he Houdry Litol process was developed to purify the
Tlight aromatic fraction produced as a byrproduct in the coking of coal. This oil, designated as secondary light oil, is obtained by suubbing coke oven gas. The light oil, after removal of materials lighter than benzene and heavier than C8 aromatics, usually has an aromatics concentration of 90-95%. The traditional method for purifying light oil is to wash it with sulfuric acid, followed by distillation to separate benzene, toluene, xylene, and solvent naphtha cuts. The thiophene content of benzene produced by acid washing is hvh100 to 400 p.p.m.-and precludes utilization of this benzene in many chemical reactions, particularly where sulfur sensitive catalysts are employed. As a result, coke oven benzene has been forced into a secondary position with respect to petroleum derived benzene, which contains less than 1 p.p.m. thiophene. A solution to the dilemma faced hy the coke oven light oil processor is provided by a single-step catalytic technique. This process purifies coke oven secondary light oils to high purity benzene, toluene, and xylene, and is also capable of dealkylating the toluene and xylene to benzene at high selectivitieswhenever desired. The process consists of passing secondary light oil, which typically boils in the range of 66-150" C., over appropriate catalysts together with hydrogen at elevated temperature (1050-1150° F.) and pressure (500900 p.s.i.g.). The nonaromatic materials-mainly paraffins, olefins, diolefins, naphthenes, and sulfur compounds-are completely converted to lighter hydrocarbons and to hydrogen sulfide. Substituted aromatics are partially hydrodeakylated to produce additional benzene. The reactor effluent is stabilized to remove light hydrocarbons and dissolved hydrogen, claytreated, and fractionated into pure benzene, toluene,
HYDF
UPGRADING GOKE OVEN AROMATICS A.
K. LOGWINUK L.
FRIEDMAN
A.
H. W E l S S
and xylene. When desled, toluene and/or xylene can be completely hydrcdealkylated to benzene by recycling over the catalysts. In addition, the basic catalytic process can be used to produce naphthalene from coal tar middle oil feed stocks. Goals of the Process
The need of the light oil refiner is to dispose of byproduct, secondary light oil at a maximum profit. Fuel value for light oil is an unprofitable situation. Conventional acid washing is not adequate when the BTX cannot be sold at market prices that will justify the acid washing expenses and yield losses. There has been a need for a process that would produce products of desired quality at combination of yield and cost that will permit recovery of investment. The process requirements that correspond to this are : -PURIFICATION. Benzene, toluene, and xylene must be produced at a purity equivalent to or better than that of the petroleum derived products. Benzene must meet the following specifications: Freeze point: Thiophene : Acid wash color: -OPTIONAL
>5.40 c.
