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Green diesel derived from sustainable biomass is an alternative and potential energy source to petroleum fossil fuel replacement in response to reducing carbon footprint and achieving a circular economy, which has sparked public interest and concern in advancing renewable energy development. Catalytic deoxygenation (CDO) is a promising method because it can process a wide variety of feedstocks and produce a diverse range of fuels. The CDO of soybean oil (SO) was executed using a modified low-cost dolomite catalyst denoted as NiO-CD catalyst and its performance has been compared with commercial zeolite heterogeneous-based catalysts such as ZSM-5, HY-zeolite and FCC. The NiO-CD catalyst exhibited exceptional deoxygenation ability, attaining an 88.6 % removal efficiency of oxygenated compounds, markedly surpassing all commercially available zeolite catalysts. The highest degree of CDO of SO via decarboxylation/decarbonylation (deCOx) reaction was achieved due to improvement in particle size, mesoporous structure and the presence of the synergistic effect of modified bi-functional acid-base properties of NiO-CaO/MgO catalyst. To investigate the effect of NiO-CD catalyst loading ranging from 1 to 7 wt%, a One Factor At a Time (OFAT) optimisation study was performed. The current study found that an optimised NiO-CD catalyst loading of 5 wt% yielded the highest green diesel (50.5 wt%) with an 88.63 % hydrocarbon composition. The influence of catalyst loading on deoxygenation activity is significant in green diesel production using NiO-CD catalyst.

Energy generation from waste biomass offers a promising solution for reducing greenhouse gas emissions and promoting a circular economy. This study investigates the energy potential of various organic materials, including rice husk, soybean, lemon myrtle, waste coffee ground, and empty fruit bunch, co-pyrolysed with HDPE at 500 °C and 50:50 blending ratio for 1 h. Proximate, ultimate, and thermogravimetric analyses were conducted up to 700 °C to determine elemental composition and thermal behaviour. Dulong's formula, modified Dulong's formula, and Vandralek's equation were utilised to assess energy content. Proximate analysis revealed rice husk as the highest in volatile matter (73.08 %), while waste coffee ground had the lowest (32.0 %), and HDPE showed 89.90 %. Ultimate analysis showed organic waste carbon ranges from 25.59 % to 48.75 %, and HDPE at 82.24 %. Pyrolysis reactions yielded distinct distributions of bio-oil, char, and gas, with empty fruit bunch producing the highest oil percentage (26.49 %), lemon myrtle yielding the highest gas (31.07 %), and waste coffee ground favouring char production (74.89 %). Discrepancies in heating values were observed, with Dulong's formula underestimating values for rice husk, soybean, and waste coffee ground (−10 % to −35 %) and slightly overestimating for lemon myrtle, empty fruit bunch, and HDPE (1 %–25 %). The modified Dulong formula accentuated underestimations, particularly for soybean (−451 %). The Vandralek formula showed positive error ranges (8 %) for biomass samples but underestimated HDPE. This study underscores biomass and HDPE as viable alternatives to conventional energy sources and suggests avenues for future research while highlighting environmental benefits.

In this work, a pseudo-equilibrium model (PEM) is developed for prediction of yield and product from devolatilisation of empty fruit bunch (EFB). The yield of individual species (H2, CO, CO2, CH4, bio-oil, tar, and char) from the primary decomposition of EFB is expressed empirically. Subsequently, they are the inputs to the secondary reaction region. In the secondary reactions zone, the water-gas shift reaction (WGSR) is treated under equilibrium conditions, but kinetically modified by a factor to predict the concentration of the four gases (H2, CO, CO2, and H2O) which participated in this reaction. Meanwhile, the methane, bio-oil and tar are modelled separately in a purely kinetic environment by applying a plug flow reactor (PFR) model to estimate the conversion of both species. The model is further to investigate the effects of changes in the operating conditions of devolatilisation such as temperature and carrier gas flow rate. The results showed a good prediction for tar yield with low root mean square (RMS = 0.003) compared to experiments, and conversion (59.7%) compared to experiments (51.5%) at 850 °C. A sensitivity analysis for the pyrolysis model was conducted to investigate the effects of process temperature and nitrogen gas flowrate. Tar yield was significantly reduced at high temperatures. Meanwhile, the change of nitrogen flowrate resulted in slight increase of tar yield. Reasonable predictions were obtained for other products.

Sludge palm oil (SPO) is waste generated in the palm oil industry. The discharge of SPO together with palm oil mill effluent has created a major problem due to its difficulty in the treatment process. The feasibility of SPO as a raw material for biofuel production was investigated via catalytic pyrolysis process using heterogeneous Malaysian dolomite catalyst. The effects of operating temperatures and reaction times in the catalytic pyrolysis using Malaysian dolomite catalyst were assessed. The condition for the reaction parameters investigated is as followed: operating temperatures of 350 ◦C, 400 ◦C, and 450 ◦C, reaction times of 30, 45 and 60 minutes, under a constant of 100 ml/min of nitrogen flow rate and 5 wt.% catalyst loading. At a reaction temperature of 350 ◦C the SPO conversion was very low even at longer reaction times. The longer reaction times gave higher SPO conversion at an operating temperature of 400 °C with the range of conversion between 45.7 to 58.3 wt.%. At temperature 450 ◦C the conversion achieved an average of 93.1 ± 1.0 wt.%. Only a slight change at longer times was observed at this temperature. At a temperature of 400 ◦C and 45 min of reaction times, the pyro-oil obtained from the process contained the highest hydrocarbon content (83.90 %) and lowest oxygenated compound content (16.10 %), even though the conversion was lower than at 450 ◦C. The product selectivity was highest in the diesel range at the reaction temperature of 400 ◦C. Thus, with further improvement in catalyst modification together with optimized operating conditions, SPO can be used as a feedstock in the catalytic pyrolysis for producing biofuel in the range carbon number of diesel, gasoline and kerosene.

Fossil fuels have provided humans with an enormous and stable primary energy source to rapidly develop advanced technologies, increasingly efficient machines and industries, as well as greater varieties of consumer products. While humans enjoy the conveniences of the modern world, critical global issues have also been created, such as an exponential hike in waste generation, rapid depletion of finite fossil fuels, greater environmental pollution, and climate change. Two major anthropogenic wastes are biomass waste and plastic waste. Each year, 464 million tonnes of plastic waste are generated globally, with only 20% recycled, 25% incinerated, while 55% landfilled. Likewise, 140 billion tonnes of biomass from the agriculture sector and 181.5 billion tonnes of lignocellulosic biomass from forestry and agricultural residues are produced worldwide annually, with only 40% and 4.5% biomass reuse respectively. This mountainous underutilised biomass and plastic wastes presented a good opportunity for recycling into biofuels instead of landfilling or open dumping, thus promoting circular bioeconomy. Pyrolysis stands out as a promising thermochemical route to synthesize biofuels, and co-pyrolysis of biomass and plastic benefits from synergistic interactions between both feedstocks, enhancing the yield and quality of biofuels. Therefore, in this review, the synergistic mechanism of biomass and plastic co-pyrolysis is described, and recent advances in this field are comprehensively presented. The importance of applying circular bioeconomy frameworks on biomass and plastic wastes are also highlighted.

This work investigates the optimization of reaction parameters with the Taguchi method for catalytic deoxygenation of waste cooking oil (WCO) as an alternative renewable fuel process. Commercial sulphated-ferric (II) oxide/alumina oxide catalyst has the potential as a deoxygenation catalyst due to its good physicochemical properties which enhance the removal of oxygenated species. The obtained pyrolysis oil analysed by GC-MS revealed the selectivity of the pyrolysis oil mostly in the range of light diesel and kerosene fraction. From an analysis of variance (ANOVA), temperature awarded the most significant impact (86.62%) in this catalytic deoxygenation as compared to three other parameters followed by reaction time > N2 flow > catalyst loading. From the GC-MS analysis, the maximum renewable diesel fraction of 49.66% was obtained at 400 °C, 1 wt% of catalyst, 90 min of reaction time and 20 cm3/min N2 flow. The predicted model by Taguchi in the present study validated by the experimental work shows a promising application in optimising the catalytic pyrolysis process for future use.

This review provides the recent advances in triglyceride catalytic pyrolysis using heterogeneous dolomite catalysts for upgrading biofuel quality. The production of high-quality renewable biofuels through catalytic cracking pyrolysis has gained significant attention due to their high hydrocarbon and volatile matter content. Unlike conventional applications that require high operational costs, long process times, hazardous material pollution, and enormous energy demand, catalytic cracking pyrolysis has overcome these challenges. The use of CaO, MgO, and activated dolomite catalysts has greatly improved the yield and quality of biofuel, reducing the acid value of bio-oil. Modifications of the activated dolomite surface through bifunctional acid–base properties also positively influenced bio-oil production and quality. Dolomite catalysts have been found to be effective in catalyzing the pyrolysis of triglycerides, which are a major component of vegetable oils and animal fats, to produce biofuels. Recent advances in the field include the use of modified dolomite catalysts to improve the activity and selectivity of the catalytic pyrolysis process. Moreover, there is also research enhancement of the synthesis and modification of dolomite catalysts in improving the performance of biofuel yield conversion. Interestingly, this synergy contribution has significantly improved the physicochemical properties of the catalysts such as the structure, surface area, porosity, stability, and bifunctional acid–base properties, which contribute to the catalytic reaction’s performance.

In the present work, nickel (Ni), zinc (Zn), copper (Cu), cobalt (Co) and iron (Fe) are tested as catalyst dopants on Malaysian dolomite calcined at T = 900 °C (CMD900). The physicochemical properties of all synthesised catalyst are investigated by X-ray diffraction, Brunauer–Emmett–Teller surface area, temperature-programmed desorption of carbon dioxide and scanning emission microscopy. The synthesised catalysts are tested on the basis of the deoxygenation (DO) reaction of waste cooking oil to produce liquid fuels under N2 atmosphere. The chemical composition of the liquid product is identified by gas chromatography–mass spectroscopy. The overall study suggests that Ni/CMD900 catalyst exhibits the highest performance with over 67.0% conversion and high selectivity (80.2%) with a high proportion of saturated linear hydrocarbons that corresponds to green diesel. Result indicates that Ni/CMD900 is a highly potential DO catalyst with 19.8% oxygenated compound, which is favourable for decarboxylation and/or decarboxylation predominates.

In this study, the dehydrogenation of cyclohexanol to cyclohexanone over nitrogen-doped reduced graphene oxide (N-rGO) Cu catalyst has been reported. The N-rGO support was synthesized by chemical reduction of graphite oxide (GO). The synthesized N-rGO was used as a support to prepare the Cu/N-rGO catalyst via an incipient wet impregnation method. The as-prepared support and the Cu/N-rGO catalyst were characterized by FESEM, EDX, XRD, TEM, TGA, and Raman spectroscopy. The various characterization analysis revealed the suitability of the Cu/N-rGO as a heterogeneous catalyst that can be employed for the dehydrogenation of cyclohexanol to cyclohexanone. The catalytic activity of the Cu/N-rGO catalyst was tested in non-oxidative dehydrogenation of cyclohexanol to cyclohexanone using a stainless-steel fixed bed reactor. The effects of temperature, reactant flow rate, and time-on-stream on the activity of the Cu/N-rGO catalyst were examined. The Cu/N-rGO nanosheets show excellent catalytic activity and selectivity to cyclohexanone. The formation of stable Cu nanoparticles on N-rGO support interaction and segregation of Cu were crucial factors for the catalytic activity. The highest cyclohexanol conversion and selectivity of 93.3% and 82.7%, respectively, were obtained at a reaction temperature of 270 °C and cyclohexanol feed rate of 0.1 ml/min. Copyright © 2020 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Chemical and physical analysis was performed to identify the molten slag composition and its ability to be used as alternative catalyst in pyrolysis of waste cooking oil. The implementation such type of catalytic material could be useful in reducing the process cost. To increase the efficiency (increase the active site) of molten slag, it was modified by acid washing that resulted in an increase in the acidity from 159 to 1224 µmol/g. The results showed that the yield of bio-fuel was increased and the product selective to n-C15 upon the modification of molten slag by acid treatment. Copyright © 2020 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

In this work, the comparative study on the performance of K2O/SiO2 and calcined dolomite catalysts was conducted via deoxygenation of waste cooking oil (WCO). KSi catalyst has the potential as a deoxygenation catalyst due to mesoporous structure catalyst with high base properties which enhance oxygen removal. The result found that K2O/SiO2 catalyst could be used in the deoxygenation of WCO generating a high yield of pyrolysis oil as compared to thermal deoxygenation and calcined dolomite catalyst. Besides that, the reusability and regeneration of the K2O/SiO2 catalyst were evaluated in the deoxygenation reaction using WCO as a feedstock. Five consecutive runs of reusability test and three successive cycles with two regenerations were performed. The reusability and followed by regeneration tests were conducted at conditions: 30 min of reaction time, 390 ± 5 °C reaction temperature and 150 cm3/min of N2 flow rate. The liquid products obtained from each cycle were analyzed by GC–MS. The deoxygenation of WCO using K2O/SiO2 catalyst rendered higher selectivity towards diesel products (C13-C24). The K2O/SiO2 catalyst presented a good performance in reusability and regenerability test with only ∼19.3–22.4% dropped in pyrolysis oil yield after 5 consecutive runs and only ∼11.20–13.23% drop in diesel yield after regeneration. The results showed that K2O/SiO2 catalyst has tremendous stability in the deoxygenation of WCO into green diesel and could be the alternative deoxygenation base catalyst for the deoxygenation process.

Malaysian Dolomite has shown potential deoxygenation catalyst due to high capacity in removing oxygen compound and produce high quality of biofuel with desirable lighter hydrocarbon (C8-C24). The performance of this catalyst was compared with several commercial catalysts in catalytic pyrolysis of Waste Cooking Oil. Calcination at 900 °C in N2 produced catalyst with very high activity due to decomposition of CaMg(CO3)2 phase and formation of MgO-CaO phase. The liquid product showed similar chemical composition of biofuel in the range of gasoline, kerosene and diesel fuel. Furthermore, Malaysian Dolomite showed high reactivity with 76.51 % in total liquid hydrocarbon and the ability to convert the oxygenated compounds into CO2, CO, CH4, H2, hydrocarbon fuel gas, and H2O. Moreover, low acid value (33 mg KOH/g) and low aromatic hydrocarbon content were obtained in the biofuel. Thus, local calcined carbonated material has a potential to act as catalyst in converting waste cooking oil into biofuel.

The conversion of biomass into hydrogen-rich syngas has been getting attention recently, as it has potential sustainability benefits of agricultural residues. In this study, gasification of empty fruit bunch (EFB) was performed using various calcined Malaysian dolomite catalysts, which were denoted as P1, P2, and P3. The physicochemical properties of the catalysts were examined using X-ray fluorescence (XRF), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and scanning electron microscopy (SEM). The effect of various catalyst to biomass (C/B) ratios (varied in the range of 0.05–0.3 in an increment of 0.05) of P1, P2, and P3 catalyst in EFB gasification was evaluated at a gasifier temperature of 850°C. The gas produced was analyzed by gas chromatography (GC). The effect of various C/B ratios on tar conversion was also examined. The result showed that, with lower impurities in calcined dolomites and high content of active sites (CaO–MgO), improved characteristics of P1 and P2 in crystalline structure contributes to a significant reduction in tar cracking (~78 and 75%, respectively) and higher H2 yield (32.25 mg H2/g EFB).

Fluoride is important for human health, but high level of fluoride concentrations can be threatening for both humans and animals as well as damaging to the environment. This paper delineates on fluoride adsorption onto palm kernel shell-based anion resins under various fluoride concentrations and temperatures. The equilibrium fluoride adsorption capacity demonstrated by the resins was observed 2.32 mg/g. Pseudo second-order model and Weber-Morris diffusion model were employed to evaluate the uptake rate and behavior of fluoride adsorption. The correlation coefficients (R2) between experimental data and pseudo second-order model predictions was almost unity at all concentrations (5, 10 and 15 mg/L), indicating goodness of fit of the model. On the other hand, the thermodynamic study revealed the endothermic nature of the process indicated by the positive value of enthalpy change (2.671 kJ/mol). Moreover, the process is dominantly physical in nature along with a slight contribution of chemisorption.

Stringent environmental standards have made the removal of Cr(VI) from water an important problem for environmental scientist and engineering. Heterogeneous photocatalysis using suspended photocatalyst is an interesting technique to consider for this application. In this work, the influence of particle size of suspended CdS on the photocatalytic reduction of aqueous Cr(VI) ion was investigated. The efficiency of Cr(VI) reduction was monitored through UV-visible analysis. The experimental results showed that the nanoparticle size has a dramatic effect on the adsorption and reduction of Cr(VI). As surface area increased from 44.2±0.6 to 98.7±0.5 m2/g due to particle size reduction, the rate of Cr(VI) reduction nearly doubled in the first 20 min of visible light irradiation. The results evidenced the inverse relationship between the apparent reduction rate constant and the CdS particle size. Conversely, the half-life (t1/2) period of the photocatalytic reduction has a direct relationship with CdS particle sizes.

Aluminium dross, a waste material produced by dissolution of aluminum scrap, was characterized physically and chemically by various analysis techniques for a potential to be used as catalyst. Using catalyst from waste materials reduced the cost for synthesizing of new catalyst. An efficient catalyst derived from industrial solid waste was modified by acid washing for using in a pyrolysis of waste cooking oil. The modification of aluminum dross resulted in increased surface area (from 0.96 to 68.24 m2/g), acidity (from 315 to 748 µmol/g) and thermal stability. Pyrolysis waste cooking oil was used to test the performance of aluminum dross as catalyst before and after modification. The product analysis showed a better result than the unmodified material based on increased yield of bio-oil and improved selectivity.

In this study, Malaysian dolomites as secondary catalysts are placed at the downstream of the fluidized-bed gasifier. Three types of Malaysian dolomites with different elemental ratios of CaO-MgO content denoted as P1, P2, and P3 are investigated with EFB gasification reaction at different cracking temperatures (700–900 °C). The performance of the catalysts with a variation of catalyst to biomass weight ratio (C/B) (0.05 to 0.30 w/w) is evaluated. The findings showed that the total gas yield increased by 20%, hydrogen increased by 66%, along with an almost 99% reduction in tar content with P1 catalyst with the following reaction conditions: gasification temperature of 850 °C, equivalence ratio (ER) of 0.25, and cracking temperature of 900 °C. Malaysia dolomite could be a secondary catalyst to provide a better alternative, tar-free hydrogen-rich gas with the possibility of regeneration and re-use.

Carbon nanotubes (CNTs) have the potential to act as a catalyst support in many sciences and engineering fields due to their outstanding properties. The CNT-coated monolith was synthesized over a highly active Ni catalyst using direct liquid injection chemical vapor deposition (CVD). The aim was to study the optimum condition for synthesizing CNT-coated monoliths. The Taguchi method with L9 (34) orthogonal array design was employed to optimize the experimental conditions of CNT-coated monoliths. The design response was the percentage of carbon yield expressed by the signal-to-noise (S/N) value. The parameters including the mass ratio of Ni to citric acid (Ni:CA) (A), the injection rate of carbon source (B), time of reaction (C), and operating temperature (D) were selected at three levels. The results showed that the optimum conditions for CNT-coated monolith were established at A1B2C1D2 and the most influential parameter was D followed by B, C, and A. The ANOVA analysis showed the design was significant with R-squared and standard deviation of the factorial model equal to 0.9982 and 0.22, respectively. A confirmation test was conducted to confirm the optimum condition with the actual values of the average percentage of carbon yield deviated 1.4% from the predicted ones. The CNT-coated monoliths were characterized by various techniques such as field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and Raman spectroscopy.

Polyethylene terephthalate (PET) bottle is one of the common plastic wastes existed in the municipal solid waste in Malaysia. One alternative to solve the abundant of PET wastes is chemical recycling of the wastes to produce a value added product. This technology not only can decrease the PET wastes in landfill sites but also can produce many useful recycled PET products. Bis(2-hydroxyethyl) terephthalate (BHET) obtained from glycolysis reaction of PET waste was purified using crystallization process. The hot distilled water was added to glycolysis product followed by cooling and filtration to extract BHET in white solid form from the product. The effect of three operating conditions namely crystallization time, crystallization temperatures and amount of distilled water used to the yield of crystallization process were investigated. The purity of crystallization products were analyzed using HPLC and DSC. The optimum conditions of 3 hours crystallization time, 2 °C crystallization temperature and 5:1 mass ratio of distilled water used to glycolize solid gave the highest yield and purity of the crystallization process. © 2015 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

Scrap printed circuit boards (PCBs) are the most abundant wastes that can be found in the landfills in Malaysia and this disposal certainly poses serious detrimental to the environment. This research aims to investigate optimum temperature for pyrolyzing waste PCBs, find out the best catalyst to be used in accelerating PCBs’ pyrolysis, select suitable ratio of catalyst to PCBs for higher oil yield and examine kinetics pyrolysis of the waste PCBs’ decomposition. Operating temperatures ranged from 200 to 350 ˚C of PCB’s pyrolysis were conducted with the optimum temperature obtained was 275 ˚C. Fluid cata-lytic cracking (FCC) catalyst, zeolite socony mobil-5 (ZSM-5), H-Y-type zeolite and dolomite were used to accelerate PCB’s pyrolysis at 275 ˚C and FCC was identified as the best catalyst to be used. Differ-ent ratios of FCC to waste PCBs such as 10:90, 20:80, 30:70, 40:60 and 50:50 were applied in the pyro-lysis at 275 ˚C and ratio of 10:90 was selected as the suitable ratio to be utilized for maximum yield. The kinetic study was done through thermogravimetric analysis on waste PCBs under various heating rates and different particle sizes. The GC-MS analysis revealed that compounds detected in the pyro-oil have the potential to be used as fuel. © 2014 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)