Question 1

By-product utilization in integrated steel plants: which fertilizer is commonly manufactured in the by-products (coke ovens) plant using ammoniacal liquor from coke oven gas?

Accepted Answer

Introduction / Context: Integrated steel plants generate coke oven gas (COG) containing ammonia, among other components. Recovering ammonia from COG and converting it into marketable fertilizer improves resource efficiency and reduces emissions. The question asks which fertilizer is typically produced from this by-product stream. Given Data / Assumptions: Coke oven gas contains ammoniacal liquor (NH3 dissolved in water). By-product plants scrub and recover ammonia. On-site neutralization options exist for fertilizer manufacture. Concept / Approach: The recovered ammonia is commonly neutralized with sulfuric acid to form ammonium sulfate crystals. The process is well-established at steelworks due to available sulfuric acid logistics and straightforward crystallization. Urea and CAN require different feedstocks and process trains; phosphate fertilizers are not made directly from COG ammonia without separate phosphoric acid routes. Step-by-Step Solution: Scrub ammonia from COG to obtain ammoniacal liquor.React NH3 with H2SO4 to form (NH4)2SO4.Crystallize and dry to produce saleable ammonium sulfate fertilizer. Verification / Alternative check: Process descriptions of steel by-product plants consistently list ammonium sulfate production via ammonia recovery and sulfuric acid neutralization. Why Other Options Are Wrong: Urea: requires CO2 and NH3 synthesis loop; not a direct COG by-product route. CAN: made by mixing ammonium nitrate with limestone; not typical to COG. SSP/TSP: phosphate fertilizers requiring phosphate rock and acids; unrelated to COG ammonia alone. Common Pitfalls: Assuming all nitrogen fertilizers can be made from any ammonia source without considering the specific process chains. Final Answer: Ammonium sulfate ((NH4)2SO4).

Question 2

Role of naphtha in a fertilizer complex: in the front-end of an ammonia plant, naphtha is primarily used as a source of which component via steam reforming?

Accepted Answer

Introduction / Context: Ammonia synthesis requires a syngas mixture of hydrogen and nitrogen. While modern plants commonly use natural gas (methane), some plants use naphtha as the hydrocarbon feed for reforming. Understanding what naphtha contributes clarifies the front-end design of fertilizer complexes. Given Data / Assumptions: Naphtha is a light petroleum fraction with C5–C10 hydrocarbons. Front-end includes primary steam reformer and secondary reformer/air addition. Downstream shift, CO2 removal, methanation, and synthesis loop are standard. Concept / Approach: Steam reforming of hydrocarbons generates hydrogen and carbon oxides. Nitrogen is supplied separately by air addition (secondary reformer or ASU), not from naphtha. Oxygen for partial oxidation comes from air; naphtha itself is not an oxygen source. Therefore, naphtha’s primary role is to provide hydrogen (and carbon for CO/CO2) via reforming reactions; part of it may also be burned as fuel, but the key purpose is as H2 feedstock for syngas makeup. Step-by-Step Solution: Feed naphtha + steam to the primary reformer → produce H2, CO, CO2.Introduce air in the secondary reformer → supply N2 and partial oxidation heat.Shift CO to CO2; remove CO2; polish syngas; send H2 + N2 to synthesis loop. Verification / Alternative check: Process flow diagrams for naphtha-based ammonia plants show hydrocarbon reforming as the hydrogen source, with nitrogen introduced by controlled air injection. Why Other Options Are Wrong: Fuel only: reformer fuel is a separate duty; feedstock role is primary here. N2 and O2 are introduced via air/ASU, not from naphtha. Argon is a minor inert from air, not produced from naphtha. Common Pitfalls: Confusing the combustion fuel duty with the chemical feedstock role; both can be hydrocarbons but serve different functions. Final Answer: Hydrogen (H2) feedstock.

Question 3

Phosphate fertilizers: Triple superphosphate (TSP) is chemically represented by which principal compound?

Accepted Answer

Introduction / Context: Single and triple superphosphates are produced by acidulating phosphate rock to yield water-soluble phosphate forms. Knowing the dominant chemical species helps in understanding nutrient availability and fertilizer quality specifications. Given Data / Assumptions: TSP is made by reacting phosphate rock with phosphoric acid. End product should be largely water-soluble P2O5. The main calcium phosphate present is monocalcium phosphate. Concept / Approach: Triple superphosphate contains a high percentage of water-soluble phosphate as monocalcium phosphate, Ca(H2PO4)2. In contrast, unacidulated rock is principally tricalcium phosphate (insoluble), and single superphosphate contains a mixture including gypsum. Calcium metaphosphate or dicalcium phosphate do not represent the principal, intended soluble form in TSP fertilizer. Step-by-Step Solution: Recognize TSP manufacturing: phosphate rock + H3PO4 → Ca(H2PO4)2.Identify the desired water-soluble form: monocalcium phosphate.Select Ca(H2PO4)2 as the correct representation. Verification / Alternative check: Product specifications for TSP list high water-soluble P2O5, consistent with monocalcium phosphate content dominating the formulation. Why Other Options Are Wrong: CaF2 · 3 Ca3(PO4)2 and 3 Ca3(PO4)2: components of raw rock (fluorapatite/tricalcium phosphate), largely insoluble. Ca(PO3)2 and CaHPO4: not the main compound in TSP; different solubility and usage. Common Pitfalls: Confusing single vs. triple superphosphate chemistries; remembering that “triple” indicates higher proportion of monocalcium phosphate from phosphoric acid digestion. Final Answer: Ca(H2PO4)2 (monocalcium phosphate).

Question 4

Agronomic roles of phosphatic fertilizers: which statements about their benefits are generally correct?

Accepted Answer

Introduction / Context: Phosphorus is a macronutrient required for energy transfer (ATP/ADP), nucleic acids, and membrane phospholipids. Phosphatic fertilizers supply readily available phosphate that influences both early vegetative development and later reproductive phases. This question consolidates common agronomic observations regarding phosphorus application across crop stages. Given Data / Assumptions: Balanced fertilization practices are followed. Phosphorus is the limiting macronutrient in the scenarios described. Soil fixation and placement practices are appropriately managed. Concept / Approach: Early in the season, adequate phosphorus supports rapid root growth and seedling vigor, enhancing establishment and nutrient/water uptake. In reproductive phases, phosphorus is associated with improved flowering, fruit set, and seed development. Additionally, phosphorus can moderate excessive vegetative growth driven by surplus nitrogen, promoting timely maturity and stronger stalks, thereby “lessening” some negative effects of over-application of N (like lodging and delayed maturity). Step-by-Step Solution: Relate P to ATP-driven processes → early vigor and rooting (supports option a).Connect P to reproductive metabolism → better flowering/fruiting (supports option b).Balance N with P → improved maturity, reduced lodging (supports option c).Therefore, all listed statements align with the known roles of phosphorus. Verification / Alternative check: Extension bulletins and crop physiology texts consistently report enhanced early growth and reproductive performance with adequate P, and the importance of N:P balance to avoid excessive vegetative growth. Why Other Options Are Wrong: “None of these” contradicts well-established agronomic effects. Common Pitfalls: Overlooking soil P fixation (especially in calcareous or strongly acidic soils) which can mask benefits unless placement and rates are optimized. Final Answer: All of the above.

Question 5

Ammonia plant front-end catalysis: which catalyst is commonly used for steam reforming of naphtha to generate hydrogen-rich syngas?

Accepted Answer

Introduction / Context: Steam reforming converts hydrocarbons into hydrogen and carbon oxides and is the backbone of most hydrogen generation systems feeding ammonia synthesis. Catalyst choice must balance activity, cost, and resistance to coking and sulfur poisoning. This item focuses on the standard catalyst for reforming light hydrocarbons like naphtha. Given Data / Assumptions: Naphtha feed pretreated to remove sulfur (e.g., via ZnO guard bed). High-temperature tubular primary reformer with fired furnace. Goal is robust H2 production at reasonable cost. Concept / Approach: Nickel on alumina or other ceramic supports is the industrial workhorse for steam reforming of hydrocarbons because it provides high activity for C–H bond activation at a far lower cost than noble metals. While Pt or Rh have high activity, they are typically reserved for specific oxidation or partial oxidation duties due to cost. Silica gel is not a reforming catalyst; ZnO is used upstream to remove H2S, not as the reforming catalyst itself. Step-by-Step Solution: Identify process: endothermic steam reforming of naphtha.Recall standard catalyst: Ni-based on porous support.Select nickel catalyst as the correct option. Verification / Alternative check: Process licensors and textbooks consistently specify Ni-based catalysts for primary reformers in ammonia plants. Why Other Options Are Wrong: Pt/Rh: too costly for primary reforming duty in large plants. Silica gel: not a catalyst for reforming. ZnO: guard for sulfur removal, not the reformer catalyst. Common Pitfalls: Confusing guard bed materials with the actual reforming catalyst, or assuming noble metals are used simply because they are “better.” Cost and availability rule in large-scale ammonia plants. Final Answer: Nickel (Ni) on porous support.

Question 6

Application issues with ammonium nitrate: Why is ammonium nitrate commonly mixed with limestone (e.g., as CAN) and not used “as-is” as a straight fertilizer?

Accepted Answer

Introduction / Context: Ammonium nitrate (AN) is a high-nitrogen fertilizer with desirable agronomic properties, but it presents handling and safety challenges. Many markets offer it as calcium ammonium nitrate (CAN), where limestone or dolomite reduces caking, hygroscopicity, and explosive potential. Understanding the reason for blending clarifies logistics and regulatory practices. Given Data / Assumptions: Considering bulk storage, transport, and field application at ambient temperature. Fertilizer-grade AN vs. stabilized/conditioned forms. Standard safety and moisture conditions encountered in warehouses. Concept / Approach: Pure ammonium nitrate readily absorbs moisture (hygroscopic), leading to caking and handling difficulties. More critically, under certain confinement and contamination conditions it can undergo rapid decomposition and detonation; blending with limestone dilutes AN, reduces sensitivity, and improves physical stability. The blend also buffers acidity upon soil application. AN is a solid at room temperature, and its nitrogen content is actually high (about 33–35%); therefore, low content or “liquid” state are not the governing issues. Step-by-Step Solution: Identify hazards: hygroscopicity → caking; explosive potential → safety risk.Explain mitigation: add limestone to produce CAN, improving stability and safety.Conclude: as-is AN is avoided in many contexts due to these handling/safety concerns. Verification / Alternative check: Industry guidance and regulations often restrict pure AN storage; CAN is widely permitted due to reduced hazard classification and better physical properties. Why Other Options Are Wrong: “Highly acidic”: AN solutions are mildly acidic, but acidity is not the primary reason for not using AN straight. “Liquid at room temperature”: false; AN is a crystalline solid. “Very low nitrogen content”: incorrect; AN is ~35% N. “Phytotoxic at any dose”: untrue when applied at recommended rates. Common Pitfalls: Confusing agronomic considerations with safety/handling realities; overlooking national regulations that target pure AN due to security and accident history. Final Answer: It is hygroscopic and explosive in nature, creating storage and safety hazards.

Question 7

In fertilizer technology, ammonium phosphate (e.g., mono- or diammonium phosphate) supplies both nitrogen (N) and phosphorus (P). It is classified as which type of fertiliser?

Accepted Answer

Introduction / Context: Fertilisers are grouped as straight (one primary nutrient), mixed (physical blends of two or more straights), and complex (two or more primary nutrients chemically combined in one compound). Ammonium phosphate products such as monoammonium phosphate (MAP) and diammonium phosphate (DAP) contain both nitrogen and phosphorus in a single chemical compound, so understanding their correct classification is fundamental for agronomy and process engineering. Given Data / Assumptions: Material: ammonium phosphate (MAP/DAP). Primary nutrients present: nitrogen (as NH4+) and phosphorus (as phosphate). Context: standard fertiliser industry definitions. Concept / Approach: The key is whether multiple nutrients are present by mere physical mixing or as part of one chemical compound. Ammonium phosphate forms via reaction of ammonia with phosphoric acid; the N and P are chemically bound within one salt lattice. Therefore, by definition, it is a complex fertiliser (multi-nutrient in chemical combination), not simply a physical blend (mixed) and not a straight nitrogenous or straight phosphatic product. Step-by-Step Solution: Identify nutrient count: contains at least two primaries (N and P).Check production route: ammonia + phosphoric acid → ammonium phosphate (chemical reaction).Apply definition: chemical combination with 2+ nutrients → complex fertiliser.Conclude classification: complex. Verification / Alternative check: Product safety data sheets and agronomic texts list MAP (11-52-0) and DAP (18-46-0) as NP complex fertilisers because N and P are in one compound rather than a physical mix. Why Other Options Are Wrong: Nitrogenous: would contain only N as the primary nutrient (e.g., urea, ammonium sulphate). Phosphatic: would contain only P as the primary nutrient (e.g., single superphosphate). Mixed: implies physical blending, which is not the case here. Compound-only-non-fertiliser: irrelevant distractor. Common Pitfalls: Confusing “compound” in the chemical sense with “mixed” in fertiliser logistics. Complex equals chemically combined multi-nutrient, not just co-granulated blends. Final Answer: complex

Question 8

An NPK fertiliser supplies nitrogen (N), phosphorus (P), and potassium (K) together. Based on standard industry definitions, NPK is classified as which type of fertiliser?

Accepted Answer

Introduction / Context: “NPK” denotes fertilisers that deliver the three primary macronutrients together. Classification matters for manufacturing, agronomy, and customs codes. Many commercial NPKs are produced by reacting precursors to form granules in which nutrients are present in chemical combination and/or co-granulated matrices—meeting the definition of complex fertilisers in standard fertiliser technology texts. Given Data / Assumptions: NPK contains N, P, and K in one product. Industry classification differentiates mixed (physical blends) versus complex (chemical combination of 2+ nutrients). Question targets the canonical category used in fertiliser technology MCQs. Concept / Approach: Complex fertilisers provide two or three primaries in one chemically combined product (e.g., nitrophosphate-based NPKs, ammonium phosphates with potash incorporated). While some NPKs are simple blends (mixed), the classification commonly taught for “NPK fertiliser” in process technology is complex, emphasizing chemical reaction routes and co-granulation to produce single granules with multiple nutrients. Step-by-Step Solution: Identify nutrient multiplicity: N + P + K together.Relate to definition: 2–3 primaries chemically combined/co-granulated → complex.Therefore, choose “complex.”Note: “mixed” refers to physical blending only. Verification / Alternative check: Manufacturing routes such as nitrophosphate and slurry granulation produce NPK complex fertilisers where each granule contains multiple nutrients, consistent with the complex category. Why Other Options Are Wrong: Mixed: physical blend, not necessarily chemically combined. Nitrogenous or phosphatic: single-nutrient categories. Micronutrient-only: NPK targets macronutrients. Common Pitfalls: Assuming all bagged NPKs are mere blends; many are complex products by design. Final Answer: complex

Question 9

Urea yield in synthesis can be increased by using excess ammonia and higher pressure/temperature. In practice this is avoided primarily because of which combined drawbacks?

Accepted Answer

Introduction / Context: Urea manufacture from ammonia and carbon dioxide is equilibrium-limited and sensitive to operating conditions. While excess ammonia and higher pressure/temperature can push conversion, plant designers balance yield against materials, by-product formation, and economics. Understanding these trade-offs is essential in fertiliser process design. Given Data / Assumptions: Raising pressure and temperature and using excess NH3 can increase apparent conversion. Biuret forms more readily at higher temperature and longer residence. Corrosion in the urea carbamate environment is severe and worsens under harsher conditions. Higher P/T demands thicker, costlier equipment. Concept / Approach: Process intensification must consider product quality (biuret limits for agriculture), equipment life (corrosion/embrittlement), and capital/operating costs. The cumulative penalty often outweighs incremental yield gains, so industry uses optimized, not extreme, conditions and employs stripper/recirculation schemes instead of simply forcing equilibrium with P/T and NH3 excess. Step-by-Step Solution: Relate higher T to biuret formation: 2 urea → biuret + NH3 (undesirable for seeds).Recognize corrosion intensification in carbamate service; alloy selection becomes expensive.Account for mechanical design: higher P/T → thicker walls, higher CAPEX and energy.Therefore, all three drawbacks apply. Verification / Alternative check: Vendor literature and design handbooks specify biuret limits and corrosion-resistant alloys (e.g., 25-22-2) to manage these risks, confirming the multi-factor constraint. Why Other Options Are Wrong: Any single factor alone understates the practical limitation. None of these: contradicted by known issues. Common Pitfalls: Focusing solely on equilibrium without considering kinetics, corrosion, and specification limits for product biuret. Final Answer: all (a), (b) & (c)

Question 10

Identify the correct chemical formula for sodium tripolyphosphate (STPP), a common builder in detergents and a phosphate fertiliser intermediate.

Accepted Answer

Introduction / Context: Sodium tripolyphosphate (STPP) is widely used as a sequestrant in detergents and appears in phosphate fertiliser process streams. Correct stoichiometry helps with mass balances and environmental compliance calculations (e.g., phosphorus loading). Given Data / Assumptions: Compound name: sodium tripolyphosphate. We seek the empirical formula reflecting three phosphate units and five sodium cations. Concept / Approach: “Tripolyphosphate” indicates three tetrahedral phosphate units linked via two P–O–P bridges, carrying an overall charge of 5− balanced by five Na+. Hence the formula Na5P3O10 is standard in handbooks and labels for STPP (often as the hexahydrate in commerce, but the anhydrous formula is Na5P3O10). Step-by-Step Solution: Interpret the name: tri- (three) phosphate units linked → P3 backbone.Count oxygens: 4 per PO4 minus 2 bridging oxygens shared → total 10.Balance charge: 5− anion requires 5 Na+ → Na5P3O10.Confirm with standard references. Verification / Alternative check: Material safety data sheets and chemical catalogs list STPP as Na5P3O10 (with hydrates noted separately), verifying the formula. Why Other Options Are Wrong: Na4P3O8 and Na3P4O6: incorrect stoichiometry and phosphorus count. Na2PO4 or Na3PO4: monophosphates, not tripolyphosphate. Common Pitfalls: Confusing the anhydrous formula with hydrate compositions; hydrates add water molecules but do not alter the Na:P:O ratio of the anion. Final Answer: Na5P3O10

Question 11

Ammonia synthesis converters differ by internal catalyst arrangement and cooling. In which converter design is the catalyst arranged as a single continuous bed?

Accepted Answer

Introduction / Context: Industrial ammonia converters handle an exothermic, equilibrium-limited reaction. Different licensors/designs arrange catalyst in multiple beds with inter-bed cooling or as variants such as single continuous beds. Recognising which design employs a single continuous bed is a classic fertiliser technology question. Given Data / Assumptions: Design names provided: Fauser-Montecatini, Claude, Uhde, Kellogg. We compare on catalyst bed arrangement. Concept / Approach: Historically, the Claude converter is noted for a single continuous catalyst bed arrangement, whereas modern Uhde/Kellogg/ICI variants typically employ multiple beds with quench or indirect cooling and often radial flow to control temperature and pressure drop. Therefore, the design featuring a single continuous bed corresponds to the Claude converter. Step-by-Step Solution: Identify single-bed hallmark: continuous catalyst packing without inter-bed breaks.Associate with licensor: Claude converter → single continuous bed.Cross-check: Other designs (Uhde, Kellogg, Fauser-Montecatini) use multi-bed/quench/indirect cooling configurations.Select “Claude.” Verification / Alternative check: Industry summaries highlight Uhde/Kellogg multi-bed radial-flow converters; in contrast, exam references attribute the single continuous bed configuration to Claude designs. Why Other Options Are Wrong: Fauser-Montecatini: generally multi-bed with heat exchange/quench. Uhde and Kellogg: widely documented as three-bed radial-flow converter designs. ICI quench: classical multi-bed quench scheme. Common Pitfalls: Mixing up “radial-flow” (direction) with “number of beds” (staging). Radial flow can still be multi-bed. Final Answer: Claude

Question 12

Approximate nutrient analysis: what is the nitrogen content (by mass) of ammonium sulphate fertiliser, (NH4)2SO4, expressed as a percentage?

Accepted Answer

Introduction / Context: Quick estimation of nutrient percentages is common in agronomy and plant design. Ammonium sulphate is a straight nitrogenous fertiliser widely used for basal application and as a source of both NH4+-N and sulphur (as sulphate). Its nitrogen content is about one-fifth by mass, a figure frequently needed for dosage calculations. Given Data / Assumptions: Chemical formula: (NH4)2SO4. Atomic masses (approx.): N = 14, H = 1, S = 32, O = 16. Concept / Approach: Compute mass fraction of nitrogen in the salt: two nitrogen atoms contribute 28 units to the total formula mass. The total formula mass is 2*(14+41) + 32 + 416 = 2*18 + 32 + 64 = 132. The nitrogen percentage ≈ 28/132 ≈ 0.212 ≈ 21%. Many handbooks round this to about 20–21% for practical agronomic use. Step-by-Step Solution: Calculate N mass: 2 * 14 = 28.Calculate total mass: 132.Compute percent N: (28 / 132) * 100 ≈ 21.2%.Choose the closest listed value: 20%. Verification / Alternative check: Fertiliser specification sheets commonly list ammonium sulphate as 21-0-0-24S, aligning with the computed value. Why Other Options Are Wrong: 5%: far below the calculated value. 50% or 65%: unrealistically high for this salt. 35%: not supported by stoichiometry. Common Pitfalls: Neglecting hydrogen’s contribution or miscounting oxygen, which skews the denominator. Final Answer: 20

Question 13

Identify what potassic (potash-based) fertilisers generally do NOT promote in crops, compared with nitrogenous fertilisers that primarily drive vegetative growth.

Accepted Answer

Introduction / Context: Nutrient roles differ: nitrogen encourages lush vegetative growth; phosphorus aids rooting and energy transfer; potassium enhances water regulation, enzyme activation, disease resistance, and improves starch and sugar formation. Distinguishing these roles helps avoid imbalanced fertilisation strategies. Given Data / Assumptions: Focus on potassic fertilisers (e.g., muriate of potash, sulphate of potash). Trait comparisons include vegetative growth vs. quality attributes such as starch and sugar accumulation. Concept / Approach: Potassium is most associated with improved tuber filling, starch/sugar content, lodging resistance, and stress tolerance. Rapid early vegetative growth of stems and leaves is typically nitrogen-driven. Therefore, potassic fertilisers do not primarily promote early stems-and-leaves expansion; instead, they elevate quality and resilience characteristics. Step-by-Step Solution: Map nutrient to function: K → osmotic balance, enzyme activation, quality (starch/sugar), fiber strength.Contrast with N: promotes leafy biomass in early stages.Select the trait that is not K-driven: early stems & leaves.Confirm other listed traits are K-associated (starch, sugar, fiber strength). Verification / Alternative check: Agronomy guides cite K’s positive effect on tuber/grain filling and sugar content; N is cited for canopy expansion and leaf chlorophyll. Why Other Options Are Wrong: Starches of potatoes & grains, sugar of fruits & vegetables, fibrous materials: all align with potassium’s roles. Tuber quality and disease resistance: also K-related benefits. Common Pitfalls: Overapplying nitrogen expecting quality improvements that are actually K-dependent, leading to soft tissue and disease susceptibility. Final Answer: stems & leaves during early stage of plant growth

Question 14

Select the option that is NOT a commercially used primary feedstock for producing ammonia synthesis gas (H2 + N2 route).

Accepted Answer

Introduction / Context: Ammonia synthesis gas (syngas for the Haber–Bosch loop) is produced by reforming or gasifying carbonaceous feedstocks to make hydrogen, combined with nitrogen from air separation or the secondary reformer. Recognising standard commercial feedstocks is essential for evaluating plant siting and economics. Given Data / Assumptions: Commercial routes: steam methane reforming of natural gas, naphtha reforming, coal/coke oven gas routes. “Feedstock” here means the principal carbon/hydrogen source entering reforming/gasification. Electrolysis-based “green hydrogen” exists but is distinct from using water as a reformer feedstock in conventional plants. Concept / Approach: Natural gas and naphtha are common feedstocks for reforming; coal and coke oven gas are used where gas or liquids are scarce. “Tar” is a by-product contaminant from gasification, not a standard primary feedstock for ammonia syngas. Water supplies steam or is split by electrolysis to make hydrogen, but as a direct reforming feedstock in the conventional sense it is not the carbon source; thus the “not commercially used feed-stock” answer focuses on tar. Step-by-Step Solution: List standard feedstocks: natural gas, naphtha, coal/coke oven gas.Identify “tar”: a problematic impurity from gasifiers, requiring removal/reforming, not a feedstock.Water: process utility/oxidant for reforming or electrolysis medium, not the conventional carbonaceous feed.Therefore, the clearly incorrect feedstock is tar. Verification / Alternative check: Industry statistics show the majority of ammonia capacity based on natural gas; significant capacities exist on naphtha and coal/coke oven gas. “Tar” appears in gas cleanup sections as a contaminant to be cracked or removed, not as a purchased feed. Why Other Options Are Wrong: Naphtha and Coal/coke oven gas: established commercial feedstocks. Natural gas: the dominant global feedstock. Water: while used for steam and electrolysis, the question targets primary feedstock; tar remains the best “not used” choice. Common Pitfalls: Confusing gasification by-products with feedstocks; tar must be minimized, not fed. Final Answer: Tar

Question 15

For the exothermic equilibrium reaction N2 + 3 H2 ⇌ 2 NH3, the total gas moles decrease. To obtain high single-pass equilibrium conversion, the synthesis should be operated at which pressure regime?

Accepted Answer

Introduction / Context: Ammonia formation reduces the number of gas molecules (from 4 to 2) and releases heat. Le Chatelier’s principle predicts how pressure and temperature influence equilibrium. Understanding this is central to converter design and loop pressure selection. Given Data / Assumptions: Reaction: N2 + 3 H2 ⇌ 2 NH3, exothermic. Total moles decrease across the reaction. Goal: maximize equilibrium conversion in a single pass. Concept / Approach: Increasing pressure shifts equilibrium toward the side with fewer moles (ammonia). Lowering temperature also favors ammonia but slows kinetics; thus practical plants use elevated pressure and moderate temperature to balance rate and equilibrium. Therefore, high pressure improves single-pass conversion significantly versus low or atmospheric pressure. Step-by-Step Solution: Apply Le Chatelier’s principle to moles change: fewer moles on product side.Increase pressure → equilibrium shifts to reduced-volume side (NH3).Select the correct option: “high pressure.”Note: excessively high temperature reduces equilibrium yield despite rate enhancement. Verification / Alternative check: Equilibrium calculations show rising ammonia mole fraction with pressure at fixed temperature, consistent with industrial practice (converter pressures typically many tens to over one hundred bar). Why Other Options Are Wrong: Low/atmospheric pressure: shift equilibrium toward reactants. Very high temperature: lowers equilibrium NH3 despite faster kinetics. Vacuum: opposite of desired effect. Common Pitfalls: Equating kinetic advantages of high temperature with better equilibrium—these effects oppose each other for exothermic reactions. Final Answer: high pressure

Question 16

When anhydrous liquid ammonia reacts with orthophosphoric acid (H3PO4), which fertiliser product is formed?

Accepted Answer

Introduction / Context: Neutralisation of phosphoric acid with ammonia is a core route to produce NP fertilisers. Depending on the ammonia-to-acid ratio, monoammonium phosphate (MAP) or diammonium phosphate (DAP) is obtained, both collectively termed ammonium phosphate fertilisers. Given Data / Assumptions: Reactants: anhydrous NH3 and H3PO4 (orthophosphoric acid). Reaction carried out under standard fertiliser plant conditions (scrubber/neutraliser or pipe reactor). Concept / Approach: NH3 neutralises acidic protons on H3PO4 to form ammonium phosphate salts. A 1:1 NH3:H3PO4 basis forms MAP (NH4H2PO4), while higher NH3 produces DAP ((NH4)2HPO4). “Superphosphate” and “triple superphosphate” are produced instead by reacting phosphate rock with sulphuric or phosphoric acid, not with ammonia directly. Step-by-Step Solution: Identify acid–base neutralisation: NH3 + H3PO4 → ammonium phosphate(s).Determine likely products by ratio: MAP or DAP.Exclude superphosphates (acidulation of rock, not NH3 neutralisation).Select “ammonium phosphate.” Verification / Alternative check: Process flow diagrams for NP plants show ammonia neutralisers producing MAP/DAP slurry that is granulated and dried, confirming the product identity. Why Other Options Are Wrong: Superphosphate and triple superphosphate: manufactured by acidulating phosphate rock, not by reacting NH3 with H3PO4. Potassium nitrate: unrelated salt from KNO3 processes. None of these: incorrect because ammonium phosphate is formed. Common Pitfalls: Confusing NP neutralisation chemistry with superphosphate route; these are distinct process lines in phosphate fertiliser plants. Final Answer: ammonium phosphate

Question 17

In industrial chemistry, “synthesis gas” (syngas) is a fuel-gas mixture used for chemical synthesis. Which single component is an essential constituent present in all synthesis gas formulations?

Accepted Answer

Introduction / Context: Synthesis gas, commonly called syngas, is the foundational feed for several cornerstone processes such as ammonia, methanol, oxo-synthesis, and Fischer–Tropsch conversions. While exact compositions vary by final product and production route, a unifying feature is the presence of hydrogen, which participates directly in hydrogenation and reduction reactions central to these syntheses. Given Data / Assumptions: Syngas refers to process gas produced by reforming, gasification, or partial oxidation, tailored for downstream synthesis. Typical constituents considered: H2, CO, CO2, steam, and sometimes N2 as diluent; O2 is not a constituent of the product syngas stream. The question asks for an essential constituent across all practical formulations. Concept / Approach: Most synthetic routes require hydrogen either as a direct reactant (e.g., methanol from CO/CO2 + H2; hydrocarbon chains from CO + H2) or as the entire reductant in ammonia manufacture (after removing CO/CO2 and adding N2). Therefore, H2 is the common denominator. CO, while very common in syngas for methanol or Fischer–Tropsch, is not required for ammonia syngas, which is essentially H2 + N2 after CO cleanup. Step-by-Step Solution: Identify key syntheses using syngas: methanol (needs H2), Fischer–Tropsch (needs H2), ammonia (needs H2).Compare compositions: ammonia “syngas” contains H2 + N2 with CO minimized to trace; methanol/F–T syngas contains CO + H2.Determine universal constituent: H2 is present in all cases, whereas CO is absent in ammonia make-up gas.Conclude that hydrogen is the essential component across all syngas applications. Verification / Alternative check: Process block diagrams show reforming/gasification produce CO + H2; ammonia trains include shift, CO2 removal, and methanation to strip CO/CO2, leaving H2 for synthesis with N2. Methanol/F–T retain CO with H2, again requiring H2. Why Other Options Are Wrong: O2: syngas is produced in oxygen-limited environments and O2 is not a product constituent.CO2: may be present but is typically removed or minimized for most syntheses.N2: essential only for ammonia; not required for methanol or Fischer–Tropsch. Common Pitfalls: Assuming CO is universal because many texts define syngas as CO + H2; forgetting that ammonia process gas is H2-rich with CO driven to near zero. Final Answer: H2

Question 18

In ammonia (NH3) synthesis over promoted iron catalysts (Haber–Bosch), which substance acts as a key promoter for the active iron phase?

Accepted Answer

Introduction / Context: Industrial ammonia synthesis relies on magnetite-derived iron catalysts modified by structural and electronic promoters. These promoters enhance activity, selectivity, and stability under high pressure and moderate temperature. Recognizing the correct promoter system is a common exam theme in fertilizer and catalysis modules. Given Data / Assumptions: Catalyst base: Fe (from Fe3O4 pre-cursor reduced in situ). Operating conditions: high pressure with H2/N2 feed; strong poisons (e.g., CO) removed upstream. Promoters include oxides that tune basicity/electronic properties and mechanical robustness. Concept / Approach: Potassium oxide (K2O) is a classic electronic promoter for ammonia synthesis catalysts. It increases surface basicity, improves nitrogen adsorption/activation, and enhances electron density at iron active sites. Structural promoters like Al2O3 and CaO improve dispersion and sintering resistance, but K2O’s role as an electronic promoter is particularly emphasized in textbooks. Step-by-Step Solution: Identify the ammonia catalyst family: promoted iron.List common promoters: K2O (electronic), Al2O3 and CaO (structural), sometimes SiO2 as support/structural aid.Check options: only K2O fits the standard promoter profile for NH3 synthesis iron catalysts.Select K2O as the correct answer. Verification / Alternative check: Process literature consistently cites K2O-promoted iron (with Al2O3, CaO) as the workhorse system in Haber–Bosch loops; ruthenium catalysts are used in some modern plants but the question targets the conventional iron system. Why Other Options Are Wrong: SiO3: not a standard promoter; SiO2 may act as support/structural component, not the primary promoter cited.V2O5 and U2O3: unrelated to conventional NH3 iron catalyst promotion; V2O5 is associated with SO2 oxidation, not ammonia synthesis. Common Pitfalls: Confusing structural supports with electronic promoters; mixing catalyst systems from unrelated processes (e.g., vanadia for sulfuric acid plants). Final Answer: K2O

Question 19

India’s largest-capacity nitrogenous fertilizer ammonia plants (about 2,700 tons NH3 per day each) are located at which pair of sites?

Accepted Answer

Introduction / Context: Ammonia capacity is a key metric for the fertilizer sector, influencing urea production and national nutrient availability. Knowledge of major sites and operators is frequently tested in chemical technology examinations in India. Given Data / Assumptions: Question references large single-train capacities around 2,700 tons NH3 per day. Operators include public-sector and cooperative majors such as RCF (Rashtriya Chemicals & Fertilizers) and IFFCO (Indian Farmers Fertiliser Cooperative). Site pairs in options correspond to well-known fertilizer hubs. Concept / Approach: The pair of locations that match the cited capacity class and operator identity is Thal-Vaishet (RCF) in Maharashtra and Hazira (IFFCO) in Gujarat. These complexes are prominent for large-scale ammonia-urea operations and have historically belonged to the top capacity bracket in India. Step-by-Step Solution: Identify operator and geography in each option.Match with known mega-capabilities: RCF Thal-Vaishet and IFFCO Hazira meet the ~2,700 t/d specification.Exclude others that either have different capacities or are associated with different corporate entities or older capacities.Select the pair Thal-Vaishet and Hazira. Verification / Alternative check: Industry reports and plant profiles place these locations among the largest ammonia producers by single-train capacity in India, supporting the selection. Why Other Options Are Wrong: Talcher/Ramagundam and Korba/Talcher as FCI options do not correspond to the cited largest single-train capacity category.Haldia/Namrup under HFC represent different capacity and corporate contexts, not the named largest installations. Common Pitfalls: Mixing up corporate acronyms (RCF, IFFCO, FCI, HFC) or assuming all legacy sites share the same modern capacities. Final Answer: Thal-Vaishet (RCF, Maharashtra) and Hazira (IFFCO, Gujarat)

Question 20

Identify the form of phosphoric acid with the empirical formula HPO3: which named type of phosphoric acid corresponds to HPO3?

Accepted Answer

Introduction / Context: Phosphoric acids appear in several condensation states depending on the degree of dehydration: orthophosphoric (H3PO4), pyrophosphoric (H4P2O7), and metaphosphoric (general formula (HPO3)n). Correctly mapping molecular formulas to these named forms is essential in fertilizer chemistry and inorganic nomenclature. Given Data / Assumptions: HPO3 is provided as the empirical unit. We are to choose the named acid family that corresponds to this unit. No polymerization degree n is specified, so we refer to the repeating unit. Concept / Approach: Metaphosphoric acid is represented by (HPO3)n, where n can be 1 (monomeric metaphosphoric) or greater (polymeric ring or chain structures). Orthophosphoric acid is H3PO4, and pyrophosphoric acid is H4P2O7, both inconsistent with HPO3. Therefore, HPO3 maps directly to the metaphosphoric family. Step-by-Step Solution: Compare given formula HPO3 with standard acids.Orthophosphoric: H3PO4 → not equal.Pyrophosphoric: H4P2O7 → not equal to a single HPO3 unit.Metaphosphoric: (HPO3)n → matches the given empirical unit. Verification / Alternative check: Chemical handbooks list metaphosphoric acid as derived by dehydration of orthophosphoric acid, yielding the HPO3 repeating unit; polyphosphates and metaphosphates are widely used in industry. Why Other Options Are Wrong: Pyro- and ortho- formulations have different stoichiometries and hydrogen/oxygen counts.“None of these” is incorrect because metaphosphoric exactly matches. Common Pitfalls: Confusing empirical and molecular formulas or forgetting that metaphosphoric can polymerize (n > 1). Final Answer: Metaphosphoric acid

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