Industrial Process Lecture Notes (Lecture 5: Gas Experiment / Full Organic Experiment Workflow)

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Gas Experiment Workflow

Apparatus Connection Method

“Three-stage connection”: preparation $\rightarrow$ purification $\rightarrow$ drying

(purge with gas $\rightarrow$) preparation ($\rightarrow$ purification $\rightarrow$ drying) $\rightarrow$ reaction $\rightarrow$ collection / testing $\rightarrow$ protection $\rightarrow$ tail gas treatment

Connection order: lay out the apparatus first, then the connectors

• A. Preparation
• B. Purification
• C. Drying
• D. Reaction
• E. Collection
• F. Protection
• G. Tail gas treatment

Common Operations and Their Purpose

Gas Purging

$N_2$ / $CO_2$ / air ($O_2,CO_2,H_2O,...$)

• Before the reaction: purge out all air (common in reducing agent preparation experiments)
• After the reaction: blow all the generated gas into (some apparatus) to fully absorb it, reducing error (common in quantitative experiments)
• Before disassembling the apparatus: blow all the generated gas into (some apparatus) to fully absorb it, preventing air pollution (common in preparation experiments)

Heating Setup

Heating methods: water bath ($\le$ 100°C), oil bath / sand bath ($\gt$ 100°C)

Using an alcohol lamp:

• Thermal reduction reactions ($H_2$ / $CO$ / $NH_3$): pass in gas, verify purity, light the lamp, extinguish the lamp, remove the gas supply after cooling, then weigh
• When a catalyst is involved ($N_2+H_2$ / $SO_2+O_2$ / $NH_3+O_2$ / $NH_3+NO_x$): heat first (preheat)
• Gas collection by water displacement: remove the delivery tube first, then the alcohol lamp (purpose: prevent suck-back)

Protective Setup

Prevents $H_2O$ / $O_2(g)$ / $CO_2(g)$ (from the air or subsequent apparatus) from entering (some apparatus), which would cause product hydrolysis / oxidation / error (in quantitative experiments)

Tail Gas Treatment

Absorbs excess (some reagent), preventing air pollution reagent / preventing suck-back apparatus

Apparatus Improvements

Missing tail gas treatment / purification / protection / suck-back prevention / wide mouth (to prevent clogging)

Add, at (some location), a (some vessel) containing (some reagent)

Organic Experiment Workflow

Experimental Apparatus (three-necked flask, condenser, separating funnel, water separator)

Water Separator

• Control the stopcock so the water level stays just below the side-arm opening
• Favours reflux of the organic layer, improving raw material utilization
• Sign that the reaction has ended: the water volume in the separator stops increasing

Buchner Funnel (vacuum filtration setup)

Advantage: speeds up filtration, preventing product degradation from prolonged air exposure

Workflow

Setup $\rightarrow$ charging $\rightarrow$ reaction $\rightarrow$ cooling $\rightarrow$ separation $\rightarrow$ washing $\rightarrow$ evaluation

1. Setup: leak check / seal check / connect water to the condenser (in from the bottom, out from the top) / purge air…
2. Charging: boiling stones / porcelain chips (if forgotten: add after cooling) charging order for esterification: ethyl acetate: (1) ethanol, (2) concentrated $H_2SO_4$, (3) acetic acid (dropwise); others: (1) n-butanol + acetic acid, (2) add concentrated $H_2SO_4$ dropwise
3. Reaction: water bath ($\lt$ 100 °C), maintain temperature (fast reaction rate, product distills off promptly), reflux (improves raw material utilization), control rate ($\Delta H\lt 0$ to prevent side reactions), stir (speeds up the reaction, prevents localized overheating)
4. Cooling: prevent oxidation / hydrolysis / volatilization (seal the system)…
5. Separation: extraction / back-extraction, distillation (info needed: solubility / melting-boiling point), filtration / vacuum filtration, recrystallization ($s\rightarrow aq\rightarrow s$)
6. Washing: water $\rightarrow$ salt / base $\rightarrow$ water, an unfamiliar solvent, drying
7. Evaluation: calculate yield / judge side reactions

Difficult Operations

Washing

1. Water wash: removes water-soluble impurities (e.g. $H_2SO_4$, ethanol, acetic acid)
2. Salt / base wash: removes acidic impurities remaining in the product (reagents: $NaOH,Na_2CO_3,NaHCO_3$, mainly $Na_2CO_3$) or converts the product into a soluble salt that moves into the aqueous phase (back-extraction, e.g. acetylsalicylic acid)
3. Re-wash with water: removes the (reagent) left over from the previous step / $Na^+$ salts (some products need acidification) / wash with a solvent such as ethanol (helps dissolve impurities)

Temperature Control

1. Prevents excessive temperature from causing product decomposition / volatilization / oxidation / side reactions
2. Distills off the generated (some product) promptly (may help drive the equilibrium forward)
3. Prevents bumping, side reactions, suck-back, acid fumes, etc.

Experimental Evaluation

Yield Calculation

$\eta=\frac{m_{real}}{m_{theorem}}\times 100\%$; the actual value $m_{real}$ is given in the problem, and the theoretical value $m_{theorem}$ must be calculated

Side Reactions

Dehydration reaction: preparing cyclohexene from cyclohexanol dehydration

Substitution reaction: preparing o-nitrotoluene from toluene

Ways to Improve Utilization

• Reflux
• Distilling off
• For an $A+B$ reaction, add excess $A$ to drive the equilibrium forward and carry $B$ along with it
• Use a water separator
• Catalyst selectivity