MPa CO2 Research Articles

Fast CO2 Sequestration, Activation, and Catalytic Transformation Using N-Heterocyclic Olefins

N-Heterocyclic Olefin (NHO) with high electronegativity at the terminal carbon atom was found to show a strong tendency for CO2 sequestration, affording a CO2 adduct (NHO-CO2). X-ray single crystal analysis revealed the bent geometry of the binding CO2 in the NHO-CO2 adducts with an O-C-O angle of 127.7-129.9°, dependent on the substitute groups of N-heterocyclic ring. The length of the C(carboxylate)-C(NHO) bond is in the range of 1.55-1.57 Å, significantly longer than that of the C(carboxylate)-C(NHC) bond (1.52-1.53 Å) of the previously reported NHC-CO2 adducts. The FTIR study by monitoring the ν(CO2) region of transmittance change demonstrated that the decarboxylation of NHO-CO2 adducts is easier than that of the corresponding NHC-CO2 adducts. Notably, the NHO-CO2 adducts were found to be highly active in catalyzing the carboxylative cyclization of CO2 and propargylic alcohols at mild conditions (even at ambient temperature and 0.1 MPa CO2 pressure), selectively giving α-alkylidene cyclic carbonates in good yields. The catalytic activity is about 10-200 times that of the corresponding NHC-CO2 adducts at the same conditions. Two reaction paths regarding the hydrogen at the alkenyl position of cyclic carbonates coming from substrate (path A) or both substrate and catalyst (path B) were proposed on the basis of deuterium labeling experiments. The high activity of NHO-CO2 adduct was tentatively ascribed to its low stability for easily releasing the CO2 moiety and/or the desired product, a possible rate-limiting step in the catalytic cycle.

Enhanced hydroformylation by carbon dioxide‐expanded media with soluble Rh complexes in nanofiltration membrane reactors

A novel process for continuous hydroformylation in CO2‐expanded liquids (CXLs) is demonstrated using bulky phosphite ligands that are effectively retained in the stirred reactor by a nanofiltration membrane. The reactor is operated at 50°C with a syngas pressure of 0.6 MPa to avoid CO inhibition of reaction rate and selectivity. The nanofiltration pressure is provided by ∼3.2 MPa CO2 that expands the hydroformylation mixture and increases the H2/CO ratio in the CXL phase resulting in enhanced turnover frequency (∼340 h−1), aldehydes selectivity (>90%) and high regioselectivity (n/i ∼8) at nearly steady operation. The use of pressurized CO2 also reduces the viscosity in the CXL phase, thereby improving the mass‐transfer properties. Constant permeate flux is maintained during the 50 h run with Rh leakage being less than 0.5 ppm. This technology concept has potential applications in homogeneous catalytic processes to improve resource utilization and catalyst containment for practical viability. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4287–4296, 2013

Carbon Dioxide-Facilitated Low-Temperature Hydrogen Desorption from Polyaminoborane

Gaseous CO2 environments dramatically enhance the thermolytic dehydrogenation of polyaminoborane (PAB) at 85 - 90 °C. By exposing PAB to 2.07 MPa CO2, 5.48 wt % hydrogen based on the mass of ammonia borane (AB) desorbs in less than 1 h, while 4 h is required to generate 5.04 wt % hydrogen by maintaining PAB at 120 °C without using CO2. The total hydrogen desorbed from the initial AB is 11.38 wt % under the CO2 atmosphere at 85 °C, including the hydrogen release during the transition from AB to PAB. The main contributing factors to the facile hydrogen release are the promoting effect of newly formed formic acid and the exothermic effect of the reaction between PAB and CO2. Spectroscopic and elemental analyses of the solid spent PAB confirm the degree of dehydrogenation and indicate that the decomposed residue has an empirical formula of BN0.86H2.34(CO2)0.17.

Cycloaddition Reaction of Carbon Dioxide to Epoxides Catalyzed by Polymer‐Supported Quaternary Phosphonium Salts

Polymer‐supported quaternary phosphonium salt (PS‐QPS) was explored as effective catalyst for the coupling reaction of carbon dioxide with epoxides. The results indicated that cyclic carbonates with high yields (98.6%) and excellent selectivity (100%) could be prepared at the conditions of 5 MPa CO2, 150°C, and 6 h without the addition of organic solvents or cocatalysts. The effects of various reaction conditions on the catalytic performance were investigated in detail. The catalyst is applicable to a variety of epoxides, producing the corresponding cyclic carbonates in good yields. Furthermore, the catalyst could be recovered easily and reused for five times without loss of catalytic activity obviously. A proposed mechanism for synthesis of cyclic carbonate in the presence of PS‐QPS was discussed. The catalyst was characterized by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and Fourier transform infrared (FT‐IR) spectrum. It is believed that PS‐QPS is of great potential for CO2 fixation applications due to its unusual advantages, such as easy preparation, high activity and selectivity, stability, low cost, and reusability.

Microporous organic networks bearing metal-salen species for mild CO2 fixation to cyclic carbonates

This work shows that porous solid systems for catalytic carbon dioxide fixation can be developed by a direct assembly of metal-salen containing building blocks with organic connectors through a carbon–carbon bond formation reaction. For use as a dihalo building block, Al, Cr, Co-salen building blocks with two iodo groups were prepared. Sonogashira coupling of these building blocks with tetra(4-ethynylphenyl)methane resulted in microporous organic networks (MONs) bearing Al, Cr, and Co-salen species (Al-MON, Cr-MON, Co-MON). Scanning electron microscopy (SEM) showed that the materials had granular or spherical shapes. Brunauer–Emmett–Teller (BET) analysis revealed surface areas of up to 522–650 m2 g−1, and microporosity (<2 nm). The thermal stability of the materials was dependent on the degree of networking. Their chemical components were characterized by solid-phase 13C-nuclear magnetic resonance spectroscopy (NMR) and X-ray photoelectron spectroscopy (XPS). The materials containing metal-salen (M-MON) showed excellent chemical conversion of carbon dioxide with epoxide to cyclic carbonates under mild conditions (60 °C and 1 MPa CO2). Among the M-MONs, the Co-MON showed the best reactivity for carbon dioxide conversion to cyclic carbonates with 1400–1860 TON and 117–155 h−1 TOF. The size effect of epoxides in CO2 fixation was observed due to the microporosity of Co-MON.

Palladium-catalyzed synthesis of indole-3-alkynones via direct carbonylation of indoles

A new method has been developed for the Pd-catalyzed direct carbonylation of indoles with phenylacetylenes. The process involved the initial iodination of the indole to afford the corresponding 3-iodo-indole, which was subsequently carbonylated with a variety of different alkynes using Pd(0) to yield the indole-3-alkynones. In contrast to the traditional Pd-catalyzed oxidative carbonylation strategy, which involves the Pd(II)-mediated activation of the aromatic C-H bonds, the aromatic C-H bonds in the current process were activated by iodine oxidation, eliminating the problems associated with the reduction of Pd(II) to Pd(0) under the CO atmosphere. Following an extensive screening process, Pd(OAc)2/CuI was identified as the most efficient catalyst system for the reaction in the presence of a base and iodine as an oxidant under mild conditions (0.2 MPa CO, 90 °C). The reaction provided the desired products in moderate to excellent isolated yields (up to 94%) and good tolerance to a variety of different functional groups. The structure of a representative alkynone product (3he) was unambiguously verified by X-ray single crystal structure analysis. Furthermore, the carbonylation products underwent a three-component reaction with sodium azide and benzyl bromide to give the corresponding 1,2,3-triazole analogues in the absence of any catalyst, thus expanding the synthetic application of the current methodology. 采用共合成法制备了一系列不同硅氨基含量的介孔氧化硅 SBA-15, 在其孔道中引入 Keggin 型钨磷酸, 且其含量随硅氨基含量的增加而增加. 考察了不同处理温度下杂多酸的热稳定性, 发现焙烧后钨物种能在 SBA-15 孔道内高度分散. 以 H2O2 为氧化剂, 研究了该催化剂在环己烯环氧化反应中的催化活性, 考察了杂多酸负载量和焙烧温度对催化活性的影响. 结果表明, 400 °C 处理后的钨磷酸催化剂具有高的反应活性和重复使用性能.

An Approach for Micropropagation of Blueberry (&amp;lt;i&amp;gt;Vaccinium corymbosum&amp;lt;/i&amp;gt; L.) Plants Mediated by Temporary Immersion Bioreactors (TIBs)

A new procedure for blueberry (Vaccinium corymbosum L.) micropropagation in programmed Temporary Immersion Bioreactors (TIBs based on two separate bottles) was developed for the commercial genotypes Biloxi, Sharp Blue and Brillita. Plant cultures were developed in a controlled environment with 0.4 MPa CO2 enrichment, sucrose-reduced medium, and light intensity of 60 mM m-2·s-1. Principal component analysis showed that component 1 (C1) grouped 64.08% of the total variability, while the first two components accounted for 86.97%. Representation of the principal components demonstrated three clusters corresponding with the blueberry genotypes, and within each cluster plants micropropagated in agar-base medium grouped separately from those plants multiplied in TIBs. Both plant number and total internodes traits (related to the productive efficiency) were demonstrated superior in blueberries propagated in TIBs. Additionally, when transferred to greenhouse conditions, blueberries propagated in TIBs showed higher adaptability and growing rates than those cultured by the conventional approach, altogether evidencing the occurrence of a photomixotrophic stage in the vitroplantlets cultured in TIBs.

Controlling crystal phase transition from form II to I in isotactic poly-1-butene using CO2

Controlling crystal phase transition from modification II to I in isotactic Poly-1-butene (iPB-1) using CO2 is presented in this article. The intrinsic kinetics of CO2-induced phase transition from modification II to I in iPB-1 at 40 °C and different CO2 pressures were detected using in situ high-pressure Fourier transform infrared spectroscopy (FTIR) and correlated by Avrami equation. Sorption of CO2 in iPB-1 matrix was measured at 40 °C and different CO2 pressures using both FTIR and magnetic suspension balance (MSB) and the diffusivity was determined by Fick's second law. An algorithm combining the CO2 diffusion and induced phase transition was subsequently proposed to calculate the CO2 concentration as well as the phase transition degree in the iPB-1 matrix with different thickness at different saturation time. The calculated phase transition degree in the iPB-1 agreed well with the FTIR results. In addition, the yield stresses of iPB-1 specimens annealed in the air and 6 MPa CO2 at 40 °C with different durations were also experimentally investigated. The algorithm was applied to predict the phase transition degree of the iPB-1 specimens. The appropriate CO2 treatment time for getting high yield stress was in consistent with that predicted by the algorithm.

Insights into the deactivation and reactivation of Ru/TiO2 during Fischer–Tropsch synthesis

The catalytic performance of Ru/TiO2 for the production of hydrocarbons via Fischer–Tropsch synthesis (FTS) has been evaluated in this work. Ru/TiO2 exhibits high CO conversion rates (523K, 2.5MPa H2, 1.25MPa CO) that decrease significantly with time-on-stream. To recover the initial catalytic performance, different treatments using H2 or air have been tested. The evolution of the catalyst structure during FTS and after the re-activation protocols have been explored by a combination of ex situ and in situ techniques. Ru agglomeration, oxidation, and formation of Ru–volatile species are not responsible for the observed deactivation. However, Raman and infrared (FTIR) spectroscopy have confirmed the presence of coke and alkyl chains on the spent catalysts. These species hinder the adsorption of the reactants on the active sites and are the primary reason for the observed decrease in the catalytic activity. These carbonaceous species can be removed by severe thermal treatments in air. However, this latter treatment drastically alters the morphology of the Ru/TiO2, which leads to a substantial loss of catalytic activity.

Corrosion Characteristics of 2205 Duplex Stainless Steel in High Temperature and High Pressure Environment Containing H&lt;sub&gt;2&lt;/sub&gt;S/CO&lt;sub&gt;2&lt;/sub&gt;

The corrosion characteristics of 2205 duplex stainless steel in high- temperature and high-pressure (HT and HP) environments containing H2S/CO2 are investigated in this paper. After corroded 720 hours in the condition of 3.5 MPa H2S, 3.5 MPa CO2, 205°C, 15% NaCl and a sulfide content of 3g/L, one layer of comparably thick corrosion product are formed on the surface of the specimens. The corrosion products, which are relatively porous, lose its protection to the matrix. Lots of pitting are found on the surface of the steel and intercrystalline fracture and transcrystalline fracture are generated in the bottom of the pitting, which indicates its high sensitivity to stress corrosion crack (SSC). Also, the phenomenon of selective corrosion, a priority corrosion of α phase and minor corrosion or non-corrosion of γ phase, is observed after the corrosion process.

Cyclic carbonate synthesis from epoxides and CO2 over cyanocobalamin/n -Bu4 NI

The synthesis of cyclic carbonates from epoxides and carbon dioxide catalyzed by cyanocobalamin and n-Bu4NI system was achieved under 0.8?MPa CO2 pressure at 140 degrees C without organic solvents. Propylene carbonate was obtained in 99% yield within 6?h under the optimized reaction conditions. The cyanocobalamin catalyst could be recycled with water and retained moderate catalytic activity. Copyright (c) 2012 John Wiley & Sons, Ltd.

Dissolution rates of alkaline rocks by carbonic acid: Influence of solid/liquid ratio, temperature, and CO2 pressure

Dissolution rates of alkaline rocks, including wollastonite (CaSiO3), olivine (Mg2SiO4), and phlogopite (KMg3AlSi3O10(OH)2), with high pressure aqueous CO2 solution were measured to examine the feasibility of CO2 fixation via carbonation. Influence of solid/liquid ratio (1.0–10g/250mL), temperature (303–353K), and CO2 pressure (1.0–3.0MPa) on the extraction rates of calcium or magnesium ions was investigated. Under the experimental conditions studied, the calcium ion extraction rate from wollastonite was the highest among the three rock samples studied. The calcium concentration reached about 120mg/L, and about 12% of the calcium in wollastonite sample was extracted after 60min at 353K with 1.0MPa CO2. The calcium and magnesium extraction ratios from the alkaline rocks were much lower than those from waste concrete powder. Increasing the extraction time and temperature would be an effective way to promote calcium extraction from wollastonite.

CO2 Copolymers from Epoxides: Catalyst Activity, Product Selectivity, and Stereochemistry Control

The use of carbon dioxide as a carbon source for the synthesis of organic chemicals can contribute to a more sustainable chemical industry. Because CO(2) is such a thermodynamically stable molecule, few effective catalysts are available to facilitate this transformation. Currently, the major industrial processes that convert CO(2) into viable products generate urea and hydroxybenzoic acid. One of the most promising new technologies for the use of this abundant, inexpensive, and nontoxic renewable resource is the alternating copolymerization of CO(2) and epoxides to provide biodegradable polycarbonates, which are highly valuable polymeric materials. Because this process often generates byproducts, such as polyether or ether linkages randomly dispersed within the polycarbonate chains and/or the more thermodynamically stable cyclic carbonates, the choice of catalyst is critical for selectively obtaining the expected product. In this Account, we outline our efforts to develop highly active Co(III)-based catalysts for the selective production of polycarbonates from the alternating copolymerization of CO(2) with epoxides. Binary systems consisting of simple (salen)Co(III)X and a nucleophilic cocatalyst exhibited high activity under mild conditions even at 0.1 MPa CO(2) pressure and afforded copolymers with >99% carbonate linkages and a high regiochemical control (∼95% head-to-tail content). Discrete, one-component (salen)Co(III)X complexes bearing an appended quaternary ammonium salt or sterically hindered Lewis base showed excellent activity in the selectively alternating copolymerization of CO(2) with both aliphatic epoxides and cyclohexene oxide at high temperatures with low catalyst loading and/or low pressures of CO(2). Binary or one-component catalysts based on unsymmetric multichiral Co(III) complexes facilitated the efficient enantioselective copolymerization of CO(2) with epoxides, providing aliphatic polycarbonates with >99% head-to-tail content. These systems were also very efficient in catalyzing the terpolymerization of cyclohexene oxide, propylene oxide and CO(2). The resulting terpolymer had a single glass-transition temperature and a single thermolysis peak. This Account also provides a thorough mechanistic understanding of the high activities, excellent selectivities, and unprecedented stereochemical control of these Co(III)-based catalysts in the production of CO(2) copolymers . The catalysis occurs through a cooperative monometallic mechanism, in which the Lewis acidic Co(III) ion serves as electrophile to activate then epoxide and the nucleophilic counterion or cocatalyst serves as a nucleophile to initiate polymer-chain growth. The high activity and excellent regioselectivity observed in the epoxide ring-opening reactions results from epoxide activation through the moderate electrophilicity of the Co(III) ion, the fast insertion of CO(2) into the Co-O bond, and the facile dissociation of the propagating carboxylate species from the central metal ion. The reversible intra- or intermolecular Co-O bond formation and dissociation helps to stabilize the active Co(III) species against reversion to the inactive Co(II) ion. We also describe our laboratory's recent preparation of the first crystalline CO(2)-based polymer via highly stereospecific copolymerization of CO(2) and meso-cyclohexene oxide and the selective synthesis of perfectly alternating polycarbonates from the coupling of CO(2) with epoxides bearing an electron-withdrawing group.

Efficient pathway for CO2 transformation to cyclic carbonates by heterogeneous Cu and Zn salen complexes

A series of silica supported Salen type Zn(II) and Cu(II) complexes were prepared and characterized. The obtained materials were characterized by X-ray diffraction (XRD), sorption measurement (BET), Fourier transform infrared spectroscopy (FT-IR), atomic absorption spectroscopy (AAS), atomic force microscopy (AFM), scanning electron micrograph (SEM), thermal and elemental analysis. The chemical fixation of CO2 to form cyclic carbonates in the presence of a Lewis base was efficiently performed by this heterogeneous catalyst system. Very high yield and conversions were obtained at 1.0 MPa CO2 atmosphere without an addition of any solvent. The active heterogeneous Cu-DTBSA was efficiently transformed CO2 into cyclic carbonates while the reusability of the Cu-DTBSA is eight times with minimal decrease in yield.

Bimetallic Co-Fe nanocrystals deposited on SBA-15 and HMS mesoporous silicas as catalysts for Fischer–Tropsch synthesis

Fischer–Tropsch synthesis (493K, 0.62MPa CO, 1.24MPa H2) has been performed over monometallic and bimetallic Co and/or Fe clusters deposited on mesoporous silicas (HMS and SBA-15). Catalysts have been prepared by incipient wetness impregnation and characterized by N2 adsorption–desorption isotherms, X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), and transmission electron microscopy (TEM).HMS supported Co-Fe catalyst showed the highest activity and C5+ hydrocarbon selectivity, while Co-Fe/SBA-15 catalyst revealed the highest selectivity to alcohols. Both bimetallic catalysts were more active toward the C2–C4 hydrocarbon fraction, with an enhancement in the selectivity to C2, C3 and 1-C4 olefins. Both bimetallic catalysts showed greater chain growth probability values than the monometallic iron based catalysts although their performance in catalytic tests were more close to the iron catalyst.

Corrosion of N80 tubing steel in brine at 1·2 MPa CO2 containing trace amounts of H2S

The corrosion of N80 tubing steel was measured electrochemically in an autoclave at an overall carbon dioxide pressure of 1·2 MPa. Both potentiodynamic polarisation curves and electrochemical impedance data were analysed to obtain the relevant kinetic parameters. The influences of H2S pressure and immersion time on the corrosion of N80 were analysed in detail. The results indicate that protective sulphide scales may form at higher partial pressures of H2S and greatly decreased the corrosion rate of N80 steel as the immersion time increased. Thus, the capacitive loop shrinks gradually in the low frequency region and eventually shifts to a single capacitive loop at low H2S concentration, whereas at higher H2S concentrations, the capacitive loop gradually disappeared, and diffusion controlled processes then predominated owing to the formation of a protective corrosion scale at longer immersion times.

Mg‐Silicate Carbonation Based on an HCl‐ and NH3‐Recyclable Process: Effect of Carbonation Temperature

AbstractA new indirect mineral carbonation process is studied which could mitigate anthropogenic CO2 emissions. In this process, magnesium silicate is dissolved in HCl and the resulting MgCl2 solution is subsequently reacted with CO2 in NH3. HCl and NH3 are recovered from NH4Cl in a two‐step thermal decomposition. Carbonation is investigated from 30 °C to 180 °C at 4 MPa CO2 pressure and Mg‐carbonate morphology transformations with increasing temperature are identified. Nesquehonite (MgCO3 · 3H2O) is obtained below 70 °C, hydromagnesite (Mg5(CO3)4(OH)2 · 4H2O) is formed at 100 °C, and further temperature increase to 180 °C leads to magnesite (MgCO3) precipitation. Nesquehonite and magnesite can fix more CO2 per mole Mg than hydromagnesite.

Effect of 3-D stress state on adsorption of CO2 by coal

Abstract Though several models have been developed to describe unconfined swelling of coal exposed to adsorbing fluids such as CH 4 or CO 2 at elevated pressure, the role of stress supported by the solid framework ( i.e. an effective stress in excess of the fluid pressure) has not hitherto been considered in thermodynamic descriptions of the adsorption process. In this paper, we develop a thermodynamic model, based on statistical mechanics theory, for the equilibrium concentration of CO 2 adsorbed by stressed coal matrix material. For unconfined (zero effective stress) conditions, the model describes the change in adsorbed concentration as a combined effect of the changing chemical activity of the fluid and the changing availability of adsorption sites in the nanoporous solid matrix. For an ideal gas and an adsorbate under unconfined conditions, this model reduces to the widely applied Langmuir model. When the solid framework of the coal matrix material in subjected to a general stress state σ ij the adsorption energy of a single molecule is increased by a general stress–strain work term. The effect of this in the adsorption model is that the adsorbed concentration is reduced by several percent to several tens of percent for effective stress magnitudes similar to those expected in situ during (E)CBM production. This prediction was confirmed by a preliminary experiment, performed on a sample of Brzeszcze 364 high volatile bituminous coal at 15 MPa fluid pressure, a temperature of 40 °C, and an effective hydrostatic stress or confining pressure of 1–25 MPa. This showed that the equilibrated adsorption capacity at 1 MPa effective stress of 1.38 mmol·g coal − 1 was reduced by almost 10% at 25 MPa effective stress. Combining our thermodynamic model with poroelasticity, a full constitutive equation is derived, which describes the competitive relation between adsorption-induced swelling strain and poroelastic compression, as a function of adsorbed concentration, fluid pressure and state of stress. Our equations offer a basis for full coupled modelling of the problem of injecting or producing a (single) fluid phase such as CO 2 into or from a coal seam under in situ (E)CBM conditions. Moreover, the model provides a means to estimate the effect of “self-stressing” as a result of adsorption of CO 2 by coal under confined in situ conditions. A first analysis of this effect for coal initially at 25 MPa effective stress, with CO 2 injection at 15 MPa, showed an increase in effective stress to 35–105 MPa, which would lower CO 2 uptake at equilibrium by a total amount of ~ 13–30% compared to conventional adsorption measurements made at 15 MPa CO 2 pressure.

Effects of silty sand on CO2 corrosion behavior of low-Cr tubing steel

An experimental study was carried out to assess the effects of silty sand on the CO2 corrosion behavior of 1 wt% Cr (1Cr) and 3 wt% Cr (3Cr) tubing steel under 0.5 MPa CO2 at 100°C and 1.5 m/s flow velocity. The 1Cr and 3Cr specimens both suffered general corrosion, but the surface was coarser in the pure CO2 corrosion environment. Under silty sand conditions, severe pitting corrosion occurred on the 1Cr specimens and some acicular pitting appeared on the 3Cr specimens. The average corrosion rates of 1Cr and 3Cr steels increased by factors of 3 and 1.6, respectively. The corrosion products were analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and electrical impedance spectroscopy (EIS). The results show that silty sand acts as an inclusion in corrosion product films and reduces the homogeneity and density of the products, rather than abrading the corrosion film. Ion-diffusion channels may build up around the irregular silty sand; this would degrade the protective capabilities of the product films and aggravate corrosion.

Development of Crystallization in PLA during Solid-State Foaming Process using Sub-Critical CO2

Crystallinity of PLA is an important factor that affects its processability, mechanical strength, biodegradability, and service temperature. In this paper crystallization of PLA in solid state foaming process was studied in two main aspects: gas sorption in saturation stage, and heating as well as stretching in foaming stage. During CO2 saturation the equilibrium crystallinity jumped from 9.7% at 2 MPa to 26.4% at 3 MPa CO2 pressure. Further increases in saturation pressure did not increase the crystallinity. In the gas sorption stage of the process, it was found that the crystallization reached equilibrium at approximately the same time as the gas sorption reached equilibrium. Within the range of 2 to 5 MPa saturation pressures and 60 to 100°C foaming temperatures, a maximum crystallinity of 26.8% was observed in the foamed PLA. Crystallinity increased with the extent of cell-wall stretching during the foaming process.