Gas 2025 Issue

volumes and compositions. The primary sources are the crude oil distillation CDU (atmospheric and vacuum), coking units (delayed and fluid), and fluidised catalytic cracker (FCC) sections. Other sources may involve hydrocracking, hydro - treating, reforming, and gas processing units. Clariant has come across combined off-gas streams as well as separated fractions (saturated and unsaturated). Due to the diverse range of feedstocks, ROG compositions vary significantly. However, drawing from three decades of industry experience serving multiple units, Clariant can provide insight into the typical composition patterns it has observed. It needs to be noted that the analysis of ROG compositions is difficult given the many components and impurities down to ppb levels (see Table 1 ). In many cases, the refinery and its respective engineering, procurement, and construction (EPC) partners provide expected/simulated ROG compositions in the absence of real analytical data. Trace impurities are rarely analysed and require offline laboratory test equipment una - vailable on-site. Clariant has offered to receive real ROG feed samples for trace analysis and testing in its laboratories to support a streamlined design for its clients. With modernised global exploitation of various quality oil reserves and the increasing focus on circularity, the authors believe that the composition of ROG and other off-gases may change due to more complexity and, most importantly, higher levels of contamination such as heavy metals, alkali metals, sulphur, and nitrogen compounds. Why ROG purification? Historically, ROG served primarily as fuel gas for refinery operations, powering furnaces, boilers, and process heaters. However, evolving economic and environmental imperatives have transformed this practice from a practical solution to the efficient use of valuable resources. ROG streams contain valuable components, including eth - ylene, propylene, and hydrogen – key elements in modern crude oil-to-chemical (COTC) operations. While stream com - positions vary significantly across applications, all require the removal of common contaminants such as oxygen, nitric oxides, and acetylene. These compositional variations dic- tate specific catalyst, adsorbent, and process configurations for optimal recovery. Modern uses of ROG include further processing and/or treatment to separate and recover valuable components to

ROG compositions with multiple components and impurities

Component Hydrogen H₂ Oxygen O₂ Water H₂O

Averaged, mol%

Range, mol%

20.57

9.5-30.0 0.0-0.5 0.0-0.88

0.12 0.49

Nitric oxide NOx

<1 ppm

n.a.

Carbon monoxide CO Carbon dioxide CO₂

0.43 0.14

0.1-1.9 0.0-0.6 1.8-40.0 0.0-0.31 1.2-35.0 0.6-30.5 0.0-0.2 0.4-28.0 1.1-11.7 0.1-12.6 0.0-3.8 0.0-0.89

Methane CH₄ Acetylene C₂H₂ Ethylene C₂H₄ Ethane C₂H₆

21.73

0.09

21.63 14.28

MA/PD C₃H₄

0.04 8.98 3.00 3.37 0.86 0.13

Propylene C₃H₆

LPG

C₄ unsaturated

C₅

C₆+

Poison

Range, mol ppb

Phosphine PH₃

n.a. n.a. n.a.

1-1,000

Arsine ASH₃ Mercury Hg

0-350 0-100

Table 1

both adsorbent use for removing toxins (mercury, arsine, and phosphine) and catalytic solutions for eliminating nitric oxides, oxygen, and acetylene. Refinery off-gas positioning Figure 1 demonstrates the integration of refinery operations into the petrochemical value chain with the major down- stream uses of the most important chemical building blocks, ethylene and propylene. The refinery off-gas (ROG) purifi - cation section highlighted in green may be integrated with so-called ethylene recovery units (ERU) and/or propylene recovery units (PRU). In some cases, the purified ROG is sent to the separation section of an ethylene plant (steam cracker), including the cryogenic part, which is highly safety-relevant and requires stringent control of critical impurities. It can also be a standalone unit where typically large vol - ume off-gas streams are treated in dedicated ERU/PRUs to capture the valuable components. What is refinery offgas? ROG is derived from several processing sections in varying

Product recovery (Example)

Hydrocarbon feed or o-gas from renery or multiple sources

Quench & fractionation

Furnaces

Compression

Methane / fuel gas H

Sulphur removal & drying

Ethylene Ethane Propylene

OleMax 100 Series Ni-based catalysts

Cold recovery

Benets and considerations

NOx and O removal while also converting Ac , MA , PD using n ickel - based catalyst that is sulphur tolerant

Well suited for integrated operating complexes ( r efinery+steam cracker) Excellent performance with complex o-gas composition Improves plant economics

Propane C+

Figure 2 Category #1: Complete catalyst system to meet specifications using catalystic selective conversion of NOx, O₂, Ac, MA, PD

Gas 2025