Maximum Space Time Yield Research Articles

Catalytic performance of mesoporous VO x/SBA-15 catalysts for the partial oxidation of methane to formaldehyde

The ordered hexagonal mesoporous pure silica SBA-15 has been used as a support for preparing highly dispersed V-containing catalysts. VO x /SBA-15 samples with different V loading (1.26–5.54 wt.%) have been prepared by impregnation with an aqueous solution of NH 4VO 3, characterized by N 2 adsorption, UV-Vis spectroscopy, and H 2-TPR and then evaluated for the partial oxidation of methane to formaldehyde with oxygen. For vanadium coverages below the theoretical monolayer capacity (corresponding to ca. 4 wt.% V) the SBA-15 surface was predominantly covered by monomeric and low oligomeric vanadium oxide species, while at higher vanadium coverages agglomerated vanadium entities and even some small amounts of microcrystalline V 2O 5 were also formed. The conversion of methane (at constant temperature and GHSV) passed a maximum at a vanadium loading of 3.85 wt.%, while the maximum of activity typically occurs at lower V contents (1–2 wt.%) in amorphous vanadia-silica catalysts. This feature can be related with the much higher surface area of the mesoporous support, which allows the monolayer capacity to be reached at higher loading than in amorphous silica. The influence of the main reaction parameters (temperature, GHSV, CH 4:O 2 ratio) on the productivity of formaldehyde was studied. A maximum space–time yield (STY) of formaldehyde of about 2.4 kg kg −1 h −1 was obtained in this work for the most active VO x /SBA-15 catalyst (3.85 wt.% V) at 618 °C, GHSV=417,000 l (N) kg −1 h −1, and CH 4:O 2 molar ratio of 8:1. This value of STY HCHO is significantly higher than the maximum STY (ca. 1.3 kg kg −1 h −1) reported for VO x /SiO 2, and comparable to that recently reported for VO x /MCM-41 (ca. 2.2 kg kg −1 h −1), thus confirming the promising use of high surface area mesoporous supports for the POM reaction on vanadia based catalysts.

Process Selection and Characterisation for the Biocatalytic Hydration of Poorly Water Soluble Aromatic Dinitriles

The biotransformation of poorly water soluble aromatic dinitriles is of industrial and scientific interest. Although processes do exist for the transformation of water soluble nitriles, such as acrylonitrile, no description of a process suitable for the large scale biotransformation of poorly water soluble nitriles appears in the literature. In this work we illustrate a systematic design procedure for optimising the production of 3-cyanobenzamide from 1,3-dicyanobenzene (1,3-DCB). The regio-selective nitrile hydratase (NHase) of the well characterised Rhodococcus R312 strain was initially selected as catalyst. Isolation of the NHase at process scale however was not feasible due to the rigid cell wall of the bacteria and the poor stability of the isolated enzyme. The whole cell form of the biocatalyst was thus used even though the activity of the associated amidase could overmetabolise the amide product into the corresponding acid. To overcome productivity limitations imposed by the characteristically low aqueous solubility of this class of substrate (∼0.34gl-1 in the case of 1,3-DCB) the use of an aqueous-organic two-phase bioreactor was investigated. After screening a wide range of solvents to act as a substrate reservoir toluene was selected as the organic phase due to the most favourable combination of LogP value (2.9) and 1,3-DCB saturation concentration (∼30gl-1). The effects of phase volume ratio (0.05-0.3), wet weight biomass concentration (1.25 — 200gwwl-1) and substrate concentration in the organic phase (5-25 gl-1) were then combined in a process map to define a suitable operating window where the maximum space-time yield of amide formation could be obtained. Compared to a single-phase transformation, the two-phase process yielded 12 times as much of the amide product of which less than 8% w/w was lost due to overmetabolism.

Low-temperature methanol synthesis in catalytic systems composed of nickel compounds and alkali alkoxides in liquid phases

Catalysts prepared from NaH, tert-amyl alcohol and nickel acetate were tested for CO hydrogenation in organic solvents in the range of 353–433 K and 1.0–5.0 MPa. Methanol was produced selectively under the studied conditions. Higher temperatures and higher pressures enhanced methanol productivity; a maximum space–time yield of 0.95 kg MeOH l −1 h −1, higher than that of the conventional methanol production process, was obtained at 433 K and 5.0 MPa. The addition of methanol to the catalyst did not significantly affect the product yields, but such addition did eliminate the induction period that was observed during the run in the absence of methanol addition to the catalyst. This suggested that methanol promoted the formation of a catalytically active species and/or that a certain amount of methanol was required to run a catalytic reaction cycle smoothly, in which methanol would be a reactant. The catalysts exhibited a catalytic decline over a short period due to the consumption of the alkoxide component.

Continuous computer controlled production of formate dehydrogenase (FDH) and isolation on a pilot scale

AbstractA continuous production process has been developed up to pilot scale (300 l) for FDH production with the methylotrophic yeast Candida boidinii. A high cell mass specific FDH activity (50 U/g) is achieved by process computer controlled supply of pure methanol to operate the reactor at an optimum methanol concentration of 10 g/l. The maximum FDH spacetime yield achievable with this process control involves a residence time of 7 h. The FDH space‐time yield (STY) and FDH concentration are a function of the oxygen transfer rate (OTR) of the fermenter (maximum STY = 255 U/(l h) at kLa = 870 l/h). For a reasonable compromise between high FDH space‐time yield and high FDH concentration, an optimum residence time is adjustable by regulating the supply of nutrient salt solution in relation to the OTR of the fermenter. On a pilot scale (200 l continuously stirred tank reactor) roughly 4 million U of FDH were produced within 10 days at a residence time of 14.3 h. Isolation of intracellular FDH enzyme was performed using extraction with an aqueous two‐phase system (PEG/K2HPO4). A technical product quality of 1.2 U/mg FDH was achieved without any chromatographic purification step.