The Chemistry and Processing of Hydrocarbons PDF

The Chemistry and Processing of Hydrocarbons Energy Masters Section 2 Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Impossible without it…… • Processes based on H2 and syngas are one of the most basic processes involved in fuel, food and chemicals production and distribution. Prof.K...

The Chemistry and Processing of Hydrocarbons Energy Masters Section 2 Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Impossible without it…… • Processes based on H2 and syngas are one of the most basic processes involved in fuel, food and chemicals production and distribution. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Syngas - Production and Reactions NH3 and Methanol are both high volume Early 20th Century F-T by mid 1920’s A combination of steam reforming and partial oxidation is called autothermal reforming. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Syngas Reactions Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy H2/CO ratios from various syngas processes Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Steam Reforming (SR) of HC: Process steps and catalysts HT & LT = High and Low temps. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Reformer • A pre-reformer may be used when using higher HCs. This allows lower steam/carbon (S/C) ratio operation. Since SR and WGS are thermodynamically opposed, process is tuned for one or the other reaction. For NH3 synthesis, primary and secondary reforming are operated at high temperatures and WGS at low temperatures to favour the equilibrium yields. All stages operate in equilibrium. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Process diagram for H2 production S/C = 2.5-4.0, Texit=900-1100°C, Pexit= 20-30 atm. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Process stage 1 - Feedstock purification • S containing compounds: Reaction over CoMo/Al2O3 (to H2S) followed by scrubbing H2S by ZnO (BET area = 25m2/g) • To protect downstream Ni SMR catalyst, S should be below 0.01 ppm. • Chlorides cause corrosion in heat exchangers and poison catalysts (Cu-WGS). Cl- is scrubbed to below 5ppb with a alkaline-treated Al2O3. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Primary steam reforming • Out of the three equations, the CO and H2 formation from CnHm are endothermic. WGS is exothermic. The combined reaction is either +ve or -ve, depending upon the process conditions. Most typically, it is strongly endothermic and heat must be supplied. • See the CH4 conversion as dependednt on temperatures and pressures in the next slide. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy CH4 conversion in SR of CH4 Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Compositional requirements for syngas • Stoichiometry, M = (H2-CO2)/(CO + CO2). • • This value should be 2. However, since H 2/CO is dependent on T °C, and of H2O/CH4 ratio, these two variables are adjusted to get the desired H2/CO ratio. However, syngas with M=2 cannot be produced directly by SMR of NG, although combined SMR and CMR* can provide the appropriate stoichiometry. For example, syngas used for methanol synthesis should conform to: • 0.75 CH4 + 0.25 CO2 + 0.5 H2O Û CO + 2H2 * CO2-CH4 reforming Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Industrial conditions for Reforming/ATR Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Combined steam/CO2 reforming for syngas with H2/CO = 2 P = 25 bar Texit = 950°C Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy