Precious metals catalyst: understanding the technology (ERTC)
The Catalyst Life-Cycle. The vast majority of petroleum and petrochemical processors use catalysts that contain one or more precious metals such as platinum, palladium, ruthenium, and rhodium (commonly referred to as platinum group metals, or PGMs).
Bradford M Cook
Sabin Metal Corporation
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In addition to PGMs, many of these catalysts contain another valuable precious metal, rhenium (Re), which is most typically used in combination with platinum for reforming naphthas. Whatever their precious metals composition, all PGM and rhenium-bearing catalysts must eventually be replaced with fresh catalysts (or ‘changed out’) to restore efficacy to the process or
speed up process reactions. The spent catalysts are then sent to a precious metals refiner to recover the value contained.
What happens to the catalyst over the course of its production cycle can have a dramatic effect on the precious metals refiner’s ability to recover the PGMs and especially rhenium.
Recovering Your Precious Metals
Traditionally, precious metals catalyst refiners recover PGMs and rhenium by dissolving the spent catalysts in strong caustics or acids. This hydrometallurgical recovery process is commonly referred to in the industry as ‘digesting’.
Digestion serves well to recover the precious metals from spent process catalysts in most cases. Certain events and circumstances encountered over the life of the catalyst, however, can create many problems when trying to digest:
• Overheating during operation can harden substrates (gamma alumina converting to theta or alpha alumina), rendering them insoluble to even powerful solvents.
• Excessive fines or carbon content can prevent the exposure of the catalyst surface area to the solvents.
• Metals present in the feed, or additives introduced to extend catalyst life, can create chemical imbalances and interfere with the desired chemical reaction.
Individually, each of these factors can reduce precious metals recovery, and in combination these effects can be great. In some cases, as much as 20 or 30% of the rhenium contained can remain insoluble.
Should the insoluble materials still hold precious metals, the hydrometallurgical refiners must send them out to a copper smelter to recover the platinum group metals, but the rhenium is lost.
A refiner who uses pyro-metallurgical technology (for example, Sabin’s Pyro-Re process) can recover virtually all of the Re from spent catalyst lots, maximising the return value, because you – the catalyst owner – are paid based on the total precious metals content.
Take Away Customers are wise to watch the precious metals refinery contract language very carefully: terms regarding the values being returned should be based on total precious metals contained and not on acid-soluble precious metals content.
Removal of Contaminants
All spent catalysts are contaminated to some degree with unwanted materials and elements such as sulphur, carbon, moisture, and solvents. The pre-reclaim burn process, or kilning stage, assures spent catalysts are freed from the accumulated contaminants and that materials are free flowing for highest possible sampling accuracy.
Take Away Pre-burning may be performed at the precious metals refiner’s site or elsewhere. Significant cost and time savings can be realised if your precious metals refiner is able to provide all services from one location.
Importance of Accurate Sampling Assaying
In order to determine the precise amounts of precious metals contained in any given shipment of hydrocarbon catalyst, the process must begin with a series of steps designed to create uniformity. Once the catalyst batch is free-flowing and free from contaminants, carefully controlled sampling measures can draw a sample that is truly representative of the whole.
Most hydrocarbon processing catalysts are sampled by a process known as dry sampling, which involves the use of mesh screens, vibratory feeders, rotary samplers, and other specialised equipment.
Once accurate samples are obtained, the precious metals refiner and the catalyst owner can analyse the samples for their precious metals content independently. Most precious metal assay laboratories perform assays in triplicate by more than one method to ensure accuracy. The goal is for these independent assays to return values that are in close agreement. If this is the case, their values are averaged to arrive at a ‘mean’ valuation of the PGMs in the spent catalyst.
In a small percentage of cases, the values of the two independent assays are not within agreed tolerances, and a third sample (known as the ‘umpire’) is sent to an independent laboratory to settle the dispute.
Take Away Catalyst owners should audit their precious metals refiners and their independent laboratories at least annually, and always utilise third-party representation to ensure all processing and weighing takes place precisely as intended.
This short article originally appeared in the 2017 ERTC Newspaper, produced by PTQ / DigitalRefining.
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