Cracking The Code
December 1, 2012
Kevin M. Beirne, Sabin Metal Corp., USA, comments on how advanced catalysts enhance hydrocracking processes, showing that profits can be advanced by platinum group metals recovery and refining.
It is now more than seven decades since the practical introduction of large scale catalytic cracking for processing of crude oil. The technology has advanced significantly since then (it was first developed in Germany circa 1915 to provide coal based liquid fuels), according to a recent article by Russell Heinen, a director at INS Chemical. Catalytic cracking of crude oil led to ‘an important process breakthrough’ (the Houdry process, Figure 1) that ‘coupled the endothermic cracking reaction with the exothermic reaction of catalyst regeneration in a cyclic, continuous operation’, Heinen added. ‘Significant developments since the 1940s, however, have made catalytic processes even more important to the modern petroleum refining and petrochemical/chemical processing industries’, he continued. In his article. Heinen cited the global value of process catalysts as a US$ 13 billion business, with resultant products produced with the aid of catalysts valued at USS 500 – 600 billion.
However, it was not until the early 19605 that ‘modern’ hydrocracking became even more cost effective for many practical processing applications. This was because of the introduction of zeolite based catalysts, which offered significantly better performance than previous catalysts, including lower pressure operation that helps lower costs of building and operating hydrocrackers, according to Heinen. As would be expected, concurrent with production economies and advancements in catalytic cracking over this period, feedstock refiners have continually sought improved catalysts to help speed up processing. lower costs, reduce pollution and produce higher quality end products from lower quality feedstock. In addition, as catalyst technologies have become more sophisticated, more beneficial uses for catalysts have also kept up with improvements; namely uses for catalysts in many new hydrocarbon processing applications as well as for chemical and petrochemical products.
However, as the Heinen article points out, ‘petroleum refining…is the source for the largest share of industrial products. Upgrading crude oil technology consists almost entirely of catalytic processes…[with the] largest catalyst segment in terms of value being catalytic cracking.’ New catalyst materials being developed are not only geared towards enhanced processing throughput and use of lower quality feedstocks, but environmental pressures have also ‘become the major driving forces in catalysis and process design,’ Heinen adds.
As new catalyst developments improve the technology, in part driven by environmental regulation pressures, large scale hydrocracking has been able to help increase production throughput significantly. Efficiency of scale now makes it possible for a hydrocracking plant to easily produce 100 000 bpd of cleaner distillates from ‘increasingly difficult feedstocks such as FCC light cycle oil (LCO), heavy vacuum gas oils (HVGO), and heavy coke gas oils (HCGO)’ 2.Since there is a direct correlation between economy, lower quality (more difficult) feedstocks. and process steps to produce a variety of end products, improved catalysts have also been a key factor in enhancing profitability. Essentially, today’s sophisticated catalysts have made great strides by allowing lower grade feedstocks to be used for producing higher grade distillates, as well as minimising pollution problems through production of cleaner fuels. In fact, modern catalysts are critical for this process.
One article2 pointed out that: ‘Typical hydrocracking feedstocks include heavy atmospheric and vacuum gasoils, and catalytically or thermally cracked gasoils. These products are converted to lower molecular weight products, mainly naphtha or distillates. Sulfur, nitrogen, and oxygen removal and olefin saturation occurs simultaneously with the hydrocracking reaction; because of the high reaction temperatures and pressures (in the region of 475° C and 215 bar) more “highly developed catalysts” have been introduced into the hydrocracking process over the past few decades.’ The trend indicates that this will continue for some time.
Essentially, the hydrocracking process removes various feed contaminants (which typically include sulfur and nitrogen. along with other unwanted materials) in order to convert low quality feedstocks into more commercially useful end products. The hydrogenation occurs in fixed hydrotreating catalyst beds to improve hydrocracking ratios and to remove unwanted contaminants. From there, the process continues into reactors containing fixed hydrocracking catalyst beds that dealkylate aromatic rings, open napthene rings and hydrocrack paraffin chains.
The article went on to point out that: ‘Increased environmental regulations on gasoline and diesel have made hydrocracking an essential process, resulting in ever greater increases in worldwide capacity.’ Its authors also stressed the importance of ‘optimum catalyst design’ (to extend catalyst life cycles by improving reactor operation). This coincides with many catalyst suppliers’ efforts to continually improve their products and offer users ‘longer cycles, higher through put, and faster turnarounds, all with minimal capital investment’. Because hydrocracking allows refiners to process lower grade feedstocks, there has been widespread attention in the catalyst market for development of advanced catalysts to ultimately improve profit margins. In fact, because of these advances. there have been nearly 100 new hydrocracking systems put online around the world in the past 10 years. Many of these ‘new refineries and refinery expansions are targeting operating capacities of 400 000 bpd or higher’, the article concluded.
Despite the global recession, there is still significant demand for gasoline and diesel fuels. especially in developing nations. Some estimates put the growth rate in China and India alone at approximately 40% over the next two decades. On the other hand, the demand for less refined products such as fuel oil is declining. This is one reason why many refiners are employing more sophisticated hydrocracking processes with more sophisticated catalyst materials. This trend is likely to continue.
Modern hydrocracking technology employs complex catalysts composed of one or more platinum group metals (PGMs), including platinum, palladium, ruthenium and rhodium, and occasionally rhenium, gold, silver or other precious metals, depending upon application. Catalyst compositions typically include soluble or insoluble alumina. silica/alumina or zeolites in configurations that include monolithic structures. beads, pellets, powders or extrudates, depending upon application (Figure 2). As a result of a continuous hydrocracking process (generally over a number of years), these catalysts lose their efficacy (mainly because of process contaminants) and must be replaced by ‘fresh’ catalysts. When that occurs, their precious metals content must be recycled (recovered, refined and returned to their owners, either in the form of new metals or dollars) so as to acquire fresh catalysts to start the process over.
While the value of PGMs and other precious metals varies constantly on world markets, the amount of PGMs in a typical spent catalyst lot (250 metric t is no longer uncommon) could easily reach a few million dollars. Obviously this justifies careful consideration with regard to who will recover and refine those precious metals. and how they intend to do this. While there are many different policies and procedures employed by precious metals refiners, there are also many pitfalls and potholes along the route towards maximum metals recovery and thus maximum return values to catalyst owners.
Today, considerable research and development is going on to improve hydrocracking catalysts to fill many existing and new applications. including creating new catalyst materials with less PGM content that could cost less and work longer in hydrocracking processes. Heinen mentions that: ‘In the last two decades. catalyst developments have been transitioning from an art into a science based on advances in physical and chemical instrumentation plus computer based modelling tools…There’s no doubt that looking ahead many of these goals will be achieved.’ However, until these breakthroughs occur, global feedstock refiners employing hydrocracking processes are still faced with using PGM bearing and other precious metal bearing catalysts at significant cost for their production processes.
Many refineries operate a precious metals (or asset) recovery department in one form or another. This function is usually treated as an independent profit centre. As such, its mandate is to reduce waste and enhance revenue. To that end, finding and working with the right precious metals refiner for spent PGM bearing hydrocracking catalysts can make a major difference in precious metals returns. Perhaps almost as important, however, is the protection the PGM refiner can provide with regard to the legal implications involved if it violates an environmental regulation during the recovery process.
Prices for PGMs have been volatile over the past few decades, sometimes with capricious and unpredictable trends. For example, a few years ago platinum (perhaps the most common precious metal used for hydrocracking catalysts) was valued at USS 1545/tr.oz. Palladium. also a commonly used catalyst component, was valued at USS 518/tr.oz. Today, their values (at the time of writing) are: platinum at USS 1635/tr.oz. and palladium at USS 680/tr.oz. While precious metals costs represent only a small portion of the total processing dollar when compared to plant and equipment, personnel, etc., they can still be significant when costs, leasing charges, delays in recovery and refining processing time are factored in. Furthermore, the legal implications that may cost an organization tens or even hundreds of thousands of dollars if its precious metals refiner commits an environmental infraction must also be considered.
With all of these dynamics, it is clearly worthwhile to work with a precious metal refining organisation that:
- Provides highest possible returns for PGMs from spent catalysts.
- Provides rapid processing turnaround time.
- Complies with applicable environmental standards concerning process effluent disposal or atmospheric discharges at its refining facilities.
Choosing the wrong refiner can end up being an expensive and troublesome mistake, and there are many criteria to consider when selecting a precious metals refiner. The fundamentals come down to specific areas which can be controlled and which apply to virtually all precious metal bearing materials. These include the policies and procedures associated with the refiner’s sampling, assaying, environmental policies and processing turnaround time, including global logistics. This function, in particular, can be quite problematic, especially when hazardous materials are shipped internationally.
Three different sampling techniques are used to accurately determine the amount of precious metals present in materials for recovery: dry sampling, melt sampling and solution sampling. Each of these techniques offers distinct advantages: determining the most appropriate sampling method depends upon the type of material being processed as well as its estimated precious metals content.
The principle of sampling involves ‘reducing’ large quantities of precious metal bearing material (sometimes many tons) into small quantities (down to a few grams). Samples are then extracted for analysis from different fractions and/or different stages of the resultant sub lot. The sampling procedure begins by converting precious metal bearing spent catalysts into a homogenous mass so that molecules of precious metals and other constituents are evenly distributed. Results of sampling the homogenous mass thus represent an accurate ratio of the precious metals content in the overall matrix.
Dry sampling is used whenever materials cannot be dissolved in solution or are inappropriate to melt either because of their structure, or because of the cost associated with melting versus the possible return. Because it is difficult to achieve homogeneity, dry sampling is more complex and potentially less precise than melt or solution sampling; in fact, this method requires more judgmental skills than the others. Materials for dry sampling are homogenized, generally by grinding large pieces into smaller and ever finer particles. The material is allowed to freefall in a stream into a crosscut, timed automatic sampler. Representative samples are also taken periodically and sampling accuracy is typically ±2% relative. Because precious metal bearing catalysts are used in many sizes, configurations and applications, determining the best sampling technique is crucial to recovering the most value from the spent catalyst. The composition of hydrocracking catalysts means that they are usually sampled with this technique.
Accurate and repeatable assaying procedures, on the other hand, require sophisticated instrumentation for measuring precious metals content of materials being reclaimed. A well equipped analytical laboratory utilises advanced x-ray fluorescence equipment, atomic absorption (AA) and inductively coupled plasma (ICP) emission spectroscopy, and also incorporates classic volumetric, gravimetric and fire assay techniques. These combined methods help provide the most thorough and precise approach for determining precious metals content in spent catalyst materials, thus assuring highest possible returns. Generally, specific assaying techniques are determined by the types of materials being processed.
The speed at which catalysts are processed and their precious metal recovered (reclamation turnaround time) must also be considered. Faster processing turnaround reduces interest charges accrued for leasing replacement precious metals to continue timely production. It also minimizes the need for purchasing precious metals on a volatile spot market for use in the timely manufacture of catalysts. allowing uninterrupted processing or production. In addition, a refiner’s ‘in house’ capabilities for pre-burning spent catalysts avoid the necessity for trans shipment of large lots of spent catalysts, which can introduce an entirely new set of problems.
While there are a number of nuances and fine details associated with the fundamentals, refiner selection criteria must essentially cover (in as much detail as possible) the refiner’s sampling, assaying and processing procedures. For example, at the end of their life cycle, hydrocracking catalysts are typically contaminated by sulfur, carbon, moisture and other unwanted elements depending upon how they were employed. These spent catalysts exhibit high loss on ignition (L0I) characteristics (caused by high moisture content), in addition to other contaminants. Removal of these contaminants is critical to the downstream sampling process. The reason for this is that the materials must be free flowing (with low L0I) initially to arrive at a final evaluation sample. It is here that pre-burning can make a key difference; if the high moisture content and other contaminants are not removed, a suitably accurate sample cannot be obtained by the refiner, thus eliminating the possibility of providing a fair and true return value to the customer.
This first step, ‘pre-burning’, is critical to the sampling process. As important (at least from a financial perspective) is where and how the contaminants are removed. Here. many catalyst users must first ship large lots of spent catalysts (perhaps as much as 250 metric t) to an independent facility where strip burning removes their hydrocarbon content, such as benzene, and coke burning removes carbon. In addition. another furnace may be required for drying of fine particulates and other materials to eliminate moisture content, leading to lots of added time and logistics charges.
Pre-burning spent catalysts is accomplished with an indirectly fired rotary kiln (Figure 3). This significantly enhances sampling accuracy and thus helps assure the maximum value of remaining precious metals; furthermore, it can also significantly reduce overall refining costs when it is handled directly at the refiner’s facility. This is a key issue with regard to the total cost of recovery and refining and, by inference, the overall profitability of the precious metals bearing catalyst management/asset recovery program. The typical rotary kiln will remove up to 25% of the materials’ sulfur content and up to 40% carbon content. usually at a rate of 300 – 1000 lbs./hr.
Added turnaround time and additional costs are the two main considerations associated with off site strip and coke burning of spent catalyst materials. Unless these capabilities are available at the refiner’s facility, catalyst users must pay substantial transportation charges for shipping to an independent, off site facility. While there, it would not be uncommon for the material to remain up to a month for processing before it would again have to be shipped to the refiner to start the actual sampling, analyzing, recovery and refining process. The PGMs are unavailable to the catalyst user during this time, and therefore new metal must be acquired at current market prices and interest rates. adding unnecessary expenses.
There is another, equally important advantage of having the PGM refiner handle the ‘pre-burning’ or contamination removal procedures in house: the control (or ‘accountability’) the refiner has over the catalyst lot, eliminating all possibility that materials could be mixed in with unrelated materials from another organization. When that happens, there is obviously no way an accurate determination of its actual value could be calculated.
Choosing the wrong refiner with regard to possible unlawful effluent or atmospheric discharges could become a real nightmare. with regard to legal implications associated with processing procedures. When selecting a refiner, it is also important to be aware of how the materials of the refiner’s other customers are processed. It is necessary to determine how any solid. liquid or gaseous byproduct is handled at the processing facility. Ideally there should be no hazardous waste materials shipped from a precious metals processing facility. When this is not possible, however, the refiner must ship them under approved procedures. Some (but not all) refiners do ship them under approved procedures and conditions.
In addition, minimal pollutants should be emitted before, during or after refining. Exhaust air quality should be managed with state of the art pollution control systems. The process water evaporation procedure should minimize all causes of pollution. While each of these functions is fundamental, there are many hidden pitfalls surrounding them with regard to environmental compliance. Requesting detailed documentation on environmental law compliance may also be of help.
One way to determine if a refiner meets applicable environmental regulations, regardless of jurisdiction, is to check its use of appropriate pollution abatement technology such as afterburners, bag houses, wet scrubbers and liquid effluent neutralizing equipment. Also, the refiner’s approval status with all applicable agencies at local, state and federal levels should be evaluated. Most precious metals refiners will be pleased to provide copies of all required documentation, which could include permits under the Clean Air and Water Acts and prove that the company qualifies as a bona fide precious metals refiner as specified in Subpart F of the Resource Conservation Recovery Act (RCRA) regulations and the preamble to the Boiler and Industrial Furnace (BIF) Rule and its amendments. There also exists another, more recent series of laws under the overall umbrella of the USA PATRIOT Act that could have significant negative impact on precious metals users and refiners. The scope of this law is so broad that it would make good sense to review it thoroughly before engaging any precious metals refiners for spent hydrocracking catalyst materials.
Finally, the refiner should assist with all areas of insured point to point logistics / transportation, including segregated and hazardous materials, and hazardous waste, virtually anywhere in the world. That means full compliance with all customs, transportation, safety and environmental regulations.
These aforementioned considerations are all essential when evaluating and working with a precious metals refiner for PGM bearing hydrocracking catalyst materials. All areas are important. but the issue of a refiner’s compliance with regard to environmental regulations might possibly be the most critical in the final analysis. All else being equal (getting maximum and timely returns of precious metal values), a refiner’s environmental violations could create problems. These steps, and the refiner’s overall policies with regard to applicable pollution codes and standards compliance, should provide the wherewithal to select (and confidently work with) the right precious metals refiner for any application. In any case. the relationship with that refiner must be viewed as a ‘partnership’ and should be based upon mutual trust and fair treatment.
1. HEINEN, R., IHS Chemical. ‘Catalyst developments: the last 90 years’. Hydrocarbon Processing, July 2012.
2. TORCHIA, D; ARORA, A; VO, L. ‘Clean, green, hydrocracking machine’. Hydrocarbon Engineering, June 2012.