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This study systematically investigated the co-slagging characteristics of high-rank coal and biomass ashes considering entrained flow slagging gasifier. Despite favourable performance parameters, coal might not be feasible for entrained flow gasification because of not forming slag within the gasifier operating temperature (1200–1500 °C). To overcome this issue, co-gasification can be a potential solution, which simultaneously helps to reduce the carbon footprint and environmental impact. Hence, this study studied the feasibility of co-gasification of coal and biomass by testing co-slagging behaviour of bituminous coal and pine park biomass ashes. The slag viscosity is measured using a Brookfield DV-III Ultra rheometer coupled with a high-temperature furnace. Results show that pure coal ash does not form slag using the maximum furnace temperature of 1670 °C. However, co-slagging by 50/50 (wt./wt.) ratio of coal and biomass ash (PB50) significantly drops the slagging temperature due to the higher fluxing agents (i.e. CaO) in biomass ash. The temperature of critical viscosity was determined to be 1390 °C using PB50 ash, which maintained the maximum industrial viscosity limit of 25 Pa s up to the temperature of 1360 °C.

In this work, a marine microalga Tetraselmis suecica was pyrolyzed in a fixed-bed reactor in the presence of a series of zeolite (Si/Al = 30) supported Ni catalysts to increase the hydrocarbon composition of the pyrolysis oil by a two-step process - devolatilization followed by catalytic treatment. A 3 wt% Ni-loading on zeolite showed the highest hydrocarbon content of 55.38%, in which aliphatic hydrocarbons and aromatic hydrocarbons were 35.21% and 20.17%, respectively. Besides, the oxygen-containing compounds decreased from 42.88% to 9.55% while the nitrogen-containing compounds decreased from 40.68% to 35.07%. The activity of the Ni-loaded catalysts was found to increase up to 3 wt % Ni-loading and decrease at higher loadings in similar lines to catalyst acidity measurements. Besides, the catalytic activity decreased with an increase in crystallite size of Ni at higher Ni loadings. The results indicate that the Ni-loaded catalysts can deoxygenate pyrolysis oils, but it is necessary to address the removal of the nitrogenous compounds. Pyrolysis temperature and Ni-loading play an important role in the removal of oxygen and nitrogen from the bio-oil. The quality of the bio-oil can be affected by the presence of strong acid sites, nickel-loading and the pore size.

This paper presents an in-depth review of recent research on catalytic pyrolysis of microalgae and suitable approaches for bio-oil upgrading. The performance of three types of catalysts commonly used in pyrolysis, particularly focusing on microalgae pyrolysis are examined and compared. Also, two deoxygenation methods of catalytic pyrolysis and hydrodeoxygenation and two denitrogenation methods of adsorptive denitrogenation and hydrodenitrogenation for microalgae bio-oil upgrading are reviewed. It is evident that metal-loaded zeolites, particularly loaded with Ni and Pd, are the most favourable catalysts for the reduction of oxygen compounds and partial reduction of nitrogenous compounds from the microalgae bio-oil. Alternative methods for nitrogen removal are necessary for the application of microalgae pyrolysis bio-oils. Adsorptive denitrogenation is found to be the method of interest for dealing with the major nitrogen-containing compounds. The potential adsorbents used for denitrogenation include activated carbon, activated alumina and metal-exchanged zeolites; these all can effectively remove the nitrogen-containing compounds. Besides, all of them can be regenerated by solvent washing or thermal treatment up to five times. A multi-step process with the initial step of devolatilization and followed by catalysis and adsorption is necessary for the best removal of oxygeneous and nitrogenous compounds simultaneously from microalgae bio-oil. Though, there are some challenges in production of high-quality bio-oil from catalytic pyrolysis of microalgae, these processes are of interest for application on commercial scale. Further research and development are still required to maximize the yield and improve the quality of bio-oil from fast and catalytic pyrolysis of microalgae.

This study investigates the yield and quality of bio-oil produced from catalytic and non-catalytic pyrolysis of microalgae Chlorella vulgaris using Ni supported zeolite (Si/Al = 30) prepared by two different methods, ion exchange (IE) and wet impregnation (WI) to examine the effect of catalyst preparation methods on the bio-oil quality. The experiments were also conducted to investigate the effect of different temperatures (300–600 °C) and catalyst to algae ratio (1:5, 1:2, 1:1 and 2:1) on the yield and quality of bio-oil. The results showed that catalytic pyrolysis using Ni supported zeolites produced high hydrocarbon, less oxygenated and acid compounds compared to non-catalytic pyrolysis. The catalyst preparation method did not affect the yield but had an effect on the bio-oil composition. The results obtained from this study are useful in developing the catalytic pyrolysis process to refine bio-oils for commercial use.

A bench scale, two-stage, thermo-catalytic reactor equipped with a continuous feeding system was used to pyrolyse pure and waste plastics. Experiments using five zeolitic and clay-based catalysts of different forms (pellet and powders) and different plastic feedstocks – virgin HDPE, HDPE w1aste and mixed plastic waste (MPW) were compared to the control experiments – pyrolysis without catalyst. Results indicated that the two pelletized catalysts were the most promising for the conditions employed. Of these two, one with higher acidity and surface area was highly selective for the gasoline fraction (C 5 –C 11 ) giving 80% from the total medium distillate conversion using virgin HDPE as feedstock. It also produced the least amount of olefins (17% for virgin HDPE, 4% for HDPE waste and 2% for MPW) and coke ( 12 –C 25 ) giving 63% from the total medium distillate conversion using virgin HDPE as feedstock. The amount of coke deposited on the catalyst surface depended mainly on the mesopore volume, with less coke deposited as the mesopore volume increased. The variation in catalyst selectivity with acidity strength due to Lewis sites on the catalyst surface controls selectivity towards carbon chain length.

This two-part study firstly investigated Tetraselmis suecica grown in different CO2 (0.04–15% v/v) concentration through indoor and outdoor cultivation systems. A high CO2 concentration led to a high lipid content, and low nitrogen and oxygen content, which are desirable for transport fuel production. Pyrolysis characteristics were investigated by TG-IR and synchrotron IR microscopy. The results show Tetraselmis suecica grown in 10% CO2 had the highest decomposition rate corresponding to more volatile products produced during the main thermal cracking stage and derived from protein-and lipid-corresponding functional groups. Moreover, a high reaction temperature and CO2 concentration resulted in a low retention of surface functional groups. The nitrogen functional groups initially decomposed at a temperature range of 250–300 °C and still remained at 550 °C, while the lipid-corresponding functional groups completely disappeared at a temperature range of 400–500 °C. Besides, the decomposition of chemical components followed the order of carbohydrate, protein and lipid.

Catalytic pyrolysis is a useful technique for the conversion of scrap tyres into liquid fuels. Zeolite catalysts were employed in the pyrolysis of scrap tyres for the production of aromatic rich fuel. Deactivation of zeolite catalysts during pyrolysis reaction was investigated which played an important role in the product quality and composition. Herein, the performance of microporous zeolite catalysts and mesoporous MCM-41 catalyst was evaluated in a two-stage fixed bed reactor for the pyrolysis of scrap tyres. Comparative studies showed the increase in the production of aromatic compounds up to 23.7% over zeolite catalyst as compared to 18.7% over MCM-41 catalyst. However, Zeolite Y catalyst exhibited higher coke formation led to the rapid deactivation. The stability of zeolite catalysts is addressed by the incorporation of Cerium metal within the framework of two zeolite catalysts namely Zeolite Y and ZSM-5 through the ion-exchange technique. Parent and spent catalysts were characterised using synchrotron FT-IR spectroscopy, temperature-programmed desorption of ammonia (NH3-TPD), N2 Physisorption, scanning electron microscopy (SEM), inductively coupled plasma-optical emission spectrometry (ICP-OES), energy-dispersive X-ray spectroscopy (EDX), and hydrogen temperature-programmed reduction (H2-TPD). A higher percentage of aromatics were produced over the large pore Zeolite Y. Cerium ion-exchange decreased the formation of coke from 8.1% to 5.7% over submicron and large pore Zeolite Y catalyst. Moreover, naphthalene production decreased over both Ce-Zeolite Y and Ce-ZSM-5.

In-situ synchrotron FTIR studies were conducted using four Victorian brown coals and one Thailand lignite to examine the evolution of functional groups from the surface of the sample during pyrolysis from room temperature to 550 °C. TGA data showed that the pyrolysis of all coals is comprised of a drying stage (30–200 °C) and devolatilization stage (200–900 °C). FTIR data showed that compared to Victorian brown coals, less surface functional groups were found in Thailand lignite. The loss of functional groups from Thailand lignite was observed during drying, and the devolatilization consisted of two stages. For Victorian brown coals, the concentration of oxygen contained hydroxyl and carboxyl groups decreased during the drying stage, due to the removal of water, and breakdown of weakly bonded alkene and alkyne. When temperature gradually increased during devolatilization stage, more functional groups were released. However, by 550 °C, the groups at the wavenumber of 1700–1340 cm−1 (carbonyl, carboxylate, aromatic ring, CH3 and CH2 groups) remained in the sample. Based on the spectra taken of two chars from the same brown coals, these groups were not completely removed until 1000 °C.