## 2 Materials and Methods
### Identification of Levers for Reducing GHG Emissions
#### 2.4.3 GHG Emission Reduction Applied Specifically to Kerosene Production at  
Refinery Level  
Jet fuel production is a hydrogen-demanding process. Today, jet fuel is mainly generated in Merox or kerosene hydroreating (KHT) units plus a smaller fraction (perhaps 20%) from hydroracking units (HCK). The hydrogen consumption of both KHT and HCK units depends on feed quality, unit design and operation. Alternatively, to typical refinery hydrogen supply (mainly obtained from catalytic reforming unit (CRU) or made by steam methane reforming (SMR) of natural gas), the use of low-carbon hydrogen can deliver significant benefits.  
Decarbonising options of KHT hydrogen include a dedicated KHT-scale SMR with CCS, by replacing the natural gas feed to the main SMR unit with biogas, or by a dedicated electrolyser to produce \"green\" hydrogen using low-carbon electricity. It might also be possible to replace the gas used to provide process energy by low-carbon energy, for example biogas from anaerobic digestion, or in the longer-term, electrical heating using low-carbon energy.  
The achievable GHG savings depend on the relative GHG intensities of green hydrogen versus fossil hydrogen. This assessment assumes that the hydrogen supplied to the KHT can be treated as SMR hydrogen, and thus is taken to have a baseline WTT GHG intensity of 104 gCO2 eq/MJ H2. Hydrogen produced by SMR with CCS has a WTT GHG intensity of 39.7 gCO2 eq/MJ H2 whilst electrolyser hydrogen with renewable electricity is assumed to have a GHG intensity of 9 gCO2 eq/MJ H2. Clearly these savings have to be properly allocated to the whole final fuels pool, in proportion to the hydrogen consumed for its production.  
As sulphur reduction becomes more and more important for aviation, alterative processes could be considered to lower the impact of this stage. Merox processing (to change the type of sulphur compounds) is a low-intensity liquid-phase process that does not consume hydrogen, but requires process energy for liquid mixing, stripping, etc. There is growing interest in lower sulphur jet fuel, which could constrain the potential for adopting Merox more widely. Therefore, it is highly unlikely KHT users would opt to switch to Merox as a GHG reduction measure; thus, Merox is not examined in any further detail.  
A potential alternative approach for removing sulphur is adsorption where a solid is used to separate sulphur compounds from liquid hydrocarbon. The solid adsorbent is then regenerated for reuse, leaving a high-sulphur stream for further treatment. An example of this is the Phillips S-Zorb process where a handful of commercial plants have been constructed for gasoline desulphurisation. In principle, the technology can also be applied to distillates such as jet, but--to date--no commercial plants have been built. A critical issue is adsorbent regeneration, in which S-Zorb is performed using hydrogen. S-Zorb requires one-third to half the amount of hydrogen that is necessary for kerosene hydrotreaters. However, the data also suggest that S-Zorb's energy consumption is approximately double that of the kerosene hydrotreater. On that basis, the GHG implications look broadly comparable with KHT.