Recovery Of Homogeneous Catalysts Research Articles

Organic Solvent Nanofiltration in Pharmaceutical Applications.

Separation and purification in organic solvents are indispensable procedures in pharmaceutical manufacturing. However, they still heavily rely on the conventional separation technologies of distillation and chromatography, resulting in high energy and massive solvent consumption. As an alternative, organic solvent nanofiltration (OSN) offers the benefits of low energy consumption, low solid waste generation, and easy scale-up and incorporation into continuous processes. Thus, there is a growing interest in employing membrane technology in the pharmaceutical area to improve process sustainability and energy efficiency. This Review comprehensively summarizes the recent progress (especially the last 10 years) of organic solvent nanofiltration and its applications in the pharmaceutical industry, including the concentration and purification of active pharmaceutical ingredients, homogeneous catalyst recovery, solvent exchange and recovery, and OSN-assisted peptide/oligonucleotide synthesis. Furthermore, the challenges and future perspectives of membrane technology in pharmaceutical applications are discussed in detail.

Recovery of Homogeneous Platinoid Catalysts from Pharmaceutical Media: Review on the Existing Treatments and the Perspectives of Membrane Processes.

Catalyst recovery is a major challenge for reaching the objectives of green chemistry for industry. Indeed, catalysts enable quick and selective syntheses with high reaction yields. This is especially the case for homogeneous platinoid catalysts which are almost indispensable for cross-coupling reactions often used by the pharmaceutical industry. However, they are based on scarce, expensive, and toxic resources. In addition, they are quite sensitive and degrade over time at the end of the reaction. Once degraded, their regeneration is complex and hazardous to implement. Working on their recovery could lead to highly effective catalytic chemistries while limiting the environmental and economic impacts of their one-time uses. This review aims to describe and compare conventional processes for metal removal while discussing their advantages and drawbacks considering the objective of homogeneous catalyst recovery. Most of them lead to difficulty recycling active catalysts due to their ability to only treat metal ions or to chelate catalysts without the possibility to reverse the mechanism. However, membrane processes seem to offer some perspectives with limiting degradations. While membranes are not systematically the best option for recycling homogeneous catalysts, current development might help improve the separation between pharmaceutical active ingredients and catalysts and enable their recycling.

Recovery of homogeneous photocatalysts by covalent organic framework membranes

Transition metal-based homogeneous photocatalysts offer a wealth of opportunities for organic synthesis. The most versatile ruthenium(II) and iridium(III) polypyridyl complexes, however, are among the rarest metal complexes. Moreover, immobilizing these precious catalysts for recycling is challenging as their opacity may obstruct light transmission. Recovery of homogeneous catalysts by conventional polymeric membranes is promising but limited, as the modulation of their pore structure and tolerance of polar organic solvents are challenging. Here, we report the effective recovery of homogeneous photocatalysts using covalent organic framework (COF) membranes. An array of COF membranes with tunable pore sizes and superior organic solvent resistance were prepared. Ruthenium and iridium photoredox catalysts were recycled for 10 cycles in various types of photochemical reactions, constantly achieving high catalytical performance, high recovery rates, and high permeance. We successfully recovered the photocatalysts at gram-scale. Furthermore, we demonstrated a cascade isolation of an iridium photocatalyst and purification of a small organic molecule product with COF membranes possessing different pore sizes. Our results indicate an intriguing potential to shift the paradigm of the pharmaceutical and fine chemical synthesis campaign.

Better than Distillation: Electrochemical Recovery of Homogeneous Catalysts

Better than Distillation: Electrochemical Recovery of Homogeneous Catalysts

Conceptual study of co-product separation from catalyst-rich recycle streams in thermomorphic multiphase systems by OSN

Homogeneous transition metal catalysts allow for high selectivity at mild reaction conditions. However, very high recoveries of the precious catalyst are decisive for the development of economic processes, especially in case of reactions with an atom economy below 100% since co-products and their potential accumulation have to be considered. To address this issue, an innovative process concept is investigated, which exploits thermomorphic multiphase systems combined with organic solvent nanofiltration for homogeneous catalyst recovery and co-product removal. In this concept, the reaction takes place at elevated temperature in a homogeneous liquid phase, while the reactor effluent is cooled down, inducing a phase split. This allows for the separation of a product-rich non-polar and a catalyst-rich polar phase that is recycled into the reactor. The current article investigates this concept considering a reductive amination reaction as case study based on an experimental membrane screening and a model-based evaluation. DuraMem 150 (T1) proved to be the best membrane for all tested solvents as catalyst ligand rejections higher than 99% and a removal of the co-product water were achieved. The model-based evaluation indicated a final OSN-process of three stages for the solvent methanol and the requirement of a subsequent solvent recovery that is realized by distillation.

Frontispiece: Thermomorphic Multiphase Systems: Switchable Solvent Mixtures for the Recovery of Homogeneous Catalysts in Batch and Flow Processes

Thermomorphic Multiphase Systems (TMS) enable the application of transition metal catalysts in a homogeneous reaction environment with subsequent separation of catalyst and products after reaction. A change in temperature is used to switch from monophasic to biphasic mixtures. Common solvents and catalysts without distinct modification allow for straightforward application of TMS. This concept extends the toolbox of homogeneous transition metal catalysis in chemical process technology. For more details, see the Review article by J. M. Dreimann et al. on page 11586 ff.

Thermomorphic Multiphase Systems: Switchable Solvent Mixtures for the Recovery of Homogeneous Catalysts in Batch and Flow Processes.

Over the past 20 years, thermomorphic multiphase systems (TMS) have been used as a versatile and elegant strategy for the recovery and recycling of homogeneous transition-metal catalysts, in both batch-scale experiments and continuously operated processes. TMS ensure a homogeneous reaction in a monophasic reaction mixture at reaction temperature and the recovery of the homogeneous transition-metal catalyst through liquid-liquid separation at a lower separation temperature. This is achieved by using at least two solvents, which have a highly temperature-sensitive miscibility gap. The suitability of commercially available solvents makes this approach highly interesting from an industrial point of view. For the first time, herein, all studies in the area of TMS are reviewed, with the aim of providing a concise and integral representation of this approach for homogeneous catalyst recovery. In addition to the discussion of examples from the literature, the thermodynamic fundamentals of the temperature-dependent miscibility of solvents are also presented. This review also gives key indicators to compare different TMS approaches, for instance. In this way, new solvent combinations and in-depth research, as well as improvements to existing approaches, can be addressed and promoted.

Greener Solvents in Homogeneous Catalyst Recovery

Greener Solvents in Homogeneous Catalyst Recovery

Technological evaluation of organic solvent nanofiltration for the recovery of homogeneous hydroformylation catalysts

The prevalence of homogeneous catalysts, to produce high value commodities in the surfactant and detergent range by upgrading inter alia syngas and short chain olefins, through metathesis, hydroformylation and hydrogeneration, is hampered by the expensive, waste generating and destructive thermal separation methods required for the recovery of these catalysts. By using the membrane technology of organic solvent nanofiltration (OSN), the successful recovery of two commercially available homogeneous catalysts, the rhodium-based complex, HRh(CO)(PPh3)3, and the cobalt-based complex, Co(C5H7O2)3, from the solvents representative of the hydroformylation and hydrogenation reactions, with the STARMEM 240 membrane, was performed. The energy-efficiency of OSN for homogeneous catalyst recovery, commonly alluded to in literature, was investigated by performing a technological evaluation between OSN and a conventional downstream recovery process such as distillation. It was found that, using the ST-240 membrane, catalyst concentrations in the permeate stream can be successfully reduced to near negligible amounts (<5ppm), similar to that of distillation but with significant energy and cost savings of up to 85% and 75%, respectively, for the different reaction systems.

Temperature-Controlled Reaction–Separation for Conversion of CO2 to Carbonates with Functional Ionic Liquids Catalyst

Carboxylic acid-based ionic liquids (CAILs) were designed and synthesized. They displayed temperature-dependent dissolution–precipitation transitions in propylene carbonate (PC) by controlling the chain length of the carboxyl group. It was found that it could be attributed to the temperature-controlled hydrogen-bond formation/broken between the CAILs components and PC by NMR investigations and DFT calculations. Such a unique phase behavior was successfully utilized for the cycloaddition reaction of CO2 with epoxides. Due to the activation of epoxide assisted by the hydrogen bond, the optimal ILs could show a 92% yield of PC within 20 min and quickly precipitate out from a homogeneous system at room temperature for easy recycling. The reversible phase transition phenomenon supplied an efficient way to combine activity and recovery of homogeneous catalysts, which is a benefit for energy-saving and industrial applications.

Carboxymethylcellulose‐supported palladium nanoparticles generated in situ from palladium(II) carboxymethylcellulose as an efficient and reusable catalyst for ligand‐ and base‐free Heck–Matsuda and Suzuki–Miyaura couplings

A novel palladium(II) carboxymethylcellulose (CMC‐PdII) was prepared by direct metathesis from sodium carboxymethylcellulose and PdCl2 in aqueous solution. Its catalytic activities were explored for Heck–Matsuda reactions of aryldiazonium tetrafluoroborate with olefins, and Suzuki–Miyaura couplings of aryldiazonium tetrafluoroborate with arylboronic acid. Both reactions proceeded at room temperature in water or aqueous ethanol media without the presence of any ligand or base, to provide the corresponding cross‐coupling products in good to excellent yields under atmospheric conditions. The CMC‐PdII and carboxymethylcellulose‐supported palladium nanoparticles (CMC‐Pd0) formed in situ in the reactions were characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, inductively coupled plasma atomic emission spectrometry, and scanning and transmission electron microscopies. The homogeneous nature of the CMC‐Pd0 catalyst was confirmed via Hg(0) and CS2 poisoning tests. Moreover, the CMC‐Pd0 catalyst could be conveniently recovered by simple filtration and reused for at least ten cycles in Suzuki–Miyaura reactions without apparently losing its catalytic activity. The catalytic system not only overcomes the basic drawbacks of homogeneous catalyst recovery and reuse but also avoids the need to fabricate palladium nanoparticles in advance. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Thermomorphic solvent selection for homogeneous catalyst recovery based on COSMO-RS

One method that has shown much promise due to its simplicity and effectiveness in homogeneous catalyst recovery is the use of thermomorphic solvent systems (TMS). In this contribution, a novel method for TMS solvent selection based on quantum chemical predictions of catalyst solubility and phase equilibrium is presented. This allows for solvent effects on the catalyst to be incorporated directly into the solvent screening process. A framework for TMS design is developed and implemented using the hydroformylation of 1-dodecene and the rhodium-Biphephos catalyst as an example reaction system. In this way, several promising TMS systems were identified. Experiments were then performed to validate the model based on catalyst partitioning and phase equilibrium. This was followed by conducting a series of reactions to investigate feasibility of the new TMS systems in the actual hydroformylation. In the end it was shown that although some problems arise from inconsistencies in phase equilibrium predictions, the method does provide a functioning a priori basis for TMS development.

Mineral Oil/Methanol: A Cheap Biphasic Reaction Medium with Thermomorphic Properties and Its Application to the Palladium‐Catalyzed Carbonylation of Nitrobenzene to Methyl Phenylcarbamate

AbstractWe developed the methanol/mineral oil system as a new thermomorphic solvent mixture that allows homogeneous catalyst recovery without the use of water or fluorinated solvents. Mineral oil (nujol) is cheap and shows a very limited miscibility with methanol at room temperature but becomes completely miscible at high temperatures. Here we report the synthesis of some phenanthrolines substituted with long‐chain alkyl groups, which render them soluble in hydrocarbons and insoluble in methanol, and their application to the palladium‐catalyzed carbonylation of nitrobenzene to methyl phenylcarbamate. Both the reagents and products of the catalytic reaction are much more soluble in methanol than in hydrocarbons, so an easy separation of the catalyst is possible.

Silica adsorbent design and process evaluation for recovery of homogeneous catalysts by reverse flow adsorption

AbstractThe goal of this work is to demonstrate the stability of reverse flow adsorption process for recovery of homogeneous catalysts and to study the influence of catalyst and adsorbent properties for optimizing the RFA process operation. Data used in simulations were obtained from our previous work. Two models are developed to describe the reversible adsorption. One which describes the adsorption of the metal containing species and second model that describes adsorption of the free ligand. It is shown that stable operation is reached, where leaching of metal is prevented. The RFA process can be applied for wide ranges of the catalyst's stability constants [100–1012 (dm3/mol)2] and it is specially applicable for the recovery of homogeneous catalysts that have a low metal concentration. Values of the adsorbent (βM = 0.8, α = 1850, PeP = 376.4, dp = 100 μm and εb = 0.5) and the column characteristics (Bo = 1.74 × 104 and N = 6.6 × 104) that provide a sharp concentration profile inside the bed are determined. Simulation of the recovery of Rh catalyst in the BASF hydroformylation process required a total adsorption bed volume of 6% of reactor volume. © 2008 American Institute of Chemical Engineers AIChE J, 2008

Polymeric Membrane Nanofiltration and Its Application to Separations in the Chemical Industries

AbstractThe application of membrane technology, particularly water‐based nanofiltration, as a separation process in the chemical industries has increased tremendously in recent years. However, the use of membranes capable of molecular separation in non‐aqueous systems (e.g. nanofiltration) is a relatively new and growing application of membrane technology. The main challenge in applying polymeric nanofiltration membranes to non‐aqueous systems is that the polymers developed for water‐based applications are not suitable. Polyimide is a particularly interesting polymer as it has excellent chemical resistance, and membranes produced from it provide desirable separation properties – i.e. economically viable flux and good separation of nanoscale molecules. Various research works have shown that commercial polyimide organic solvent nanofiltration (OSN) membranes, trademark STARMEM™,1 are robust and suitable for performing molecular separations. This work will discuss in detail the use of STARMEM™ in a pharmaceutical application. The EIC‐OSN process was developed for separating the enantiomers of chiral compounds in pharmaceutical applications. High optical purity (94.9%) of (S)‐phenylethanol from rac‐phenylethanol was achieved through the use of STARMEM™122. Process simulation of the ideal eutomer‐distomer system predicted that the highest theoretical resolvability from this process would be 99.2%. Other application areas of OSN are varied, including purification and fractionation in the natural products industry, homogeneous catalyst recovery, monomer separation from oligomers, etc. Currently, OSN is used in a small number of processes including a very large petrochemical application, but it has the potential to be applied to a wide range of separations across the full spectrum of the chemical industries.

Adsorption of homogeneous catalysts over functionalized silica adsorbents: Modelling of the competitive adsorption isotherms

The reverse flow adsorption (RFA) was proposed as a novel concept for the recovery of homogeneous catalysts. For the modelling of the RFA process it is important to have a good description of the adsorption of various complex species present in the solution. Therefore the goal of this paper is to develop an adequate model which can describe the adsorption of a homogeneous catalyst. In this research bis(triphenylphosphine) cobalt(II)dichloride ( CoCl 2 ( PPh 3 ) 2 ) was selected as a model catalyst. Since in a solution CoCl 2 ( PPh 3 ) 2 is always in equilibrium with its free metal centre CoCl 2 ( M ) , free ligand PPh 3 ( L ) and other complex forms, CoCl 2 ( PPh 3 ) and CoCl 2 ( PPh 3 ) 2 ( ML and ML 2 ), three models were evaluated ( M , M – ML and M – ML – ML 2 ) that combine the equilibrium of the complex forms present in the solvent with its competitive adsorption on the functionalized silica. Comparison of the model results with the experimental adsorption data shows that the model which takes all three forms M , ML and ML 2 , into account describes the results most consistently. The 2-(2-pyridyl)ethyl-functionalized silica and 3-(1-morpholino)propyl-functionalized silica were selected as promising adsorbents.

Evaluation of functionalized silica's for the adsorptive recovery of homogenous catalysts through interaction with the metal centre

The goal of this paper is the evaluation of functionalized silica's for the recovery of homogeneous catalysts by adsorption via its metal centre. As model catalysts, we selected bis(triphenylphosphine)cobalt(II)dichloride (CoCl 2(PPh 3) 2), bis(triphenylphosphine)palladium(II)dichloride (PdCl 2(PPh 3) 2) and tris(triphenylphosphine)rhodium(I)dichloride (RhCl(PPh 3) 3). Twelve functionalized groups selected from four classes containing one or more N-, O-, P- or S-atoms were evaluated. A preliminary selection of the adsorbents was done by investigating the adsorption of the metal salts for the cobalt and the palladium complex. The results could be explained by the Hard and Soft Acid Base (HSAB) theory. For the most suitable functionalized adsorbents, these experiments were extended by introducing the ligand in the system which promoted the competition of the functionalized groups on adsorbent and the ligands present in solution. These experiments demonstrated that different complex species are adsorbed. 2-(2pyridyl)ethyl-functionalized silica is selected as a promising adsorbent for adsorption of the CoCl 2(PPh 3) 2 from acetonitrile, while 3-(mercapto)propyl-functionalized silica is selected as a promising adsorbent for adsorption of the PdCl 2(PPh 3) 2 and RhCl(PPh 3) 3 from DMF. The presence of a ligand, an increase of the temperature and the presence of a solvent with the donor properties can decrease the adsorption equilibrium and need to be taken into account.

Vapor–liquid–liquid equilibria of perfluorohexane + CO 2 + methanol, +toluene, and +acetone at 313 K

Homogeneous catalysts offer many advantages over heterogeneous catalysts, such as higher activities and selectivities. However, recovery of homogeneous catalysts is often complicated by difficulties in separating these complexes from the reaction products. The use of gaseous carbon dioxide (CO 2) as miscibility switch for organic and fluorous phases has been proposed to overcome this limitation. By using CO 2 as a cosolvent, polar organic reactants can be homogenized with catalysts immobilized in a fluorous phase without using elevated temperatures. The phase behavior underlying this concept is investigated. High-pressure phase equilibria for the systems containing carbon dioxide, an organic (methanol, toluene, or acetone), and perfluoro- n-hexane were measured using a variable-volume view cell, by a method capable of rapid and facile measurement of compositions and density in both phases with no sampling or calibration.

Integrated Recovery and Recycling of Homogeneous Catalysts by Reverse Flow Adsorption: Selection of Suitable Adsorbents

A promising concept for the recovery of homogeneous catalysts is Reverse Flow Adsorption. In actual homogeneous catalyzed processes, a homogeneous transition-metal catalyst is at equilibrium with its free transition-metal center and ligands. Therefore, to apply Reverse Flow Adsorption, a combination of two adsorbents has to be used to reversibly adsorb: the transition-metal center and its ligands. The transition-metal center can be adsorbed by a suitable ligand immobilized onto a solid carrier, while the ligand is adsorbed by an immobilized transition-metal. Two groups of potential adsorbents were selected by the Hard and Soft Acid and Base (HSAB) theory for the adsorption of Co(II) and PPh3: (1) phosphor (polymer bound PPh3), sulfur (polymer bound methylsufanylmethyl) and chloride (polymer bound benzylchloride) functionalized adsorbents and (2) metal (Ag+, Co2 + and Na+) functionalized Amberlyst 15. The CoCl2 adsorption decreased, as predicted by the HSAB theory, according to: P > S > Cl. Metal functionalized adsorbents adsorbed the PPh3 with capacities decreasing as predicted by the HSAB theory: Ag+ > Co2 + > Na+. All adsorption interactions proved to be reversible.

CO2-Induced Miscibility of Fluorous and Organic Solvents for Recycling Homogeneous Catalysts

Fluorous biphasic chemistry enables the recovery of homogeneous catalysts but presents engineering challenges because of issues concerning phase contacting and solvent loss. The addition of gaseous CO2 to fluorous−organic biphasic systems results in a single homogeneous liquid phase at temperatures well below the upper critical solution temperature of the binary liquid mixture. This phenomenon is due to the high solubility of CO2 in both organic liquids and fluorocarbons, and it facilitates reactions and can also reduce fluorous solvent losses. We demonstrate two homogeneously catalyzed reactions, a hydrogenation and an epoxidation, which result in an enhancement in the turnover frequency of 70% and 50%, respectively, for the CO2-merged phase relative to the fluorous biphasic system. This creates new opportunities for the use of fluorous-sequestered catalysts.