Acid catalyst regeneration control

Details Acid catalyst regeneration control Acid catalyst regeneration control

1998-12-07

2001-05-08

Soderquist, Arlen (Department: 1743)

Chemistry: analytical and immunological testing

Condition responsive control

C250S338100, C422S062000, C436S037000, C436S039000, C436S040000, C436S060000, C436S061000, C436S100000, C436S101000

Reexamination Certificate

active

06228650

ABSTRACT:

BACKGROUND OF THE INVENTION
Hydrogen fluoride (HF) alkylation is an important refinery process in which isobutane is reacted with olefins to produce highly-branched isoparaffins as illustrated in
FIG. 1
for use in gasoline blending. In this process, hydrofluoric (HF) acid functions as the catalyst and recirculates through the reactor. The recirculating HF acid catalyst is not pure; it contains a small amount of water and a reaction byproduct called acid-soluble oil. The catalyst is also saturated with the hydrocarbons involved in the process (e.g., alkylate and isobutane). In the HF alkylation process, it is important to monitor and control the purity of the catalyst since excessive amounts of water and acid-soluble-oil (ASO) have deleterious consequences: Excessive water, for example, can cause rapid corrosion of the carbon steel reactor.
Controlling the composition of the catalyst requires knowing the concentrations of HF acid, water, and ASO in the recirculating catalyst. Therefore, operators must take samples of the catalyst periodically and have these components measured by classical analytical techniques. There are several problems associated with this approach: First of all, HF acid will cause serious burns if it contacts skin. Because of this hazard, collecting and analyzing these samples carries potential for injury. Another problem is that the analytical methods used for these measurements lack precision, especially the method for ASO. This often makes it difficult to determine if the composition of the catalyst has changed from sample to sample. Finally, samples are drawn from the reactor only once or twice a day, and the analyses require several hours. This makes it difficult to follow the composition of the catalyst when processing changes do occur.
In the past few years, there has been a great deal of interest in on-line monitoring of various refinery process streams. In part, this interest has been spurred by advances in analytical technology that have greatly expanded the capabilities for process monitoring.
Accordingly an object of this invention is to continuously analyze process streams containing HF acid catalyst.
A more specific object is to use improved control schemes in acid catalyst processes, which result in tighter process controls, higher productivity and improved product quality.
Yet another object of this invention is to reduce exposure of refining personnel to hazardous process chemicals.
SUMMARY OF THE INVENTION
According to this invention, the foregoing and other objects and advantages are achieved in a method and apparatus for controlling an HF acid regenerator column, which employs an isobutane stripping charge in effecting separation of HF acid, ASO and H
2
O. The HF acid regenerator, which is one column in an HF alkylation process which also includes a reactor, a settler vessel, a source of fresh HF acid, and a suitable hydrocarbon stream, employs an NIR triple or quadruple component analyzer/controller configured to control acid catalyst strength. In a first embodiment of a regeneration control system the ASO/H
2
O output of the NIR triple-component analyzer maintains a desired ASO/H
2
O concentration in the catalyst recirculating through the reactor by manipulating the temperature of the stripping isobutane charge to the regeneration column. This scheme allows more ASO/H
2
O to be withdrawn in the regenerator bottoms stream as the stripping fluid temperature is reduced. In another embodiment of the control scheme, HF/ASO output values from the NIR analyzer/controller manipulate temperature of the regenerator feed heater to increase HF/ASO content in the regenerator bottoms stream as the spent acid catalyst feed temperature is lowered. In a third embodiment of the regenerator control scheme, which would be employed when sulfolane additive is present in the process acid catalyst, the H
2
O output from the NIR analyzer/controller manipulates flow rate of a side draw stream such that an increased draw rate reduces H
2
O levels in the process catalyst.
Other objects and advantages of this invention will be apparent from the foregoing brief description of the invention and the appended claims as well as the detailed description and the drawings which are briefly described as follows:


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patent: 5527980 (1996-06-01), Carlson
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patent: 5681749 (1997-10-01), Ramamoorthy
patent: 8-301793 (1996-11-01), None

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