cold flow improvement and a significant and costly yield loss into smaller LPG fragments. Alternatively and much more preferred, the latest generation dewaxing catalysts, which perform the skeleton isomerisation without any yield loss into useless gas products, can also be used. This is a very economically attractive route, improv - ing the cold flow properties of any diesel stream. Both catalyst methods will avoid the use of costly cold flow improving additives. Using the catalytic dewaxing route will certainly take up some reactor volume for this type of catalyst. However, using the latest generation and most active ULSD hydrotreating catalysts will overcome this potential issue, as the latest generation ULSD catalysts are often 10-20% more active than previous generation catalysts and can operate at a higher LHSV. In other words, the higher activity of the ULSD catalysts will provide room for the dewaxing catalysts without cycle shortage. Furthermore, it is important to ensure that the dedicated dewaxing catalysts have active metals to increase stability and provide a significant hydrotreat - ing activity. Using the right combination of ULSD and dewaxing catalysts will ensure a long and stable cycle and provide significant economic benefits. Topsoe has numerous references of dewaxing cat - alysts in ULSD units significantly improving diesel cold-flow properties. A Danny Verboekend, Chief Technology Officer, Zeopore Technologies NV, danny.verboekend@zeopore.com Paraffinic components in standard diesel feedstocks tend to crystallise when temperatures drop below 10ᵒC. Improving the cold flow properties implies sub - stantially lowering the so-called cloud point (CP) – the threshold temperature at which a specific fuel starts to become waxy, opaque, and more viscous. Dewaxing of diesel and lubricants may be necessary in colder oper - ating environments or during winter. Dewaxed prod - ucts ensure optimal performance, reduce emissions, and prevent malfunction or damage to diesel engines and other machinery. The cold flow properties of a feedstock can be improved by either catalytic dewaxing or using additives or blending with (valuable) other finished products. Additives and blending are often expensive routes and offer little flexibility in managing oppor - tunity crudes. From an economic standpoint, the pre - ferred approach is catalytic dewaxing. In catalytic dewaxing, the aim is to selectively con - vert the fraction with the highest cloud or melting point (linear paraffins) to products with significantly lower CPs. In selective cracking, it is targeted to specif - ically crack the large linear paraffins into molecules of smaller carbon number, whereas in isomerisation, one targets to selectively isomerise these waxy components into branched paraffins (see Figure 1 ). In both catalytic dewaxing scenarios, the technical and economic chal - lenge is to control the cracking degree, as undesired (over)cracking of molecules leads to expensive diesel yield loss and the formation of undesired streams of lights/gases.
It is definitely possible to get some return on your original purchase cost by sending the catalyst for metal recovery. Depending on the type of catalyst/metal used, these returns could be from low to high. There are cer - tain thresholds that the catalyst needs to have in order to get value back. However, even small returns on your metals are better then landfilling spent catalysts. Metals that are great for recovery are nickel, copper, zinc, cobalt, molybdenum, tungsten, and, of course, precious metals such as platinum, rhodium, palladium, and ruthenium. Most recovery processes are done using either a hydro-metallurgic process or a pyro-metallurgic pro - cess. The best method is selected depending on the percentage of metals, contaminants, and final product. The final product could be used again for new cat - alysts or used in a completely different industry (for example, car batteries). The limit of quantity of metal required on spent cat - alyst for an economic return also depends on the mar - ket rate of the metals. Catalysts without metallic value are also interesting for recycling or reuse. In general, landfilling can be reduced significantly in an economy that tends to reuse, recycle, and be circular. A Brad Cook, Vice President - Sales and Marketing, Sabin Metal, bcook@sabinmetal.com In terms of precious metals (PM) catalysts, the answer is “absolutely”. In most recycling scenarios, the net value returned to PM catalyst users exceeds 90% of the PM original loading, including the cost of all recovery services and shipping charges. In order to ensure that the full value of the PM content is returned, however, far more crucial and costly details are always in play: the honesty/integrity of the precious metals refiner; the accuracy of sampling and analysis; and the hid - den contractual and technical details (loss on ignition, splitting limits, and lot size). Learn more about these topics at www.sabinmetal.com/knowledge-center. Q How can we improve the cold flow properties in the ULSD from our gasoil hydrotreater? A Per Zeuthen, Senior Director, Haldor Topsoe, pz@ topsoe.com The cold flow properties of a given diesel are dictated by the wax components or the amount of normal paraffins in the stream. The more carbon atoms there are in the normal paraffins, the higher the melting point and the poorer cold flow properties of a given stream. To lower the cold flow properties of the produced ULSD from a given gasoil hydrotreater will thus require a modification of the wax components. Such a required modification or manipulation of the wax components is not possible by a conventional hydrotreating catalyst; we have to use a cat - alyst that is able to impact the normal paraffin molecules. This can be done catalytically by shortening the length, means of carbon atoms numbers, of the wax molecules by a conventional cracking reaction using some of the more old-fashioned catalyst types. This will provide a
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