7/25/2019 Reaction Engineering and Catalysis

1/3

Available online at www.sciencedirect.com

Reaction engineering and catalysisEditorial

overviewTheodore T

TsotsisCurrent Opinion in Chemical Engineering 2012,

1:269271

For a complete overview see the Issue

Available online 20th July 2012

2211-3398/$ see front matter, # 2012 Elsevier Ltd.

All rights reserved.

http://dx.doi.org/10.1016/j.coche.2012.07.001

Theodore T Tsotsis

Robert E. Vivian Professor of EnergyResources, Mork Family Department ofChemical Engineering and Materials Science,

University

of

Southern

California,

UniversityPark, Los Angles, CA 90089-1211, USAe-mail: tsotsis@usc.edu

Theodore T. Tsotsis is the Robert E. VivianProfessor of Energy Resources at theUniversity of Southern California. His currentresearch interests are in the areas of reactionengineering, reactor design, membrane andadsorbent preparation/characterization, andthe modelling of transport and reaction incomplex porous media.

Reaction

and

Reactor

Engineering

are

among

the

oldest

disciplines

in

the

field of Chemical

Engineering

and

have

played

a pivotal

role

in

the

de-

velopment of

manufacturing,

and

the

chemical

and

petrochemical

indus-

tries. Despite

their

maturity,

however,

they

continue

to

be

the

arena

of

many

lively and intensive R&D activities. This themed issue of Current Opinionin Chemical

Engineering

contains

ten

short

review

articles

that

provide

only

a small sampling of the so many new and exciting things which are currently

taking place

in

this

all

important

area

of

Chemical

Engineering.

This

write-up attempts

to

provide

a

short

overview

of

the

diverse

mix

of

interesting

topics which

are

covered

by

these

review

papers.

Adesinas paper focuses on CO2(dry as it is better known) reforming of light

hydrocarbons (C1C4)

for

syngas

production,

which

has

attracted

consider-

able recent

attention

because

of

concerns

about

global

warming,

and

the

obvious benefit

of

being

able

to

utilize

CO2. The process also has the added

flexibility of

producing

syngas

with

a H2:CO ratio more amenable to further

downstream use

in

FischerTropsch and methanol syntheses. Unfortu-

nately, catalyst

coking

is

a

problem

with

dry

reforming,

and

thus

substantial

recent research activities are focusing on efforts to overcome this problem.As detailed

in

the

paper,

they

include

the

development

of

carbon-tolerant

catalysts, adding

an

oxidant

to

the

reforming

mixture,

the

distributed

feeding of

reactants,

and

unsteady-state

reactor

operation.

Adesina

briefly

reviews such

past

efforts.

He

then

proceeds

to

describe

efforts

by

his

group

in which

CO2is used as co-feed of a forced periodically operated reformer in

order to

minimize

coking

even

at

the

low

steam

to

carbon

ratio

of 1. His

studies have also revealed that a basic oxide supported Ni-containingcatalyst promoted

with

alkaline-earth

or

rare-earth

metals

performs

as

well

or better than expensive noble metals.

Nature-inspired chemical engineering (NICE), which studies the funda-

mental mechanisms

determining

a

desired

property

or

function

in

nature,

particularly in

biology,

and

attempts

to

apply

the

same

mechanism/prin-ciples in

the

context

of

chemical

engineering

is

the

focus

of

Coppens

paper.

He notes

that

application

of

biological

mechanisms

in

reaction

engineering

requires substantial

adaptations,

because

the

relevant

time

scales

and

available building

elements

are

different.

For

example,

in

reaction

engin-

eering one

is

able

to

manipulate

parameters

such

as

temperature

and

pressure, which

are

much

less

tunable

in

biological

systems.

Coppens

likens

NICE to

an

abstract

portrait

which

preserves

essential

aspects

of

the

subject, without

being

its

literal

representation,

emphasizing

key

features

that serve

a

desired

objective.

According

to

him,

NICE

aims

to

innovate

guidedby nature but without mimicking it. Coppens uses three examples toillustrate

how

biological

mechanisms

can

be

adapted

to

guide

innovative

www.sciencedirect.com Current Opinion in Chemical Engineering 2012, 1:269271

http://www.sciencedirect.com/science/journal/22113398/1/3http://dx.doi.org/10.1016/j.coche.2012.07.001mailto:tsotsis@usc.eduhttp://dx.doi.org/10.1016/j.coche.2012.03.001http://dx.doi.org/10.1016/j.coche.2012.03.001http://dx.doi.org/10.1016/j.coche.2012.03.002http://dx.doi.org/10.1016/j.coche.2012.03.002http://dx.doi.org/10.1016/j.coche.2012.03.002http://dx.doi.org/10.1016/j.coche.2012.03.001mailto:tsotsis@usc.eduhttp://dx.doi.org/10.1016/j.coche.2012.07.001http://www.sciencedirect.com/science/journal/22113398/1/3

7/25/2019 Reaction Engineering and Catalysis

2/3

solutions

to

technical

challenges

in

Reaction

and

ReactorEngineering.

They

include:

first,

the

use

of

optimized,

hierarchical

networks to bridge scales, and to minimize

transport limitations,

and

to

realize efficient,

scalable

solutions; second, careful balancing offorces at one or more

scales

to

achieve

superior

reactor

performance,

a

keyexample being

enzyme

nano-confinement;

third,

emer-

gence of complex

functions

from

simple

components,

using

dynamics

as

an

organizing

mechanism. Coppens

believes that

NICE

complements

the

ongoing

revolution

in bio-inspired

chemistry

and

materials

synthesis,

which

already finds

applications

in

enzyme-mimics

and

anti-

body-mimics

for

catalysis,

and

in

artificial

photosynthesis.

Direct

solid

fuel

use

for

electricity

production

using

chemical looping

combustion

(CLC)

is

discussed

in

the

paper

by

Fan

and

coworkers.

According

to

the

authors,

this novel

approach

shows

the

potential

to

have

higher

energy efficiency than competing technologies in a car-

bon-constrained scenario, whereby CO2 must be separ-

ated and sequestered. The paper first focuses on the

selection

of

oxygen

carriers

via

thermodynamic

analysis,with iron-based

materials

being

considered

as

a particu-

larly promising

candidate.

Then

various

CLC

reactor

configurations

are

compared,

based

on

the

modes

of

reducer design and operation, and are shown to signifi-

cantly

impact

the

overall

system

performance.

The

authors conclude,

based

on a

review

of

recent

experimen-

tal studies

by

their

group and

others,

that

direct

solid

fuel

CLC is

a

promising

technology,

and

they

identify

optimal

reducer design

(to

provide

effective

gassolid contact),

and favorable

thermodynamics

of

the

oxygen

carrier

as

the important challenges for the commercial scale appli-cation of

the

process.

With

renewed

focus

on

the

use

of

energy

sources

other

than crude,

such

as

coal

and

biomass,

there

has

been

in

recent years

quite

a bit

of

new

interest

in

the

FischerTropsch

Synthesis

(FTS)

reaction.

The

paper

by

Glasser,

Hildebrandt and coworkers reviews recent reaction andreactor engineering

advances

in

this

area.

As

they

note,

despite the fact that FTS has been studied for over 80

years an

adequate

description

of

its

kinetics

still

seems

to

be lacking. The authors report, for example, a number of

recent experimental

results

by

their

group

and

others

that

are not

explained

by

any

of

the

existing

kinetic

models.Their paper

reviews

some

of

these

recent

findings

with

thegoal

of

shedding

light

on

phenomena

occurring

during

the FTS

reaction

that

determine

the

overall

rate

and

selectivity, and

in

particular

the

olefin

to

paraffin

ratios

of

the lower

MW

hydrocarbon

products.

Their

paper

notes

that the

volatile

liquid-phase

being

present

during

FTS

may have

a great

effect

on

the

observed

kinetics,

and

proposes that

the

FTS

reactor

maybe

be

best

modeled

as

a reactive

distillation

system,

whereby

the

interaction

between phenomena such as vapor liquid equilibrium,partial reaction

equilibrium

and

kinetics

can

lead

to

complex

behavior

and,

thus,

explain

the

conflictingreports

among

various

researchers

studying

the

system.

The topic

ofNOxreduction in lean-burn vehicle engines

is discussed in the paper by Harold. Its particular focus is

the so-called

lean

NOx trap

(LNT),

which

is

an

adsorptivecatalytic

reactor

in

which

NOx is stored (in the form of

nitrates)

in

the

presence

of

excess

O2, and is subsequently

reduced

during

a

brief

regeneration.

As

Harold

notes,

this

is a

transient

multi-functional

reactor

that

is

called

upon

to carry

out

NO

oxidation,

NOxstorage, and reduction, all

within a

12 min cycle, attaining in the process NOxconversions

exceeding

95%.

The

paper

reviews

studies

by Harolds

group

on

the

coupling,

under

transient

con-

ditions, between

reaction

and

transport,

and

describes

the

current

insight

linking

catalyst

composition

and

structure

to conversion

and

selectivity.

The

current

technical

hur-

dles facing

the

emerging

lean

NOx reduction technol-

ogies are also nicely described.

One of the primary challenges in the conversion of

biomass

to

renewable

fuels

and

chemicals

is

removingthe oxygen-containing

functional

groups.

The

paper

by

Kruger, Nicolakis

and

Vlachos

discusses

catalytic

dehy-

dration as

an

effective

way

to

deoxygenate

biomass

that

avoids the environmental challenges facing the current

approaches using

inorganic

acids.

The

paper

reviews the

use of

microporous

and

mesoporous

catalysts

for

this

reaction, and

tries

to

correlate

their

characteristics

such

as degree

and

type

of

acidity,

mesoporosity,

and

hydro-

phobicity

to

their

performance.

Review

of

recent

studies

indicates that

heterogeneous

catalysts

show

good

promise, but the lack of fundamental understandingmay be

limiting

their

commercial

use;

potential

technical

barriers

that

need

to

be

overcome

are

discussed.

Ethylene

oxide

is

one

of

the

most

important

intermedi-

ates in

the

chemical

industry,

being

used

to

produce

a

variety of

chemicals,

including

various

glycols,

glycol

ethers and polyols, ethoxylates, ethanolamines, amongothers. Direct

catalytic

epoxidation

of

ethylene

by

air

or

oxygen is currently the dominant production technology

having today

largely

replaced

the

earlier,

more

complex

routes. Salmi and coworkers note in their paper that no

general agreement

exists

presently

concerning

its

reac-

tionmechanism

and

kinetics.

They

describe

using

micro-reactors as

a

tool

for

the

rapid

and

precise

investigations

of

epoxidation

kinetics.

Their

paper

reviews

and

screens

rival kinetic

models,

and

proposes

a more

general kinetic

model for

ethylene

oxide

formation

consistent

with

their

experimental

data

on

silver

catalysts.

Fuel cells

find

today

application

in

many

diverse

areas.

Sundmacher

and

coworkers

in

their

paper

indicate

that

despite significant

progress

that

has

been

made

in

the

last

two decades, substantial further improvements in per-formance and

reduction

in

costs

are

potentially

possible.

270 Reaction engineering and catalysis

Current Opinion in Chemical Engineering 2012, 1:269271 www.sciencedirect.com

http://dx.doi.org/10.1016/j.coche.2012.05.001http://dx.doi.org/10.1016/j.coche.2012.05.001http://dx.doi.org/10.1016/j.coche.2012.05.001http://dx.doi.org/10.1016/j.coche.2012.05.001http://dx.doi.org/10.1016/j.coche.2012.05.001http://dx.doi.org/10.1016/j.coche.2012.02.001http://dx.doi.org/10.1016/j.coche.2012.02.001http://dx.doi.org/10.1016/j.coche.2012.02.001http://dx.doi.org/10.1016/j.coche.2012.02.001http://dx.doi.org/10.1016/j.coche.2012.02.001http://dx.doi.org/10.1016/j.coche.2012.02.001http://dx.doi.org/10.1016/j.coche.2012.02.001http://dx.doi.org/10.1016/j.coche.2012.02.002http://dx.doi.org/10.1016/j.coche.2012.06.003http://dx.doi.org/10.1016/j.coche.2012.06.003http://dx.doi.org/10.1016/j.coche.2012.06.003http://dx.doi.org/10.1016/j.coche.2012.06.003http://dx.doi.org/10.1016/j.coche.2012.06.003http://dx.doi.org/10.1016/j.coche.2012.06.003http://dx.doi.org/10.1016/j.coche.2012.06.002http://dx.doi.org/10.1016/j.coche.2012.06.002http://dx.doi.org/10.1016/j.coche.2012.06.002http://dx.doi.org/10.1016/j.coche.2012.06.002http://dx.doi.org/10.1016/j.coche.2012.06.002http://dx.doi.org/10.1016/j.coche.2012.06.002http://dx.doi.org/10.1016/j.coche.2012.02.003http://dx.doi.org/10.1016/j.coche.2012.02.003http://dx.doi.org/10.1016/j.coche.2012.02.003http://dx.doi.org/10.1016/j.coche.2012.02.003http://dx.doi.org/10.1016/j.coche.2012.02.003http://dx.doi.org/10.1016/j.coche.2012.02.003http://dx.doi.org/10.1016/j.coche.2012.02.003http://dx.doi.org/10.1016/j.coche.2012.06.002http://dx.doi.org/10.1016/j.coche.2012.06.003http://dx.doi.org/10.1016/j.coche.2012.02.002http://dx.doi.org/10.1016/j.coche.2012.02.001http://dx.doi.org/10.1016/j.coche.2012.02.001http://dx.doi.org/10.1016/j.coche.2012.05.001

7/25/2019 Reaction Engineering and Catalysis

3/3

They

identify,

in

particular,

four

areas

in

fuel

cell

researchwhere chemical

reaction

engineers

can

make

significant

contributions. They include: first, understanding their

nonlinear

dynamic

electrochemical

behavior,

second,

improving mass and heat integration, third, being

able to

use

renewable

biomass

as

a

primary

energy

source,and fourth,

using

enzymes

for

catalyzing

the

electrode

reactions.

The focus

of

the

paper

by

Subramanian

is

on

non-

traditional solvents

and

on

how

they

may

be

exploited

to develop

sustainable

chemical

processes.

The

empha-

sis, in

particular,

is

on

gas-expanded

liquids

(GXL)

gener-

ated by

mixing

liquid

solvents

and

compressed

near-

critical gases,

such

as

CO2 and light olefins. Subrama-

nians group

and

others

have

shown,

in

lab-scale

studies,

that the

enhanced

solubility

and

transport

properties

of

GXL compared

to

conventional

liquid

solvents

allow

them to carry out reactions at mild conditions, with

increased selectivity, and also provide for the facile

separation

of

catalyst

and

products.

Examples

are

pro-vided of

using

GXL

for

industrially

important

hydrofor-

mylations and epoxidations. According to Subramanian,

GXL show

particularly

good

promise

for

application

in

the biorefining industry.

Liu, Sahimi

and

Tsotsis

summarize

in

their

paper

recent

efforts by

their

team

in

producing

hydrogen

from

coal

and

biomass using

membrane-based

reactive

separations.

They report

on

the

development

of

a

technology,

they

term the

one-box process, to

produce

pure

hydrogen

from coal-derived

and

biomass-derived

syngas

in

the

presence

of

its

common

impurities

via

the

water

gas

shift

reaction, and

by

using

commercial-scale

carbon

molecular

sieve membranes

and

impurity-tolerant

commercial

cat-

alysts. They

also

discuss,

in

addition,

the

use

of

com-

mercial-size

Pd

and

Pd-alloy

membranes

during

production

of

ultra-pure

hydrogen

from

coal

and

biomass.

Details about the recent field-testing of the technology

are also provided.

Editorial

overview Tsotsis 271

www.sciencedirect.com Current Opinion in Chemical Engineering 2012, 1:269271

http://dx.doi.org/10.1016/j.coche.2012.02.005http://dx.doi.org/10.1016/j.coche.2012.02.005http://dx.doi.org/10.1016/j.coche.2012.06.001http://dx.doi.org/10.1016/j.coche.2012.06.001http://dx.doi.org/10.1016/j.coche.2012.06.001http://dx.doi.org/10.1016/j.coche.2012.06.001http://dx.doi.org/10.1016/j.coche.2012.06.001http://dx.doi.org/10.1016/j.coche.2012.06.001http://dx.doi.org/10.1016/j.coche.2012.06.001http://dx.doi.org/10.1016/j.coche.2012.02.005