A system for the production of a biomass-based sulfonated catalyst for the solketal synthesis

Abstract

A system for the production of a sulfonated, biomass-based catalyst for solketal synthesis, comprising: a dissolving unit designed to accommodate cellulose and concentrated sulfuric acid and enabling the portionwise addition of cellulose to the sulfuric acid, wherein the cellulose is dissolved in the sulfuric acid using a magnetic stirrer; a hydrothermal treatment unit configured to take the dissolved cellulose mixture from the dissolution unit and heat this mixture at 80 °C for 18 hours to obtain a carbonaceous residue; a washing plant connected to the hydrothermal treatment plant and configured to wash the cool, carbonaceous residue with deionized water; and a drying unit configured to dry the washed sulfonated biomass-based catalyst (C-SO3H) overnight at 80 °C under vacuum.

Description

AREA OF INVENTION

[0001] The present disclosure relates to the synthesis of a sulfonated, biomass-based catalyst, in particular a system for producing a sulfonated, biomass-based catalyst for the solketal synthesis, wherein the cellulose-based heterogeneous solid carbon catalyst is synthesized by the system by enabling the treatment of cellulose with concentrated sulfuric acid under harmless hydrothermal conditions. BACKGROUND OF THE INVENTION

[0002] Biodiesel is one of the most promising renewable energy sources and, due to the existing infrastructure, is considered the easiest replacement for conventional diesel fuel to implement.

[0003] Glycerol is produced as a byproduct of biodiesel production through transesterification, accounting for approximately 10 wt% of the mass balance. With the continued expansion of biodiesel production, a glycerol surplus is expected, driving research into converting this feedstock into higher-value compounds. Glycerol can be converted into various valuable products, including solketal, a fuel additive produced by acetalization with acetone.

[0004] Solketal is a versatile compound that can improve the octane rating of gasoline, reduce deposit formation, act as a solvent and plasticizer, function as an antifreeze, and be used as a suspension agent in pharmaceutical preparations. It is also a useful fuel additive that can lower emissions and has proven to be more environmentally friendly than other gasoline additives.

[0005] Numerous homogeneous acid catalysts, such as H3PO4, HCl, and p-toluenesulfonic acid, have been used for the acetalization of glycerol. However, their use is limited due to inaccurate purification and complicated product separation. Heterogeneous catalysts offer advantages such as easy separation, reusability, straightforward handling, attractive acid-base properties, hydrothermal stability, low cost, high availability, and non-toxicity.

[0006] Various heterogeneous catalysts for the conversion of glycerol to solketals have been described in the prior art, including resins, mesoporous silicon dioxide, clay minerals, zeolites, layered α-zirconium phosphate, sulfated organometallic frameworks, hydrophobic zirconium organophosphonates, and mixed metal oxides. However, most of these catalysts are moisture-sensitive, require complex synthesis procedures, are unstable, toxic, or expensive. Therefore, there is growing interest in the synthesis of catalysts from biomass, as this provides natural precursors that are safe, inexpensive, and environmentally friendly.

[0007] The hydrothermal carbonization (HTC) of biomass can lead to highly stable, functionalized carbon materials. Therefore, there is a need for a biogenic, biodegradable, and environmentally friendly biomass-based catalyst that overcomes the limitations of existing catalysts while efficiently converting glycerol to solketal.

[0008] In light of the foregoing, the present invention provides a system for the production of a sulfonated, biomass-based catalyst for solketal synthesis. SUMMARY OF THE INVENTION

[0009] The present invention relates to a sulfonated, biomass-based catalyst for the synthesis of solketal by acetalization of glycerol, a byproduct of biodiesel production. The invention provides a system for the production of a sulfonic acid-functionalized carbon-containing material (C-SO3H) obtained from cellulose by hydrothermal carbonization with concentrated sulfuric acid under harmless conditions. The catalyst is biogenic, biodegradable, and environmentally friendly, thus overcoming the limitations of existing heterogeneous catalysts. The produced C-SO3H catalyst is used for the microwave-assisted acetalization of glycerol with acetone for the synthesis of solketal, a valuable biofuel additive. Under optimized reaction conditions (molar ratio of glycerol to acetone 1:5, catalyst loading 7 wt.At -%, temperature 70 °C, reaction time 10 minutes, the system achieves a solketal yield of 97.1 ± 0.4%. The catalyst is characterized by excellent reusability and retains at least 90% of its catalytic activity even after five catalytic cycles. This makes it highly efficient for the industrial production of biofuel additives from glycerin waste.

[0010] The present disclosure relates to a system for the production of a sulfonated, biomass-based catalyst for solketal synthesis. The system comprises a dissolution unit for receiving cellulose and concentrated sulfuric acid, in which the cellulose is dissolved portionwise in the sulfuric acid using a magnetic stirrer. The dissolved cellulose mixture is transferred to a hydrothermal treatment unit, which receives the mixture from the dissolution unit and heats it at 80 °C for 18 hours to obtain a carbonaceous residue. This residue is cooled and subsequently washed with deionized water in a washing unit. The washed residue is then dried overnight at 80 °C under vacuum in a drying unit.

[0011] One objective of the present disclosure is to provide a system for the production of a sulfonated, biomass-based catalyst for solketal synthesis.

[0012] Another objective of the present disclosure is to facilitate the synthesis of a sulfonated, biomass-based catalyst from cellulose that is biogenic, biodegradable and environmentally friendly, overcoming the limitations of moisture sensitivity, toxicity, instability and high cost of existing heterogeneous catalysts for glycerol acetalization.

[0013] Another objective of the present disclosure is the development of a catalyst preparation system based on hydrothermal carbonization under harmless conditions, which is simple and economical and eliminates the need for elaborate synthesis techniques such as those required for conventional heterogeneous catalysts.

[0014] Another objective of the present disclosure is to enable the efficient conversion of glycerol, a waste product of biodiesel production, into solketal with high yield and selectivity, thereby utilizing glycerol waste and contributing to the sustainability of the biodiesel industry.

[0015] Another objective of the present disclosure is to provide a reusable and recyclable catalyst that maintains high catalytic activity over multiple reaction cycles, thereby reducing catalyst consumption, lowering operating costs and minimizing waste generation in industrial applications.

[0016] However, another objective of the present disclosure is to enable rapid solketal synthesis under optimized reaction conditions by means of microwave-assisted acetalization, thereby reducing reaction time and energy consumption while achieving high conversion rates suitable for the industrial production of biofuel additives.

[0017] To further clarify the advantages and features of the present disclosure, the invention is described in more detail with reference to specific embodiments illustrated in the accompanying drawings. It is understood that these drawings merely show typical embodiments of the invention and are therefore not to be understood as limiting its scope of protection. The invention is described and explained in more detail and with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE IMAGES

[0018] These and other features, aspects and advantages of the present disclosure will be better understood when the following detailed description is read with reference to the accompanying drawings, in which identical symbols represent identical parts, wherein: Fig. Figure 1 shows a block diagram of a system for the production of a sulfonated, biomass-based catalyst for solketal synthesis according to an embodiment of the present disclosure; Fig. Figure 2 shows a scheme of the acetalization of glycerol using C-SO3H as a solid catalyst according to an embodiment of the present disclosure; Fig. Figure 3 illustrates selected XPS analyses of the C-SO3H catalyst (a), experimental deconvolution spectra for C (b), O (c) and S (d) according to an embodiment of the present disclosure; and Fig. Figure 4 illustrates the reusability of the C-SO3H catalyst in the acetalization of glycerol over 5 cycles according to an embodiment of the present disclosure.

[0019] Furthermore, those skilled in the art will recognize that the elements in the drawings are simplified and not necessarily drawn to scale. For example, the flowcharts illustrate the process by highlighting the main steps to facilitate understanding of this disclosure. With regard to the construction of the device, one or more components may be represented in the drawings by conventional symbols. The drawings may show only those specific details relevant to understanding the embodiments of this disclosure, so as not to clutter the drawings with details that are already apparent to those skilled in the art from the description contained herein. DETAILED DESCRIPTION:

[0020] To facilitate understanding of the principles of the invention, reference is made below to the embodiment illustrated in the drawings, which is described using specific terms. It is understood, however, that this does not limit the scope of protection of the invention. Rather, modifications and further developments of the illustrated system, as well as further applications of the inventive principles depicted therein, are conceivable, insofar as they would typically occur to a person skilled in the art in the field of the invention.

[0021] It will be clear to those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not to be understood as a limitation thereof.

[0022] References to “an aspect”, “another aspect”, or similar phrases in this description mean that a particular feature, structure, or property described in connection with the embodiment is included in at least one embodiment of the present disclosure. Therefore, phrases such as “in one embodiment”, “in another embodiment”, and similar expressions in this description may, but do not necessarily, all refer to the same embodiment.

[0023] The terms "includes," "comprehensive," or similar expressions denote non-exclusive inclusion. Thus, a procedure or method containing a list of steps does not only include those steps but may also include further steps not explicitly listed or inherent in the procedure or method. Likewise, the statement "includes..." for one or more devices, subsystems, elements, structures, or components, without further limitations, does not preclude the existence of other devices, subsystems, elements, structures, or components.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meanings generally known to those skilled in the art in the field to which this invention belongs. The systems, methods, and examples described herein serve only for illustration and are not to be understood as limiting.

[0025] Embodiments of the present disclosure are described in detail below with reference to the accompanying drawings.

[0026] Fig. Figure 1 shows a block diagram of a system for the production of a sulfonated, biomass-based catalyst for solketal synthesis according to an embodiment of the present disclosure.

[0027] The system (100) according to Fig. 1 comprises: a dissolution unit (102) that receives cellulose and concentrated sulfuric acid and allows the portionwise addition of cellulose to the sulfuric acid, the cellulose being dissolved in the sulfuric acid by means of a magnetic stirrer; a hydrothermal treatment unit (104) that receives the dissolved cellulose mixture from the dissolution unit and heats this mixture at 80 °C for 18 hours to obtain a carbonaceous residue; a washing unit (106) connected to the hydrothermal treatment unit and used to wash the cool carbonaceous residue with deionized water; and a drying unit (108) configured to dry the washed sulfonated biomass-based catalyst (C-SO3H) overnight at 80 °C under vacuum.

[0028] In one embodiment, the dissolving unit (102) is configured to absorb cellulose and sulfuric acid in a ratio of 1 g cellulose to 10 ml sulfuric acid.

[0029] In one embodiment, the washing unit (106) is configured to wash with distilled water until no unreacted sulfate ions remain, which is confirmed by a barium chloride test.

[0030] In one embodiment, the system (100) further comprises a storage unit (110) with a desiccator (110a) for storing the dried C-SO3H catalyst.

[0031] In one embodiment, the system (100) further comprises a reaction unit (112) configured to utilize the prepared C-SO3H catalyst for the acetalization of glycerol with acetone under microwave irradiation for the synthesis of solketal, wherein the reaction unit (112) is configured to accommodate glycerol, acetone and the C-SO3H catalyst in a microwave tube and enables microwave-assisted acetalization under optimized reaction conditions.

[0032] In one embodiment, the system (100) further comprises a product separation unit (114) connected to the reaction unit (112) and configured as follows: After completion of the reaction, the reaction mixture is centrifuged, the solution is decanted to separate the C-SO3H catalyst, and the decanted solution is concentrated by rotary evaporator to remove excess acetone and obtain the solketal product.

[0033] In one embodiment, the system (100) further comprises a catalyst recycling unit (116) configured to enable the recycling of the produced catalyst by: filtering the reaction mixture after completion of the reaction; washing the recovered C-SO3H catalyst with methanol and chloroform; and drying the recovered catalyst in a vacuum oven at 80 °C for 5 hours. The recovered catalyst can be reused for subsequent acetalization reactions.

[0034] In one embodiment, the catalyst recycling unit (116) is configured such that the C-SO3H catalyst can be reused for at least five catalytic cycles, retaining at least 90% of the catalytic activity.

[0035] The present invention relates to a system for the synthesis of a heterogeneous, solid carbon catalyst based on cellulose, which is further used for the production of solketal by acetylation of glycerol, wherein the system is configured to enable the treatment of cellulose with concentrated sulfuric acid under harmless hydrothermal conditions.

[0036] Fig. Figure 2 illustrates a scheme of the acetalization of glycerol using C-SO3H as a solid catalyst according to an embodiment of the present disclosure.

[0037] The synthesis of a biogenic, biodegradable, and environmentally friendly cellulose-based acid catalyst is achieved through the hydrothermal carbonization of cellulose. This catalyst is used for the synthesis of solketals from glycerol acetal. For catalyst preparation, 1 g of cellulose is used. Cellulose was added portionwise to 10 ml of H₂SO₄ and stirred in a magnetic stirrer until complete dissolution. The mixture was then heated at 80 °C in a drying oven for 18 h. After cooling to room temperature, the residue was washed with deionized water. Washing with distilled water continued until no unreacted sulfate ions were detectable (using a barium chloride test). The product, C-SO₃H, was dried overnight at 80 °C under vacuum. The prepared catalyst was stored in a desiccator for further use. The sulfur content was used to calculate the -SO₃H- density of the C-SO₃H catalyst.The density of the -OH, -SO3H, and -COOH functional groups on the catalyst surface was determined using a modified Boehm titration. The combined -COOH / -SO3H... -Density was determined using NaHCO3 and total acid density using NaOH. This allowed for the extrapolation of the -OH density, while the -COOH density could be extrapolated after determining the -SO3H density by SEM-EDX. 100 mg of the catalyst was stirred for 24 h at 50 °C with 20 mL of a 0.1 M aqueous NaHCO3 / NaOH solution. The catalyst was then rinsed with argon. The catalyst was separated from the aqueous solution by filtration and washed 2-3 times with deionized water. 100 mL of deionized water was added to dilute the filtrate. A 10 mL sample of this solution was titrated against 0.01 M HCl using phenolphthalein as an indicator. X-ray powder diffraction (XRD) was performed using Cu-Kα radiation (λ = 10⁻⁶⁰°) on a PANalytical X'Pert Pro diffractometer. The operating currents and voltages used were 100 mA and 40 kV, respectively.The sample was degassed for 4 hours at room temperature and then analyzed at 70 °C using a Micromeritics ASAP 2010 surface and porosity detector. Analysis was performed using the Brunauer-Emmett-Teller (BET) method. Scanning electron microscopy (SEM) was performed using a JEOL JSM-7600F microscope. Energy-dispersive X-ray spectroscopy (EDX EDS) was conducted with a beam current of 80 mA, a voltage of 20 kV, and a magnification of 1500x. The catalyst was dispersed in ethanol, dropwise onto a copper mesh, and dried in a drying oven prior to analysis. Transmission electron microscopy (TEM) images were acquired using a JEOL JEM2100 microscope. For XPS analysis, an ESCALAB Xi+ system with dual Mg Kα / Al Kα microfocused monochromatic Al Ka ​​X-ray sources and a dual Al / Mg Kα source was used. TGA was performed with a Metter Toledo TGA / DSC 1 at a heating rate of 10 °C min. -1and a constant N2 flux at around 50 °C. The Nicolet iS50 spectrometer was designed for FT-IR at 600 °C. - Analysis used.

[0038] As in Fig. As shown in Figure 2, the prepared catalyst was used for the acetalization of glycerol. Glycerol, acetone, and catalyst were placed in a 10 mL microwave tube and heated under microwave irradiation. Various reaction parameters were investigated: substrate ratio (1:2–1:6), catalyst quantity (1–7 wt%), temperature (40–80 °C), and reaction time (4–12 min). The optimized reaction conditions were: substrate ratio 1:5 (2 mmol glycerol, 0.184 g) mmol acetone (0.58 g)), catalyst quantity 7 wt% (0.013 g), temperature 70 °C, and reaction time 10 min. After completion of the reaction, the mixture was centrifuged, the supernatant was decanted, and the catalyst was reused. The decanted solution was concentrated by rotary evaporator to remove excess acetone.

[0039] The obtained solketal product was analyzed by gas chromatography-mass spectrometry (GC-MS) and NMR. The glycerol conversion and the selectivity between solketal (the five-membered cyclic solketal) and acetal (the corresponding six-membered cyclic acetal) were verified by GC-MS using equations (1) and (2). Glycerol conversion (%) = Moles of glycerol converted / Initial amount of glycerol × 100 Solketal selectivity (%) = Mole sol complex formed / Mole glycerol converted × 100

[0040] To confirm the formation of the desired product, the FT-IR spectra of glycerin, solketal product and commercially available solketal were also analyzed. The acetalization reaction would follow pseudo-first-order kinetics. Since acetone was present in excess, the reverse reaction could be neglected. Therefore, the reaction rate (r) can be written as follows: r=−d[G]dt=k[G]

[0041] In the above expression, k, [G], and t denote the rate constant, the glycerol concentration, and the reaction time, respectively. The first-order rate constants were calculated by observing the conversion at different time points according to Eq. 4.

[0042] The activation energy (E a ) was calculated using the values ​​of the rate constants at different temperatures (40-70 °C) in the Arrhenius equation (Eq. 5). −ln(1−X)=kt ln k=−EaRT+ln A

[0043] In the equations above, X is the glycerol conversion at time t, T is the reaction temperature, A is the pre-exponential factor, and R is 8.314 JK. -1 mol -1.

[0044] After completion of the reaction, the system is configured to filter the reaction mixture and wash the catalyst with methanol and chloroform. The recovered catalyst is then dried in a vacuum drying oven at 80 °C for 5 h. Catalyst recovery is repeated four more times under optimal reaction conditions (glycerol to acetone ratio GTAR 1:5, 7 wt% catalyst loading, 70 °C and 10 min) to test the catalyst's reusability.

[0045] Regarding catalyst characterization, the SEM analysis showed that the C-SO3H -The catalyst exhibits a sponge-like character with a micro- and mesoporous structure. During hydrothermal treatment, the cellulose fiber network becomes disordered at various locations, resulting in cellulose fragments in the nano- and micrometer range. These fragments assume a spherical shape to minimize their contact with the environment, although the overall morphology is less homogeneous than that of simple sugars. Irregular particles visible in the SEM images arise from aggregation due to water removal during hydrothermal carbonization. TEM analysis at a resolution of 20 nm revealed that the structure consists of sheet-like carbonaceous frameworks. EDS analysis confirmed the presence of the elements C, O, and S. The catalyst contains 4.20 wt% sulfur (corresponding to 1.31 mmol g). -1 ) and is therefore highly acidic. SEM mapping images showed a homogeneous composition.

[0046] Fig. Figure 3 shows selected XPS analyses of the C-SO3H catalyst (a), experimental spectra of deconvolution for C (b), O (c) and S (d) according to an embodiment of the present disclosure.

[0047] As in Fig. As shown in section 3, the XPS analysis identified sulfur mainly as SO3H. - Groups. SO3H-functionalized carbon materials exhibited high Brønsted acidity (Ho ≤ -11), comparable to concentrated sulfuric acid. The results showed that the catalyst surface consists of carbon, oxygen, and sulfur. An overview scan was performed in the range of 0 to 900 eV ( Fig. 3(a)). The peaks at 165 eV, 283 eV and 532 eV confirmed the presence of sulfur, carbon and oxygen. As in Fig. As shown, the C1s spectrum exhibited peaks at 283.35 eV and 288.25 eV, corresponding to CC / C=C and C=O (from COOH), respectively. As shown in Fig. The O1s spectrum, as depicted, showed a main maximum at 530.05 eV with a shoulder at 534.10 eV, which is assigned to CO and C=O. The maximum in the range of 166.30–167.05 eV corresponds to bound sulfonic acid groups (SO3H). The BET analysis yielded a specific surface area of ​​447 m². 2 G -1 , a pore radius of 30,020 Å (6 nm pore diameter) and a pore volume of 0.157 cm³ 3 G -1 The N₂ adsorption-desorption curve showed a type IV isotherm with a characteristic hysteresis loop in the relative pressure range of 0.42–0.95, confirming the mesoporous structure of the catalyst surface. The pore size is comparable to that of mesoporous materials, as reflected in the maxima in the mesoporous region of the pore size distribution curve. FT-IR analysis identified functional groups: The band at 3397 cm⁻¹ -1 corresponds to the -OH stretching vibration, the peaks at 1693 cm -1 and 1571 cm-1 indicate C=C and CO bonds, and the peak is at 1021 cm -1 The presence of -SO3 groups was confirmed. XRD analysis showed a broad peak at 20°C (15-25°C), indicating successful carbonization of the cellulose with randomly arranged layers of amorphous carbon. The material exhibits a highly disordered and amorphous structure with randomly arranged -SO3H, -COOH, and -OH groups bound to layers of polycyclic aromatic carbon. TGA analysis in the temperature range of 50-600°C revealed: a mass loss of approximately 13% at 68-100°C due to moisture evaporation, catalyst stability up to 200°C, a mass loss of approximately 18% at 200-300°C due to functional group decomposition, and a mass loss of approximately 24% at 420-550°C due to the oxidation of carbon-containing substances to CO and CO2. The modified Boehm titration yielded a total acid loading of 4.56 mmol g.-1 , which is higher than the sulfonic acid loading (1.31 mmol g) due to the presence of -OH and -COOH groups -1 ).

[0048] The synthesized C-SO3H catalyst was used for the acetalization of glycerol with acetone to form the solketal. The reaction was carried out by mixing glycerol and acetone in a molar ratio of 1:4 and adding 3 wt% catalyst (based on glycerol). The reaction mixture was placed in a reaction vessel with a PTFE-coated lid and heated to a reaction temperature of 70 °C using microwave radiation (100 Pa, 50 W power). The reaction vessel was stirred in a microwave reactor for 10 minutes. After cooling, the reaction mixture was filtered through Whatman filter paper No. 41, washed with ethanol, and concentrated by rotary evaporator to obtain the product. The glycerol conversion was monitored by thin-layer chromatography (TLC) on aluminum oxide foil. The product was then analyzed using1 H-NMR and 13 Identified by 13C NMR spectroscopy as 2,2'-dimethyl-1,3-dioxolane-4-methanol (solketal). 1 The ¹H NMR spectrum (500 MHz, 28 °C) showed signals at the following δ values: 4.24–4.03 m, 3.80–3.72 m, 3.60–3.59 m, 1.45 s, and 1.38 s. 13 The 13C NMR spectrum (125 MHz, 28 °C) showed signals at the following δ values: 109.4, 76.13, 65.69, 63.01, 30.93, 26.71, and 25.27 ppm. GC-MS analysis revealed an intense signal at 5.26 min and another, smaller signal at 5.60 min, confirming the synthesis of the R and S isomers of the solketal and thus the selective solketal synthesis. FT-IR analysis showed that the bands were located at 1376, 1155, 1118, and 1046 cm⁻¹. -1 The solketal spectrum was absent from the glycerol spectrum, confirming the conversion of glycerol to solketal. The reaction parameters were optimized as described below.

[0049] Influence of the glycerol-acetone molar ratio: The acetal formation reaction was investigated at 70 °C with glycerol-acetone molar ratios (GTAR) of 1:2, 1:3, 1:4, 1:5, and 1:6. The solketal yield improved from 62.1 ± 0.4% to 97.1 ± 0.4% when the ratio was increased from 1:2 to 1:5. Excess acetone shifts the equilibrium to the right, thus promoting product formation. At high glycerol concentrations (or low amounts of acetone), the mixture exhibits high viscosity, which hinders homogenization of the reaction medium. A low acetone concentration shifts the equilibrium in the opposite direction and reduces the product yield. A slight decrease in yield was observed when the molar ratio was increased from 1:5 to 1:6, possibly due to saturation of the active sites. Therefore, 1:5 was determined to be the optimal GTAR.

[0050] Influence of catalyst loading: The influence of the catalyst loading was investigated at 1, 3, 5, 7, and 9 wt% using the optimal GTAR of 1:5 at 70 °C. The solketal yield increased from 60.2 ± 0.3% to 97.1 ± 0.4% when the catalyst concentration was increased from 1 to 7 wt%. This is attributed to the increasing number of accessible active sites. A further increase in the catalyst loading to 10 wt% reduced product formation due to hydrolysis. The optimal catalyst loading for high solketal production was determined to be 7 wt%.

[0051] Influence of reaction temperature: The influence of temperature was investigated at 40, 50, 60, 70, and 80 °C under optimal conditions (GTAR = 1:5, catalyst loading: 7 wt%). The conversion reached a maximum of 97.1 ± 0.4% at 70 °C. Increasing the reaction temperature above 70 °C resulted in reduced solketal formation. This decrease could be attributed to the evaporation of acetone, even under pressure. Since solketal is a kinetically controlled product, an increase in temperature can favor the formation of the thermodynamic product (six-membered ring). Therefore, 70 °C was determined to be the optimal temperature for solketal formation.

[0052] Influence of reaction time: The influence of reaction time was investigated by varying it between 2 and 12 minutes while keeping all other factors constant (GTAR 1:5, temperature 70 °C, catalyst loading 7 wt%). The conversion increased from 61.2 ± 0.4% to 97.1 ± 0.4% when the reaction time was increased from 2 to 10 minutes. This is due to the increasing number of reacting molecules forming new bonds after cleaving existing ones. However, extending the reaction time to 12 minutes resulted in a lower conversion of 96.1 ± 0.3%. With increasing reaction time, the product may have been hydrolyzed by the formation of water, which would explain the decrease in yield.

[0053] The optimized reaction conditions for a maximum solketal yield of 97.1±0.4% were determined as follows: molar ratio of glycerol to acetone of 1:5, catalyst loading of 7 wt%, reaction temperature of 70°C and reaction time of 10 minutes.

[0054] The kinetics of the acetalization reaction of glycerol were investigated at 40, 50, 60, and 70 °C using the prepared C-SO3H catalyst under reaction conditions with a glycerol-to-acetone molar ratio (GTAR) of 1:5 and a catalyst loading of 7 wt% for 4, 6, 8, and 10 minutes. The reaction rate of the uncatalyzed reaction was negligible compared to the catalyzed reaction. Extending the reaction time from 4 to 10 minutes increased the glycerol conversion at 40 °C from 30.2 ± 0.3% to 60.7 ± 0.4%, at 50 °C from 37.3 ± 0.3% to 68.8 ± 0.3%, at 60 °C from 51.7 ± 0.2% to 77.5 ± 0.2%, and at 70 °C from 62.6% to 97.4%. After 10 minutes of reaction time, the solketal yield improved from 60.2 ± 0.3% to 97.1 ± 0.3% when the temperature was increased from 40 °C to 70 °C. The reaction followed pseudo-first-order kinetics.Plotting -ln(1-X) against the reaction time at different temperatures yielded linear curves, confirming the pseudo-first-order nature of the reaction. The activation energy (Ea) was determined to be 23.65 kJ mol. -1 calculated values ​​comparable to previous literature values, in which the activation energy for previously described catalysts was in the range of 24.7–84.1 kJ mol. -1 lay.

[0055] The activity of the present C-SO3H - The catalyst was compared with various existing catalysts. The turnover frequency (TOF) of the C-SO3H catalyst was 0.9019 mol g. -1 h -1 , thus surpassing many heterogeneous catalysts for the production of solketals. Exceptions include the HNO3-modified montmorillonite clay catalyst (TOF 1.226 mol g). -1 h -1 ) and sulfated zirconium oxide (TOF 1.449 mol g -1 h -1However, these two catalysts showed lower conversion and selectivity compared to the present catalyst, and sulfated zirconium oxide also required a longer reaction time. The present C-SO3H catalyst achieves a high glycerol conversion of 97.1 ± 0.3% with complete selectivity (100%) for solketal. The reaction exhibited a low activation energy of 23.65 kJ mol⁻¹. -1 The catalyst exhibited high stability during the reaction and was reusable up to five times without requiring heat treatment for reactivation. To investigate the heterogeneity of the C-SO3H- KatalysatorsHot filtration was performed. The catalyst was filtered off under hot conditions after four minutes of reaction time, with a product conversion of 62.3 ± 0.4%. The reaction was continued for a further 20 minutes with the catalyst-free, filtered reaction mixture, resulting in a conversion of 64.8 ± 0.3% – an increase of only 1.5%. This demonstrates that no significant amounts of soluble, catalytically active species were present in the filtrate and thus confirms the heterogeneous nature of the catalyst.

[0056] Fig. Figure 4 illustrates the reusability of the C-SO3H catalyst in the acetalization of glycerol via Figure 5. Zyklen according to one embodiment of the present disclosure.

[0057] Based on Fig.4. The catalyst was further tested by five reuses under optimal reaction conditions. After each catalytic experiment, the catalyst was separated by filtration, regenerated by thorough washing with methanol and chloroform, and then dried in a drying oven at 80 °C for 5 hours. The regenerated catalyst was then used for further catalytic tests. With repeated reuse of the catalyst, a steady and slight decrease in glycerol conversion was observed. The catalyst exhibited excellent catalytic activity and could be reused five times without any significant loss of activity. The solketal conversion in the fifth reaction cycle was 82.1 ± 0.4% with complete preservation of selectivity.Reaction residues deposited at the active sites, as well as the formation of carboxylate and sulfonate esters through the reaction of the -CO₂H and -SO₃H acid centers with glycerol, could be the cause of the loss of activity. SEM analysis of the catalyst after the fifth reuse showed a similar morphology to that of the fresh catalyst. EDS analysis of the fifth recycled catalyst revealed a slight decrease in sulfur content from 4.20 wt% (fresh catalyst) to 3.51 wt%, which may be responsible for the decreasing catalytic activity upon repeated reuse. PXRD and FT-IR analyses of the recycled catalyst confirmed the similarity between the fresh and recycled catalysts and thus their stability upon repeated reuse.

[0058] Under mild reaction conditions, the catalyst converted 97.1 ± 0.4% of the glycerol to the solketal with 100% selectivity. The specific activity of the catalyst was TOF 0.9019 mol g. -1 h-1 The high activity is due to its mesoporous structure, large surface area, and high acidity. Hot filtration tests showed minimal leaching of the active component, making the catalyst an exemplary heterogeneous catalyst. Even after five reuses, a high conversion of 82.1 ± 0.2% of the glycerol in the solketal was still achieved, demonstrating the catalyst's high stability.

[0059] The drawings and the preceding description illustrate embodiments. Those skilled in the art will recognize that one or more of the described elements can be combined to form a single functional element. Alternatively, certain elements can be divided into several functional elements. Elements of one embodiment can be added to another. For example, the process flows described here can be modified and are not limited to the manner described herein. Furthermore, the actions of a flowchart need not be performed in the sequence shown; nor do all actions necessarily need to be carried out. Actions that do not depend on other actions can be performed in parallel with the other actions. The scope of protection of the embodiments is in no way limited by these specific examples. Numerous variations, whether explicitly stated in the description or not, such as...Differences in structure, dimensions, and materials are possible. The scope of protection of the embodiments is at least as comprehensive as described by the following claims.

[0060] The advantages, other benefits, and problem solutions have been described above with reference to specific embodiments. However, the advantages, benefits, problem solutions, and any components that can effect or enhance an advantage, benefit, or solution are not to be construed as critical, necessary, or essential features or components of the claims. REFERENCES 100 The present disclosure is described in detail below with reference to the accompanying drawings. 102 resolution units 104 Hydrothermal Treatment Unit 106 Washing machine 108 drying units 110 storage space 110a Desiccator 112 reaction unit 114 Product separation unit 116 Catalyst recycling plant

Claims

[1] A system for the production of a sulfonated, biomass-based catalyst for solketal synthesis, comprising: a dissolving unit designed to accommodate cellulose and concentrated sulfuric acid and enabling the portionwise addition of cellulose to the sulfuric acid, wherein the cellulose is dissolved in the sulfuric acid using a magnetic stirrer; a hydrothermal treatment unit configured to take the dissolved cellulose mixture from the dissolution unit and heat this mixture at 80 °C for 18 hours to obtain a carbonaceous residue; a washing plant connected to the hydrothermal treatment plant and configured to wash the cool, carbonaceous residue with deionized water; and a drying unit configured to dry the washed sulfonated biomass-based catalyst (C-SO3H) overnight at 80 °C under vacuum. [2] System according to claim 1, wherein the dissolving unit is configured to absorb cellulose and sulfuric acid in a ratio of 1 g cellulose to 10 ml sulfuric acid. [3] System according to claim 1, wherein the washing unit is configured to wash with distilled water until no unreacted sulfate ions remain, which is confirmed by a barium chloride test. [4] System according to claim 1, further comprising a storage unit with a desiccator for storing the dried C-SO3H catalyst. [5] System according to claim 1, further comprising a reaction unit configured to use the prepared C-SO3H catalyst for the acetalization of glycerol with acetone under microwave irradiation for the synthesis of solketal, wherein the reaction unit is configured to accommodate glycerol, acetone and the C-SO3H catalyst in a microwave tube and enables microwave-assisted acetalization under optimized reaction conditions. [6] System according to claim 5, further comprising a product separation unit connected to the reaction unit, configured as follows: After completion of the reaction, the reaction mixture is centrifuged, the solution is decanted to separate the C-SO3H catalyst, and the decanted solution is concentrated by rotary evaporator to remove excess acetone and obtain the solketal product. [7] System according to claim 5, further comprising a catalyst recycling unit configured to facilitate the recycling of the manufactured catalyst by: Filtration of the reaction mixture after completion of the reaction. Washing of the recovered C-SO₃H catalyst with methanol and chloroform. The recovered catalyst is dried in a vacuum oven at 80 °C for 5 hours. The recovered catalyst can be reused for subsequent acetalization reactions. [8] System according to claim 7, wherein the catalyst recycling unit is configured such that the C-SO3H catalyst can be reused for at least five catalytic cycles, retaining at least 90% of the catalytic activity.

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