99.9% and gas flow rate of 30 mL / min) into the cavity, and use the circuit to program the temperature of the cantilever chip from room temperature to 800°C at a heating rate of 10°C / min, and record the curve of the resonant frequency of the cantilever chip changing with time / temperature;

[0031] (2) Remove the above cantilever beam chip from the cavity, and then coat the free end of the cantilever beam in the chip with lignin precursor material as a sample;

[0032] (3) The above-mentioned cantilever beam chip is put back into the cavity and the electrical and gas circuit connections are completed. Under the same programmed temperature control and atmosphere conditions, the heating process of step (1) is repeated to detect mass loss. As a high-sensitivity resonant mass sensor, the resonant frequency of the cantilever beam will shift with the change of sample mass. By monitoring and recording the change of the cantilever beam resonant frequency (Δf) with time / temperature in real time, and based on its inherent calibration relationship with mass change (Δm), the frequency shift curve is directly converted into the real-time mass change curve, that is, the thermogravimetric (TG) curve and its derivative (DTG) curve are obtained, thereby realizing the continuous and quantitative detection of sample mass loss during pyrolysis.

[0033] While detecting mass loss, the infrared beam of the infrared spectrometer is incident on the surface of the cantilever beam sample through the optically transparent window on the cavity. The reflected infrared signal is collected by the spectrometer and transmitted to the detector to acquire the reflective infrared spectrum in real time.

[0034] By using a cantilever beam chip and an infrared spectrometer, measurements such as Figure 2 The thermogravimetric-infrared curves shown indicate that the decrease in mass represents the decrease in lignin in the precursor material. The results show that lignin pyrolysis has three continuous and clearly defined stages. According to the infrared results, the breakage of the lignin skeleton and the formation of valuable products mainly occur in the second stage of pyrolysis.

[0035] like Figure 3 As shown, a thermogravimetric-in-situ infrared (TGA) experiment was subsequently conducted at 30°C / min. The results showed that at 30°C / min, the CH peak rapidly decreased, and the characteristic peaks of the aromatic skeleton changed drastically. It can be inferred that the product may contain a high content of phenols and aliphatic hydrocarbons.

[0036] like Figure 4 As shown, introducing 5% H2 into the wall cavity caused the disappearance of the condensation shift of the aromatic skeleton characteristic peaks under the H2 atmosphere. Thermogravimetric-infrared results indicate that hydrogen effectively suppressed the deep condensation of the aromatic skeleton.

Claims

1. A thermogravimetric-infrared combined characterization method for in-situ analysis of lignin thermal decomposition products, characterized in that, Includes the following steps: (1) Place the resonant cantilever chip into a cavity with an optically transparent window and connect it to an external circuit through an electrical adapter on the cavity; introduce gas into the cavity, program the temperature of the cantilever chip through the circuit, and record the curve of the cantilever chip resonant frequency changing with time / temperature. (2) Remove the above cantilever beam chip from the cavity, and then coat the free end of the cantilever beam in the chip with lignin precursor material as a sample; (3) The above cantilever beam chip is put back into the cavity and the electrical and gas circuits are connected. Under the same programmed temperature control and atmosphere conditions, the heating process of step (1) is repeated to detect mass loss and obtain the thermogravimetric curve and its differential curve. While detecting mass loss, the infrared beam of the infrared spectrometer is incident on the surface of the cantilever beam sample through the optically transparent window on the cavity. The reflected infrared signal is collected by the spectrometer and transmitted to the detector to acquire the reflective infrared spectrum in real time.

2. The thermogravimetric-infrared joint characterization method according to claim 1, characterized in that, The heating temperature range of the resonant cantilever beam chip in step (1) is from room temperature to 1000℃.

3. The thermogravimetric-infrared joint characterization method according to claim 1, characterized in that, The gas flow rate in step (1) is 1 mL / min to 1 L / min, and the gas concentration ranges from 0.01% to 100%.

4. The thermogravimetric-infrared joint characterization method according to claim 1, characterized in that, The temperature rise rate of the programmed temperature control in step (1) is 1℃ / min to 100℃ / min.

5. The thermogravimetric-infrared joint characterization method according to claim 1, characterized in that, The infrared spectrometer scanning range in step (3) is 400~4000 cm⁻¹. -1 .

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