FINAL TECHNICAL REPORT

September 1, 1995, through August 31, 1996

Project Title: DESULFURIZATION OF ILLINOIS COALS WITH HYDROPEROXIDES OF VEGETABLE OILS AND ALKALI

DOE Cooperative Agreement Number: DE-FC22-92PC92521 (Year 4)

ICCI Project Number: 95-1/1.1D-2P

Principal Investigator: Gerard V. Smith, SIU

Other Investigators: Ricky D. Gaston, SIU

Ruozhi Song, SIU

Jianjun Cheng, SIU

Feng Shi, SIU

Yaguang Wang, SIU

Project Manager: Ken K. Ho, ICCI

ABSTRACT

The goal of this project is to develop an inexpensive method to remove organic sulfur from pyrite-free and mineral-free coal using base, air, and readily available farm products. This is accomplished by treating coals with alkali, impregnating coals with polyunsaturated oils, converting the oils to their hydroperoxides, and heating. Since these oils are relatively inexpensive and easily applied, this project could lead to a cost effective method for removing organic sulfur from coals. Moreover, the oils are environmentally safe; they produce no noxious products and improve burning qualities of the solid products.

IBC-108 coal, (contains only 0.4% pyrite and 2.7% organic sulfur) was first treated with NaOH at two different concentrations and four different times, and with NH₄OH at two different concentrations and two different temperatures. Pretreating IBC-108 coal with bases removes 13% to 23% of the sulfur, and NaOH is a better treatment than NH₄OH in most of the experiments. Higher temperatures, higher base concentrations, and longer treatment times remove more sulfur. Na₂CO₃ is more effective than NaOH for oil extraction after the oil treatment.

To test for effectiveness of sulfur removal, eight coal samples were treated with NaOH (two concentrations at four different times) were further treated with linseed oil at three temperatures, four different times, and two oil to coal ratios. The combination of NaOH pretreatment, then oil treatment, followed by Na₂CO₃ extraction, removes 23% to 50% of the sulfur. The best result is achieved by pretreating with 5% NaOH for 20 hr (23% sulfur removal) followed by oil treatment at 100^oC for 5 hr with a 1:1 oil to coal ratio (50% sulfur removal in total). More sulfur is removed with a 1:1 oil to coal ratio than a 1:10 ratio under most conditions. However, the effects of time of oil treatment are complex. Sulfur removal is favored by longer oil treatment in some cases, but disfavored in other cases. This demonstrates that other experimental parameters are important, such as temperature, concentration of base, time of base pretreatment, and oil to coal ratio.

"U.S. DOE Patent Clearance is NOT required prior to the publication of this document."

EXECUTIVE SUMMARY

This project proposes to remove organic sulfur from coal, maintain its BTU, and increase its volatiles, by a new process of pretreating with alkali and impregnating with polyunsaturated vegetable oils. Catalyzed by coal, air converts these oils into their hydroperoxides which are powerful oxidizing agents. A similar agent, peroxyacetic acid, has shown in a previously funded ICCI project to desulfurize coal. But polyunsaturated vegetable oils have advantages which make them attractive for treating coal. First, these compounds are inexpensive, renewable natural products available from Illinois farms; second, they possess chemical properties which can be directed toward oxidizing organic sulfur; third, they furnish carbonaceous residues which will increase BTU's and volatiles; and fourth, they are environmentally safe and produce no noxious products.

Preliminary experiments at SIUC have shown that IBC-108 coal impregnated with linseed oil and heated in air at 50-100^oC has its organic sulfur removed. The results show that coal catalyzes formation of hydroperoxides in the oil and these hydroperoxides oxidize the organic sulfur with minimum loss of BTU. Additionally, experiments have shown that pretreating IBC-108 coal with NaOH increases the amount of organic sulfur removed during subsequent treatment with linseed oil. This project proposes to build on this new evidence to aim at a technically feasible and economically viable process step.

Three tasks are proposed: Task 1 will select the base for pretreating and extraction. Tests will examine NaOH and NH₄OH at two different concentrations followed by treatment with linseed oil at 100^oC for 15 hours, then extraction with two different bases, NaOH and Na₂CO_3.. Task 2 will determine the ability of the above selected base in combination with linseed oil to remove organic sulfur from IBC-108 coal. Tests of base pretreatment will be conducted at 25^oC, two different concentrations, and four different times. Tests of oil treatment will be conducted at two different oil:coal ratios, three different reaction times, three different temperatures, and with two different extraction solutions. This task will produce 144 experiments with accompanying plots of sulfur removal as function of temperature and time and will be used to study reaction rates and the mechanism of sulfur removal. Task 3 will determine the mass balance along with the volatiles and BTU changes from the experiments in Tasks 1 and 2 creating a data base of 152 analyses of mass balances, volatiles, and BTU's along with plots of their dependence on temperature and time. All of these data will be examined for clues to the mechanism of organic sulfur oxidation and removal from Illinois coals.

During the first quarter we completed screening of the bases for pretreating the coal and for extracting the oil after oil treatment. The bases selected for the pretreatment are NaOH and NH₄OH with two concentrations (5% and 1%) each and for the oil extraction are 5%NaOH ad 5%Na₂CO₃. The pretreatmets were carried out at either 25^oC or 100^oC for 15 hours.

Conclusions reached during the first quarter were that pretreating IBC-108 coal with bases removes 13% to 23% of the sulfur. NaOH is a better treatment than NH₄OH in most experiments and Na₂CO₃ is better than NaOH for the final extraction. Higher temperatures and higher base concentrations remove more sulfur. Thereby, treatments with 5% NH₄OH at 100^oC in the presence of bubbling O₂ or with 5% NaOH at 25^oC remove more sulfur (21-23%) than any other treatment with alkali alone. However, even more sulfur is removed from the pretreated coal by linseed oil treatment followed by base extraction. And the best results (about 40% sulfur removal) are obtained with the combinations of 5% NaOH-OIL-5%Na₂CO₃ (B-O-C), 1% NH₄OH-OIL-5%Na₂CO₃ (N1-O-C), and 5% NH₄OH (100^oC)-OIL-5% Na₂CO₃ (N₁₀₀-O-C). Based on these results, NaOH was selected for pretreating the coal and Na₂CO₃ was selected for the oil extraction in the later experiments.

During the second quarter we tested the ability of the selected base (NaOH) in combination with linseed oil to remove organic sulfur from IBC-108 coal. Tests of NaOH pretreatment were performed at 25^oC with two base concentrations (5% and 1% NaOH) at four different times (20hr, 10hr, 5hr, and 1hr). Tests of oil treatment were conducted at 125^oC for three different times (20hr, 10hr and 5hr) with two different ratios of oil:coal (1:1 and 1:10).

The conclusions reached during the second quarter were that about 17% to 23% of sulfur is removed under these conditions, the sulfur removal is slightly favored by higher base concentration and longer time, more sulfur is removed from the NaOH pretreated coal by linseed oil treatment followed by Na₂CO₃ extraction. The best result (43% sulfur removal) is given by pretreating the coal with 1% NaOH for either 1hr or 5hr followed by oil treatment for 5hr with 1:1 oil to coal ratio.

During the third and the final quarters more experimental parameters were systematically varied to determine the effectiveness of linseed oil and NaOH for sulfur removal from IBC-108 coal. The eight coal samples pretreated with NaOH were further treated with linseed oil at 100^oC and 75^oC for three different times (20hr, 10hr, and 5hr) and two oil to coal ratios (1:1 and 1:10). The BTU's were measured for all the samples.

The combinations of NaOH pretreatment, then oil treatment followed by Na₂CO₃ extraction remove 23% to 50% sulfur form the IBC-108 coal. The best result is achieved by pretreating with 5% naOH for 20 hr (23% sulfur removal) followed by oil treatment at 100⁰C for 5 hr with a 1:1 oil to coal ratio (50% sulfur removal in total, exp.93). More sulfur is removed with a 1:1 oil to coal ratio than a 1:10 ratio under most conditions of the investigation. The effects of time of oil treatment are complex. Sulfur removal is favored by longer oil treatment in some cases, but disfavored in other cases. This demonstrates that other experimental parameters are important, such as temperature, concentration of base, time of base pretreatment, and oil to coal ratio.

The conclusions reached during the final two quarters were that up to 50% sulfur is removed from the IBC-108 coal, the BTU loss is minimal, sulfur removal is favored by high oil to coal ratio, but the effects of other experimental parameters is very complex.