Recent advances in the science and technology of ultra low sulfur diesel (ULSD) production

This paper is a selective review on design approaches and associated catalysis and chemistry for deep desulfurization and deep dearomatization (hydrogenation) of hydrocarbon fuels, particularly diesel fuels. The challenge for deep desulfurization of diesel fuels is the difficulty of removing the refractory sulfur compounds, particularly 4,6-dimethyldibenzothiophene, with conventional hydrodesulfurization processes. The problem is exacerbated by the inhibiting effect of polyaromatics and nitrogen compounds, which exist in some diesel blend stocks on deep HDS. With the new Environmental Protection Agency (EPA) Tier II regulations to cut the diesel sulfur from current 500 ppmw down to 15 ppmw by June 2006, refineries are facing major challenges to meet the fuel sulfur specification along with the required reduction of aromatics contents. The principles and problems for the existing hydrodesulfurization processes, and the concepts, advantages and disadvantages of various new approaches will be discussed. Specifically, the following new design approaches for sulfur removal will be discussed: (1) novel catalysts for ultra-deep hydrodesulfurization under conventional HDS process conditions; (2) new design concept for sulfur-tolerant noble metal catalysts for low-temperature hydrogenation; (3) new desulfurization process by sulfur adsorption and capture under H2; (4) new desulfurization process by selective adsorption at ambient temperature without H2 and a related integrated process concept; (5) oxidative desulfurization in liquid-phase; and (6) biodesulfurization.

New design approaches to ultra-clean diesel fuels by deep desulfurization and deep dearomatization

The main purpose of this review is to update the information on gasification tar, the most cumbersome and problematic parameter in any gasification commercialization effort. The work aims to present to the community the scientific and practical aspects of tar formation and conversion (removal) during gasification as a function of the various technological and technical parameters and variables.

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Biomass Gasifier "Tars": Their Nature, Formation, and Conversion

Sulfur compounds represent one of the most common impurities present in the crude oil. Sulfur in liquid fuel oil leads directly to the emission of SO2 and sulfate particulate matter (SPM) that endangers public health and community property; and reduces the life of the engine due to corrosion. Furthermore, the sulfur compounds in the exhaust gases of diesel engines can significantly impair the emission control technology designed to meet NOx and SPM emission standards. The research efforts for developing conventional hydrodesulfurization and alternative desulfurization methods such as selective adsorption, biodesulfurization, oxidation/extraction (oxidative desulfurization), etc. for removing these refractory sulfur compounds from petroleum products are on the rise. Research laboratories and refineries are spending huge amounts of money in finding a viable and feasible solution to reduce sulfur to a concentration of less than 10 mg l−1. This paper reviews the current status in detail of various desulphurization techniques being studied worldwide. It presents an overview of novel emerging technologies for ultra-deep desulfurization so as to produce ultra-low-sulfur fuels.

An evaluation of desulfurization technologies for sulfur removal from liquid fuels

Dibenzothiophene, 4-methyldibenzothiophene, and 4,6-dimethyldibenzothiophene are typical thiophenic sulfur compounds that exist in diesel fuels Using toluene solutions of the model compounds, experiments were carried out to compare the reactivity of the different dibenzothiophenes in oxidation reactions, a key step for oxidative desulfurizations A series of polyoxometalate/H2O2 systems were evaluated for dibenzothiophene oxidation The H2O2 solutions of phosphotungstic acid and its salt were very active catalyst systems for the model compound oxidation, while their molybdenum counterpart systems were much less active The H2O2 solutions of silicotungstic and silicomolybdic compounds were the least active catalyst systems for the reaction Oxidation reactivities decreased in the order of dibenzothiophene>4-methyldibenzothiophene>4,6-dimethyldibenzothiophene, the same reactivity trend that exists in HDS However, the oxidation of the dibenzothiophenes was achieved under mild reaction conditions and it was easy to increase reaction temperature or reaction time to achieve high oxidation conversions, even for the least reactive 4,6-dimethyldibenzothiophene Apparent activation energies of dibenzothiophene, 4-methyldibenzothiophene, and 4,6-dimethyldibenzothiophene oxidation were 538, 560, and 587 kJ/mol, respectively These activation energies indicated a decrease in reactivity of dibenzothiophenes as methyl substitutes increased at the 4 and 6 positions on dibenzothiophene rings Interestingly, in a formic acid/H2O2 system, the oxidation reactivity of the dibenzothiophenes showed the reverse trend, suggesting that steric hindrance might play a role when bulky polyoxoperoxo species, which likely form in a hydrogen peroxide solution, act as catalysts

Oxidation reactivities of dibenzothiophenes in polyoxometalate/H2O2 and formic acid/H2O2 systems

The oxidation of model sulfur compounds (thiophene derivatives, benzothiophene derivatives, and dibenzothiophene derivatives), straight run-light gas oil (SR-LGO, S:  1.35 wt %), and vacuum gas oil (VGO, S:  2.17 wt %) were conducted with a mixture of hydrogen peroxide and formic acid. The thiophene derivatives with 5.696 to 5.716 electron densities on the sulfur atoms could not be oxidized at 50 °C. Benzo[b]thiophene with 5.739 electron density and other benzothiophene and dibenzothiophenes with higher electron densities could be oxidized. The sulfur compounds in SR-LGO and VGO appeared to be oxidized to a detectable levels (c.a., 0.01 wt % S) by GC-FPD analysis. The IR spectra of oxidized SR-LGO and VGO showed that sulfones were formed by oxidation. The removal of sulfur compounds by extraction became more effective for the oxidized samples than for the original samples. Lighter sulfur compounds were preferentially extracted. The extraction efficiencies of solvents, i.e., N,N‘-dimethylformamide (DMF), a...

Oxidative Desulfurization of Light Gas Oil and Vacuum Gas Oil by Oxidation and Solvent Extraction

Hydrodesulfurization (HDS) of light gas oil was investigated using sulfided Co−Mo/Al2O3 catalyst. The behavior of dibenzothiophene, monomethyldibenzothiophenes (C1-DBTs) and dimethyldibenzothiophenes (C2-DBTs) in HDS was traced under the following conditions:  temperature, 280−400 °C; LHSV, 2−10 h-1; and gas/oil, 1000 and 125 NL (L-(NTP))/L. The HDS of these compounds was treated as a pseudo-first-order reaction. The ratio of the rate constants of 4-methyldibenzothiophene (4-MDBT) and DBT to that of 4,6-dimethyldibenzothiophene (4,6-DMDBT) diminished relative to those of the model reactions. The activation energies of DBTs increased in the order DBT 4-MDBT, and further, 4,6-DMDBT was not inhibited. The results indicated that the selectivity for biphenyls in the HDS of DBT was highe...

Deep Hydrodesulfurization of Light Gas Oil. 1. Kinetics and Mechanisms of Dibenzothiophene Hydrodesulfurization

本研究では, オゾン発生装置により空気または酸素からオゾンを発生させ, ジベンゾチオフェン (DBT) および4,6-ジメチルジベンゾチオフェン (4,6-DMDBT) をそれぞれ150ppmおよび145ppm含む水素化処理油の50°C, 常圧での酸化反応を行った。空気または酸素から発生させたオゾンにより, 軽油中の低濃度の難脱硫性硫黄化合物であるDBTおよび4,6-DMDBTを100%DBTsスルホンに酸化することができた。また, 4,6-DMDBTの方がDBTよりも反応性が高かった。オゾンによる軽油の酸化反応にギ酸を加えるとDBTs転化率が増加した。さらに, 空気を原料としたオゾンによるDBTの酸化反応でも反応時間を2倍にすることで酸素原料の場合と同等のDBTs転化率が得られることが分かった。酸化反応後, ヘテロ原子が酸化され有機化合物が高分子量化したゴム状物質が6.0%析出し, 元素分析の結果, 原料軽油中のヘテロ原子のほとんどを含んでいることが分かった。

Oxidative Desulfurization of Middle Distillate Using Ozone

The oxidation of dibenzothiophene (DBT) was conducted using t-butyl hypochlorite (t-BuOCl) in the presence of several catalysts. In a flow reactor under ambient pressure at 30-70°C, more than 90% of DBT could be oxidized in the decahydronaphthalene (decalin) solution. The catalyst was necessary to oxidize dibenzothiophene with t-BuOCl, and γ-alumina (Al2O3) supported catalysts have relatively high activities. At the same time, the activities of the metal-loaded Al2O3 catalysts had shown the same activities as those of the Al2O3 support, indicating that the Al2O3 support itself possessed such activity. Further, the effect of a variety of model compounds found in light gas oil (LGO) such as n-pentadecane, 2, 4, 4-trimethylpentene, xylene, and indole on the oxidation of DBTs were also investigated.

https://www.jstage.jst.go.jp/article/jpi1958/44/1/44_1_18/_pdf

Shujiro Otsuki

Papers

Oxidative Desulfurization of Light Gas Oil and Vacuum Gas Oil by Oxidation and Solvent Extraction

Deep Hydrodesulfurization of Light Gas Oil. 1. Kinetics and Mechanisms of Dibenzothiophene Hydrodesulfurization

Oxidative Desulfurization of Middle Distillate Using Ozone

Oxidative Desulfurization of Middle Distillate

Elucidation of dimethylsulfone metabolism in rat using a 35S radioisotope tracer method