Question 1

Urea process chemistry: The dehydration of ammonium carbamate to yield urea in high-pressure synthesis loops is best characterized as which type of reaction step?

Accepted Answer

Introduction / Context: Modern urea plants produce urea via a two-step sequence: rapid formation of ammonium carbamate from ammonia and carbon dioxide, followed by its dehydration to urea with release of water. Distinguishing the thermal nature of each step is essential for energy integration and equipment design in high-pressure synthesis sections. Given Data / Assumptions: Step 1: 2 NH3 + CO2 → NH2COONH4 (exothermic, equilibrium-limited). Step 2: NH2COONH4 → NH2CONH2 + H2O (dehydration to urea). No solid catalyst is used in standard high-pressure urea synthesis. Concept / Approach: The dehydration of ammonium carbamate to urea requires heat input and proceeds more readily at elevated temperatures under high pressure to keep reactants in the liquid phase. This step is endothermic, in contrast to the preceding carbamate formation which is exothermic. Plants therefore recover heat from exothermic sections and supply heat to drive dehydration, while carefully controlling pressure and residence time to achieve the desired conversion before downstream recovery and recycling. Step-by-Step Solution: Identify step: ammonium carbamate → urea + water.Classify energetics: requires heat input = endothermic.Confirm that no heterogeneous catalyst is required; process is thermally driven at pressure. Verification / Alternative check: Plant heat balances show duty added in the synthesis section for dehydration, with coolers handling the earlier exotherm from carbamate formation. Why Other Options Are Wrong: Exothermic: applies to carbamate formation, not dehydration. Autocatalytic: no product-driven catalysis is involved. Catalytic: standard designs do not rely on solid catalysts for this step. Athermal: contradicted by measured heat duties. Common Pitfalls: Confusing the thermodynamics of the two sequential steps; remembering “first exothermic, then endothermic” helps avoid mistakes. Final Answer: Endothermic.

Question 2

Thermal process identification: Heating a mixture of coke, sand (silica), and phosphate rock in an electric furnace is carried out for the manufacture of which principal product?

Accepted Answer

Introduction / Context: Two broad industrial routes handle phosphate rock: the “wet process,” producing phosphoric acid and superphosphates via sulfuric or phosphoric acid, and the “thermal process,” producing elemental phosphorus in electric furnaces. Recognizing which inputs map to which output is foundational for chemical process selection and environmental controls. Given Data / Assumptions: Feed solids: phosphate rock, silica (sand), and coke. Reactor: electric furnace at very high temperature. Target product in the thermal route: elemental phosphorus. Concept / Approach: In the thermal process, carbon reduces phosphate to elemental phosphorus gas while silica combines with calcium oxide to form a molten calcium silicate slag. The volatile P4 is then condensed under water to yield white/yellow phosphorus. Wet-process phosphoric acid and superphosphates are not produced in the electric furnace; they are made by acidulation at much lower temperatures and different unit operations (digesters, filters, granulators). Step-by-Step Solution: Match inputs (rock + silica + coke) with the thermal reduction chemistry.Identify the volatile product: elemental phosphorus vapor.Condense to collect P4 → confirms the product is elemental phosphorus. Verification / Alternative check: Process descriptions show tap slag removal and P4 recovery under water—signatures of the electric furnace route. Why Other Options Are Wrong: Phosphoric acid, SSP, TSP, and MAP involve acidulation with sulfuric or phosphoric acid and often granulation, not high-temperature carbothermic reduction. Common Pitfalls: Conflating similarly named “phosphate” products; remember: furnace → P4, wet process → acids/superphosphates. Final Answer: Elemental phosphorus (P4).

Question 3

Definition of “gas-based” fertilizer plant: A fertilizer plant is classified as gas-based when it uses which gas as the primary hydrogen source for ammonia manufacture?

Accepted Answer

Introduction / Context: Ammonia synthesis requires hydrogen, traditionally obtained by reforming hydrocarbons. Industry shorthand categorizes plants by the primary feedstock to the hydrogen unit. A “gas-based” plant refers specifically to facilities using natural gas—largely methane—as the principal hydrogen source via steam reforming or autothermal reforming. Given Data / Assumptions: Hydrogen is produced upstream of the Haber–Bosch loop. Feedstock options include natural gas, naphtha, coal/coke oven gas, and others. Classification is based on main feedstock, not minor supplements. Concept / Approach: “Gas-based” denotes natural gas-based hydrogen production, which is common due to methane's high hydrogen-to-carbon ratio, established steam methane reforming technology, and widespread pipeline infrastructure. While coke oven or producer gases can contain hydrogen and be processed, plants using these are typically called “by-product gas-based” or classified under separate schemes, not the standard “gas-based” label in fertilizer sector reporting. Step-by-Step Solution: Identify definition: gas-based ≈ natural gas feed to reformers.Associate with SMR/ATR → hydrogen-rich syngas for NH3.Select “Natural gas (methane-rich)” as correct. Verification / Alternative check: National fertilizer statistics typically segregate capacity as gas-based (natural gas), naphtha-based, fuel oil/LSHS-based, or coal-based, confirming the accepted usage. Why Other Options Are Wrong: Coke oven gas and producer gas can be hydrogen sources but are not the standard meaning of “gas-based” in this context. Coal gasification routes are categorized as “coal-based.” Refinery fuel gas varies and is not the canonical definition. Common Pitfalls: Assuming any gaseous feed qualifies; sector nomenclature specifically points to natural gas-based hydrogen generation. Final Answer: Natural gas (methane-rich).

Question 4

Fertilizer terminology: “Nitrolime” is chemically known as which compound?

Accepted Answer

Introduction / Context: Trade names and common names for fertilizers can be confusing because similar-sounding terms refer to different chemical compounds. “Nitrolime” is a traditional name that does not correspond to calcium nitrate, ammonium nitrate, or CAN. Recognizing the correct mapping prevents mistakes in nutrient analysis and handling practices. Given Data / Assumptions: “Nitrolime” historically refers to a nitrogenous fertilizer produced by the calcium carbide–derived cyanamide route. Modern product labeling may vary by country, but classical chemistry texts are consistent. Options list common nitrogen fertilizers to test recognition. Concept / Approach: “Nitrolime” is the commercial name for calcium cyanamide (CaCN2), a fertilizer that also acts as a soil amendment and nitrification inhibitor under some conditions. It is distinct from calcium nitrate [Ca(NO3)2], ammonium nitrate [NH4NO3], and mixtures like calcium ammonium nitrate (CAN). Since “calcium cyanamide” is not among the selectable answers except as a distractor in the extended list, “None of these” is the correct choice within the options presented. Step-by-Step Solution: Map “nitrolime” → calcium cyanamide (CaCN2).Scan options: calcium nitrate, ammonium nitrate, CAN — none match CaCN2.Therefore select “None of these.” Verification / Alternative check: Reference tables of fertilizer common names clearly list nitrolime as calcium cyanamide, historically produced from calcium carbide and nitrogen at high temperature. Why Other Options Are Wrong: Calcium nitrate, ammonium nitrate, and CAN are different salts with distinct properties and analyses. Common Pitfalls: Confusing “lime” in the name with calcium nitrate or CAN; the “nitro” element here refers to nitrogen content via cyanamide chemistry, not nitrate. Final Answer: None of these.

Question 5

Composition of rock phosphate: What is the principal phosphate mineral present in natural rock phosphate deposits?

Accepted Answer

Introduction / Context: Rock phosphate is the naturally occurring raw material for phosphate fertilizers. Its composition determines beneficiation strategies and acidulation chemistry. The dominant mineral is a form of apatite—commonly fluorapatite—rather than the water-soluble calcium phosphates seen in finished fertilizers. Given Data / Assumptions: Typical deposits contain fluorapatite-like minerals approximated by Ca10(PO4)6F2 and related substitutions. Monocalcium and dicalcium phosphates are manufactured, more soluble species not found as the main mineral in unprocessed rock. Fluorspar (CaF2) may occur as an impurity but is not the main phosphate carrier. Concept / Approach: The apatite family (fluorapatite, hydroxyapatite, carbonate apatite) provides the bulk of phosphorus in rock phosphate. Because the options listed do not include “fluorapatite/tricalcium phosphate apatite,” and instead present soluble fertilizer salts or non-phosphate minerals as distractors, the correct response within the provided choices is “None of these.” Step-by-Step Solution: Recall: natural rock phosphate ≈ apatite family, not MCP/DCP.Identify that fluorspar is CaF2 without phosphate.Conclude: none of the listed answers accurately represents the main constituent. Verification / Alternative check: Mineralogy references and fertilizer industry texts consistently state that rock phosphate is predominantly fluorapatite or related apatites. Why Other Options Are Wrong: Monocalcium and dicalcium phosphates are products of acidulation/neutralization, not the native ore mineral. Fluorspar contains no phosphate groups and is not the main constituent of phosphate rock. Common Pitfalls: Equating fertilizer product salts with the minerals found in ores; the ore must be chemically processed to produce soluble fertilizer forms. Final Answer: None of these.

Question 6

Benefits of bio-fertilizers: Bio-fertilizers are cheaper, renewable, and non-polluting. Which aspects of soil performance do they improve when applied appropriately?

Accepted Answer

Introduction / Context: Bio-fertilizers are preparations of beneficial microorganisms such as Rhizobium, Azotobacter, Azospirillum, and phosphate-solubilizing bacteria that enhance nutrient availability to plants. Beyond nutrient supply, sustained use can influence soil physical properties and water relations by promoting root growth and microbial biomass, which contribute to aggregation. This question consolidates these recognized benefits into a single selection task. Given Data / Assumptions: Appropriate carrier-based inoculants applied to compatible crops and soils. Good agronomic management that allows microbes to survive (moisture, temperature, pH). Time scale long enough to reflect changes in soil structure. Concept / Approach: Primary benefits are nutritional: nitrogen fixation (symbiotic and free-living), phosphate solubilization/mobilization, and production of growth-promoting substances. Secondary benefits accrue as enhanced root biomass and microbial by-products (e.g., polysaccharides) stabilize soil aggregates, improving porosity and reducing bulk density. Over seasons, these changes can raise the soil's effective water holding capacity by increasing meso- and micropores and improving infiltration and retention dynamics. Step-by-Step Solution: Identify direct effect: nutrient supply via fixation and solubilization (supports option a).Connect microbial activity and root exudates to aggregation and better structure (supports option b).Link improved structure to enhanced water storage and plant-available water (supports option c).Therefore, choose “All (a), (b) and (c).” Verification / Alternative check: Long-term trials with legume inoculation and phosphate-solubilizing bacteria report improved soil aggregate stability indices and water infiltration, alongside yield responses due to enhanced nutrient availability. Why Other Options Are Wrong: Picking only one aspect understates the multi-faceted benefits. “None of these” contradicts established agronomic outcomes. Common Pitfalls: Expecting immediate physical changes after a single application; structural and water-holding improvements emerge over time with continuous biological activity and organic matter inputs. Final Answer: All (a), (b) and (c).

Question 7

In ammonia synthesis (Haber–Bosch), plain iron is not used alone as the catalyst. What is the principal reason additional promoters are required rather than relying on iron by itself?

Accepted Answer

Introduction / Context: Ammonia synthesis uses a promoted iron catalyst (typically magnetite-derived iron with potassium, alumina, and calcium promoters). This question probes why unpromoted, plain iron is not used alone, highlighting the need for structural and electronic promoters to sustain activity under severe temperature–pressure conditions. Given Data / Assumptions: Operating window roughly 400–500 °C and high pressure. Reaction is exothermic; temperature control is essential. Catalyst must resist sintering and maintain active surface area. Concept / Approach: Plain iron tends to sinter and lose dispersion at elevated temperatures, especially above about 520 °C. Promoters such as K2O (electronic promoter) and Al2O3/CaO (structural promoters) stabilize the iron, inhibit crystal growth, and maintain active sites for N2 dissociation, thereby preserving activity over long runs. Step-by-Step Solution: Relate catalyst life to temperature: higher temperatures accelerate sintering of plain iron particles.Explain promoter roles: structural promoters inhibit sintering; alkali promoters enhance chemisorption and electron density.Link to practice: industrial catalysts are promoted magnetite-derived systems, not plain iron.Hence select the option citing rapid activity decline above about 520 °C. Verification / Alternative check: Historical and modern licensor data emphasize promoted iron formulations; deactivation by sintering at excessive temperature is a well-documented risk, managed by promoters and temperature control. Why Other Options Are Wrong: Decomposes ammonia under all conditions: iron can catalyze decomposition at high T, but this does not preclude its use; promoters manage performance. Oxidised above 500 °C: the converter atmosphere is highly reducing (H2-rich), not oxidising. None of these / iron liquid: iron is solid at these temperatures, and the main issue is sintering/structural stability. Common Pitfalls: Confusing catalyst decomposition of ammonia at very high temperature with normal synthesis conditions where equilibrium and kinetics are balanced using promoted catalysts. Final Answer: Its activity declines rapidly if heated above 520 °C due to sintering and structural changes

Question 8

In industrial urea manufacture (NH3 + CO2 → ammonium carbamate → urea), what is the effect of increasing the NH3/CO2 molar ratio in the synthesis section?

Accepted Answer

Introduction / Context: Urea plants first form ammonium carbamate from ammonia and carbon dioxide, then dehydrate it to urea. Manipulating the NH3/CO2 ratio affects equilibria, corrosion, and physical properties. Understanding how excess ammonia influences conversion is central to process optimization and energy balance in high-pressure synthesis loops. Given Data / Assumptions: Operating at high pressure and moderate temperature in the synthesis zone. Carbamate formation is favored by excess NH3. Downstream recovery strips/recycles unconverted NH3 and CO2. Concept / Approach: Raising the NH3/CO2 ratio drives formation of ammonium carbamate and subsequently favors the dehydration route to urea, increasing the single-pass conversion of CO2. Although excess ammonia is later recovered, within the synthesis section this ratio shift improves conversion and can also beneficially affect melt properties (e.g., reduce specific volume/viscosity), but the primary textbook takeaway is the conversion gain for CO2. Step-by-Step Solution: Recognize key equilibrium: NH3 + CO2 + NH3 ⇌ NH4NH2COO (carbamate).Leverage excess NH3 to push equilibrium rightward.Higher carbamate formation supports greater conversion of CO2 to urea in the reactor.Therefore, select “increased degree of conversion of CO2 to urea.” Verification / Alternative check: Process design literature cites higher NH3/CO2 improving CO2 conversion at the expense of larger recycle duties—managed by stripper/condenser sections. Why Other Options Are Wrong: Decreased NH3 conversion or overall yield: inconsistent with equilibrium shift toward carbamate/urea. Decreased specific volume only: while melt properties may change, the dominant effect tested is conversion increase. Ammonia-free operation: not applicable. Common Pitfalls: Ignoring the recycle loop: higher NH3/CO2 aids conversion but increases ammonia recovery load; the question focuses on conversion effect within synthesis. Final Answer: Increased degree of conversion of CO2 to urea

Question 9

Among common nitrogenous fertilisers, which product contains the highest percentage of nitrogen by mass?

Accepted Answer

Introduction / Context: Fertiliser selection depends on nutrient analysis. Nitrogen content (% N) varies widely among salts and determines application rates, transport economics, and suitability for specific crops and soils. This question checks recognition of typical nitrogen percentages for widely used products. Given Data / Assumptions: Typical analyses: urea ≈ 46% N; ammonium sulphate ≈ 21% N; CAN ≈ 26–27% N; calcium nitrate ≈ 15.5% N. Moisture and grade variations are small relative to these benchmark values. Concept / Approach: Compare standard guaranteed analyses. Urea has the highest nitrogen concentration among common solid fertilisers, making it the most nitrogen-dense option for many field applications where chloride sensitivity or volatilization risks are managed appropriately. Step-by-Step Solution: Recall urea contains two amide groups: high N mass fraction (~46%).Check competitors: CAN blends nitrate and ammonium nitrogen (~26–27%).Calcium nitrate and ammonium sulphate are significantly lower in % N.Therefore, select “Urea.” Verification / Alternative check: Label guarantees and agronomy references consistently list urea as the highest %N among mainstream nitrogen fertilisers. Why Other Options Are Wrong: Calcium nitrate: ~15.5% N, mainly valued for rapid nitrate availability. CAN: ~26–27% N, buffered with limestone/dolomite. Ammonium sulphate: ~21% N plus sulphur; beneficial where S is needed. Ammonium chloride: ~25–26% N and chloride-sensitive for some crops. Common Pitfalls: Confusing nutrient density with agronomic suitability; highest %N is not always the best choice due to volatilization and crop/soil constraints. Final Answer: Urea

Question 10

During wet-process ortho-phosphoric acid manufacture via hydrochloric acid leaching (forming CaCl2 in solution), which solvent is used to extract H3PO4 from the CaCl2 liquor?

Accepted Answer

Introduction / Context: In variants of the wet-process route employing hydrochloric acid to digest phosphate rock, calcium ends up as CaCl2 in solution alongside phosphoric acid. Solvent extraction can separate H3PO4 from CaCl2 brine. Recognising the appropriate solvent is a staple process-chemistry question. Given Data / Assumptions: Leaching medium: hydrochloric acid → CaCl2-rich liquor. Target: extract H3PO4 into an organic phase. Candidate solvents: lower alcohols and hydrocarbons. Concept / Approach: Isopropanol (iso propyl alcohol) forms extractable complexes/associates with phosphoric acid and is miscible in ways that permit phase separation with salt-laden aqueous phases; hydrocarbons like hexane/toluene are poor for polar acid extraction. Butyl alcohol may be used in some systems, but the canonical choice for this wet-process step is isopropanol. Step-by-Step Solution: Identify polar target: strong inorganic acid (H3PO4).Match solvent polarity and distribution behavior: isopropanol efficiently extracts H3PO4 away from CaCl2 brine.Reject non-polar solvents (toluene/hexane) which do not extract H3PO4 effectively.Select isopropanol as the standard answer. Verification / Alternative check: Process descriptions and exam keys cite isopropanol extraction for H3PO4 from CaCl2 solutions, enabling subsequent solvent recovery and acid concentration. Why Other Options Are Wrong: Butyl alcohol: less typical choice in this context. Toluene/hexane: insufficient polarity for strong acid extraction. Acetone: miscibility issues and not standard for this operation. Common Pitfalls: Overlooking the salt-out effect of CaCl2; appropriate polar solvent selection is critical for phase disengagement. Final Answer: Iso propyl alcohol (isopropanol)

Question 11

Which of the following is NOT classified as a plant micro-nutrient (trace element) for growth and metabolism?

Accepted Answer

Introduction / Context: Plant nutrients are grouped into macronutrients (required in large amounts) and micronutrients (required in trace quantities). Clear classification aids fertiliser formulation and diagnosis of deficiency symptoms in crops. Given Data / Assumptions: Typical micronutrients: B, Cl, Cu, Fe, Mn, Mo, Zn, Ni. Macronutrients: N, P, K, Ca, Mg, S, plus C, H, O from air/water. Concept / Approach: Carbon is a fundamental macronutrient obtained primarily from atmospheric CO2 through photosynthesis, not a trace element supplied as a micro-nutrient in fertilisers. In contrast, chlorine, iron, boron, and molybdenum are classic micro-nutrients supplied in small amounts through soil amendments or foliar feeds. Step-by-Step Solution: List canonical micronutrients and compare with the options.Recognise that carbon is a bulk element acquired from CO2 and organic matter, not a trace mineral fertiliser component.Therefore, select “Carbon.”Other listed elements (Cl, Fe, B, Mo) are established micro-nutrients. Verification / Alternative check: Agronomic texts and extension guides consistently classify C as a macronutrient, while B, Cl, Fe, and Mo are trace elements with defined deficiency/toxicity ranges in soils and plant tissues. Why Other Options Are Wrong: Chlorine, Iron, Boron, Molybdenum: all are required in small amounts and classed as micro-nutrients. Common Pitfalls: Confusing the term “micro-nutrient” with “minor importance”; micro-nutrients are critical despite low required quantities. Final Answer: Carbon

Question 12

Tricresyl phosphate (TCP), an important plasticiser, is produced by reacting cresylic acid (cresols) with which phosphorus reagent?

Accepted Answer

Introduction / Context: Tricresyl phosphate is an aryl phosphate ester widely used as a plasticiser and flame retardant. Understanding its synthesis route clarifies esterification chemistry of phenols with phosphorus halides and oxyhalides. Given Data / Assumptions: Reactant phenols: cresylic acid (o-, m-, p-cresols). Target ester: tricresyl phosphate (TCP). Common phosphorus reagents: POCl3, P2O5, phosphates. Concept / Approach: Phenolic hydroxyls react with phosphorus oxychloride (POCl3) to form triaryl phosphate esters, with HCl as a by-product, often in the presence of a base or catalyst. P2O5 is a dehydrating agent and does not directly furnish the triaryl phosphate ester in the same way; inorganic phosphates (ammonium/calcium) are unsuitable reagents for direct ester formation. Step-by-Step Solution: Identify desired functional group transformation: phenolic OH → aryl phosphate ester.Match reagent: POCl3 reacts via substitution forming P–OAr bonds and eliminating HCl.Exclude non-esterifying salts and dehydrants for this specific synthesis.Therefore, select phosphorus oxychloride (POCl3). Verification / Alternative check: Industrial routes to triaryl phosphates typically employ POCl3 or similar reagents (e.g., PCl3 with oxidation), confirming the choice. Why Other Options Are Wrong: P2O5: primarily a dehydrating agent; not the standard reagent for TCP synthesis. Ammonium/calcium phosphate: salts, not reactive acylating agents for ester formation. H3PO4 only: insufficient for direct triaryl phosphate esterification under practical conditions. Common Pitfalls: Assuming any phosphorus-containing compound can produce phosphate esters; reactive oxyhalides are required. Final Answer: Phosphorus oxychloride (POCl3)

Question 13

Crop nutrition focus: which primary nutrient is required in comparatively greater amounts for leafy crops to drive vigorous vegetative growth?

Accepted Answer

Introduction / Context: Different crop types emphasize different nutrient profiles. Leafy vegetables (e.g., spinach, lettuce) prioritize vegetative growth—leaf area and chlorophyll—over reproductive structures, so their fertilisation regimes often emphasize nitrogen compared with other macronutrients. Given Data / Assumptions: Leafy crops require strong canopy development. Nitrogen is a key component of amino acids and chlorophyll. Balanced nutrition remains important to avoid lodging or nitrate accumulation. Concept / Approach: Nitrogen application promotes cell division, protein synthesis, and chlorophyll formation, directly increasing leaf area index and biomass. While phosphorus supports rooting/energy transfer and potassium enhances water regulation and quality, nitrogen allocation is comparatively higher for rapid vegetative growth phases typical of leafy crops. Step-by-Step Solution: Identify growth target for leafy crops: leaves and stems.Map nutrient roles: N → vegetative vigor; P → roots/energy; K → quality and stress tolerance.Conclude nitrogen is required in greater proportion within a balanced plan.Select “Nitrogen.” Verification / Alternative check: Agronomy recommendations commonly show higher N rates for leafy vegetables, with staged split applications to minimize losses and quality issues. Why Other Options Are Wrong: Phosphorus and Potassium: essential but not the primary driver of leafy biomass. Carbon: obtained from CO2, not a fertiliser focus. Magnesium: key for chlorophyll but required in smaller amounts; not the main rate-limiting nutrient. Common Pitfalls: Over-applying nitrogen without considering environmental losses or nitrate accumulation; split applications and soil testing are best practice. Final Answer: Nitrogen

Question 14

The Montecatini (Fauser–Montecatini) process is widely associated with the manufacture of which fertiliser product?

Accepted Answer

Introduction / Context: Industrial fertiliser processes are often identified by licensor names or companies that pioneered them. Montecatini (later part of Montedison) and Fauser contributed important technology platforms in nitrogen fertilisers. This question tests recognition of the association between the Montecatini name and urea manufacture in classical process-technology curricula. Given Data / Assumptions: Historical Italian developments connected Montecatini/Fauser to nitrogen chemicals. Multiple fertilisers listed as distractors share overlapping chemistry. We seek the process most commonly linked to the Montecatini name in MCQ references. Concept / Approach: While modern plants frequently cite licensors such as Stamicarbon, Snamprogetti, and Toyo, exam texts attribute a widely used urea-manufacturing route to Montecatini/Fauser, emphasizing high-pressure synthesis of ammonium carbamate followed by dehydration and efficient recycle of unconverted reactants. Step-by-Step Solution: Identify Montecatini contributions to nitrogen fertiliser technology.Match to candidate products: urea is the textbook association.Exclude CAN and TSP, which have distinct, well-known process routes (AN neutralisation/prilling with limestone; phosphoric acid reaction with phosphate rock).Select “Urea.” Verification / Alternative check: Historical summaries list Montecatini among early leaders in urea process development alongside other licensors; MCQ answer keys typically map Montecatini to urea. Why Other Options Are Wrong: CAN: associated with blending/neutralisation of AN with limestone/dolomite. TSP: produced by reacting phosphate rock with phosphoric acid, not a Montecatini-branded process. Ammonium chloride: produced from by-product HCl–ammonia neutralisation, unrelated. Common Pitfalls: Confusing licensor names across different nitrogen processes; Montecatini is most closely tied to urea in many references. Final Answer: Urea

Question 15

Soils and fertilisers: identify the wrong statement among the following assertions.

Accepted Answer

Introduction / Context: Fertiliser facts often mix agronomy and industrial production knowledge. This item asks you to spot the single incorrect statement, requiring understanding of plant uptake forms, soil amendments, physical quality of fertilisers, and by-product origins in heavy industry. Given Data / Assumptions: Plant-available nitrogen forms are ammonium (NH4+) and nitrate (NO3−). Calcium sources (e.g., lime, gypsum-containing fertilisers) can ameliorate soil acidity. Granular fertilisers are controlled in size for flowability and lower retained moisture. By-product streams from coke ovens include ammonia. Concept / Approach: By-product ammonia from coke-oven gas is typically converted to ammonium sulphate, not ammonium nitrate. Therefore, the claim that ammonium nitrate fertiliser is a by-product of integrated steel plants is wrong. The other statements align with standard agronomic and process understanding. Step-by-Step Solution: Evaluate (a): correct—plants absorb N as NH4+ or NO3− before amino acid synthesis.Evaluate (b): correct—calcium inputs can raise pH or buffer acidity.Evaluate (c): correct—granular products target narrow size bands for application quality and lower moisture pickup.Evaluate (d): incorrect—coke ovens yield ammonium sulphate, not ammonium nitrate, as the classical by-product fertiliser.Evaluate (e): correct—balanced fertilisation is best practice. Verification / Alternative check: Steel-industry by-product fertiliser literature consistently references ammonium sulphate recovery from coke-oven gas scrubbers. Why Other Options Are Wrong: (a), (b), (c), (e) are correct statements; only (d) is wrong in standard references. Common Pitfalls: Confusing nitrate and sulphate salts of ammonia in by-product routes; nitric acid production is not integral to coke-oven operations. Final Answer: Ammonium nitrate fertiliser is obtained as a by-product in integrated steel plants with by-product coke ovens.

Question 16

In fertiliser terminology, “NPK” denotes a product containing nitrogen, phosphorus, and potassium together. In general usage, NPK refers to which broad type of fertiliser?

Accepted Answer

Introduction / Context: NPK-labelled products deliver the three primary macronutrients in one application. Depending on manufacturing, these may be physical blends (mixed fertilisers) or chemically combined granules (complex fertilisers). Many curricula and general usage equate the term “NPK” on a bag with a mixed fertiliser when contrasted against single-nutrient straights. Given Data / Assumptions: NPK indicates simultaneous presence of N, P, and K. Options provided do not include “complex,” focusing the classification on broad market categories. Question seeks common interpretation in basic fertiliser classification. Concept / Approach: In everyday trade language and introductory texts, NPK typically denotes a mixed fertiliser, meaning two or more straight fertilisers are blended to a specified analysis. Although some NPKs are complex (chemically combined), within the choices given here, “mixed” is the most appropriate classification differentiating it from single-nutrient products like “potassic.” Step-by-Step Solution: Identify that NPK includes all three macronutrients.Map to the available categories; “mixed” means multi-nutrient blend in general usage.Exclude “potassic,” which would indicate only potassium-bearing fertilisers.Therefore, select “mixed.” Verification / Alternative check: Fertiliser marketing and extension guides commonly refer to granular blends as “mixed NPKs,” reserving “straights” for single-nutrient products and “complex” for chemically combined multi-nutrient salts. Why Other Options Are Wrong: Potassic: single-nutrient K fertilisers only. Liquid or solid: physical state, not classification by nutrient composition. Micronutrient-only: NPK concerns macronutrients. Common Pitfalls: Assuming all NPKs are complex fertilisers; the question context and options point to the general “mixed” category. Final Answer: mixed

Question 17

In industrial ammonia (NH3) manufacture, when the hydrocarbon feed is fuel oil rather than natural gas, the make-up synthesis gas is chiefly generated by which process route?

Accepted Answer

Introduction / Context: Ammonia plants require a large stream of make-up synthesis gas containing hydrogen (and nitrogen after air addition). The route used to create this gas depends strongly on the hydrocarbon feed. Light feeds like natural gas are ideally handled by steam reforming. However, for heavier feeds such as fuel oil or vacuum residues, partial oxidation becomes the practical front-end. This question tests your ability to match the correct gas-generation technology to a heavy liquid feedstock. Given Data / Assumptions: Feedstock: heavy hydrocarbon (fuel oil), not methane-rich gas. Target: produce synthesis gas suitable for downstream shift, CO2 removal, methanation, and ammonia synthesis. Industrial constraints: coking tendency, heat balance, and reactor design for heavy feeds. Concept / Approach: Steam reforming excels with light hydrocarbons because they crack and mix with steam without severe coking at tube surfaces. Heavy liquids rapidly coke reformer tubes and burners, making conventional tubular steam reforming unsuitable. Partial oxidation (sub-stoichiometric combustion with oxygen) handles heavy feeds by generating a hot raw synthesis gas (H2, CO, CO2, H2O) in a refractory-lined vessel. The high temperature suppresses coke formation, and the downstream shift converts CO to more H2. Hence, for fuel oil, partial oxidation is the industry choice. Step-by-Step Solution: Identify feed as “heavy”—steam reforming is problematic due to coking.Recall partial oxidation uses O2 to partially burn the feed, yielding H2 + CO at very high temperature.Downstream: apply water–gas shift and CO2 removal to reach H2-rich gas for Haber–Bosch.Therefore, the correct selection is partial oxidation. Verification / Alternative check: Process lineups for oil-based ammonia plants specify POX (with an air separation unit for oxygen) rather than primary fired tubular steam reformers. Many designs may add a small steam addition (autothermal) but the core step remains partial oxidation for heavy feeds. Why Other Options Are Wrong: Steam reforming: ideal for methane/naphtha but not for fuel oil due to coking and heat transfer limits.Hydrocracking/hydrogenation: refining processes for upgrading oil, not for bulk synthesis-gas generation. Common Pitfalls: Assuming one universal front-end for all hydrocarbons; ignoring how feed quality dictates the gas-generation technology. Final Answer: Partial oxidation

Question 18

Urea plant front end: What is the composition and physical state of the fresh feed entering the high-pressure urea synthesis autoclave (reactor)?

Accepted Answer

Introduction / Context: Commercial urea synthesis operates at high pressure and uses two steps: formation of ammonium carbamate from NH3 and CO2, followed by its dehydration to urea and water. The entering feed composition and phase are deliberately chosen to favor carbamate formation and control corrosion and heat balance. Recognizing the correct feed state helps interpret process flow diagrams and operating procedures. Given Data / Assumptions: High-pressure synthesis loop operating typically at 130–180 bar and elevated temperature. NH3 is fed in excess to push equilibrium toward carbamate formation. CO2 is available from the upstream ammonia plant and is densified. Concept / Approach: Industry practice is to feed excess liquid ammonia together with liquefied (dense phase) carbon dioxide into the autoclave. At these pressures and moderate temperatures, CO2 can be handled in a liquid/dense phase, and ammonia is kept as a liquid as well. The excess of NH3 improves kinetics and conversion to carbamate and moderates corrosion. Therefore, “excess liquid ammonia and liquefied CO2” characterizes the fresh feed correctly. Step-by-Step Solution: Identify objective: efficient carbamate formation in HP section.Set NH3 to excess to drive equilibrium and stabilize operation.Feed CO2 in liquefied form under HP to facilitate mixing and reaction.Hence, choose “excess liquid ammonia and liquefied CO2.” Verification / Alternative check: Licensor documentation (e.g., Stamicarbon/Saipem concepts) illustrates liquid NH3 feed and dense CO2 feed lines merging prior to or inside the autoclave/reactor, with interstage heat recovery and HP carbamate condensers. Why Other Options Are Wrong: Compressed CO2 gas: technically CO2 can be gaseous, but plants densify it; the textbook answer emphasizes liquefied CO2 handling.Options with “compressed ammonia gas” misrepresent the usual NH3 liquid feed regime in HP urea synthesis. Common Pitfalls: Confusing the downstream stripper/recycle sections with the HP feed point; overlooking why excess NH3 is used (conversion and material compatibility). Final Answer: Excess liquid ammonia and liquefied CO2

Question 19

Wet-process phosphoric acid strength: Approximately what percentage (by mass) of P2O5 does typical wet-process phosphoric acid contain?

Accepted Answer

Introduction / Context: Wet-process phosphoric acid is produced by digesting phosphate rock with sulfuric acid. The resulting acid strength is commonly expressed as percent P2O5, a conventional industry metric. Knowing the typical concentration is essential for downstream uses like manufacture of triple superphosphate, nitrophosphate, and numerous NPK fertilizers. Given Data / Assumptions: Process: sulfuric acid attack on phosphate rock followed by filtration of gypsum. We refer to the typical, commercial wet acid product before further concentration. Concentration is expressed as percent P2O5 equivalent. Concept / Approach: Standard wet-process acid streams usually fall around 26–32% P2O5, often rounded to “about 30% P2O5.” This strength balances filtration performance, corrosion, and energy costs. Stronger acid can be produced by evaporative concentration, but the base wet acid commonly referenced in fertilizer technology texts is near 30% P2O5. Step-by-Step Solution: Recall wet-process acid typical range ≈ 26–32% P2O5.Identify the nearest option representing the conventional value.Select “30.”Note: higher strengths (40+% P2O5) require additional concentration steps. Verification / Alternative check: Plant data sheets and fertilizer handbooks frequently cite base wet acid near 28–30% P2O5 before concentrators or hemihydrate processes are applied. Why Other Options Are Wrong: 10: too dilute for standard trade acid.50 or 70: represent concentrated or merchant-grade acid after additional evaporation, not the base wet-process output. Common Pitfalls: Mixing P2O5 percentages with H3PO4 wt%—they are related but not numerically identical; always check the basis used in a question. Final Answer: 30

Question 20

Hydrogen from coke-oven gas (as practiced historically at Rourkela): which commercial separation method is used at scale to recover H2 from the coke-oven gas stream?

Accepted Answer

Introduction / Context: Coke-oven gas is a by-product gas containing hydrogen, methane, CO, nitrogen, and other components. In integrated steel-fertilizer complexes, part of the hydrogen requirement for ammonia can be met by recovering H2 from this gas. Understanding the practical, scalable separation method is critical for appreciating legacy hydrogen sources in fertilizer plants. Given Data / Assumptions: Coke-oven gas includes H2 along with permanent gases and light hydrocarbons. Recovery is on a commercial scale, not laboratory-scale polishing. Rourkela is cited as a historical example in the fertilizer context. Concept / Approach: Cryogenic separation exploits differing condensation/boiling points to separate hydrogen from heavier gases at very low temperatures. On large streams like coke-oven gas, cryogenic plants are industrially proven. Alternatives listed here are unsuitable at scale: palladium adsorption selectively allows H2 permeation but is expensive and used for ultra-pure polishing, not bulk recovery. Amine solutions (ethanolamine) remove acid gases like CO2 and H2S, not hydrogen; pyrogallol solutions absorb oxygen, not a route to bulk H2 recovery. Step-by-Step Solution: Identify bulk separation requirement: large throughput H2 recovery.Select technology that scales: cryogenic fractionation of light gas mixtures.Exclude chemisorption/absorption routes that target CO2/O2 rather than H2.Conclude cryogenic operations are the correct industrial method. Verification / Alternative check: Historic flowsheets show cryogenic units paired with purification (e.g., small methanation/PSA polishing) in steel-fertilizer complexes using coke-oven gas hydrogen. Why Other Options Are Wrong: Palladium adsorption: niche, high cost, suited to purification not bulk separation.Amine/pyrogallol absorption: remove acid gases or oxygen, not hydrogen. Common Pitfalls: Confusing H2 purification with H2 recovery; mixing up acid gas scrubbing with hydrogen separation. Final Answer: Cryogenic operations (low-temperature cooling)

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