Catalysis 2023 Issue

Co-processing renewables in a hydrocracker Understanding and controlling the impact on catalyst performance, yields, and product properties is key to renewables co-processing in hydrocracking units

Peter Andreas Nymann and Pronit Lahiri Topsoe

T he demand for having part of the product slate from refineries consisting of renewable materials is increasing. Hydrotreating units have been the pri - mary choice so far, but hydrocracking units are also quite suitable and will be unavoidable in the future, especially when processing more demanding second- and third-gen - eration feedstocks. Extensive pilot plant testing and a fundamental under- standing of chemistry supported by industrial operation from several units worldwide have put Topsoe in a position to support refineries in this challenging effort. Topsoe has been collaborating with refineries navigating through the energy transition to reduce CO 2 emissions originating from the use of fossil-based feedstocks. Renewable feedstock challenges The world energy sector is going through an energy transi - tion and looking for solutions to decarbonise energy produc - tion. Part of this is facilitated by replacing fossil feedstocks with renewable resources and treating these in the existing refinery framework to produce fuels that are fully compat - ible with the hydrocarbon fuels in the market today. Processing of renewable feedstocks, like first-generation feedstocks such as palm oil and other triglyceride-based hydrocarbons, has therefore been widely applied in recent years. Several projects constructing new standalone units or revamping existing hydroprocessing units to either co-process or solely process renewable feedstocks have materialised. Co-processing renewable feedstocks in hydrotreating units is now well established, and refineries are looking for more ways to include renewable feedstocks in their exist - ing units. Furthermore, the increased demand for includ- ing renewable feedstocks in the energy system and the availability of renewable feedstocks directs the industry to incorporate second- and third-generation renewable feedstocks. This introduces new and more demanding requirements to convert these challenging feedstocks into on-spec fuels. One way is to co-process renewables in hydrocracking units. The hydrocracker has advantages and disadvan - tages when it comes to co-processing renewables. If the economic uplift from processing renewable feedstocks is lower than that of normal hydrocracker feedstock, or the

renewable feedstock should cause severe performance deficits in the hydrocracker, co-processing in the hydro - cracker might not be feasible. Understanding the impact on the performance of the hydrocracking unit when introducing new feedstock types, such as first-, second- and third-generation renew - able feedstocks, is therefore of utmost importance for this evaluation. Feedstocks and chemistry In recent years, the most applied renewable feedstocks in refinery units have been triglycerides. These typically originate from what is referred to as virgin oils, more com - monly known as first-generation feedstocks. More recently, second-generation feedstocks like used cooking oil (UCO), palm oil mill effluent (POME), and others have been con - sidered. Second-generation renewable feedstocks are typi - cally byproducts from the production of virgin oils. Going forward, third-generation feedstocks like pyrolysis oils derived from municipal sewage waste, byproducts from the paper and pulp industry, wood, plastic, or tyres are being investigated. The triglycerides are characterised by consisting of three glycerol chains with a typically even carbon number and a backbone of propane connected by oxygen atoms (see Figure 1 ). Hydrotreating reactions include saturation of double bonds inside chains, breaking of triglyceride into pro - pane from the backbone and paraffins from the side chains, and the reaction of oxygen atoms with hydrogen, forming water, CO or CO2. They occur readily over hydrotreating catalysts and are well known in several hydroprocessing units worldwide. Many second- and third-generation feeds are more com - plex than the first-generation feeds and hold more complex molecules. Consequently, they result in a different boiling range of the products as well as different properties. Unlike the triglycerides that generate straight chained molecules boiling in the distillate boiling range, the second- and third- generation feedstocks contain ring structures with different heteroatoms that need more hydrogenation and eventually cracking to bring them into the transportation fuel boiling range and to ensure that these products fulfil other product specifications, such as cold flow properties and densities. Hydrotreating of triglycerides requires significant

Catalysis 2023