NEW PROCESSES AND CATALYSTS SOLVE PROBLEMS OF FEED CONTAMINANTS

The petroleum refining catalyst industry is facing a rough road ahead. New catalysts will be needed to meet the U.S. 1990 Clean Air Act Amendments, not to mention other emissions regulations.

And as if this weren't enough, the world's supply of light, sweet crude is rapidly declining. Refiners are increasingly faced with processing heavier crudes with higher sulfur and metals contents.

Both of these factors will likely lead, if they have not already, to increased research and development budgets for catalyst manufacturers. Catalyst suppliers' and process licensors' efforts to meet these increasing demands are already well under way.

C5 HYDROGENATION

Institut Francais du Petrole (IFP) has developed a new feed preparation process for tertiary amyl methyl ether (TAME) and alkylation units, according the company's newsletter, IFP Technology Update. The process can be used with either HF or H2SO4 alkylation units.

Converting the C5s to TAME and alkylate--which are high-octane, low-Rvp blending stocks--increases octane barrel yields.

Unfortunately, C5 streams contain diolefins, which negatively affect TAME and alkylation unit performance.

Diolefins need to be removed from the system because they can consume or contaminate catalysts and, in the case of alkylation plants, increase acid consumption.

IFP has consequently developed a selective hydrogenation process, called HY-5. The process will not only convert diolefins to olefins with minimum hydrogen usage, says the company, but it will also isomerize some of the olefins to higher-value olefins and increase the production of TAME precursors (Fig. 1).

Table 1 shows how the HY-5 process can upgrade a fluid catalytic cracking unit C5 cut. Note the almost total disappearance of the diolefins, and the isomerization of 2-methyl-1-butene and 1-pentene to higher-value components (2-methyl-2-butene and 2-pentene).

HY-5 CATALYST

The process is based on IFP's proven catalyst, LD-2773, which has been adapted specifically for hydrogenating FCC cuts. Features include:

High activity (can operate in conditions similar to catalysts for C4 hydroisomerization).
High resistance to sulfur compounds (tolerates several hundred ppm sulfur).
High selectivity (olefin yield is above 100%).
High isomerization activity.
Long service life and cycle length.
Minimum hydrogen consumption.

BENEFITS

Installed upstream of a TAME plant, IFP says the process allows greater flexibility in feedstock quality. Catalyst cycles and life are extended because polymer laydown is minimal.

TAME yield increases because the nonreactive 3-methyl-1-butene is isomerized to 2-methyl-2-butene, one of the basic feedstocks for TAME.

The greatest benefit, according to IFP, is the monetary savings from spent acid regeneration costs and the corresponding investment for unneeded capacity. With the process upstream of alkylation, acid consumption can be reduced by 60% (Table 2).

The process can also treat a mixture of C4s and C5s as feed to an alkylation plant with practically no C4 olefin losses. In addition, alkylate color is improved, the end point is lower, and there are less gum-formers.

The next licensee will start up in fourth quarter 1992.

RESIDUE HYDROTREATING

Chevron Research & Technology Co., Richmond, Calif., has developed a technology that significantly increases the flexibility of residue hydrotreaters, or resid desulfurization (RDS) units, to process heavier, higher-metal feedstocks.

The technology was presented at the National Petroleum Refiners Association annual meeting, Mar. 22-24 in New Orleans. Authors of the paper were Bruce E. Reynolds and R.W. Bachtel of Chevron Research & Technology, and K. Yagi of Idemitsu Kosan Co. Ltd.

The process, called Onstream Catalyst Replacement (OCR), efficiently removes feed metals onto an OCR catalyst while the unit remains on stream. The technology can be incorporated into new RDS units or retrofitted to existing units.

The first commercial use of the technology is an OCR retrofit of a 50,000 b/d Chevron-licensed RDS unit that started up earlier this year at the Aichi refinery of Idemitsu Kosan.

An obvious application for the process is the removal of Ni + V from RDS feedstocks, which greatly reduces the primary cause of RDS catalyst deactivation.

The advantage of OCR, according to Chevron, is in its more efficient use of catalyst and the ability to remove spent catalyst while operating.

This makes it attractive to couple an OCR reactor to downstream RDS reactors.

The required OCR reactor volume is significantly less than the RDS hydro-demetallization (HDM) reactor, even with a feed Ni + V of only 80 ppm (Fig. 2). This advantage increases greatly as feed Ni+V content increases.

Alternatively, an OCR/RDS system with the same reactor volume as an all-RDS system can process feeds with significantly higher Ni+V content to the same RDS-section run length. This provides a way to retrofit RDS units for higher Ni + V content or longer run lengths.

This retrofit can be done by either converting an existing RDS reactor into an OCR reactor or by adding a new OCR reactor. The choice is dictated by the size of the existing reactors and the desired operating severity of the revamped unit.

Table 3 shows the results of a conceptual study of the economic benefits of retrofitting an RDS unit with an OCR reactor.

PROCESS DESCRIPTION

An OCR reactor differs from an RDS reactor in that it operates with the feed upflow and contains the necessary internals to allow addition and withdrawal of OCR catalyst. Fresh catalyst is added at the top of the reactor and spent catalyst is withdrawn from the bottom (Fig. 3).

The catalyst gradually moves from the top to the bottom of the reactor in a plug flow fashion. This counterflow of catalyst and feed oil ensures that only the most-spent catalyst is removed from the reactor.

This is highly efficient because the spent catalyst typically contains greater than twice the Ni+V content of the reactor average. The OCR reactor therefore retains good catalytic activity.

The OCR reactor serves as a guard to minimize the Ni+V that contacts the downstream RDS catalyst. Spent catalyst is withdrawn, and fresh added, at least once per week to maintain constant Ni+V removal. This avoids rapid aging of the RDS catalyst, which occurs in conventional fixed-bed systems when the HDM-type catalyst loses activity.

The periodic removal of spent OCR catalyst also ensures that interstitial deposition of metals and coke is minimized. The upflow of oil in the reactor imparts a slight motion to the catalyst. This discourages agglomeration from any deposition that does occur. High-metal feedstocks (250 ppm Ni+V) can therefore be processed without reactor plugging or catalyst removal difficulties.

A key aspect of this technology is the catalyst. The first generation of OCR catalyst has been tailored for high HDM activity and metals capacity. It is a highly attrition-resistant, spherical material that moves readily inside the reactor. It is easy to transfer and does not have problems with breakage.

CATALYST MOVEMENT

The amount of catalyst that must be transferred each week is only 2-8% of the reactor volume, depending on the Ni+V content of the feed. The catalyst transfer system is not in continuous use, which allows ample time for maintenance between transfers.

The system can be adjusted for more frequent catalyst transfers, such as when processing a highly contaminated feed.

Catalyst is transferred as a low-velocity oil slurry. The slurry is created by "lifting" and entraining the catalyst in an oil stream. It flows by means of a small pressure differential. The low velocity prevents catalyst attrition and erosion of lines and valves.

The simplified procedure for catalyst transfer is as follows:

Isolate OCR reactor from high-pressure and low-pressure vessels.
Add oil and catalyst to low-pres-sure vessel.
Equalize low-pressure and high-pressure vessel pressure.
Transfer oil/catalyst slurry to high-pressure vessel.
Isolate low-pressure vessel.
Equalize high-pressure vessel and OCR reactor pressure.
Open valves, transfer slurry to OCR reactor.
Complete transfer, flush valves, isolate and depressurize high-pressure vessel.

Catalyst withdrawal is done in a similar manner.

All of the catalyst transfer procedures, which follow Chevron standards for safety and reliability, are designed into a computer-driven semiautomatic sequencer.

COMMERCIAL APPLICATION

The first commercial application of the technology started up at Idemitsu Kosan's Aichi refinery in May of this year. The Gulf-designed, two-train hydrotreater was retrofitted with two new OCR reactors.

The retrofit will allow the refinery to process heavier, lower-cost feedstocks while extending run length from 1 to 2 years. The product from the OCR/RDS unit is sent to an existing residue fluid catalytic cracking unit.

A second OCR will be installed as part of a new RDS unit at Idemitsu Kosan's Hokkaido refinery. Start-up is scheduled for fourth quarter 1994. Additional commercial applications of the technology are under study.