Richard Gunawan

Thermal stability and kinetics of decomposition of ammonium nitrate in the presence of pyrite.

The interaction between ammonium nitrate based industrial explosives and pyrite-rich minerals in mining operations can lead to the occurrence of spontaneous explosion of the explosives. In an effort to provide a scientific basis for safe applications of industrial explosives in reactive mining grounds containing pyrite, ammonium nitrate decomposition, with and without the presence of pyrite, was studied using a simultaneous Differential Scanning Calorimetry and Thermogravimetric Analyser (DSC-TGA) and a gas-sealed isothermal reactor, respectively. The activation energy and the pre-exponential factor of ammonium nitrate decomposition were determined to be 102.6 kJ mol(-1) and 4.55 x 10(7)s(-1) without the presence of pyrite and 101.8 kJ mol(-1) and 2.57 x 10(9)s(-1) with the presence of pyrite. The kinetics of ammonium nitrate decomposition was then used to calculate the critical temperatures for ammonium nitrate decomposition with and without the presence of pyrite, based on the Frank-Kamenetskii model of thermal explosion. It was shown that the presence of pyrite reduces the temperature for, and accelerates the rate of, decomposition of ammonium nitrate. It was further shown that pyrite can significantly reduce the critical temperature of ammonium nitrate decomposition, causing undesired premature detonation of the explosives. The critical temperature also decreases with increasing diameter of the blast holes charged with the explosive. The concept of using the critical temperature as indication of the thermal stability of the explosives to evaluate the risk of spontaneous explosion was verified in the gas-sealed isothermal reactor experiments.

Mediating acid-catalyzed conversion of levoglucosan into platform chemicals with various solvents

Acid-catalyzed conversions of levoglucosan have been investigated in mono-alcohols, poly-alcohols, water, chloroform, toluene, acetone, N,N-dimethyl formamide, dimethyl sulfoxide and some mixed solvents, aiming to mediate conversion of sugars into platform chemicals with solvents. The mono-alcohols can stabilize soluble polymers and thus suppress formation of insoluble polymers. Water does not have such an effect, leading to lower yields of levulinic acid. Chloroform cannot effectively dissolve levoglucosan, leading to “dissolving” of levoglucosan in the catalyst and the consequent rapid polymerization. Acetone reacted with sugars, forming substantial amounts of polymer. N,N-Dimethyl formamide poisoned the acid resin catalyst, leading to negligible conversion of levoglucosan. Dimethyl sulfoxide (DMSO) mainly catalyzed the conversion of levoglucosan into 5-(hydroxymethyl)furfural (HMF), 2,5-furandicarboxaldehyde, and the sulfur ether of HMF. DMSO has a low ability to transfer protons, which helps to avoid further contact of HMF with catalytic sites and stabilizes HMF.

Acid-catalyzed conversion of mono- and poly-sugars into platform chemicals: Effects of molecular structure of sugar substrate

Hydrolysis/pyrolysis of lignocellulosic biomass always produces a mixture of sugars with distinct structures as intermediates or products. This study tried to elucidate the effects of molecular structure of sugars on their acid-catalyzed conversions in ethanol/water. Location of carbonyl group in sugars (fructose versus glucose) and steric configuration of hydroxyl groups (glucose versus galactose) significantly affected yields of levulinic acid/ester (fructose>glucose>galactose). The dehydration of fructose to 5-(hydroxymethyl)furfural produces much less soluble polymer than that from glucose and galactose, which results in high yields of levulinic acid/ester from fructose. Anhydrate sugar such as levoglucosan tends to undergo the undesirable decomposition to form less levulinic acid/ester. Catalytic behaviors of the poly-sugars (sucrose, maltose, raffinose, β-cyclodextrins) were determined much by their basic units. However, their big molecular sizes create the steric hindrance that significantly affects their followed conversion over solid acid catalyst.

Production of value-added chemicals from bio-oil via acid catalysis coupled with liquid–liquid extraction

Sugar/sugar derivatives in bio-oil can be effectively separated from aromatics via water/chloroform extraction. Subsequent acid-treatment in methanol converts the sugars into levulinic acid/ester and the sugar derivatives into fuel additives. Further extraction with CH2Cl2/CHCl3 could efficiently separate methyl levulinate and levulinic acid from other products.

Esterification of bio-oil from mallee (Eucalyptus loxophleba ssp. gratiae) leaves with a solid acid catalyst: conversion of the cyclic ether and terpenoids into hydrocarbons.

Bio-oil from pyrolysis of mallee (Eucalyptus loxophleba ssp. gratiae) leaves differs from that obtained with wood by its content of cyclic ethers, terpenoids and N-containing organic compounds. Upgrading of the leaf bio-oil in methanol with a solid acid catalyst was investigated and it was found that the N-containing organics in the bio-oil lead to deactivation of the catalyst in the initial stage of exposure and have to be removed via employing high catalyst loading to allow the occurrence of other acid-catalysed reactions. Eucalyptol, the main cyclic ether in the bio-oil, could be converted into the aromatic hydrocarbon, p-cymene, through a series of intermediates including α-terpineol, terpinolene, and α-terpinene. Various steps such as ring-opening, dehydration, isomerisation, and aromatization were involved in the conversion of eucalyptol. The terpenoids in bio-oil could also be converted into aromatic hydrocarbons that can serve as starting materials for the synthesis of fine chemicals, via the similar processes.