Nor Yuliana Yuhana

A circular economy for polyethylene terephthalate (PET) aims to achieve complete material recirculation and reduce dependence on fossil-based feedstocks. Among recycling strategies, depolymerization offers the greatest potential for true circularity. This work investigates deep eutectic solvent (DES)-assisted PET depolymerization using a tetrabutylammonium bromide/sulfolane (TBABr/Sulf) system. A four-factor, three-level Box–Behnken design was employed, where reaction time, NaOH concentration, PET/solvent ratio, and water content were selected as independent variables, with PET weight loss as the response. The optimized conditions of 35 min reaction time, 5.9 wt% NaOH, a PET/solvent ratio (g/g) of 0.061, and a 1:1 water-to-DES ratio achieved 97% PET depolymerization and 93.8% TPA recovery. The process achieved a relatively low PET/DES (g/g) utilization ratio of 0.12 and required at least 40% less NaOH than other DES-based alkaline hydrolysis reported in the literature. The identity and quality of the recovered TPA were confirmed by FTIR, NMR, DSC, and elemental analysis. Under microwave-assisted conditions, TBABr/Sulf was successfully reused over three consecutive cycles while maintaining 100% depolymerization efficiency with consistent TPA quality. Collectively, these results demonstrate the technical potential of the proposed DES-assisted PET depolymerization process, particularly in terms of reduced solvent and alkaline requirements, shortened reaction time, and demonstrated solvent recyclability.

Conventional production methods of aragonite production utilize chemical inducers to promote the evolution of the calcite crystalline phase to the aragonite phase of calcium carbonate. The chemical inducers used require a considerable amount of magnesium chloride (MgCl₂) to induce crystallization, which is a major operational cost. Application of such materials in large amounts can be a deterrent to achieving a sustainable and economically feasible end-product derived from carbon dioxide (CO₂) molecules. A number of previous research works focused mainly on optimizing the usage of MgCl₂ or introducing alternative chemical inducers for aragonite production. In this work, we are proposing the usage of natural seawater as it is a naturally available and abundant resource to induce the synthesis and continuous production of aragonite compounds. Due to inconsistent quality and salinity of the natural seawater sampled, harvested, and dried, Red Sea Salt is utilized, blended at 33 g/L throughout the laboratory experiments for better statistical control, and is referred to as blended or artificial seawater. A methodology of utilizing seawater, which has a considerable concentration of MgCl₂ compound, can be utilized as a sustainable, natural, and economically feasible natural inducer to synthesize aragonite has been developed by utilizing artificial seawater for laboratory proof of concept. The main effects identified for the optimization of aragonite synthesis are lime (CaO) feedstock concentration in seawater, reaction temperature, and reaction duration. The experiment results indicated that only by increasing temperature and reaction duration, or both, can the aragonite yield be increased. It is suggested that the range of operation to obtain > 80% aragonite purity has been identified with the reaction temperature at 90 °C, reaction duration of 10 min, and CaO concentration in seawater at 1 g/L. The quality of the aragonite synthesized via seawater is characterized using XRD, ICP, FESEM, and TGA, and compared with aragonite particles synthesized using MgCl₂ inducers. In comparison, seawater aragonite has lower residual alkalinity compared to both calcite and aragonite via MgCl₂ and has a mixture of predominantly needle-shaped crystalline structure and remnants of cubic-shaped particles, presumably calcite, suitable for application in food, beverages, and pharmaceuticals (calcium antacids, nutritional supplements, chewable, lozenges).

The US National Academy of Sciences has reported that CO₂ mineral carbonation is among the largest, most energy-efficient CO₂ utilization technologies closest to commercial scale due to its thermodynamic favorability and end-product market size. However, the natural rate of reaction is generally slow in terms of kinetics, whereby only by dramatically increasing the CO₂ dissolution rate can a major impact on the rate of reaction for CO₂ mineral carbonation happen. Hence, despite the clear advantages of CO₂ mineral carbonation over other options in Carbon Capture and Sequestration CCS technologies, the current research gaps highlighted here should be addressed to ensure future technology deployment success. Therefore, this study investigated the feasibility of the design, operation and experimental improvement of a continuous high-pressure CO₂ reactor in producing and optimizing high-quality precipitated calcium carbonates PCC synthesized for consumer and industrial application. A novel mineral carbonation reactor is hereby proposed, in which, by incorporating the application of a high-pressure or supercritical CO₂ phase into the reactor, CO₂ diffusion can be increased into the continuously fine-sprayed aqueous reaction media within the reactor to form PCC. The effective reactor volume can be simultaneously decreased from the reduced high-pressure CO₂ volume. Next, by incorporating a backpressure regulator, a continuous flow of the liquid phase in and out of the reactor can be controlled. The initial reactor design had undergone successful start-up, but experimental improvement alone was unable to provide the anticipated particle size of the calcium carbonate precipitate PCC. Optimized design of the new reactor to limit internal dead flow zones was proven to successfully reduce the particle size of precipitated calcium carbonate PCC from an initially P50/P90 of 87/131 μm to 3.8/9.1 μm. Additionally, a continuous 100 h stable run was successfully executed to thoroughly investigate the three main factors influencing the quality of PCC synthesized, in which the reactant flow rate and feedstock concentration were found to be significant, with the exception of CO₂ gas pressure. The overall 3D surface trend of the particle size spread P50/P90 of the PCC synthesized was plotted over the experimental range and found to meet most of the industrial requirements and technical specifications, except for TiO₂ replacement which requires sub-micron quality. Instantaneous electricity power consumption was also measured at various operating points. Performance-wise, the continuous high-pressure CO₂ mineral carbonation reactor in this work was calculated to be able to process a maximum of 4200 g/h lime CaO feedstock at a lime concentration of 7 g/L and flow rate of 10 g/L, using a 40 L internal volume vessel, effectively increasing the productivity of lime CaO production by several fold from what was reported by peer studies assuming similar electricity costs were used for all productivity factors under consideration.

Chemical recycling is one of the most prominent techniques that enables monomer recovery for plastics like polyethylene terephthalate (PET), which ultimately reduces the dependency on virgin material inputs. In this study, 40 deep eutectic solvents (DESs) were pre-screened using COSMO-RS to identify the best solvent for chemical recycling of PET. Quantitative evaluation was performed based on activity coefficients (γ) to assess solute–solvent interactions. Qualitatively, the sigma profile and sigma potential were analyzed to understand the polarity and affinity of each DES component. This study experimentally validated the two top-performing DESs based on COSMO-RS output. The DES formed by combining thymol with phenol (Thy/Phe (1:2)) achieved 100% PET degradation and 94.5% terephthalic acid (TPA) recovery from post-consumer PET in just 25 min. The rapid dissolution of PET into molten state accelerated the hydrolysis reaction, leading to efficient monomer recovery. The second DES, tetrabutylammonium bromide/sulfolane (TBABr/Sulf (1:7)), attained 93.7% PET degradation and 94% TPA recovery. The PET-to-solvent ratio used in this study was 0.75, while the PET-to-DES ratio in the mixture was only 0.15, the lowest reported for DES-assisted hydrolysis to date. Characterization of the recycled TPA confirmed a purity level comparable to its virgin grade, as verified by FT−IR analysis. This study presents two important outcomes. First, the use of COSMO-RS for DES selection provides a strong rationale for solvent choice in targeted reactions and processes. Second, the use of appropriate DES in this study helps reduce key parameters associated with depolymerisation process, including reaction time, temperature, and catalyst consumption.

The Global Cement and Concrete Association (GCCA) estimated that by 2050, 36% industry-wide sustainable value will be created, which includes sequestering CO₂ into the cement and concrete industry to produce commercially feasible high-value products. Direct utilization of CO₂ in the cement and concrete industry, which utilizes natural and sustainable materials, is gaining momentum. Naturally occurring mixtures of hydro magnesite and huntite are important industrial minerals which, upon endothermic decomposition over a specific temperature range, will release water and CO₂. This unique chemistry has led to such mixtures being successfully utilized as fire retardants, replacing aluminum hydroxide or Alumina Tri-Hydrate (ATH). Despite the developed marketplace for magnesium-based fire-retardant products, there is little mention of CO₂ mineral carbonation methods, which attempt to recover and convert magnesium from natural seawater or industrial waste into oxides or carbonates as part of the carbon sequestration initiative. The hypothesis to be proven in this work states that if the process of seawater mineral carbonation is prematurely quenched, Mg²⁺ ionic species in seawater adsorbed on the calcite lattice formation will be trapped and therefore recovered in various oxidized forms, such as magnesium oxides, magnesium hydro magnesite, and magnesium carbonate precipitates. A novel method to recover magnesium Mg²⁺ ions from seawater was successfully explored and documented; as such, from an initial concentration of 1250 ppm Mg²⁺ in raw seawater, the average concentration of spent Mg²⁺ ions after the reaction was as low as 20 ppm. A very efficient near-total recovery of Mg²⁺ from the seawater into the solid precipitates was recorded. Subsequently, the process for continuous seawater mineral carbonation for the production of magnesium/brucite/huntite products was successfully proven and optimized to operate with a 30 s reaction time, a dynamic feedstock concentration, [CaO] at 1 gpl in seawater and a room temperature reaction temperature (30 °C), where the average yield of the fire-retardant magnesium-based compounds was 26% of the synthesized precipitates. Approximately 5000 g of the hydro magnesite materials was molded into a fire-retardant brick or concrete wall, which was subjected to an accredited fire performance and durability testing procedure BS476-22:1987. There were encouraging results from the fire resistance testing, where the fire-retardant material passed BS476-22:1987, with performance criteria such as physical integrity failure, the maximum allowable face temperature, and a minimum duration before failure, which was up to 104 min, evaluated.

The current state of the art research, and latest engineering technology application in the synthesis of the aragonite crystalline phase of calcium carbonate is presented here. Aragonite crystalline products are highly valuable in selected industries, such as medical and personal care, and in food additives using MgCl₂ as a chemical inducer. The outcome of this literature review provides the outlook of the available research whitespace opportunity in optimizing the current process parameters and in ensuring that sustainable and economically feasible continuous production of aragonite products could be achieved. One of the major improvements proposed in this study is to investigate the methods of synthesizing aragonite crystalline particles using a continuous mineral carbonation reactor system and optimizing the operating parameters. An experimental design was established to identify all the main effects to maximize aragonite production. The three main effects investigated are the effect of feedstock or reactant concentration, the effect of reaction temperature, and the effect of reaction time towards aragonite yield in the final products synthesized. An optimized operating parameter for maximum aragonite yield at 95% purity was proposed at the reaction temperature T of 90 °C, reaction time t of 10 min, and feedstock ratio Mg-to-Ca of 0.4. Subsequently, the continuous reactor system was designed, operated, and tested for at least 50 h operation, where the lime CaO(s) feed was successfully converted into aragonite products with purity between 75 and 81%. The properties and quality of the aragonite produced were analytically characterized from the following laboratory methods which include the thermalgravimetric analysis, TGA; X-Ray Diffraction, XRD; scanning electron microscopy, SEM; and induction coupled plasma, ICP. TGA mass balance after decomposition suggests that 44% of the mass balance represents the weight of CO₂ sequestered in the aragonite crystalline carbonates. Hence, the aragonite crystalline carbonates can be labeled as a green product which sequesters 0.44 kg of CO₂ per 1 kg of precipitated aragonite products synthesized. Interestingly, SEM microscopy characterization results revealed that the aragonite precipitate has a physical morphology of needle-like shape with a good aspect ratio (length/diameter) AR of between 8.67 micron and 11.35 micron. The properties were found to be suitable for paper making fillers, medical, personal care, and food additive applications.

In this study, the properties of polymer blends of polypropylene (PP) and polylactide acid (PLA) at two different ratios of PP/PLA: 25/75 (PP25PLA75) and 50/50

The strong demand for plastic and polymeric materials continues to grow year after year, making these industries critical to address sustainability. By functioning as a filler in either a synthetic or natural starch matrix, nanoclay enables significant reductions in the impact of nonbiodegradable materials. The effect of treated nanoclay (NC) loading on the mechanical and morphological properties (EP) of epoxy is investigated in this research. The NC-EP nanocomposites were prepared via casting. The investigation begins with adding NC at concentrations of 1, 2, and 3 weight percent, followed by the effect of acid treatment on the same nanocomposites. The evaluation is focused on four mechanical tensile strength parameters: Young’s modulus, maximum load, and % elongation. The addition of NC improved the mechanical properties of the four components by 27.2%, 33.38%, 46.98%, and 43.58%, respectively. The acid treatment improved 35.9%, 42.8%, 51.1%, and 83.5%, respectively. These improvements were attributed to NC’s ability to alter the structural morphology as assessed by field emission scanning electron microscopy (FESEM), a tool for analysing the microstructure. FESEM images were used to visualise the interaction between the NC and EP nanocomposites. The dynamic mechanical properties of the hybrid nanocomposites were investigated using storage modulus, loss modulus, and tan(delta). The results have shown that the viscoelastic properties improved as the fraction of NC increased. The overall findings suggest that these nanocomposites could be used in various industrial and biomedical applications.

Economic, social, and urban developments generally require improvements in the transportation sector, which includes automobiles such as trucks, buses, trailers, airplanes, and even bicycles. All these vehicles use rubber tires. After consumption, these tires become waste, leading to enlarged landfill areas for used tires and implying additional harm to the environment. This review summarizes the growth of rubber recycling application and the sustainability of using waste rubber in the construction field. Furthermore, we provide methods to convert rubber waste to fuel or fuel additives by using tire-derived fuel and concentrate to pyrolysis, which are environmentally friendly and efficient ways. The related parameters such as temperature, pressure, and feedstock composition were studied. Most research papers observed that 500 °C is the optimal temperature at atmospheric pressure in the presence of a specific type of catalyst to improve pyrolysis rate, oil yield, and quality.