Specialty chemicals & processing catalysts
Recovering precious metals from
spent catalysts can help enhance profits,
says Kevin Beirne of Sabin Metal
Many speciality chemicals and pharmaceuticals are produced with the aid of precious metal-bearing catalysts that incorporate platinum group metals (PGMs), i.e. platinum, palladium, rhodium and ruthenium, possibly with other precious metals like rhenium, gold or silver, depending on the application. The fine chemicals that are used in the production of pharmaceuticals and some specialityEnvironment & Regulations chemicals are also produced with these catalysts which help to facilitate and/or speed up chemical processes.
As the global economy climbs out of its economic doldrums, albeit slowly, the cost of the raw materials for fine and speciality chemicals will rise and the chances are that processing costs will also rise for labour, energy, plant, equipment and other overhead factors. For this reason, it is worth examining the precious metal-bearing catalysts that help produce many of these chemicals.
The PGM-bearing catalysts used for these applications include heterogeneous palladium or platinum on carbon, palladium on calcium carbonate and various gold compounds. All function by facilitating hydrogenation and other reactions of intermediates, including APIs.
Although these catalysts typically represent a small portion of overall manufacturing costs, they are by no means insignificant, considering the value of the precious metals incorporated in the catalysts. For example, platinum as of this writing was valued at $1,567/troy ounce, palladium at $771 and gold at $1,604. At the end of a catalyst’s useful life, the value of its remaining precious metals could easily be worth a six figure sum.
When you consider the high costs associated with developing, producing, and successfully marketing new products, particularly pharmaceuticals, prudent managers must always look at ways to lower costs and add profits. One often neglected approach is to maximize the recovered value of the remaining precious metals in spent process catalysts which must be recovered and refined promptly, with the highest yields possible.
Accomplishing this calls for a precious metals refiner with the right blend of equipment, skills and experience. Such a refiner relies on a proven set of procedures to achieve high yields with fast turnaround times. Two of the most critical steps in the process include sampling and assaying large lots of spent catalyst materials.
Figure 1. PGM-bearing catalysts may contain
two or more PGMs, plus other metals
Regardless of the application, all spent catalysts share one common trait: after they lose their efficacy, they are contaminated with organic materials such as sulfur, carbon, moisture and other unwanted elements. To assure accurate evaluation of their remaining precious metals, spent catalysts are ‘pre-burned’ to remove contaminants and provide the free-flowing properties critical to assure highest possible sampling accuracy which ultimately means highest possible return values for the PGMs.
For example, carbon-based catalysts are pre-burned to remove organic contaminants in a box furnace or ‘car bottom’ where the catalyst is heated until its initial burn-off is complete. From there, the catalyst is transferred to a cooling area where the ‘roasting’ is completed and the remaining carbon can be reduced to as low as 2%, depending upon the chemistry of the catalyst.
Eliminating as much of the carbon content and liquid from the entire catalyst lot is a key factor towards achieving highest possible sampling accuracy. ‘Roasting’ spent catalysts removes moisture but not any of its other constituents. Because of the importance of this process, the precious metals refiner should provide catalyst users with complete in-house ‘roasting’ capabilities.
Removing contaminants from ceramic-based catalysts is generally accomplished by pre-burning in indirectly fired rotary kilns, multiple-hearth furnaces or fluidized bed furnaces. Because most spent precious metal-bearing catalysts exhibit high loss on ignition (LOI), these procedures burn off their moisture content. Accurate LOI data are necessary to account for any weight changes from the time the material is received, during the pre-burning process and in transit to the laboratory.
Pre-burning may be performed at the refiner’s site or elsewhere. If it is performed by a third party, the spent catalyst – perhaps 90 tons – must be shipped to that facility, which may use strip burning to remove hydrocarbons, coke burning to remove carbon and another furnace to dry fine particulates and remove moisture. The ‘reduced’ lot is then shipped to the refinery for recovery of the precious metals.
Figure 2. A custom-designed ‘car bottom’ furnace speeds processing turnaround times significantly for large volumes
When handled off-site, pre-burning involves additional turnaround time of up to several weeks, as well as additional costs for transportation and for leasing replacement metal during the time the PGMs are unavailable to the catalyst user. Added time and costs include those for re-packaging and sealing spent catalysts and having independent experts or the catalyst owners’ representatives witness these proceedings.
Besides lower costs, another important benefit of in-house pre-burning is the control the refiner has over the catalysts it processes. This eliminates the possibility that one catalyst user’s material will be mixed in with unrelated materials from another organization. When that happens, there is no way to determine the actual value of either company’s materials accurately.
A refiner should be equipped with high volume pre-burning capabilities for the material to be sampled, since the highest possible sampling accuracy requires that contaminants be removed from the mix first. The effects of high LOI after pre-burning in an oxygen environment can account for significant weight reduction in the processed spent catalyst materials, so accurate measurements are important before and after any pre-burning steps. Samples must be hermetically sealed following pre-burning to mitigate weight gain from moisture absorption.
Accurate LOI data is vital for minimizing measurement errors due to weight changes while a sample is in transit. In general, the highest accuracy results for LOI are determination when analysis is conducted as closely as possible to the sampling procedure. Consequently, catalyst owners should select a refiner who handles in-house LOI determinations under the supervision of independent inspectors.
Figure 3. Contaminants in the catalysts are
removed using an indirectly fired rotary kiln
Sampling Spent Catalysts
There are differences in how spent process catalysts are sampled from APIs and speciality chemicals; these procedures differ mainly because of the chemical composition of the substrates, or carriers, used for each of the catalytic processes.
For example, pharmaceutical manufacturers use various precious metal-bearing catalysts, all of which are used to facilitate the hydrogenation of various intermediates, whereas those used in most speciality chemical reactions are generally based on carbon substrates. These are all therefore sampled differently to the ceramic-based catalysts used in the petrochemicals industry.
Typically, a precious metals refiner will assign a tracking number to incoming spent catalyst materials which are tested for carbon, hydrocarbon and moisture content so as to verify that the catalyst materials pose no workplace hazard to the refiner and are free-flowing, in order to determine the most appropriate sampling approach.
Sampling, as the name suggests, reduces a large batch of spent catalyst into smaller amounts suitable for accurate analysis. The goal of any material sampling method is to maintain the relative amounts of component materials in the mix while reducing the amount of the material to a practical level in order to permit accurate determination of the remaining precious metals content in the catalyst.
Dry sampling involves the use of mesh screens, vibratory feeders, rotary samplers and other specialized equipment. A typical sampling process begins by extracting two portions equal to 1% and 10% of an initial material lot; this is an important consideration, since not all precious metals refiners sample 100% of spent PGM-bearing process catalysts. Then, 10% samples will be used for an LOI test, while the other 1% is further sub-divided to create smaller, laboratory-sized samples for the determination of the precious metal content.
Accurate sampling of chemical catalysts involves tight process control, to ensure that each sample has the representative composition of the initial material lot. Materials should be weighed at every step of the sampling process to minimize the effects of atmospheric conditions, such as the absorption of moisture, on any measurements. Because samples can gain or lose moisture with handling, laboratories handling them should reheat samples for an assay at high temperatures to remove any absorbed moisture from the materials and then hermetically seal the sampled materials.
Figure 4. The highest accuracy results for LOI are determined when analysis is conducted as
closely as possible to the sampling procedure
Importance of Assaying
Once accurate samples are available, the refiner and the catalyst owner may assay the samples for their precious metals content independently. Ideally, their independent assays will yield values in close agreement. If both assays are within prescribed tolerances, their values can be averaged to arrive at an agreed figure for valuation of the PGMs in the spent catalyst.
In cases where the values of the two independent assays are far apart, a third sample may be sent to an independent ‘umpire’ laboratory to determine a settlement amount. Standard industry practice requires that both parties agree on how an independent umpire’s assay is used to arrive at a final settlement.
Repeatable, accurate assaying procedures are needed to determine the amount of precious metals contained in those samples of chemical catalyst materials. Most precious metal refiners’ laboratories perform assays in triplicate by more than one method in order to ensure the accuracy of PGM measurements.
Assaying methods require specialized instruments, including X-ray fluorescence (XRF) systems, which can identify the desired precious metals, as well as any remaining contaminates which might degrade the accuracy of a determination. XRF spectroscopy can semi-quantitatively analyze over 80 elements within a few minutes per sample.
In addition, atomic absorption (AA) and inductively coupled plasma (ICP) emission spectroscopy systems can support accurate assaying methods along with classical volumetric and gravimetric assaying techniques. As with sampling, the type of spent catalyst materials being analyzed will dictate the type of assay procedure to be used.
After sampling is completed, the precious metals can be recovered from the spent catalyst by mixing the material with fluxes and smelting in an electric arc furnace to separate the precious metals from its substrates. They are recovered in the form of metal-bearing bullion that is further processed for final extraction and purification. The high grade (minimum 99.95% pure) precious metal can be sent to a catalyst manufacturer to fabricate new catalysts for chemical processing or the catalyst owners may request payment for their value.
Figure 5. A well-equipped analytical laboratory
uses advanced XRF, AA and ICP equipment
Responsibly recovering and refining precious metals requires a refiner to use well-controlled processes complying with the applicable environmental regulatory agencies as regards the reporting and managing of chemical and toxic emissions. European regulations are often more stringent than those in the US, though it is worth noticing that the US ‘Patriot’ Act effectively mandates that virtually all transactions involving precious metals must be fully traceable.
Throughout the entire refining and recovery process, a refiner must also adhere to all of the applicable environmental codes and standards covering effluent disposal and atmospheric emissions. A properly equipped refiner will have the technology appropriate for pollution abatement, including afterburners, baghouses, wet scrubbers and liquid effluent neutralizing equipment.
For example, any systems used for thermal oxidation be able to combust organic contaminants completely. Any off-gases resulting from thermal oxidation should be channeled to a baghouse or scrubber system. A refiner’s water treatment process should minimize all causes of pollution. Any atmospheric discharge must be managed with pollution control systems that result in few or no pollutants being emitted before, during and after the refining process.
A refiner should have approved status with all appropriate governing environmental agencies. Any refiner in good standing will generally be pleased to provide copies of the required documentation stating as much. One thing to remember is that a refiner must be responsible for all customers; even the violation of a pollution control law while processing another customer’s materials can have legal implications for all of his customers.
Spent catalysts from speciality chemicals and pharmaceuticals manufacture contain PGMs which must be recovered as efficiently as possible to return value to their owners. By partnering with a responsible precious metals refiner, it is possible for a user to enhance bottom line profits in the form of recovered PGMs and also do so in a legally and environmentally sound way.
Kevin M. Beirne
VP, Sales & Marketing
Sabin Metal Corporation
Tel: + 1 631 329-1717