Difficulty: Easy
Correct Answer: 3-4
Explanation:
Introduction / Context:
Natural gas composition matters because it sets the hydrogen potential and carbon dioxide load for ammonia/urea plants. A quick, practical metric is the carbon-to-hydrogen (C/H) mass ratio. For pipeline-quality natural gas dominated by methane (CH4), engineers can estimate this ratio to validate feed characterization and sizing of reformers and CO2 removal units.
Given Data / Assumptions:
Concept / Approach:
For methane, molecular mass is 16 (C = 12; H4 = 4). The mass C/H ratio therefore equals 12/4 = 3.0. Real natural gas often includes minor higher hydrocarbons (C2+), which slightly increase the C/H mass ratio but typically keep it near methane’s baseline. Thus, a sensible engineering range is 3–4 by mass for natural gas feeds in fertilizer plants.
Step-by-Step Solution:
Assume CH4 dominates → C/H by mass = 12/4 = 3.0.Account for small C2+ (ethane/propane) fractions → modestly higher C per H → ratio nudges above 3.0.Select the only plausible given range: 3–4.
Verification / Alternative check:
Gas chromatographic assays of typical natural gas show methane content often above 85–90% by volume, supporting a C/H mass ratio close to 3. The presence of inerts (N2, CO2) does not increase H; heavier alkanes raise the ratio slightly toward but seldom beyond 4 in pipeline gas.
Why Other Options Are Wrong:
8–10, 15–17, and 20–25 are far too high for methane-rich gas; 1–2 would imply a hydrogen-rich gas like refinery hydrogen streams, not natural gas.
Common Pitfalls:
Mixing atomic with mass ratios; the atomic C:H for methane is 1:4, which is not what the question asks.
Final Answer:
3-4
Discussion & Comments