Petroleum Refining Basics

Cheatsheet Content

### Introduction to Petroleum Refining - **Petroleum (Crude Oil):** A naturally occurring, complex mixture of hydrocarbons (alkanes, cycloalkanes, aromatics) with varying molecular weights and trace amounts of sulfur, nitrogen, and oxygen compounds. - **Refining:** The process of converting crude oil into more useful and valuable petroleum products (e.g., gasoline, diesel, jet fuel, lubricants, asphalt). - **Goal:** Separate crude oil into fractions and then convert these fractions into desired products through various chemical processes. ### Crude Oil Composition - **Paraffins (Alkanes):** Saturated straight or branched chain hydrocarbons ($C_nH_{2n+2}$). - Examples: Methane, propane, octane. - **Naphthenes (Cycloalkanes):** Saturated cyclic hydrocarbons ($C_nH_{2n}$). - Examples: Cyclopentane, cyclohexane. - **Aromatics:** Hydrocarbons containing one or more benzene rings. - Examples: Benzene, toluene, xylenes. - **Asphaltenes & Resins:** High molecular weight, polar compounds containing heteroatoms (S, N, O), contributing to viscosity and asphalt production. - **Impurities:** Sulfur compounds (mercaptans, sulfides), nitrogen compounds (pyridines), oxygen compounds (phenols), metals (Ni, V), salts (NaCl). ### Key Refining Processes #### 1. Separation Processes - **Atmospheric Distillation:** - Separates crude oil into fractions based on boiling points at atmospheric pressure. - Products (from top to bottom): Refinery gases, naphtha, kerosene, diesel, atmospheric gas oil, atmospheric residue. - **Vacuum Distillation:** - Further separates the heavy atmospheric residue under vacuum to prevent thermal cracking. - Products: Vacuum gas oil (VGO), lubricating oil base stocks, asphalt. - **Flash Distillation:** - Rapid vaporization of a liquid mixture when its pressure is suddenly reduced. #### 2. Conversion Processes - **Cracking:** Breaking large hydrocarbon molecules into smaller, more valuable ones. - **Fluid Catalytic Cracking (FCC):** Uses a catalyst (zeolites) at high temperatures ($450-550^\circ C$) to convert heavy gas oils into gasoline, LPG, and light cycle oil. - **Hydrocracking:** Cracking in the presence of hydrogen and a catalyst ($350-450^\circ C$, high pressure) to produce high-quality jet fuel, diesel, and naphtha with lower sulfur content. - **Thermal Cracking (Coking):** High temperature ($450-600^\circ C$) without a catalyst to produce lighter products and petroleum coke from heavy residues. - **Reforming (Catalytic Reforming):** - Converts low-octane naphtha into high-octane gasoline components (aromatics) and hydrogen using a platinum-based catalyst. - Reactions: Dehydrogenation, isomerization, cyclization. - **Alkylation:** - Combines light iso-paraffins (e.g., isobutane) with light olefins (e.g., propylene, butylene) in the presence of a strong acid catalyst (HF or $H_2SO_4$) to produce high-octane branched paraffins (alkylate) for gasoline blending. - **Isomerization:** - Rearranges the molecular structure of straight-chain hydrocarbons into branched-chain isomers to improve octane number (e.g., n-butane to isobutane). #### 3. Treatment Processes (Purification) - **Hydrotreating (Hydrodesulfurization - HDS):** - Removes sulfur, nitrogen, and oxygen impurities from petroleum fractions by reacting them with hydrogen over a catalyst (Co-Mo, Ni-Mo) at high temperatures and pressures. - Reduces environmental emissions (SOx, NOx). - **Sweetening:** - Removes corrosive sulfur compounds (mercaptans) from light products like gasoline and LPG, often converting them to less harmful disulfides. - **Desalting:** - Removes salt and suspended solids from crude oil before distillation to prevent corrosion and fouling. #### 4. Blending - Mixing various refined products in specific proportions to meet desired product specifications (e.g., octane number for gasoline, cetane number for diesel, vapor pressure). ### Major Refinery Products - **Refinery Gases:** Methane, ethane, propane, butane (used as fuel or petrochemical feedstock). - **Liquefied Petroleum Gas (LPG):** Propane and butane (fuel, petrochemical feedstock). - **Naphtha:** Light (gasoline additive, solvent) and heavy (reforming feedstock). - **Gasoline (Petrol):** Motor fuel, blend of various fractions, high octane number. - **Kerosene:** Jet fuel (Jet A, Jet A-1), heating oil, illuminating oil. - **Diesel Fuel (Gas Oil):** Fuel for diesel engines, heating oil. - **Fuel Oils:** Heavy fuel oil for industrial furnaces, power generation, marine fuel. - **Lubricating Oils:** Base oils for engine oils, industrial lubricants. - **Asphalt/Bitumen:** Paving roads, roofing. - **Petroleum Coke:** High-carbon solid, used as fuel, electrode material. ### Environmental Considerations - **Air Emissions:** SOx, NOx, particulate matter, VOCs (volatile organic compounds), greenhouse gases ($CO_2$). - **Water Discharge:** Process water containing hydrocarbons, heavy metals, salts. - **Solid Waste:** Spent catalysts, coke, sludges. - **Mitigation:** Flue gas desulfurization, low-NOx burners, wastewater treatment, carbon capture.