Nitric Acid Functionalization of Petroleum Coke to Access Inherent Sulfur

Preparation of Carbon-Based Solid Acid Catalyst from High-Sulfur Petroleum Coke with Nitric Acid and Ball Milling, and a Computational Evaluation of Inherent Sulfur Conversion Pathways

A series of petroleum coke (petcoke)-derived solid acid catalysts were prepared via nitric acid treatment with or without ball milling pretreatment. The inherent sulfur in petcoke was converted to sulfonic groups, which were active sites for the esterification of octanoic acid and methanol at 60 °C, with ester yields of 14-43%. More specifically, samples without ball milling treated at 120 °C for 3 h had a total acidity of 4.67 mmol/g, which was 1.6 times that of the samples treated at 80 °C, despite their -SO3H acidities being similar (~0.08 mmol/g). The samples treated for 24 h had higher -SO3H (0.10 mmol/g) and total acidity (5.25 mmol/g) but not increased catalytic activity. Ball milling increased the defects and exposed aromatic hydrogen groups on petcoke, which facilitated further acid oxidation (0.12 mmol -SO3H/g for both materials and total acidity of 5.18 mmol/g and 5.01 mmol/g for BP-N-3/120 and BP-N-8/90, respectively) and an increased ester yield. DFT calculations were used to analyze the pathways of sulfonic acid group formation, and the reaction pathway with NO2• was the most thermodynamically and kinetically favourable. The activities of the prepared catalysts were related to the number of -SO3H acid sites, the total acidity, and the oxygen content, with the latter two factors having a negative impact.

Sulphur retention and in-situ preparation of metal sulphide catalysts during activation of petroleum coke

Petroleum coke (petcoke) containing sulphur has limited direct applications, but stockpiling the material creates an environmental issue. Although chemical activation can be used to valorise the petcoke to activated carbon, sulphur is released creating alternative environmental problems. In this study, a new activation method for high sulphur content (∼6.5 wt%) petcoke was developed to retain sulphur and prepare transition metal sulphide catalysts simultaneously. Petcoke was mixed with tungsten and nickel precursors and then activated by KOH at 600 °C in the presence of steam. After washing, the activated petcoke had a sulphur content of 5.1 wt%, which was much higher than that in the absence of steam during activation (0.4 wt%). Sulphur was also retained (>4 wt% of sulphur) when other transition metals including molybdenum and cobalt were used. Characterization by XRD, XPS, and SEM-EDS suggested that sulphur was retained on the activated petcoke in the form of metal sulphides. Further thermodynamic analysis of the system revealed that in the presence of steam an H₂S/H₂ mixture was generated, and this mixture promoted the formation of the metal sulphide species when metal precursors were introduced. The prepared metal sulphide catalysts were active for several reactions including the photoreduction of CO₂. Overall, this study provided an effective method to prepare metal sulphide catalysts from sulphur containing carbonaceous waste.

The Effects of Physical-Chemical Evolution of High-Sulfur Petroleum Coke on Hg0 Removal from Coal-Fired Flue Gas and Exploration of Its Micro-Scale Mechanism

As the solid waste by-product from the delayed coking process, high-sulfur petroleum coke (HSPC), which is hardly used for green utilization, becomes a promising raw material for Hg⁰ removal from coal-fired flue gas. The effects of the physical-chemical evolution of HSPC on Hg⁰ removal are discussed. The improved micropores created by pyrolysis and KOH activation could lead to over 50% of Hg⁰ removal efficiency with the loss of inherent sulfur. Additional S-containing and Br-containing additives are usually introduced to enhance active surface functional groups for Hg⁰ oxidation, where the main product are HgS, HgBr, and HgBr₂. The chemical-mechanical activation method can make additives well loaded on the surface for Hg⁰ removal. The DFT method is used to sufficiently explain the micro-scale reaction mechanism of Hg⁰ oxidation on the surface of revised-HSPC. ReaxFF is usually employed for the simulation of the pyrolysis of HSPC. However, the developed mesoporous structure would be a better choice for Hg⁰ removal in that the coupled influence of pore structure and functional groups plays a comprehensive role in both adsorption and oxidation of Hg⁰. Thus, the optimal porous structure should be further explored. On the other hand, both internal and surface sulfur in HSPC should be enhanced to be exposed to saving sulfur additives or obtaining higher Hg⁰ removal capacity. For it, controllable pyrolysis with different pyrolysis parameters and the chemical-mechanical activation method is recommended to both improve pore structure and increase functional groups for Hg⁰ removal. For simulation methods, ReaxFF and DFT theory are expected to explain the micro-scale mechanisms of controllable pyrolysis, the chemical-mechanical activation of HSPC, and further Hg⁰ removal. This review work aims to provide both experimental and simulational guidance to promote the development of industrial application of Hg⁰ adsorbent based on HSPC.

Valorization of fluid petroleum coke for efficient catalytic destruction of biomass gasification tar

Large volumes of waste petroleum coke stockpiled in open yard not only represent a huge loss of valuable material but also pose a significant risk to the environment. This work proposed an innovative strategy for waste petroleum coke valorization by exploring its catalytic performance of biomass gasification tar destruction. Waste petroleum coke was firstly activated by potassium hydroxide (KOH) to obtain high specific surface area as well as low sulfur and ash contents. Petroleum coke derived catalyst showed superior performance than a commercial activated carbon derived catalyst for destruction of naphthalene as the tar model compound. The petroleum coke derived catalyst exhibited 99.1% naphthalene destruction efficiency at 800 °C but deactivated quickly under N₂ atmosphere. Under H₂ and steam atmospheres, the catalytic activities were 98.6% and 96.5% for 8 h, respectively. To study the correlation between catalytic performance and the structure of carbon catalyst, elemental analysis, scanning electron microscope (SEM) analysis, transmission electron microscope (TEM) analysis, X-ray powder diffraction (XRD) analysis, Brunauer-Emmett-Teller method (BET) analysis, Fourier transform infrared (FTIR) spectroscopy, temperature programmed oxidation (TPO) analysis and Raman spectroscopy were performed on both fresh and spent catalysts. Results demonstrated that the hydrogen-rich groups (small rings and amorphous carbon) and oxygen-containing groups may account for the good resistance to coke deposition under H₂ and steam atmospheres.

Feedstock type drives surface property, demineralization and element leaching of nitric acid-activated biochars more than pyrolysis temperature

Nitric acid activation (NA-A) effects on the surface properties, mineral phases and element compositions of biochars produced from four feedstocks at three temperatures were evaluated. NA-A increased biochar thermal stability, but its effect on ash content and surface area was feedstock-dependent, with ash content in manure pellet biochars less affected due to a high quartz content. Apart from the manure pellet biochars and the sawdust biochar produced at 400 °C, NA-A decreased the surface area of biochars by up to 100% due to reduced pore volume. Nitric acid significantly leached elements such as potassium from biochars due to protonation and their reactions with several mineral phases, such as sylvite, on the biochars (p < 0.05). This study shows that mineral phases and element compositions of nitric acid-activated biochars were driven more by the feedstock type than the pyrolysis temperature and the derived biochars would be poor adsorbents.