A Review of Advancements in Solvent Recovery from Hazardous Waste

Abstract

The recovery and reuse of organic solvents from hazardous waste is a sustainable alternative to conventional solvent disposal options. The current work explores recent breakthroughs as well as the versatility of available solvent recovery technologies. Membrane-based separation processes are emerging as superior alternatives to traditional energy-intensive distillation due to (a) recovery of high-purity products, (b) significantly reduced energy consumption, (c) lower operational expenses, and (d) emissions reduction. Nevertheless, distillation-based technologies remain relevant due to their versatility in handling complex solvent mixtures. Hybrid methods, combining the separation and energy efficiency of membranes with the resilience of distillation, offer an optimal solution that is cost-effective and has a low environmental impact. Technology hybridization reduces operational energy and emissions while overcoming the constraints of stand-alone membrane systems such as the high capital requirement. For instance, integrating vapor permeation with distillation reduces ethanol dehydration energy requirements by 63%, while hybrid pervaporation-distillation achieves a 91% reduction in life cycle emissions for isopropanol recovery in comparison to conventional methods. Vapor permeation-distillation further demonstrates 77% cost savings compared to conventional azeotropic distillation. Additionally, adsorption-based approaches, such as hot gas pressure swing adsorption, yield 83–89% isopropanol from aqueous mixtures at industrial scales. Recent advancements in membrane materials, including poly(vinyl alcohol)-silica nanoparticle composites, have improved energy efficiency and reduced CO₂ emissions during separation processes. Future advancements in solvent recovery would facilitate zero-liquid discharge and circular economy objectives, a fundamental aspect of sustainable industrial processes.

Full text

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J. Indian Inst. Sci.
A Multidisciplinary Reviews Journal
ISSN: 0970-4140 Coden-JIISAD
REVIEW
ARTICLE
© Indian Institute of Science 2025.
A Review ofAdvancements inSolvent Recovery
fromHazardous Waste
S.Srishti†, AparnaAnilkumar† andYagnaseniRoy*
Abstract | The recovery and reuse of organic solvents from hazard-
ous waste is a sustainable alternative to conventional solvent disposal
options. The current work explores recent breakthroughs as well as the
versatility of available solvent recovery technologies. Membrane-based
separation processes are emerging as superior alternatives to traditional
energy-intensive distillation due to (a) recovery of high-purity products,
(b) significantly reduced energy consumption, (c) lower operational
expenses, and (d) emissions reduction. Nevertheless, distillation-based
technologies remain relevant due to their versatility in handling complex
solvent mixtures. Hybrid methods, combining the separation and energy
efficiency of membranes with the resilience of distillation, offer an optimal
solution that is cost-effective and has a low environmental impact. Tech-
nology hybridization reduces operational energy and emissions while
overcoming the constraints of stand-alone membrane systems such as
the high capital requirement. For instance, integrating vapor permea-
tion with distillation reduces ethanol dehydration energy requirements
by 63%, while hybrid pervaporation-distillation achieves a 91% reduction
in life cycle emissions for isopropanol recovery in comparison to con-
ventional methods. Vapor permeation-distillation further demonstrates
77% cost savings compared to conventional azeotropic distillation.
Additionally, adsorption-based approaches, such as hot gas pressure
swing adsorption, yield 83–89% isopropanol from aqueous mixtures at
industrial scales. Recent advancements in membrane materials, includ-
ing poly(vinyl alcohol)-silica nanoparticle composites, have improved
energy efficiency and reduced CO₂ emissions during separation pro-
cesses. Future advancements in solvent recovery would facilitate zero-
liquid discharge and circular economy objectives, a fundamental aspect
of sustainable industrial processes.
1 Introduction
e increasing demand for sustainable practices in industrial operations has intensied interest in
zero-liquid discharge systems as well as the recovery of valuable resources from euent streams1.
Consequently, recovering organic solvents from industrial euent streams has gained prominence.
Organic solvents, when utilized as reaction media in their various industrial applications, contribute to
large volumes of hazardous wastewater (euent) aer use2. As per international (and national) regula-
tions, euent streams comprising used solvents must be recovered (puried for reuse) or incinerated,
but reports suggest that the existing treatment plants in India remain under-utilized3. Solvent-intensive
S. Srishti and Aparna
Anilkumar contributed
equally to this work.
1Centre forSustainable
Technologies, Indian
Institute ofScience,
Bengaluru, Karnataka
560012, India.
*yroy@iisc.ac.in

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S. Srishti
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industries worldwide generate signicant quan-
tities of waste, with the pharmaceutical sector
for instance, producing 20–80 kg solvent waste
per kg product. Conventional disposal meth-
ods, such as incineration and osite treatment,
pose environmental and economic challenges,
varying by region. Solvent recovery oers a sus-
tainable alternative, reducing emissions and
costs while aligning with global policies4. Most
organic solvents are volatile, and ineective eu-
ent treatment may contribute to volatile organic
compound (VOC) emissions in the air and pho-
tochemical smog formation5. Moreover, waste-
water streams comprising organic solvents have
higher chemical oxygen demand (COD) and
total organic carbon (TOC) levels, due to which
most local wastewater treatment plants can only
partially treat such streams6–8. While euent
regulations vary regionally and depending on
the source, generic permissible limits tend to be
100mg/L for COD (optimal COD for unpolluted
water being < 20mg/L), below 50mg/L for TOC,
between 6 and 9 pH, and less than 1000mg/L
total dissolved solids (as TDS > 2000 mg/L may
harm soil)9–12. Meanwhile, independent reports
conrm that water bodies near industrial hubs
are polluted by partly treated euents, negatively
impacting the local ecosystems, as well as the
health and livelihoods of the local populace13,14
(Fig.1).
Solvent recovery is a technique to recover/
recycle organic solvents from industrial euents
containing a mixture of various solvents (includ-
ing water), other valuable products/by-products,
and impurities. Practicing solvent recovery aligns
with environmental regulations, keeps contami-
nants out of the environment, and minimizes
exposure to hazardous materials4. Solvent recov-
ery methods, when eectively employed, can
reclaim (at relatively high purity) up to 80% of
the organic solvents present in hazardous waste
streams, reducing industrial waste generation15.
ey minimize the need for disposal and promote
a more sustainable waste management approach,
but technology selection is the key decision
impacting their capacity for waste reduction16,17.
Compared to solvent incineration and disposal,
there is a signicant reduction in greenhouse gas
emissions, both direct and indirect (due to reduced
virgin solvent usage), as will be evidenced in later
sections18. With the prevalent literature empha-
sizing the integration of sustainable practices in
various industrial sectors, a central feature of most
analyses involves Life Cycle Impact Assessments
(LCIA). A crucial tool to evaluate the environmen-
tal impact of a process, from emissions to resource
utilization, LCIAs facilitate a holistic approach to
sustainable solvent management. eir ndings
underscore that practicing solvent recovery reduces
dependence on virgin solvents (oen derived from
petrochemical sources). Studies show that, in the
pharma industry, for instance, the manufacture of
virgin solvents accounts for 50–60% of total energy
usage and ≈50% of total emissions18. us, solvent
recovery minimizes the costs and emissions asso-
ciated with virgin solvent usage. However, there is
a need for continued technological innovation to
improve the operational eciency of conventional
solvent recovery methods while cost-eectively
reducing the industrial ecological footprint.
Recent assessments of the environmental sus-
tainability of solvent recovery show that solvent
recovery reduces pollution by 908,800kg/year and
CO₂ emissions by 887,500 kg/year, saving 12.46
million kWh annually. Compared to conventional
distillation-incineration, hybrid methods like
pervaporation-distillation cut emissions by 93%19.
It is to be noted that LCIAs can comprehensively
capture the environmental consequences of incin-
eration or various solvent recovery methods, even
Figure1: Summarizing the available pathways for waste solvent streams generated from various indus-
trial applications: dumping (disposal to the environment), incineration, or solvent recovery for reuse.
AQ1
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when comparing disparate technologies such as
distillation and membrane separation. Evaluating
the impacts on human health, climate change, and
resource utilization throughout the process lifecy-
cle allows for a more informed approach toward
solvent usage, promoting a transition toward sus-
tainable practices.
Solvent recovery technology is crucial for cir-
cular economy and global sustainability. Improved
solvent reuse eciency and waste reduction reduce
industrial processes’ environmental impact. Mem-
brane-based separations, hybrid recovery systems,
and energy-ecient distillation improve recovery
rates and save costs. Solvent recovery reinforces
Zero Liquid Discharge (ZLD) processes; ensuring
wastewater treatment and recycling, eliminating
liquid waste discharge, and maximizing resource
utilization. ese solutions align with international
eorts to reduce resource depletion, pollution, and
industrial sustainability, creating a more resilient
and circular economy.
is paper oers a data-driven examination of
solvent recovery, emphasizing the advantages of
membrane-based and hybrid separation techniques
for energy eciency, cost savings, and environ-
mental protection. It highlights developments in
high-selectivity membranes, their industrial viabil-
ity, and scalable hybrid topologies. In contrast to
earlier studies, it connects experimental ndings
with practical implementation issues.
2 Overview ofSolvent Recovery
Processes
Solvent recovery processes are pivotal in miti-
gating environmental impacts and maximizing
resource utilization in hazardous waste-generat-
ing industries. Each process is tailored to address
specic separation challenges, from azeotropes
and close-boiling mixtures to thermally sensi-
tive compounds. Table1 summarizes these tech-
nologies, highlighting their operating parameters,
principles, advantages, limitations, and potential
solutions for overcoming separation challenges.
Each process has been explored in detail
below to further elucidate its practical relevance
and performance in real-world scenarios. Such
detailed analysis will oer valuable insights into
optimizing these techniques for specic separa-
tion needs and advancing their implementation
in industrial settings.
2.1 Distillation‑Based Solvent Recovery
Distillation-based technologies are the most
widely applied for separating the components of
a liquid mixture. e separation process relies on
the mixture components having dierent vapor
pressures (volatilities)20. Distillation-based sol-
vent recovery is highly relevant to industries
such as chemicals, pharmaceuticals, nutraceu-
ticals, etc., wherein solvents are frequently used
in chemical reactions, cleaning, or extraction
processes, thus forming mixtures from which
pure solvents must be recovered31. e mixture
components are selectively boiled o and subse-
quently condensed to be collected in their puri-
ed form. is reclamation process reduces the
emissions associated with virgin solvent usage
while eliminating hazardous waste disposal, thus
mitigating the environmental impacts of the pri-
mary process32,33. Moreover, distillation-based
solvent recovery signicantly reduces greenhouse
gas emissions compared to solvent disposal and
incineration4,34.
While distillation remains essential to indus-
trial applications, the unique characteristics of
each distillation operation create challenges in
applying complex separation processes, especially
when tailored to solvents with diverse proper-
ties. ese complexities in separation processes
signicantly inuence life-cycle inventory (LCI)
data, with the complications in computing life-
cycle impact assessments (LCIA) arising as a
consequence25. Distillation techniques, whether
simple or enhanced (fractional, steam, extractive,
vacuum, etc.), are designed for specic mixture
types and boiling point ranges. e separation
eciency can be enhanced through adjustments
such as system pressure or process conguration
(e.g., adding a fractionating column). Distilla-
tion’s versatility and eectiveness make it indis-
pensable in sectors beyond solvent recovery, with
applications extending to desalination and liquid
purication. As such, distillation remains a core
unit process to the extent that distillation-based
separation processes account for 7–8% of the
world’s energy consumption26.
2.1.1 Distillation
e distillation recovery process feeds the liquid
mixture into a distillation column comprising
multiple trays/stages, as seen in Fig.2. e liquid
at the bottom of the column is heated, evaporat-
ing the volatile constituents, which then rise. e
fumes at the top of the column are condensed so
that the denser fractions descend to the bottom.
e rising vapor and descending liquid are con-
tacted on each consecutive tray/stage of the col-
umn such that the more volatile components are
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Table 1: Comparative analysis ofseparation processes: operating parameters, principles, advantages, limitations, andsolutions tochallenges.
Process Operating parameters Principle Advantages Limitations Solutions tochallenges Refs
Distillation Pressure: Atmospheric
Temperature: Based on boiling
points of components
Separation due to difference in
components’ boiling points Established, scalable technol-
ogy
High separation efciency
Energy-intensive
Ineffective for azeotropes or
close-boiling mixtures
Thermal degradation risks
Heat integration to reduce
energy use
Pre-treatment for close-boiling
mixtures
20, 16
Vapor permeation Feed Temp.: Above boiling
point of components
Permeate Pressure: Sub-atmos-
pheric
Separates components from
vapor feed via selective
membrane permeation
Low fouling risk
Effective for vapor feeds
Energy-efcient
High-temperature membrane
stability required
More energy-intensive than
pervaporation
Development of high-temper-
ature resistant membranes
Integration with distillation for
efciency
21–23
Pervaporation Feed Temp.: 50–100°C
Permeate
Pressure: Sub-atmospheric
(vacuum)
Membrane: Hydrophilic or
hydrophobic
Selectively permeates com-
ponents through a dense
polymer membrane
Ideal for azeotropes
Energy-efcient
Suitable for heat-sensitive
mixtures
Membrane fouling
High capital cost
Difcult to scale up
Development of fouling-resist-
ant membranes
Advanced cleaning methods
for durability
23–25
Extractive distillation Pressure: Atmospheric
Temperature: Dependent on
entrainer stability
Entrainer: Miscible, non-
volatile
Uses an entrainer to alter the
relative volatility of azeo-
tropic mixtures
Effective for azeotropes
High product purity Additional steps for entrainer
recovery
High energy requirements
Environmental impact of
entrainers
Use of greener entrainers
Optimized column design for
energy efciency
26, 27
Vacuum distillation Pressure: Sub-atmospheric
(< 10kPa)
Temperature: Lower boil-
ing points achieved under
reduced pressure
Reduces pressure to lower
boiling points, minimizing
thermal degradation
Suitable for heat-sensitive
compounds
Reduced energy consumption
High initial cost
Specialized equipment
required
Limited throughput
Handling scaling and fouling
effectively
20, 28
Membrane distillation Temp.: 40–80°C
Pressure: Atmospheric
Membrane: Hydrophobic,
thermally stable
Separation by hydrophobic
membrane due to vapor
pressure gradients
Effective for desalination
Low-grade heat utilization
Energy-efcient
Membrane wetting and foul-
ing
High initial cost
Limited scalability
Durable, wetting-resistant
membranes
Improved heat recovery
mechanisms
25, 29, 30

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drawn to the vapor phase. In contrast, the liquid
phase takes up the less volatile components. More
trays (contact area for mass transfer) are required
for higher separation eciency, although the rela-
tive volatility between the components is also a
major inuencing factor. For instance, while a
12-tray distillation column recovers 95% metha-
nol from an aqueous methanol feed, the separa-
tion quality improves with the number of trays35.
While distillation can be energy-intensive,
a recent study showed that, when implemented
instead of incineration, the distillation-based
dehydration of organic solvents (used by the
semiconductor industry, e.g., NMP) achieved
40% energy savings36. Due to its global scale, the
heavy reliance of semiconductor manufacturers
on organic solvents conventionally results in high
production costs and signicant environmental
impact due to the incineration of waste streams
which could be eliminated by implementing sol-
vent recovery. Moreover, process intensication
strategies such as heat integration or pre-treat-
ment can improve energy eciency. Integrat-
ing renewable energy, with a 37% reliance on
conventional energy as backup, achieves almost
50% of annual cost savings and reduces carbon
emissions by approximately 89.4% compared to
emissions from waste disposal37. Another exam-
ple, per the literature, to pre-treat when waste
volumes surpass a single, large distillation col-
umn, is the batch distillation-recovery of acetone
from a waste solvent mixture (water–acetone-
dichloromethane). Compared to a single-column
arrangement, a dual-column conguration with
residue recycling was found to reduce CO₂ emis-
sions by 20% and increase prots by 12%, i.e.,
gaining environmental and economic benets
respectively38.
2.1.2 Extractive Distillation
Extractive distillation is used to separate sol-
vent mixtures that form azeotropes (constant-
boiling mixtures) or have low relative volatility
as illustrated in Fig.3. In these cases, no matter
how many trays a distillation column has, high
product purity cannot be achieved without the
addition of a relatively non-volatile and miscible
separating agent (entrainer) that alters the rela-
tive volatility (preferably without forming new
azeotropes) and facilitates separation27. e use
of entrainers like 1,2-propanediol and dimethyl
sulfoxide (DMSO) to separate azeotrope-forming
mixtures, such as tetrahydrofuran (THF) and
water, is well-established in the literature. Studies
on batch, semi-batch, and continuous processes
show that DMSO enables THF purication over
99 wt%, making it an eective choice to break the
azeotrope39. For ethanol-ethyl propionate sepa-
ration (during ethyl propionate manufacturing),
glycerol is a more eective entrainer than ethyl-
ene glycol, achieving 99.9% purity at a 27% lower
cost40. To ensure optimal performance for each
unique separation challenge, feasibility considera-
tions such as selectivity and residue curve maps
guide entrainer selection and process design are
essential41. Extractive distillation is also adaptable
to dierent entrainer types, i.e., light, interme-
diate, heavy, and heterogeneous variants. Pro-
cess intensication strategies, such as pressure
adjustments and advanced congurations like
heat-integrated extractive distillation, ultrasonic
distillation, and divided-wall columns, could help
reduce the energy demand and costs42,43.
A signicant development in extractive
distillation is the use of ionic liquids (ILs) as
entrainers, as demonstrated in studies involving
ethanol/water, methylcyclohexane/toluene, and
ethylbenzene/styrene systems. ILs such as [emim]
[N(CN)₂] and [hmim][B(CN)₄] showed con-
siderable energy savings (50% and 43%, respec-
tively) over traditional entrainers. While IL usage
may increase capital costs (e.g., ethylbenzene/
styrene separation costs 23% more when using
an IL instead of sulfolane), pilot studies sup-
port the potential of ILs in extractive distillation
applications where solvent recovery, selectivity,
and heat integration are the priority. For exam-
ple, 1-ethyl-3-methylimidazolium dicyanamide
Figure 2: Distillation column schematic repre-
senting a feed mixture comprised of solvent A
(more volatile, represented in red) and solvent B
(less volatile, represented in blue) which is sepa-
rated into two product streams due to the dif-
ference in their volatilities (atmospheric boiling
points) and lack of azeotrope formation.

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has demonstrated separation ecacy in ethanol
recovery, achieving up to 99.9% ethanol purity
levels in pilot-scale experiments. It is to be noted
that while the IL-based process required ≈11%
more energy than an ethylene glycol-based one,
heat integration further reduced the energy
requirement by 16%. us, the successful appli-
cation of IL entrainers for ethanol dehydration
would depend on their recoverability and the
feasibility of incorporating heat integration26.
On the other hand, for the dehydration of tert-
butanol, of the leading choices, both glycerol
and [C4MIM][SCN] oered signicant cost and
energy savings44. Ultimately, evaluating entrain-
ers, both organic and IL, must also include factors
such as toxicity, physical properties, and separa-
tion eciency.
2.1.3 Vacuum Distillation
Vacuum distillation operates columns at low
pressure, allowing liquids to boil at lower tem-
peratures, which makes it ideal for separating
temperature-sensitive compounds. is method
minimizes thermal degradation, preserving prod-
uct integrity and nding applications across vari-
ous industries45.
In nuclear fuel reprocessing, for instance,
vacuum distillation is essential for purifying
hydrocarbon-tri-butyl phosphate solvents, which
are prone to secondary degradation at high tem-
peratures. Studies show that a pilot-scale puri-
cation system integrating dehydration, thin-lm
evaporation, and vacuum distillation minimized
degradation products, preserving solvent stability
for reuse46. In bioprocessing, vacuum distillation
has been integrated downstream of batch fermen-
tation and isopropanol extraction of 2,3-butan-
ediol (2,3-BD), concentrating the stream from
90g/L to 96% product purity47. e sulphur con-
tent dropped by almost 95%, aligning with the
properties of Iraqi base oils SN150 and SN20048.
In the polymer production industry, used hydro-
carbon solvents are typically incinerated at 700–
1200°C, releasing signicant CO₂ emissions. is
study explored vacuum distillation (13–30kPa)
as a recycling method, achieving the highest
solvent yield of 77% at 170°C and 13kPa. Gas
chromatography-mass spectrometry (GC–MS)
conrmed reduced carbon atom purity with
increasing pressure. Economic analysis showed a
potential cost reduction of $33,651/year through
solvent recovery28.
ese applications underscore vacuum distil-
lation’s versatility in achieving high-purity recov-
eries across diverse elds, from bioprocessing to
fuel reprocessing and petrochemical recycling.
e technique’s ability to prevent decomposition
while ensuring product integrity establishes it as a
Figure3: Extractive distillation schematic wherein the feed mixture comprised of solvent A and solvent B
that can form a difficult-to-separate azeotrope/constant-boiling mixture has its relative volatility changed
by the addition of entrainer due to which solvent A can be separated out in the first (azeotropic) column.
The second (recovery) column thus receives a mixture of solvent B and entrainer (non-azeotrope forming)
from which solvent B can be separated out.

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critical process in sustainable and ecient solvent
and chemical recovery.
2.2 Membrane‑Based Solvent Recovery
Membrane processes present an innovative alter-
native to traditional (distillation-based) solvent
recovery by oering up to 90% less energy con-
sumption and enhanced eciency49. In addition
to being low-energy, membrane technology has
other advantages, such as diverse applications,
low emissions, and lower operational costs that
strengthen the goal of adopting solvent recovery
as a sustainable practice that aligns with mod-
ern environmental standards50. Recent studies
focus on integrating sustainability indicators and
computational optimization into solvent recov-
ery frameworks. e exploration of membrane
technology has shown promise in recovering
organic waste solvents due to its high rejection
rates for contaminants. e economic viability of
these processes is signicantly inuenced by the
ow rates of solvent-containing waste streams,
suggesting that low-euent industries may also
adopt these recovery strategies4.
e collective advancements in membrane-
based solvent recovery illustrate a comprehensive
approach that balances technological innovation
with economic considerations. By employing
systems-level frameworks, industries can better
understand the interactions between dierent
recovery processes and their impact on opera-
tional sustainability51. is section highlights
the trajectory toward more ecient, sustainable,
and economically viable solutions for solvent
recovery, establishing membrane technology as a
pivotal component in addressing the challenges
associated with hazardous solvent waste manage-
ment. e ongoing research in this eld reinforces
the importance of membrane processes in pro-
moting a circular economy and enhancing overall
resource recovery in industrial applications.
2.2.1 Pervaporation
Pervaporation is a vacuum-driven membrane-
based process that separates solvent mixtures by
selectively permeating specic components over
others due to a dierence in their size or an-
ity towards the membrane material. As depicted
in Fig.4, the permeating components are driven
through the membrane due to a chemical poten-
tial gradient and evaporate into the permeate
side, which is held at a vacuum pressure to reduce
the evaporation energy requirement. On the feed
side, the liquid mixture is received at tempera-
tures below that of distillation and pressures close
to atmospheric, due to which the energy usage
and emissions are up to 70% lower than that of
distillation-based recovery processes52. Moreo-
ver, the feed side temperatures being lower than
conventional techniques, waste heat (low vapor
quality waste steam) may be utilized to heat
pervaporation feeds. Unlike conventional tech-
niques like extractive distillation, azeotropes can
be separated without entrainers (oen harmful
chemicals such as dimethylsulfoxide or hexane),
thereby improving product quality. Pilot-scale
studies utilizing NaA zeolite membranes have
achieved nearly 90% water removal from aqueous
isopropanol53.
Figure4: Pervaporation schematic showing the liquid mixture (solvent A represented in red and solvent B
represented in blue) fed into a membrane module with a partial pressure difference across due to heating
of feed (below its boiling point) and vacuum maintained on the permeate side. Primarily, solvent B perme-
ates the membrane, due to which the reject/retentate stream is concentrated in solvent A.
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Apart from separating azeotrope-forming
mixtures, pervaporation is also useful in the case
of compounds that are harmful in vapor form,
can thermally degrade, or make mixtures that are
close-boiling54. An example of the former is the
dehydration of aqueous N, N-dimethylforma-
mide (DMF) solutions (used widely in industrial
and medical processes like acetylene extraction
and polyacrylonitrile ber production). Since
DMF recovery by distillation is challenging due
to its high boiling point, the harmful nature of
its vapor phase, and the thermal decomposition
of DMF, implementing pervaporation instead
improves energy eciency and has environ-
mental benets55. Another application area is
the recovery of VOCs from industrial wastewa-
ter streams24. Pervaporation modules, thus, e-
ciently separate multiple solvent mixtures and
can be protably scaled down for smaller eu-
ent streams in industrial applications such as
pharmaceutical solvent recovery. In other words,
pervaporation can be utilized at individual manu-
facturing plants (instead of transporting the waste
solvents to centralized treatment facilities), puri-
fying waste solvents for reuse on-site22.
Commercial pervaporation membranes
can be polymer-based, such as poly(vinyl)alco-
hol (PVA) or polydimethylsiloxane (PDMS), or
ceramic-based, such as zeolite and silica56. e
performance metrics (permeate ux vs. selectiv-
ity) of pervaporation membranes revealed that
an adsorption-diusion mechanism primarily
controls the transfer/permeation of components,
while competitive adsorption is the factor inu-
encing membrane selectivity and it can be chal-
lenging to maximize both in existing commercial
membranes57. Recent research shows that the
higher performance of polymer membranes
can be leveraged against the higher stability of
ceramics by combining polymers with inor-
ganic llers in the form of metal–organic frame-
works (MOFs). For instance, as per the literature,
Zeolitic Imidazolate Frameworks (ZIFs) inte-
grated into PDMS membranes achieved enhanced
ow and separation eciency than using the pol-
ymer alone58. Another emerging area is the use
of alternative polymers for membrane matrices,
biopolymers, and self-healing membranes59. In
terms of membrane modules, at-sheet/plate-
and-frame modules are the most prevalent due to
their low fouling propensity and pressure drop23.
However, there is potential for further develop-
ment of hollow ber membrane modules, par-
ticularly for organic solvent dehydration, due to
low fouling, high surface area per unit length, and
suitability for industrial applications60.
2.2.2 Vapor Permeation
Vapor permeation (VP), like pervaporation,
operates on the principle of selective adsorp-
tion and diusion through a membrane. Fig-
ure5 illustrates the process wherein a chemical
potential gradient across the membrane drives
components toward the vacuum on the per-
meate side22. Unlike pervaporation, the feed
is received in the vapor phase, i.e., at tem-
peratures comparable to that of distillation-
based processes21. Due to the low-pressure
vaporization (i.e., lower enthalpy of vaporiza-
tion), vapor permeation is more energy e-
cient than distillation but utilizes more energy
Figure 5: Vapor permeation schematic showing the heated (above its boiling point) vapor feed com-
prised of solvent A (red) and solvent B (blue). The partial pressure difference, augmented by vacuum on
the permeate side drives both components across but primarily solvent B permeates due to the mem-
brane’s selectivity towards it.

UNCORRECTED PROOF
9
A review of advancements in solvent
J. Indian Inst. Sci. | VOL xxx:x | xxx–xxx xxx 2025 | journal.iisc.ernet.in
than pervaporation due to the higher feed
temperatures25,61. e higher (relative to per-
vaporation) feed temperatures raise the feed
side partial pressures and, thus, the pressure
dierentials across the membrane, which drives
higher permeation62. However, raising the feed
temperature changes the membrane material
characteristics. erefore, while smaller and
more soluble (due to higher anity to the mem-
brane material) molecules typically have higher
permeability, the membrane selectivity may
reduce, allowing larger and less soluble mol-
ecules to permeate as well56. Many membrane
materials, particularly polymers, also degrade
over time when exposed to high temperatures
or aggressive chemicals, compromising their
structural integrity. Selecting a stable membrane
material (e.g., ceramic) is vital in such applica-
tions. Moreover, membranes may exhibit high
permeability but low selectivity towards the tar-
get components of a mixture, resulting in low
separation eciency. e permeation capac-
ity of the membrane can also be limited by its
physical properties and the low feed-side vapor
pressure of the target components61. As such,
the separation eciency of vapor permeation
is heavily dependent on the membrane’s physi-
cal properties, i.e., selectivity, permeability, and
stability over varying operating conditions. e
choice of membrane material is critical to selec-
tively permeate target components at a consist-
ently high ux63.
Despite its potential for energy-ecient (com-
pared to conventional techniques) separation,
vapor permeation faces several challenges that
limit its widespread adoption. Over time, the
membrane’s surface can accumulate deposits of
contaminants, which can reduce its permeabil-
ity and selectivity64. Fouling can be a signicant
problem, especially in industries where complex
mixtures are processed56. Moreover, while com-
panies such as Sterling and Sulzer Chemtech
report installing large-scale (real-world) vapor
permeation systems treating up to 62 tons of
euent per day, protable commercialization of
vapor permeation is still pending54.
Vapor permeation does have a wide range
of potential applications across various indus-
tries, such as the production of paints, coatings,
and adhesives. Utilizing hydrophobic polymer
membranes to treat VOC-contaminated indus-
trial wastewater at high feed temperatures and
pressures (with a low-pressure permeate side)
eectively removes the volatile contaminants
and improves water quality levels, with perme-
ate uxes higher than that of pervaporation65.
Hydrophilic membranes permeate water, enabling
dehydration of organic solvents and water recov-
ery from waste steam—a major energy loss in
industrial applications. Ecient steam separation
has been achieved with poly(vinyl alcohol) mem-
branes containing silica nanoparticles, enhancing
energy eciency and reducing CO₂ emissions66.
Vapor permeation has also been utilized for the
removal of VOCs such as toluene from polluted
air, with experimental studies showing relatively
high toluene permeation (especially at low feed
concentrations) when using a polydimethylsilox-
ane (PDMS) membrane. Moreover, simulation
studies showed a 95% reduction in the VOC con-
tent of air from petroleum facilities, i.e., at indus-
trial feed ow rates and compositions67.
2.2.3 Membrane Distillation
Membrane distillation utilizes a hydrophobic
membrane to separate a hot, contaminated feed
solution towards a cold permeate side. A vapor
pressure dierence is created due to the temper-
ature dierence between the two sides, induc-
ing vapor transport across the membrane29. e
membrane pores are lled with air, allowing only
vapor to pass through while rejecting non-volatile
contaminants68. As such, membrane distillation is
highly selective towards vapor-phase molecules
and can eectively recover VOCs from waste
streams69. Membrane distillation is thus promis-
ing for solvent recovery from hazardous waste
streams, where other separation techniques face
challenges due to extreme levels of contamina-
tion (e.g., heavy metals, salts, or other non-vol-
atile impurities). e hydrophobic membranes
resist fouling from oily or particulate-laden waste
streams (high rejection), extending their opera-
tional life compared to other membrane-based
technologies. Furthermore, membrane distilla-
tion operates at relatively low temperatures (≈40–
80°C) compared to distillation-based processes,
reducing energy consumption and making it
compatible with low-grade or waste heat sources.
Integrating membrane distillation with renewable
energy sources like solar thermal systems oers a
sustainable pathway for large-scale solvent recov-
ery and waste management.
With applications in industries like phar-
maceuticals, petrochemicals, and paint manu-
facturing that generate waste laden with VOCs,
membrane distillation shows signicant poten-
tial in eciently recovering solvents from waste
streams70. However, membrane distillation
faces certain limitations such as: (a) while more
AQ6

UNCORRECTED PROOF
10
S. Srishti
J. Indian Inst. Sci.| VOL xxx:x | xxx–xxx xxx 2025 | journal.iisc.ernet.in
energy-ecient than distillation, membrane dis-
tillation is still less energy-ecient than pres-
sure-driven membrane processes, (b) durable
advanced polymer or ceramic membranes are
necessary due to membrane material degradation
by aggressive solvents, and (c) prolonged expo-
sure to aggressive solvents or high concentrations
of contaminants leads to membrane wetting30
Ongoing research aims to improve the durability
and eciency of these membranes, focusing on
enhancing their chemical resistance and thermal
stability. Advanced composite membranes and
surface modications are being explored71.
2.3 Other Processes
An alternative to distillation and membrane sepa-
ration is the use of adsorption columns to pref-
erentially adsorb certain component(s) over the
other(s) in a mixture. However, the adsorbent
(e.g., silica gel, molecular sieves, or even biosor-
bents) saturates over time. us, at least two
adsorption columns are operated in tandem for
continuous operation, swinging between dierent
pressures or temperatures such that the second
column desorbs a relatively pure stream of the
previously adsorbed component. is regenerates
the adsorbent, allowing the columns to operate
over a given number of adsorption–desorption
cycles until the spent adsorbents must be replaced
and landlled. Simo etal.72 validated adsorption
modelling up to 1000 cycles against industrial
data, showing up to 11% water removal from
the ethanol–water azeotrope using 3 Å zeolite
adsorbents72. Similarly, Liu et al.73 used experi-
mental and simulation studies on hot gas pressure
swing adsorption to show that an industrial-scale
system could obtain 83–89% isopropanol yield
from its aqueous mixture. e adsorption-based
process showed signicant cost savings compared
to membrane processes at relatively large scales
due to the lower cost and higher lifetime of com-
mercial adsorbents73.
Several advanced distillation methods, such as
fractional distillation, pressure swing distillation,
xed adsorptive distillation, etc., oer enhanced
eciency and environmental benets in indus-
trial solvent recycling but can be more expensive.
Pressure swing distillation uses two columns at
dierent pressures to separate azeotropic mix-
tures. High-purity product is extracted from one
end of a column while the azeotrope is recycled
from its other end to the remaining column74.
For ethanol-ethyl propionate separation, pres-
sure swing distillation required 44% less energy
but cost 33% more than extractive distillation40.
Fractional distillation is the process of separat-
ing a mixture into its constituent components
or fractions, based on their boiling points, by
heating dierent column trays to the tempera-
tures at which the dierent fractions evaporate75.
Another up-and-coming technique, which oers
a more compact design, is falling lm distillation
using a thermosyphon system, shown to achieve
89% separation eciency in the dehydration of
monoethylene glycol (MEG), with a further 47%
reduction in energy consumption when paired
with a two-column series76.
While conventional distillation-based tech-
nologies are high-energy (and high-emissions)
and thus high in operating costs and negative
environmental impact, novel technologies like
membrane separation and advanced distil-
lation can be capital-intensive. A promising
avenue to optimize total costs while retaining
high overall separation and energy eciency is
the hybridization of disparate separation tech-
nologies such as distillation and membrane
separation. e integration of pervaporation
and distillation to recover isopropanol during
celecoxib manufacturing achieves a 91% reduc-
tion in overall life cycle emissions compared to
conventional methods17. On the other hand, a
distillation-vapor permeation conguration was
shown to oer the most signicant cost savings
for isopropanol dehydration, ≈77% compared
to azeotropic distillation. erefore, it is more
economically benecial than hybrid systems of
distillation-pervaporation with ≈70% total cost
savings compared to azeotropic distillation77.
For ethanol dehydration, Vane etal.78 showed
that using hybrid vapor permeation with distil-
lation reduces energy requirements by 63%78. It
is to be noted that its vapor phase feed makes
vapor permeation more adaptable to hybridi-
zation (than pervaporation) since vapor prod-
uct streams from distillation columns may be
fed to membrane modules without condensa-
tion, reducing the distillation (pre-treatment)
energy requirement77. Distillation columns
can also be integrated with other separation
units, such as extractors. An extractive distil-
lation process (water being the entrainer) inte-
grated with extractor units was shown to reduce
the number of processing units, energy con-
sumption, and operating costs (as compared
to conventional non-hybrid processes) when
separating a multi-component mixture of alco-
hols, esters, and ketones79. Fixed adsorptive
distillation combines distillation and adsorp-
tion columns (packed with solid adsorbents that
preferentially adsorb certain components)80.

UNCORRECTED PROOF
11
A review of advancements in solvent
J. Indian Inst. Sci. | VOL xxx:x | xxx–xxx xxx 2025 | journal.iisc.ernet.in
As Mujiburohman et al.81 proved experi-
mentally, retrotting an adsorption column
between existing distillation columns can break
the isopropanol-water azeotrope without any
entrainer, thus improving product purity81.
Similarly, reactive distillation (RD) is a distilla-
tion technique that integrates a chemical reac-
tion within the distillation apparatus, allowing
for the immediate removal of products to facili-
tate the completion of a reversible reaction.
Combining reactive distillation with pervapora-
tion signicantly increased the volatility of vari-
ous compounds in the system with the reaction
rate, while the total annualized cost (TAC) of
the RD unit progressively decreased as the reac-
tion rate intensied. Compared to conventional
RD, the optimal outcomes of the hybrid system
exhibited a 12% reduction in TAC and a 29%
reduction in energy consumption43.
Industrial scale studies conducted by Jiangsu
Jiutian High-Tech Co., Ltd. developed a 3000
t/a isopropanol separation facility hybridizing
distillation and molecular sieve membrane tech-
nology for Shenyang Sanjiu Pharmaceutical Co.,
Ltd. e isopropanol vapor (about 12 wt% water
content) was dehydrated using the vapor perme-
ation (VP) module to get the isopropanol prod-
uct. A comparable coupling plant constructed
by Jiangsu Jiutian High-Tech Co., Ltd. is the
8000 t/a distillation-molecular sieve membrane
coupling apparatus for the separation of etha-
nol and water. e VP module was positioned
at the apex of the distillation column to disrupt
the azeotrope of ethanol and water. e opera-
tional cost decreased by 31.2% vs conventional
extractive distillation. e 78 wt% acetonitrile
vapor stream from the top of the acetonitrile
concentration column was directed into the VP
module for dehydration, thereby disrupting the
azeotrope, before proceeding to the acetonitrile
atmospheric distillation column. is hybrid
process exhibited a signicant safety margin,
elevated energy eciency, and minimal liquid
circulation, resulting in reduced operational
energy consumption (the steam consumption
of the conventional process is 4 t/t, whereas the
novel process consumes 1.6–2 t/t)82.
3 Conclusions andFinal Remarks
Solvent recovery (as opposed to disposal) is a
stepping stonefor environmental safety and sus-
tainability. As the need for sustainable indus-
trial practice rises, membrane-based processes
gain prominence over traditional, energy-inten-
sive distillation-based methods due to their
ability to recover high-purity products and the
signicant reductions achieved in energy, oper-
ating costs, and emissions. Nevertheless, these
conventional technologies remain relevant on
account oftheir capacity to treat complex solvent
mixtures.
Hybridization serves as a powerful technique
to optimize both the cost-eectiveness and envi-
ronmental impact of solvent recovery processes.
By combining the energy eciency of membrane-
based systems with the robustness of distillation,
hybrid processes signicantly reduce operational
energy costs and emissions compared to conven-
tional distillation methods. Simultaneously, they
mitigate the substantial capital expenditures and
operational constraints linked to independent
membrane systems, providing increased exibil-
ity. is comprehensive strategy not only dimin-
ishes total emissions but also enhances process
eciency, oering a sustainable and economically
feasible method for attaining high-purity separa-
tions and minimizing the environmental impact
of industrial activities.
e future of solvent recovery may rely on
process intensication solutions that hybridize
distillation and membrane technologies; how-
ever, improved membranes (e.g., mixed-matrix
membranes and metal–organic frameworks
instead of commercially available options) could
be utilized to increase the process separation
eciency further. Advancements in membrane
materials, mass transport systems, and hybrid
separation processesare thus crucial to surpass-
ing current limitations in process feasibility and
optimizing separation and energy eciency.
is, in turn, could expand the applicability of
solvent recovery technologies, furthering their
adaptation to achieve zero-liquid discharge and
circular economy objectives, thus promot-
ingenvironmental sustainability.
Publisher’s Note
Springer Nature remains neutral with regard to
jurisdictional claims in published maps and insti-
tutional aliations.
Springer Nature or its licensor (e.g. a society or
other partner) holds exclusive rights to this article
under a publishing agreement with the author(s)
or other rightsholder(s); author self-archiving of
the accepted manuscript version of this article is
solely governed by the terms of such publishing
agreement and applicable law.

UNCORRECTED PROOF
12
S. Srishti
J. Indian Inst. Sci.| VOL xxx:x | xxx–xxx xxx 2025 | journal.iisc.ernet.in
Funding
is article is funded by Indian Institute of
Science.
Declarations
Conict of interest
e authors declare no conicts of interest,
whether nancial or non-nancial.
Ethical Approval
All authors have read, comprehended, and com-
plied, as relevant, with the ’Ethical Responsi-
bilities of Authors’ statement outlined in the
Instructions for Authors.
Received: 24 November 2024 Accepted: 25 February
2025
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S. Srishti is a chemical engineering
researcher and is currently a project intern
at IISc in membrane-based separations and
bioenergy. She has previously worked on
lithium-ion enrichment for battery applica-
tions. Her research experience includes
membrane separation, biogas production, and bio-methana-
tion, with contributions in dierent journals. She previously
worked as a project associate in the bioengineering and
environmental sciences laboratory at CSIR-IICT. She com-
pleted her Master’s from Osmania University, Hyderabad,
and is an HPCL-NGIC awardee. She is passionate about
exploring innovative solutions for energy and environmen-
tal challenges.
Aparna Anilkumar is a PhD student at
the Centre for Sustainable Technologies,
IISc Bengaluru. Prior to this, she has
worked as Project associate at the same
department, as well as consultant/engineer
at multiple engineering consultancies within the energy
industry. Her qualifying degree is an Integrated Masters in
Chemical Engineering from the University of Aberdeen,
Scotland. During her time at UoA, she was awarded the
Norman Levy Memorial Prize and the Atkins Engineering
scholarship.
Yagnaseni Roy is an Assistant Professor
in the Centre for Sustainable Technologies
(CST) at the Indian Institute of Science
(IISc), Bangalore. Before joining IISc, she
completed her post-doctoral training at the
University of Twente, in the Sustainable
Process Technology (SPT) group. She attained her MS and
PhD degrees at the Massachusetts Institute of Technology
(MIT), in Prof. John H. Lienhard’s group in the Mechanical
Engineering Department. Her postdoctoral and graduate
work focused on inter-species selectivity in nanoltration
(NF) and reverse osmosis (RO) membranes, using both
experimental and numerical modeling-based investigations.