Refining Report New technology appears to perform several processes in one step

A new catalyst system is the basis of a simple technology that appears to perform several conventional refinery processes in a single step.

Dubbed the Darcy process, it has shown impressive results in a small demonstration unit at a Texas Gulf Coast refinery. Inventor John Darcy says the results from the demonstration unit show that the process performs cracking, isomerization, desulfurization, and cyclization functions.

The refinery used the process to control amine and H₂S formation by treating a preflash distillate with a boiling range of 170-678° F. The distillate is produced from blends of heavy Boscan and Bachequero crude oils from Venezuela.

The stream contains 0.5-1.2 wt % sulfur, depending on the crude blend being processed, and a road octane number of about 32. The process produces a water-white naphtha stream containing less than 0.02 wt % sulfur. The product obtained using one catalyst formulation has a road octane number greater than 70, says Darcy.

A gas chromatography/mass spectroscopy analysis of the feed and products shows that the catalyst increases paraffins, isoparaffins, and naphthenes, and decreases aromatics.

Given these shifts and the changes in molecular weight distribution, the process can convert middle distillate to naphtha, as is done in the demonstration unit, or gas oil to jet fuel.

"Natural gas streams can also be treated at the well head, after the slug catcher, to sweeten the gas stream," says Darcy. "This prevents microbial-induced corrosion during pipeline transportation."

The process is owned by InterGlobal Desulfurization Systems Inc. (IDS), Corpus Christi, Tex., which purchased the rights to the process from Darcy.

The process

The catalyst is an aqueous slurry of five or six inorganic components. It costs less than 20¢/bbl of feed processed, and it is regenerable on site, says Darcy. The ratios of the components can be changed, depending on the nature of the feedstock.

The reactor in the demo unit is an 8 ft x 8 in. carbon steel pipe. The catalyst slurry is mixed with the vapor-phase feed stream at the base of the reactor. The product stream is removed from the top of the vessel, then condensed and sent to a water separator (Fig. 1 [24922 bytes]).

The catalyst attacks the sulfhydryl groups, cleaving the mercaptan molecule and removing the sulfur as an inorganic salt, according to Darcy.

"Hydrogen generated in the process is used within the process to hydrogenate olefins," he says.

This reaction not only reduces feed sulfur, but eliminates mercaptans and thiophenes, claims the inventor. Total sulfur removal at the Texas site was 99.5 wt %.

The problem

Before installation of the demo unit, the refinery had a problem with amines in its water treatment unit. The amines were being added to the preflash distillate to control naphthenic acid and H₂S. The amines were subsequently removed in the water separation step (Fig. 1 [24922 bytes]).

A 16 gal/hr demonstration unit was installed at the refinery in March 1996. It operated until February 1997. During operation of the unit, the addition of amines was unnecessary, says Darcy. This halved the chemical costs associated with water treatment at the refinery.

According to a refinery source, chemical costs for 1995 totaled $82,815. After the Darcy process was installed, chemical costs for the first two quarters of 1996 were only $19,965. Darcy says refinery officials estimated that another $20,000/year could have been saved by reclaiming fuel gas from the unit.

Fig. 1 is a flow diagram of the process, as installed at the refinery. All analytical testing for the demonstration was performed by a third-party laboratory.

Figs. 2a-2d [38450 bytes] show analyses of the feedstock and the reaction products from two separate runs using different catalyst mixtures. The concentrations of paraffins, isoparaffins, naphthenes, and aromatics are plotted as a function of number of carbon atoms.

Figs. 2a and 2d illustrate the cracking capabilities of the process. Fig. 2b shows its isomerization qualities, and Fig. 2c indicates cyclization.

Table 1 [64747 bytes] shows a distillation analysis of the feed and the two products. Table 2 [51635 bytes] shows some key components of the feed and products streams.

The data indicate changes in key components. These results support the claims that the process performs four conventional refining steps.

"It is an intriguing and scary process," said the refinery's director of technology.

The scary part is the effect a four-in-one process could have on existing refining technology.

"It does things at lower pressures and temperatures than anything I've seen before," he added.

Copyright 1997 Oil & Gas Journal. All Rights Reserved.