GATE Chemical Engineering Chemical Technology Syllabus

Chemical Technology syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Chemical Technology in GATE Chemical Engineering, not a summary of it.

1. 1

   Inorganic chemical industries

   3 topics

   • Sulfuric acid
   • Phosphoric acid
   • Chlor-alkali industry
2. 2

   Fertilizers

   4 topics

   • Ammonia
   • Urea
   • SSP (Single Super Phosphate)
   • TSP (Triple Super Phosphate)
3. 3

   Natural products industries

   3 topics

   • Pulp and Paper
   • Sugar
   • Oil and Fats
4. 4

   Petroleum refining and petrochemicals

   overview

   Examined as a single unit within Chemical Technology — no further topic split in the official outline.

5. 5

   Polymerization industries

   4 topics

   • Polyethylene
   • Polypropylene
   • PVC (Polyvinyl chloride)
   • Polyester synthetic fibers

Chemical Technology flashcards for GATE Chemical Engineering

20 of 49 cards from the Chemical Technology deck — real questions with worked answers.

1. Which industrial process is used for the modern manufacture of sulfuric acid, and what is its key catalytic step?

   The Contact process. Its key step is the catalytic oxidation of $\ce{SO2}$ to $\ce{SO3}$ over a vanadium pentoxide ($\ce{V2O5}$) catalyst: $\ce{2SO2 + O2 ->[V2O5] 2SO3}$.

2. In the Contact process, why is $\ce{SO3}$ absorbed in concentrated sulfuric acid to form oleum rather than directly in water?

   Absorbing $\ce{SO3}$ directly in water is highly exothermic and produces a dense sulfuric acid mist (fog) that is hard to condense. Instead $\ce{SO3}$ is absorbed in $\approx 98\%$ $\ce{H2SO4}$ to form oleum: $\ce{SO3 + H2SO4 -> H2S2O7}$, which is then diluted.

3. Write the reaction by which oleum is converted to sulfuric acid, and give the formula of oleum (pyrosulfuric acid).

   Oleum is $\ce{H2S2O7}$ (pyrosulfuric/disulfuric acid). $\ce{H2S2O7 + H2O -> 2H2SO4}$.

4. What does a Double Contact Double Absorption (DCDA) sulfuric acid plant achieve compared to a single absorption plant?

   DCDA shifts the $\ce{SO2 -> SO3}$ equilibrium forward by removing $\ce{SO3}$ in an intermediate absorber before a second conversion pass, raising overall conversion to about $99.7\%$ and sharply cutting $\ce{SO2}$ emissions.

5. What is the optimum catalyst inlet temperature range for the $\ce{SO2}$ converter in the Contact process, and why not higher?

   About $400$–$450\,^{\circ}\mathrm{C}$. The oxidation is exothermic, so although higher temperature speeds the rate, it lowers the equilibrium conversion (Le Chatelier); below $\sim 400\,^{\circ}\mathrm{C}$ the $\ce{V2O5}$ catalyst becomes inactive.

6. Name the two main commercial routes for manufacturing phosphoric acid and state which gives higher purity.

   The wet process (acidulation of phosphate rock with $\ce{H2SO4}$) and the thermal/furnace process (combustion of elemental phosphorus). The thermal process gives higher-purity (food-grade) acid; the wet process is cheaper and dominant for fertilizers.

7. Write the principal reaction of the wet process for phosphoric acid and name the solid by-product.

   $\ce{Ca5(PO4)3F + 5H2SO4 + 10H2O -> 3H3PO4 + 5CaSO4.2H2O + HF}$. The solid by-product is gypsum (phosphogypsum), $\ce{CaSO4.2H2O}$.

8. In the thermal (furnace) process for phosphoric acid, what two reactions occur after burning phosphorus?

   Combustion: $\ce{P4 + 5O2 -> P4O10}$, then hydration: $\ce{P4O10 + 6H2O -> 4H3PO4}$.

9. What are the three principal products of the chlor-alkali industry, and from what feed are they made?

   Chlorine ($\ce{Cl2}$), caustic soda / sodium hydroxide ($\ce{NaOH}$), and hydrogen ($\ce{H2}$), produced by electrolysis of aqueous sodium chloride (brine): $\ce{2NaCl + 2H2O -> 2NaOH + Cl2 + H2}$.

10. In a chlor-alkali cell, write the electrode half-reactions for chlorine and hydrogen evolution.

    Anode: $\ce{2Cl- -> Cl2 + 2e-}$. Cathode: $\ce{2H2O + 2e- -> H2 + 2OH-}$.

11. Compare the three chlor-alkali cell technologies (mercury, diaphragm, membrane) on product purity and environmental concern.

    Mercury cell: very pure, concentrated $\ce{NaOH}$ but uses toxic mercury. Diaphragm cell: lower NaOH purity (contains $\ce{NaCl}$), uses asbestos. Membrane cell: high-purity NaOH, lowest energy and most environmentally favorable; the modern standard.

12. Why must the anode and cathode compartments in a membrane chlor-alkali cell be separated?

    To prevent $\ce{Cl2}$ and $\ce{NaOH/H2}$ from mixing (avoiding back-reaction to form $\ce{NaOCl}$ and explosive $\ce{H2}/\ce{Cl2}$ mixtures). The cation-exchange membrane lets only $\ce{Na+}$ pass to the cathode while blocking $\ce{Cl-}$ and $\ce{OH-}$.

13. Which process synthesizes ammonia industrially, and what are its typical operating temperature and pressure?

    The Haber–Bosch process: $\ce{N2 + 3H2 <=> 2NH3}$, run at roughly $400$–$500\,^{\circ}\mathrm{C}$ and $150$–$300\ \text{atm}$ over a promoted iron catalyst.

14. Write the ammonia synthesis reaction with its enthalpy sign, and explain the choice of high pressure and moderate temperature.

    $\ce{N2 + 3H2 <=> 2NH3},\ \Delta H < 0$ (exothermic). High pressure favors the side with fewer moles (forward), increasing yield; temperature is a compromise — high enough for an acceptable rate but not so high that the exothermic equilibrium yield collapses.

15. What catalyst is used in the Haber process and what are its common promoters?

    Finely divided iron ($\ce{Fe}$, from magnetite) promoted with $\ce{K2O}$ (electronic promoter) and $\ce{Al2O3}$ (structural promoter that prevents sintering).

16. What is the principal industrial route for producing the hydrogen feed for ammonia synthesis?

    Steam reforming of natural gas (methane): $\ce{CH4 + H2O -> CO + 3H2}$, followed by the water–gas shift reaction $\ce{CO + H2O -> CO2 + H2}$.

17. Write the two-step reaction scheme for the industrial synthesis of urea from ammonia and carbon dioxide.

    Step 1 (carbamate formation, fast, exothermic): $\ce{2NH3 + CO2 -> NH2COONH4}$. Step 2 (dehydration, slow, endothermic): $\ce{NH2COONH4 -> NH2CONH2 + H2O}$.

18. Give the molecular formula and nitrogen content of urea, and state why it is a preferred nitrogen fertilizer.

    Urea is $\ce{NH2CONH2}$ (molar mass $60\ \mathrm{g/mol}$) with about $46\%$ nitrogen by mass — the highest N content of any common solid nitrogenous fertilizer, making it economical to transport per unit N.

19. In urea manufacture, what is the role of the recycle (stripping) section, e.g. in total-recycle or stripping processes?

    Because urea conversion per pass is incomplete (limited by carbamate equilibrium), unconverted $\ce{NH3}$ and $\ce{CO2}$ (as carbamate) are decomposed/stripped and recycled back to the reactor to improve overall conversion and reduce raw-material loss.

20. What is biuret in urea production, why is it undesirable, and how is its formation minimized?

    Biuret, $\ce{NH2CONHCONH2}$, forms by condensation of two urea molecules ($\ce{2 urea -> biuret + NH3}$) at high temperature. It is toxic to crops, so it is kept low (typically $<1\%$) by limiting temperature and residence time during concentration/prilling.

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