Nitric Acid Functionalization of Petroleum Coke to Access Inherent Sulfur

Qing Huang,Ye Xiao,Melanie J Hazlett,Annelisa S Schafranski,Josephine M Hill

doi:10.3390/catal10020259

Abstract

Sulfonated carbon-based catalysts have been identified as promising solid acid catalysts, and petroleum coke (petcoke), a byproduct of the oil industry, is a potential feedstock for these catalysts. In this study, sulfur-containing (6.5 wt%) petcoke was used as a precursor for these catalysts through direct functionalization (i.e., without an activation step) with nitric acid to access the inherent sulfur. Catalysts were also prepared using sulfuric acid and a mixture of nitric and sulfuric acid (1:3 vol ratio). Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and titration were used to identify and quantify the acid sites. The activities of the prepared catalysts were determined for the esterification of octanoic acid with methanol. Petcoke had few −SO3H groups, and correspondingly no catalytic activity for the reaction. All acid treatments increased the number of −SO3H groups and promoted esterification. Treatment with nitric acid alone resulted in the oxidation of the inherent sulfur in petcoke to produce ~0.7 mmol/g of strong acid sites and a total acidity of 5.3 mmol/g. The acidity (strong acid and total) was lower with sulfuric acid treatment but this sample was more active for the esterification reaction (TOF of 31 h−1 compared to 7 h−1 with nitric acid treatment).

Highlights

Petroleum coke is a by-product from the oil industry and is a solid product mainly composed of carbon (>80 wt%) [1]
Sulfonic groups were generated on the petcoke using only nitric acid, confirming that the inherent sulfur in the petcoke could be converted to surface functional groups
The number of strong acid groups ranged from ~0 on the petcoke to 0.25 mmol/g after treatment with H2 SO4, and ~0.7 mmol/g after treatment with either HNO3 or

Summary

Introduction

Petroleum coke (petcoke) is a by-product from the oil industry and is a solid product mainly composed of carbon (>80 wt%) [1]. Petcoke may contain various impurities that limit its use as a fuel or a feedstock for the production of anodes in industrial manufacturing processes [2]. Many studies have focused on the removal of sulfur from petcoke [4,5,6,7], but the organic sulfur species are integrated with the petcoke aliphatic or aromatic structure and are difficult to remove [3]. Instead of removing the sulfur, there is potential to use petcoke as a precursor for preparing carbon-based catalysts such as solid acid catalysts that have sulfur-containing surface functional groups as active sites. Solid acid catalysts are widely used in the petrochemical industry in esterification, etherification, hydration, dehydration, alkylation of aromatics and amines, and hydrocarbon cracking reactions [8]

Methods

Results

Conclusion