Near-critical Methanol Research Articles

Activity of a Sulfonated Carbon-Based Catalyst Derived from Organosolv Lignin toward Esterification of Stearic Acid under Near-Critical Alcohol Conditions.

In this study, an environmentally benign carbon-based catalyst derived from extracted bagasse lignin (EL) was successfully synthesized by solvothermal carbonization and sulfonation with methane sulfonic acid (MSA). Interestingly, the results indicated that the use of MSA as a sulfonation agent made a catalyst with higher thermal stability than conventional sulfuric acid. Thus, in comparison to the catalyst prepared by using sulfuric acid, the catalyst prepared by using MSA (EL-MSA) exhibited higher catalytic activity in the esterification of stearic acid under near-critical methanol conditions. Under optimum conditions (260 °C for 5 min, a 9:1 methanol-to-stearic-acid molar ratio, 5 wt % catalyst loading, and 10% v/v toluene), the esterification over the EL-MSA catalyst promoted a 91.1% methyl stearate yield. Moreover, the results also revealed that the high thermal stability of the EL-MSA catalyst not only affects its great catalytic activity, but it also prevents damage to the porous structure and decomposition of acidic surface oxygen-containing functional groups. It contributes to the excellent reusability of the catalyst. After the fifth run, a high yield of 82.8% was obtained. The effect of alcohol type on the catalyst performance was also studied. It was found that the EL-MSA catalyst also presented good performance toward esterification with ethanol and propanol, from which ethyl stearate and propyl stearate with a more than 80% ester yield can be achieved.

Sustainable biofuel production approach: Critical methanol green transesterification by efficient and stable heterogeneous catalyst

Bi-metallic integrated Cex-Ca1-xO catalysts with various Ce:Ca atomic ratios are synthesized through a homogeneous co-precipitation route. The synthesized heterogeneous base catalyst for transesterification of unrefined jatropha crude oil (UJCO) under near-critical methanol is the first to be reported by our group. Incorporating inorganic oxides within the metal-metal-oxide (Ce – O – Ce) increases the catalytic activity due to the highly uniform dispersion of lattice CaO on the catalyst's surface and hence predominantly increases the surface's active sites. The near-critical methanol transesterification activity results in the excellent catalytic performance of Cex-Ca1-xO when Ce:Ca at an atomic ratio of 1:1. However, its reactivity plunges when Ca species are overloaded on the composite's surface (Ce:Ca atomic ratio of 1:4). The maximum biodiesel yield of 93.39% is achieved at an optimized reaction condition of 20 min, 18 methanol/UJCO molar ratio, 260 °C (10 MPa), and 1 wt.%. In addition, the fuel properties of synthesized biodiesel are investigated and compared in accordance with international standards. This synthesized catalyst demonstrates superior activity, outstanding stability (toward moisture and FFA contents), and reusability (without needed regeneration), making it a potential candidate as a green catalyst.

Reducing the Impact of Perfusion Medical Waste on the Environment

The U.S. healthcare system generates more than five billion pounds of waste each year. Waste disposal has become a serious environmental problem facing healthcare institutions. The operating room is the second largest source of hospital waste, and no current standards exist regarding perfusion waste reuse or recycling. A typical perfusion circuit produces approximately 15 pounds of plastic that ends up incinerated once used. Contaminated perfusion circuits consisting primarily of polyvinyl chloride (PVC) and polycarbonate are difficult to sterilize, reuse, or recycle. A literature review of Internet-based and peer-reviewed publications was conducted to identify all resources that describe sterilizing, dechlorinating, reusing, and recycling of medical-grade disposable products. There are several chemical methods available to re-harvest PVC after it has been properly decontaminated and melted down. Dichlorination by near-critical methanol shows promise in the recovery of additives such as plasticizers, stabilizers, and lubricants. The reinjection of PVC may have ecological and economic advantages. Dechlorinated PVC also creates a less toxic by-product when incinerated. Although this process is not recycling, it lessens the impact of poisonous chlorine gas release into the atmosphere. Sterilizing, dechlorinating, and recycling the perfusion circuit may be a promising avenue for reducing the ecological impact of perfusion waste. Although an economically sensitive mode of reusing, reducing, and recycling a circuit does not currently exist, this presentation will explore the perfusion waste dilemma and present potential solutions in hopes of promoting future reuse and recycling opportunities.

Simultaneous Conversion of C5 and C6 Sugars into Methyl Levulinate with the Addition of 1,3,5-Trioxane.

The simultaneous conversion of C5 and C6 mixed sugars into methyl levulinate (MLE) has emerged as a versatile strategy to eliminate costly separation steps. However, the traditional upgrading of C5 sugars into MLE is very complex as it requires both acid-catalyzed and hydrogenation processes. This study concerns the development of a one-pot, hydrogenation-free conversion of C5 sugars into MLE over different acid catalysts at near-critical methanol conditions with the help of 1,3,5-trioxane. For the conversion of C5 sugars over zeolites without the addition of 1,3,5-trioxane, the MLE yield is quite low, owing to low hydrogenation activity. The addition of 1,3,5-trioxane significantly boosts the MLE yield by providing an alternative conversion pathway that does not include the hydrogenation step. A direct comparison of the catalytic performance of five different zeolites reveals that Hβ zeolite, which has high densities of both Lewis and Brønsted acid sites, affords the highest MLE yield. With the addition of 1,3,5-trioxane, the hydroxymethylation of furfural derivative and formaldehyde is a key step. Notably, the simultaneous conversion of C5 and C6 sugars catalyzed by Hβ zeolite can attain an MLE yield as high as 50.4 % when the reaction conditions are fully optimized. Moreover, the Hβ zeolite catalyst can be reused at least five times without significant change in performance.

Beneficial Effect of Water on the Catalytic Conversion of Sugars to Methyl Lactate in Near-Critical Methanol Solutions

Biomass comprises a certain amount of water, which affects the reactions in organic solutions. Generally, water facilitates the hydrolysis of methyl lactate resulting in a decrease of the yield. Ho...

Enhancement of Catalytic Activity by γ-NiOOH for the Production of Methyl Lactate from Sugars in Near-Critical Methanol Solutions

As-synthesized Ni-based Lewis acidic catalysts, with tunable concentrations of β-Ni(OH)2 and γ-NiOOH, were tested on the conversion of sugars to methyl lactate (MLA) in near-critical methanol solut...

A novel treatment method of PVC-medical waste by near-critical methanol: Dechlorination and additives recovery

Before PVC-medical waste is subjected to a waste-to-energy recovery process, the dechlorination and the recovery of additives such as plasticizer, stabilizer, and lubricant are quite important and attractive. In this work, a novel process was developed for the dechlorination and the recovery of additives from PVC-medical waste such as tube for transfusion (TFT) and sample collector for urine (SCFU) by using near-critical methanol (NCM). Reaction temperature, solid-to-liquid ratio, and reaction time have significant effect on the dechlorination of TFT and SCFU in NCM. The order of dechlorination efficiency of the samples at the same reaction conditions is as follows: TFT > Pure PVC > SCFU. When reaction temperature was controlled at 250 °C (solid-to-liquid ratio of 1:10 g/mL, reaction time of 60 min), the dechlorination efficiency reached 90%. Plasticizer such as dibutyl phthalate (DBP), dioctyl phthalate (DOP), and dimethyl phthalate (DMP) could be efficiently extracted and recovered from TFT at 250 °C by the NCM process. The recovery efficiency of DBP, DOP, and DMP decreased significantly with increasing temperature due to the further decomposition and other secondary reactions. High level of hexadecanoic acid methyl ester and octadecanoic acid methyl ester can be obtained from SCFU at 250 °C by the NCM process because of the esterification between methanol and hexadecanoic acid/octadecanoic acid, which are the important stabilizers and lubricants generally used in rigid PVC. It is noteworthy that methanol can be circulated and reused in the NCM process. This result showed that the NCM process was beneficial for both the dechlorination and the additives recovery from PVC-medical waste, and had a widespread application prospect for the waste management of PVC wastes.

Simultaneous Catalytic Conversion of C6 and C5 Sugars to Methyl Lactate in Near-critical Methanol with Metal Chlorides

Cellulose and hemicellulose make up roughly two-thirds of lignocellulose. Currently, research is mainly focused on converting them to different chemicals, which causes low utilization rates and high separation costs. In this work, the simultaneous conversion of C6 and C5 sugars from cellulose and hemicellulose to methyl lactate in near-critical methanol with 15 different types of metal chlorides was studied. The trends of the catalytic conversions of C6 and C5 sugars with different metal chlorides were similar. Methyl lactate yield initially increased and then decreased steadily with an increase in the pKa value of the metal ions, which suggested that medium Lewis acidity was favorable for the production of methyl lactate. A possible reaction mechanism was proposed. The results will provide direction for the preparation of heterogeneous catalysts for simultaneously converting cellulose and hemicellulose to methyl lactate.

Catalytic conversion of sugars to methyl lactate over Mg-MOF-74 in near-critical methanol solutions

Metal organic frameworks (MOFs) are promising heterogeneous catalysts for biomass conversion to useful chemicals. In this work, four M-MOF-74s (Co, Ni, Mg, Zn) were synthesized at room temperature. Among these, Mg-MOF-74 exhibited the best catalytic activity for conversion of sugars to methyl lactate. A final product yield of methyl lactate from glucose of 35% was achieved with complete conversion of glucose at optimal reaction conditions. Catalytic performance of conversion of five sugars to methyl lactate over Mg-MOF-74 was studied, a product yield of 47% were obtained from sucrose. Mg-MOF-74 catalyst has shown to be reusable for at least three cycles.

Catalytic conversion of furfural to methyl levulinate in a single-step route over Zr/SBA-15 in near-critical methanol

In the present study, an economic and environmentally friendly bi-functional catalyst, Zr-SBA-15, has been prepared to develop a single-step process for synthesis of methyl levulinate (MLA) directly from furfural (FAL) in near-critical methanol without added H2. The presence of Zr in SBA-15, the structure of the Zr-SBA-15 catalyst, and its physical properties have been determined by X-ray diffraction (XRD), N2 adsorption and desorption (N2-BET) and transmission electron microscopy (TEM). The Zr-SBA-15 catalyst has high activity for the production of MLA and good reusability. A possible reaction pathway containing two possible reaction pathways during this single-step synthesis of MLA has been proposed: the FAL has been transformed to β-Methoxy-2-furanethanol (MFE) and 2-Furfuryl methyl ether first, which then have been converted to MLA, and the conversion of FAL to MFE has been much easier and faster than that to 2-FME, which may be the major reaction pathway. The SBA-15 has given high activity for the conversion of FAL to MFE, and the incorporation of Zr has converted the MFE to MLA efficiently. The reaction of FAL to MFE to MLA has been found to be the dominant reaction. Finally, the catalyst has shown good reusability for at least five times without any reduction in the catalytic activity.

Kinetics of esterification of 10-undecenoic and ricinoleic acids with near-critical and supercritical methanol

FAMEs were synthesized from two different carboxylic acids using a green pathway and a new mechanistic kinetic model was developed.

Mechanistic insights into the production of methyl lactate by catalytic conversion of carbohydrates on mesoporous Zr-SBA-15

The as-synthesized Zr-SBA-15 catalysts with tunable mesoporous structures showed excellent catalytic performance for the conversion of carbohydrates to methyl lactate in a “one-pot” process using near-critical methanol or methanol–water mixture as the solvents. The effects of reaction conditions, including temperature, reaction time, and catalyst loading amount, on the conversions of carbohydrates and the yields of methyl lactate were investigated. The high yields of methyl lactate, up to 41% and 44%, were produced from pentose and hexose, respectively, in the near-critical methanol at 240°C. Moreover, the Si/Zr ratio of the Zr-SBA-15 catalysts profoundly affected the Lewis acidity and therefore the catalytic activity and selectivity to methyl lactate in the conversion of carbohydrates. The pore size of the Zr-SBA-15 catalysts, tuned by the synthesis temperature, strongly affected the formation of solid residues. The key intermediates such as glyceraldehyde, glycolaldehyde, and pyruvaldehyde were used as probe reactants to understand the mechanism. The role of the Zr-SBA-15 catalyst in the aldol- and retro-aldol condensation, isomerization, and Cannizzaro reactions of carbohydrates and their derivatives was discussed. Furthermore, 28% and 27% yields of methyl lactate were obtained from cellulose and starch, respectively, in methanol–water mixture (5wt% water and 95wt% methanol) at 240°C. The Zr-SBA-15 catalyst was relatively stable in short term without regeneration.

One-pot preparation of methyl levulinate from catalytic alcoholysis of cellulose in near-critical methanol

One-pot preparation of methyl levulinate (MLA) from cellulose in near-critical methanol was studied. Acids containing SO3H group were proven to be effective catalysts for the production of MLA from cellulose’s catalytic alcoholysis. The effects of different reaction conditions, such as an initial cellulose concentration of 10–30g/L, a temperature range from 170 to 190°C, and a sulfuric acid concentration of 0.01–0.03mol/L, on the production of MLA were investigated. The results showed the reaction temperature and acid concentration significantly affected the process of cellulose alcoholysis and the yield of MLA. A high yield of up to 55% MLA was achieved at 190°C for 5h, using 0.02mol/L H2SO4 as a catalyst.

Effects of Zr/Ti molar ratio in SO2−4/ZrO2-TiO2 calcined at different temperatures on its surface properties and glucose reactivity in near-critical methanol

Effects of Zr/Ti molar ratio in SO2−4/ZrO2-TiO2 solid acid catalyst calcined at different temperatures on its surface properties and catalytic activity were thoroughly investigated in this paper. The physicochemical characteristics of prepared samples were determined by N2 adsorptiondesorption, XRD, NH3-TPD and XPS techniques, respectively. It was found that the crystallization temperature of the samples increased after the combination of ZrO2 and TiO2; and phase transformations from the anatase to the rutile of TiO2 species and the tetragonal to the monoclinic of ZrO2 species were effectively suppressed at higher temperature. The sample with a Zr/Ti molar ratio of 3/1 calcined at 450 °C showed the highest surface area and the most acid sites among all the tested samples. The acid site densities of samples were relatively closed to each other if they were calcined at the same temperature, however, decreased with the calcination temperature. The result indicates that the sulfur content in samples is a crucial factor to control the acid site density. Calcining the sample at 650 °C and higher temperatures resulted in a significant desorption of sulfate ion on the samples. The synthesized samples were evaluated as a potential catalyst for glucose conversion under the near-critical methanol conditions (200 °C/4 MPa). The results suggested that the relatively weaker acid sites of the catalyst were more favorable for the accumulation of methyl glucosides, while the moderate acid sites were responsible for the formation of methyl levulinate. The catalytic activity for methyl levulinate production almost increases linearly with the catalyst acid site density. The catalyst deactivation is due to the loss of sulfate ion and the two catalysts with Zr/Ti molar ratios of 3/1 and 1/3 could effectively alleviate the deactivation caused by sulfate solution in the reaction medium and can be reused after calcination with the reuse rate of over 90% in terms of the methyl levulinate selectivity.

Conversion of carbohydrates biomass into levulinate esters using heterogeneous catalysts

The catalytic performances of common solid acids (ZSM-5(25), ZSM-5(36), NaY, H-mordenite, Zr 3(PO 4) 4, SO 4 2 - /ZrO 2, SO 4 2 - /TiO 2, and TiO 2) for the conversion of carbohydrates such as glucose to methyl levulinate in near-critical methanol were investigated to develop an environmentally benign catalyst with high activity. Among these catalysts employed, sulfated metal oxides (especially SO 4 2 - /TiO 2) were found to be a type of potential catalysts for prospective utilization, which showed remarkably high selectivity and yield of methyl levulinate and had negligible undesired dimethyl ether formation from the dehydration of methanol. With SO 4 2 - /TiO 2 as the catalyst, methyl levulinate in ca. 43, 33 and 59 mol% yields could be obtained from sucrose, glucose and fructose, respectively, at 473 K for 2 h reaction time with a catalyst loading of 2.5 wt.%. The heterogeneous catalyst ( SO 4 2 - /TiO 2) was easily recovered by filtration and exhibited good catalytic activities after calcination in five cycles of reusing. The surface structure and acidity variations of the fresh and recycled SO 4 2 - /TiO 2 catalysts after calcination were characterized by XRD and NH 3-TPD techniques. The results indicate that the catalyst crystallization structure was preserved after multiple cycles, the acid amount and acid strength of the catalyst reduced gradually as the increasing of recycling times.

Synthesis of methyl esters from relevant palm products in near-critical methanol with modified-zirconia catalysts

The transesterification and esterification of palm products i.e. crude palm oil (CPO), refined palm oil (RPO) and palm fatty acid distillate (PFAD) under near-critical methanol in the presence of synthesized SO 4–ZrO 2, WO 3–ZrO 2 and TiO 2–ZrO 2 (with various sulfur- and tungsten loadings, Ti/Zr ratios, and calcination temperatures) were studied. Among them, the reaction of RPO with 20%WO 3–ZrO 2 (calcined at 800 °C) enhanced the highest fatty acid methyl ester (FAME) yield with greatest stability after several reaction cycles; furthermore, it required shorter time, lower temperature and less amount of methanol compared to the reactions without catalyst. These benefits were related to the high acid-site density and tetragonal phase formation of synthesized WO 3–ZrO 2. For further improvement, the addition of toluene as co-solvent considerably reduced the requirement of methanol to maximize FAME yield, while the addition of molecular sieve along with catalyst significantly increased FAME yield from PFAD and CPO due to the inhibition of hydrolysis reaction.