The present invention relates to a method for the co-processing of waste rubber and carbonaceous material. More particularly, it relates to an improved method for liquefying waste rubber in mixture with a carbonaceous material such as coal to permit use of depolymerized rubber as a hydrogen donor solvent and carbon black reinforcing pigment as a liquefaction catalyst.
In the United States, worn and used rubber products are creating an increasingly large disposal problem. During the past few years, it is estimated that about 200 million used tires are discarded each year. Each tire contains about 15 pounds (7 kilograms) of organic materials and 2 kilograms of carbon black. If the rubber in these tires could be reprocessed with coal at about a 1-to-1 weight ratio, approximately 40,000 barrels per day of transportation fuels could be produced. In addition to the used tires, there is also a substantial amount of other waste rubber products that could be reprocessed. At the present time, most of these tires and rubber products are serving no useful purpose but are occupying significant space in waste dumps, vacant lots, and other vacant facilities.
Coal liquefaction is typically achieved by heating the coal in the presence of a hydrogen donor solvent often with an added liquefaction catalyst. The most common solvent used are fractions derived from the liquified coal or heavy fractions from the petroleum industry in a co-processing operation. The liquefaction of coal is dependent on its hydrogenation which can be a function of the hydrogen donor solvent or the ability of the catalysts to promote reaction with hydrogen gas. Representative single and two-stage coal liquefaction processes are described generally in U.S. Pat. No. 4,874,506, and other issued U.S. Patents cited therein.
Typically, particulate coal feed is slurried in a coal-derived recycle solvent and the resulting slurry is preheated to near the reaction temperature and fed with hydrogen into a catalytic reactor. The reactor operates at relatively high temperature and pressure conditions to hydroconvert and liquefy a major portion of the coal and thereby produce hydrocarbon gas and liquid fractions.
Unfortunately, a large fraction of the coal liquefaction product is a residual oil containing preasphaltenes and asphaltene compounds having a low hydrogen content. It is these heavy, hydrogen-lean fractions that are often recycled for slurrying with the incoming coal to place an additional burden on the hydrogenation reactor.