A B S T R A C T
Solvent extraction of the nitrogen compounds present in straight run gas oil (SRGO) and straight run gas oil/light cycle oil mixtures (SRGO/LCO) were studied using acetone and acetone/water mixtures. In the batch experiments, LCO content in SRGO varied from 0 to 15 %, water in acetone went from 0 to 15 % and the solvent/feed ratio changed from 1 to 3. The effect of these variables on the nitrogen removal and gain or loss of hydrocarbon weight in the raffinate products was studied. The nitrogen removal is increased by the decrease in the amount of water in acetone (0 to 15 %), and the increase of solvent/feed ratio (from 1 to 3) for all the SRGO and SRGO/LCO samples. As the amount of LCO increased in the feed, a reduction of the raffinate yield decreased, meaning that as higher the aromatic content in the feed, higher the removal of aromatic compounds.
These results were confirmed by experiments in continuous system, where SRGO and SRGO/LCO mixtures up to 40/60 were used. It was probed that as higher was the aromatic content in the feed, higher the nitrogen and aromatic removal in the raffinate, but lower the quality of the product as fuel.
Keywords: Extraction; Nitrogen; ULSD; Desulfurization; Desaromatization.
The production of ultra low sulfur diesel (ULSD) is so essential to protect life on earth that many stringent environmental regulations for this nonrenewable fuel have been established worldwide in spite of the sustained decrement in the crude oil quality. Several technological alternatives have been developed to overcome those challenges [1-3]; for example: the withdrawal of the nitrogen compounds (N-compounds) in the feedstocks processed for diesel fuel production due to its hydrodesulfurization (HDS) inhibition capabilities [4-7].
The N-compounds are frequently classified into two groups: basic (i.e. pyridines, quinolines) and neutral (i.e. indoles, carbazoles) [8-9]. While the basic N-compounds have an inhibiting effect by being adsorbed onto the Lewis and Brönsted acidic sites of refining catalysts, the neutral N-compounds tend to form gums by polymerization leading to pore and intraparticular plugging of those catalysts [10-13]. As stated by Laredo et al. , indoles and carbazoles represent 75 wt% of total N-content (300-400 wppm), and the concentration of quinolines around 25 wt%, in a straight run gas oil (SRGO). Concentrations of total N- and neutral N-compounds of light cycle oil and coker gas oil are higher than those of SRGO [14-17].
An alternative used quite often is selective adsorption of these compounds using several materials . However, until now, such a suitable high adsorption capacity, highly selective and low price material has not yet been found. Several researchers have proposed to reduce the aromatic, sulfur or nitrogen content in diesel by an extraction procedure using certain solvents [18-24]. Most of these studies are devoted to the sulfur and aromatic reduction...