Industrial Chemical Processes - Domande da esame con risposta

MTBE

The Arco process produces mainly tert-butyl alcohol and propylene oxide, with a

mechanism involving two reactions:

●​ the first reaction (peroxidation) where isobutane and pure oxygen react to form

tert-butyl alcohol and tertiary butyl hydroperoxide

liquid phase

➢​ 120-140°C

➢​ 25-35 bar

➢​ no catalyst

➢​

●​ the second reaction (epoxidation) where propylene and tertiary butyl hydroperoxide

react to form propylene oxide and tert butyl alcohol

liquid phase

➢​ lower temperature

➢​ higher pressure

➢​ Molybdenum naphthenate catalyst

➢​

A second group of reactions can be carried out in order to obtain methyl tert-butyl ether

(MTBE):

●​ dehydration of tertiary butyl alcohol to obtain isobutylene

●​ addition of methanol to obtain MTBE: 30

1.​ isobutane and pure oxygen react in the peroxidation reactor to form tert-butyl

alcohol and tertiary butyl hydroperoxide

2.​ in a vent column the unreacted isobutane is recovered from the top

3.​ after injecting some Molybdenum catalyst and propylene inside the mixture, it enters

the epoxidation reactor where propylene and tertiary butyl hydroperoxide react to

form tert butyl alcohol and propylene oxide

4.​ in a lights scrubber the unreacted propylene is recovered from the top

5.​ in the polyethylene oxide column the PO is recovered from the top

6.​ in the tert-butyl alcohol light column some light compounds are separated from the

top

7.​ in the tert-butyl alcohol column some heavy compounds and the catalyst are separated

from the bottom

8.​ from the top an aqueous mixture of tert-butyl alcohol is recovered

9.​ a part of this mixture can be processed in a water elimination (dehydration) reactor,

with a consequent drying and purification to obtain isobutene (or isobutylene)

10.​isobutene reacts with a feed of methanol to form methyl tert butyl ether (MTBE)

71. Synthesis of propylene oxide through propylene epoxidation via

ethylbenzene. Describe the process (with a sketch) with reactions,

catalyst, thermodynamics, process conditions and type of reactor

(explaining the choice). 31

●​ as for the epoxidation via isobutane or cumene, one compound is peroxidated: EB

reacts with oxygen to become EB hydroperoxide

without catalyst

➢​ 120°C

➢​ quite high pressure to maintain liquid phase

➢​ 3 reactors to obtain high residence time (for slow O solubilization)

➢​ 2

cooled by the partial vaporization of the liquid phase

➢​

●​ epoxidation → the hydroperoxide reacts with propylene to obtain propylene oxide and

the original compound alcohol (in this case methyl benzyl alcohol)

with molybdenum catalyst (the same for other epoxidation of PO)

➢​ similar conditions to maintain liquid phase

➢​ 4 reactors with interstage cooling

➢​

●​ methyl benzyl alcohol can be dehydrated to obtain styrene

Shell process produces propylene oxide with, again, two reaction:

●​ a first peroxidation where ethylbenzene reacts with oxygen to form ethylbenzene

hydroperoxide

liquid phase

➢​ 125-155°C

➢​ 10-15 bar

➢​ no catalyst

➢​ we can use air (instead of pure oxygen)

➢​ 1 hour of residence time to allow the solubilization of oxygen (slow process)

➢​

●​ an epoxidation in which the ethylbenzene hydroperoxide reacts with propylene to

obtain propylene oxide and methyl benzyl alcohol

100-130°C

➢​ 35 bar (higher pressure)

➢​ catalyst based on Molybdenum or Titanium

➢​ liquid phase

➢​

A third reaction (dehydration) is carried out to obtain styrene from methyl benzyl alcohol in

presence of an acid catalyst (usually TiO on alumina):

2 32

The plant of shell process consists in:

1.​ a feed of ethylbenzene and air enters the three peroxidation reactors in series

2.​ a fraction of the liquid phase is vaporized to consume the heat generated from the

reaction

3.​ part of the generated gas phase is vented to avoid accumulation of inserts

4.​ the other part is condensed and recycled in the reactors

5.​ catalyst (based on Molybdenum or Titanium) is added to the obtained mixture

6.​ the mixture in which we add propylene (at least 92% pure) enters the epoxidation

reactors in series (4)

7.​ the reactors are punctuated [intervallati] by intermediate heat exchangers to

decrease the temperature

8.​ two de-propanizers (recycle columns) in series work under pressure to recover

excess propylene which is recycled to the feed of the epoxidation reactors 33

9.​ the mixture enters the crude propylene oxide column where PO is separated from the

top and, with further distillation, we obtain pure PO

10.​the residue of the PO column enters the ethylbenzene recycle column where

ethylbenzene is recovered from the top and recycled at the beginning of the process

11.​the catalyst (TiO on alumina) is added to the residue of the EB column

2

12.​the mixture enters the dehydration reactor where the dehydration of the methyl benzyl

alcohol occurs, obtaining styrene

13.​a water separator divide the water stream from the main stream

14.​with other distillation is possible to separate the styrene from the catalyst which is

recycled back

72. Synthesis of propylene oxide through propylene epoxidation via

cumene. Describe the process (with a sketch) with reactions, catalyst,

thermodynamics, process conditions and type of reactor (explaining

the choice).

●​ as for the epoxidation via isobutane or EB, one compound is peroxidated: cumene

reacts with oxygen to become cumene hydroperoxide

●​ epoxidation → the hydroperoxide reacts with propylene to obtain propylene oxide and

the original compound alcohol (in this case cumene alcohol)

⍺-methyl

●​ cumene alcohol can be dehydrated to styrene which can be hydrogenated to

cumene, which is recycled

The Sumitomo process consists in the following steps:

●​ oxidation of isopropylbenzene (cumene) to obtain cumene hydroperoxide

●​ epoxidation where cumene hydroperoxide and propylene react to obtain cumene

alcohol and propylene oxide

●​ hydrogenation of cumene alcohol to obtain cumene again via -methylstyrene

α 34

In this way, cumene net consumption is zero, since the process will produce the same amount

of cumene that is consumed.

Obviously, makeup is needed, but its amount is much smaller than other feed flowrates.

The process simply consists in:

1.​ a feed of air and make-up cumene, together with the recycled cumene, enters the

oxidation reactor where cumene hydroperoxide is produced

2.​ the stream enters the epoxidation reactor where it reacts with propylene to obtain

cumene alcohol and propylene oxide

3.​ the mixture enters a distillation column where propylene oxide is recovered as

distillate from the top

4.​ the cumene alcohol is retrieved from the bottom

5.​ cumene alcohol enters the dehydration reactor where, with the elimination of a water

molecule, we obtain alpha methylstyrene

6.​ alpha methylstyrene is hydrogenated to obtain cumene

7.​ cumene is recycled back to the beginning

73. Synthesis of propylene oxide through the HPPO process. Describe

the process (with a sketch) with reactions, catalyst, thermodynamics,

process conditions and type of reactor (explaining the choice).

●​ propylene reacts with H O to obtain PO and water

2 2

weakly exothermic → fixed bed reactor

➢​ as many processes that use H O is catalyzed by TS-1 (zeolite with Ti instead

➢​ 2 2

of Al)

in water methanol mixture

➢​ quite high pressure

➢​ 35

low temperature

➢​

HPPO process consists in a single step production where propylene and hydrogen peroxide

react to form propylene oxide and water, in presence of a TS-1 catalyst (titanium silicate).

TS-1 is a highly versatile zeolite that has a unique catalytic performance in oxidation

reactions involving H O as an oxidant and it’s also very selective to epoxidation of alkenes

2 2

(like in this case).

The reaction takes place:

●​ in a water/methanol mixture

●​ below 100°C to increase selectivity

●​ at 30 bar

●​ in a fixed bed reactor

The plant consists in:

1.​ a feed of:

●​ propylene (both make-up) and recycle

●​ hydrogen peroxide H O

2 2

●​ methanol

2.​ a fixed bed reactor based on TS-1 catalyst in which the reaction takes place and a

cooling system that absorb the heat released from the reaction

3.​ a laminated valve reduce the pressure at slightly above atmospheric pressure, making

a part of the stream to vaporize

4.​ in a flash drum the two phase are separated

5.​ from the top of the flash we retrieve a gas phase rich in propylene which is

compressed and partly condensed

6.​ the two phases that have been created in the condenser are separated in a purge gas

system where we retrieve liquid propylene from the bottom which is recycled back to

the reactor 36

7.​ the gas phase is vented

8.​ from the bottom of the flash we obtain a mixture of propylene oxide and dissolved

propylene with methanol and water

9.​ the mixture of hydrocarbons is separated from the methanol and water with a

distillation

10.​further distillation separates the propylene oxide from propylene, obtaining almost

pure PO

74. Synthesis of propylene glycol. Describe the process (with a sketch)

with reactions, catalyst, thermodynamics, process conditions and type

of reactor (explaining the choice).

●​ as for the production of EG:

PO reacts with water to give PG and other poli-PG

➢​ without catalyst

➢​ high amount of water to limit poli-PG

➢​ 120°C

➢​ light pressure

➢​

Propylene glycol is produced thanks to the following reaction:

The reaction is carried out:

●​ without a catalyst

●​ at 120-190°C

●​ at 21 atm

From the reaction we obtain also some di or tri-propylene glycol, which are separated in a

vacuum distillation column.

The plant consists in:

1.​ a feed of propylene oxide and water

2.​ a reactor in which the reaction takes place 37

3.​ the stream goes through a multi-effect evaporator, that can be highly energy efficient:

the steam which is used in the first evaporator is used in the following evaporators at a

lower temperature

4.​ from the evaporators we collect steam

5.​ the traces of water are eliminated in a drying column using sulfuric acid (H SO )

2 4

6.​ with further distillations it’s possible to separate the mono propylene glycol (as the

lightest component) and the other glycols which are heavier

74. Synthesis of acetaldehyde through single stage Wacker process.

Describe the process (with a sketch) with reactions, catalyst,

thermodynamics, process conditions and type of reactor (explaining

the choice).

●​ acetaldehyde → react