Gas 2025 Issue

Product recovery (Example)

Acetylene selective hydrogenation using palladium-based catalysts. OleMax 250 Series Pd-based catalysts for selective Ac removal

O-gas from renery or multiple sources

Impurities such as AsH, PH, Hg are removed. Removal level depends on catalysts and adsorbents used. ActiSorb Series Impurities removal (optional)

OleMax 120 Series Ag-based catalysts

Compression

Methane / fuel gas H

NOx, O are selectively converted over a silver-based catalyst with minimal a c etylene conversion.

O-gas is delivered to the battery limits from the reneries.

Ethylene Ethane Propylene

Compression occurs to raise pressure, typically in multiple stages.

Cold recovery

Benets and considerations

Selectively removing each component with dierent catalyst allows for near zero ethylene loss Mild operating temperatures provide long cycle lengths Sulphur must be completely removed due to its poisoning eect on silver

Propane C+

Figure 4 Category #3: Advanced selective conversion to capture maximum olefins

cryogenic liquid recovery system. While the design and con- siderations of compressor systems are typically outside the scope of the catalyst supplier, pressure plays an important role in ROG treatment, mostly due to partial pressures of rel- evant (active) components in the gas feed. In any case, pro- ject experience is based on projects at low pressures with no compression system, as well as high-pressure cases. Impurities removal by adsorbents It is important for all stakeholders (the catalyst provider, pro- cess engineering company, and project owners) to have a very good understanding of the gas composition – the valua- ble components, contaminants like nitric oxide (NO), oxygen (O₂), and acetylene (Ac), and impurities (or poisons) such as mercury (Hg), arsine (AsH₃), and phosphine (PH₃). Processing raw refinery gas coming from several sources within a refinery complex typically involves various impuri - ties (poisons) over a wide range of concentrations (see Table 1). The downstream catalytic converter is safeguarded through the implementation of proprietary ActiSorb Series guard beds, which utilise both physical and chemical sorp- tion mechanisms to eliminate contaminants. Multiple spe- cialised ActiSorb grades have been developed, and each grade targets specific impurity profiles. Catalytic feed treatment The conversion of oxygen, NOx, and acetylenes is accom- plished using the OleMax 100 series catalyst. This widely adopted configuration demonstrates consistent perfor - mance in converting these critical components to achieve specification limits. It is necessary to discuss the use of a nickel-based cata- lyst in the presence of CO. Typically, the CO concentrations are significantly lower than 1 mol% in many of the refer - ence plants. In those cases, the CO does not have a strong impact on catalyst performance or operations. As more and more off-gas streams are evaluated for treatment options, however, cases with significantly increased CO levels have been observed. This is an area for caution because of the potential formation of nickel carbonyls (Ni(CO)₄). A sophisticated safety protocol has been developed through extensive research to maintain Ni(CO)₄ concen - trations below critical thresholds (<1 ppb) at the nickel converter outlet. While detailed process mechanisms are

beyond this article’s scope, it is noteworthy that the oper- ating conditions are specifically developed to ensure the decomposition kinetics of Ni(CO)₄ substantially exceed its formation rate by several orders of magnitude. The robust safety protocols developed for this application have gained widespread validation and acceptance among process technology licensors. O 2 and NOx removal before acetylene selective hydrogenation Category #3 deals with the treatment of low-sulphur, low-CO off-gas streams. This case provides an opportunity to use higher selectivity catalysts to further minimise olefin losses across the clean-up process (see Figure 4 ). The feed source of this case is also received from refiner - ies, for example from FCC units or other heavy feed cracking units (DCC, CPP) that produce a significant off-gas frac - tion. As with Category #2, the gas may, dependent on the specific composition, go through compression followed by physisorptive and chemisorptive removal of poisons such as arsine, phosphine, and mercury over the Actisorb series. In Category #3, the gas stream does not contain high sulphur concentrations compared to Categories #1 and #2. This facilitates the use of higher selectivity catalysts at significantly lower temperatures. The catalytic conversion is further split into two steps to make full use of the catalyst potential. NOx and O₂ can be converted at low temperatures over the OleMax 120 series, which contains silver as an active component. As visible benefits, the ethylene conversion (= losses) during this stage is almost negligible. The effluent after these two steps resembles, in principle, the feed gas from a steam cracker in a C₂ front-end con - figuration. It can be treated with state-of-the-art acetylene selective hydrogenation catalysts. Representative for sev- eral projects, in this example, the acetylene is converted by the palladium-based OleMax 250 series for high selectivity. After the acetylene removal stage, the feed stream can be separated and recovered within the battery limits of an eth- ylene plant without causing issues in the cold box section. ROG purification While previous sections outlined standard catalyst selec- tions for ROG purification, each project’s unique feed char - acteristics may necessitate modifications to these baseline

Gas 2025