Operating Characteristics and Performance of a Monolithic Downflow Bubble Column Reactor in Selective Hydrogenation of Butyne‐1,4‐diol

The effects of flow condition, bubble dispersion level, and liquid flow rate on the behavior of a novel monolithic downflow bubble column (M‐DBC) were investigated using a reaction model, the palladium‐catalyzed hydrogenation of butyne‐1,4‐diol. The stable and closely packed homogeneous bubble dispersion present in the bulk region of the M‐DBC allowed effective introduction of the gas‐liquid phase for formation of Taylor flow inside the monolith channels. The condition defined as the minimum level dispersion was required in order to obtain high selectivity towards the intermediate product, cis‐2‐butene‐1,4‐diol. Enhanced reaction rates were obtained at increasing the dispersion level and lowering the liquid flow rate. Comparison with the DBC employing 5 % Pd/C powder catalyst and 1 % Pd‐on‐Raschig‐ring revealed a better performance of the M‐DBC (1 % Pd loading) with the advantage of smaller reaction volume and intensified reaction rate. As an alternative to conventional three‐phase reactors, the M‐DBC was so simple due to its inherent characteristic operation and no specially designed device is required.     

Palladium nanoparticles stabilized in block-copolymer micelles for highly selective 2-butyne-1,4-diol partial hydrogenation

Pd nanoparticles (2 nm) stabilized in the micelle core of poly(ethylene oxide)-block-poly-2-vinylpyridine were studied in 2-butyne-1,4-diol partial hydrogenation. Both unsupported micelles (0.6 kg_Pd/m³) and supported ones on γ-Al₂O₃ (0.042 wt.% Pd) showed nearly 100% selectivity to 2-butene-1,4-diol up to 94% conversion. The only side product observed was 2-butane-1,4-diol. The catalysis was ascribed to Pd nanoparticles’ surface modified by pyridine units of micelles and alkali reaction medium (pH of 13.4). TOFs over the unsupported and supported catalysts were found to be 0.56 and 0.91 s⁻¹ (at 323 K, 0.6 MPa H₂ pressure, solvent 2-propanol/water = 7:3), respectively. Reaction kinetics fit the Langmuir–Hinshelwood model assuming weak hydrogen adsorption. The experiments on the catalyst reuse showed that Pd nanoparticles remain inside the micelle core, but the micelles slightly desorbed (less then 5%) during the catalytic run.     

Palladium supported on filamentous active carbon as effective catalyst for liquid-phase hydrogenation of 2-butyne-1,4-diol to 2-butene-1,4-diol

Structured palladium catalysts suitable for three-phase reactions have been developed based on woven fabrics of active carbon fibres (ACF) as the catalytic supports. The Pd/ACF were tested in liquid-phase hydrogenation of 2-butyne-1,4-diol showing a selectivity towards 2-butene-1,4-diol up to 97% at conversions up to 80%. The catalyst multiple reuse with stable activity/selectivity in a batch reactor was also demonstrated. The reaction kinetics was studied and the main kinetic parameters were obtained. Assuming a Langmuir-Hinshelwood kinetics and a weak hydrogen adsorption a suitable kinetic model was developed consistent with the experimental data.     

A comparative study of residence time distribution and selectivity in a monolith CDC reactor and a trickle bed reactor

A comparative study of the performance of a trickle bed reactor (TBR) and a monolith cocurrent downflow contactor (CDC) reactor in terms of selectivity and residence time distribution was conducted for the hydrogenation of 2-butyne-1,4-diol (B). Selectivity (S) towards 2-butene-1,4-diol was investigated with the solvent 2-propanol and a 30% (v/v) 2-propanol/water mixture (M) in batch recycle mode. Liquid residence time distribution (RTD) curves were obtained for both reactors. Although both reactors presented almost identical hydrodynamic behaviour, i.e. RTD, significant differences regarding selectivity towards the alkene were observed in both solvents. The use of 2-propanol gave lower selectivities in both reactors, but even then the monolith reactor was superior. In the monolith CDC, the liquid RTD curve was also obtained at different radial positions. RTD profiles across the monolith showed that from the centre to the column wall there is possibly an increased retention of material and despite this, overall selectivity does not appear to be considerably depressed by the backmixing that the above result implies in 2-propanol/water where the selectivity was found to be 100% towards the intermediate (C).

Modelling of the monolith CDC reactor was also conducted to predict RTD. The models tested were tanks-in-series, piston exchange and piston dispersion exchange; from which, piston exchange model was found to best predict and fit the experimental data.     

2-丁炔-1，4-二醇双对甲苯磺酸酯的合成工艺研究

以25％氢氧化钠为缚酸剂、以2-丁炔-1,4-二醇和对甲苯磺酰氟为原料,经磺酯化反应合成了2-丁炔-1,4-二醇双对甲苯磺酸酯。在n（对甲苯磺酰氯）：”（Na0H）;n（2-丁炔-1,4-二醇）为2．6：2．4：1、反应温度为0℃、反应时间为6h的最佳反应条件下,2-丁炔-1,4-二醇双对甲苯磺酸酯的收率迭94．1％。通过元素分析、IR以及1 HNMR对产物结构进行了表征。     

Cis–trans isomerization of olefinic alcohols promoted by Rh(I) complexes

Homogeneous hydrogenation and isomerization reaction of cis-2-butene-1,4-diol has been investigated in ethanol by using tris(triphenylphosphine)chlororhodium(I), RhCl(PPh₃)₃, and triethylamine at 303 K and 0.01–0.1 MPa partial hydrogen pressure. Under reduced H₂ pressure, the geometric isomerization reaction occurs, to a high extent, leading to trans-2-butene-1,4-diol up to 93% selectivity at 90% conversion of the cis analogous. Effects of H₂ partial pressure as well as triethylamine, added phosphine and olefin concentrations on the rate of reaction and on the products distribution were also investigated. The results obtained can be interpreted on the basis of a proposed mechanism in which RhH(PPh₃)₃ is the active species. The high selectivity towards cis-trans isomerization of cis-2-butene-1,4-diol is attributed to steric factors of the Rh(I) coordinated triphenylphosphine groups.     

两类聚酯吸氧材料的制备及性能

制备了1,4-丁烯二醇/顺丁烯二酸酐和端羟基聚丁二烯（HTPB）/顺丁烯二酸酐酯化物吸氧剂,讨论了反应时间及醇酐比对吸氧剂酯化率的影响,并且将1,4-丁烯二醇/顺酐、HTPB/顺酐吸氧剂接枝共聚到PET中得到改性吸氧材料。考察了两种吸氧材料的物理性能和吸氧性能,以及影响吸氧性能的双键保留率,催化剂用量、醇酐比。实验表明,顺酐与1,4-丁烯二醇、HTPB反应的最佳酯化时间分别为2 h和3 h,含1,4-丁烯二醇/顺酐和HTPB/顺酐的吸氧材料最大数均分子量分别为3.66万和4.97万,最大双键保留率分别为77.4%和76.3%,最大催化剂用量为1.0 g/kg,含1,4-丁烯二醇/顺酐和HTPB/顺酐的吸氧材料24 h最大吸氧量为3.17 mL/g和10.04mL/g。     

Scaling-out selective hydrogenation reactions: From single capillary reactor to monolith

Selectivity and kinetic studies of the Pd-catalysed hydrogenation of 2-butyne-1,4-diol were performed in a single capillary channel, and monoliths consisting of 1256 capillaries and 5026 capillaries in (I) the pressure range 100-300 kPa (II) the temperature range 298-328 K using a 30% v/v 2-propanol/water solvent. All reactors were operated in downflow mode such that the reaction fluid was in Taylor flow. Transport calculations indicated that liquid-solid transport resistances were low (<5%) and energies of activation were found to be in the range 32-34 kJ mol⁻¹. While the reaction was first order in hydrogen concentration, the order with respect to 2-butyne-1,4-diol changed over the concentration range investigated. A model based upon a Langmuir-Hinshelwood mechanism was applied and found to predict reasonably well the experimental reaction rates. High selectivity values towards the 2-butene-1,4-diol were found in both the single- and multiple-capillary reactors, even at 100% conversion of the alkyne.     

Selective Hydrogenation of 2-Butyne-1,4-diol to 1,4-Butanediol Over Particulate Raney® Nickel Catalysts

The current study describes the results on the selective hydrogenation of the 2-butyne-1,4-diol to 1,4-butanediol over Raney^® nickel catalysts both in batch and in CSTR mode. The detailed kinetic analysis of the reaction in batch mode revealed the existence of three characteristic regions. In the first region, A, the starting 2-butyne-1,4-diol produces primarily cis-2-butene-1,4-diol. In the second region, B, the dominant species is cis-2-butene-1,4-diol, which is either hydrogenated to 1,4-butanediol or isomerizes to trans-2-butene-1,4-diol. In the third region, C, the accumulated 4-hydroxybutanal is slowly hydrogenated to 1,4-butanediol. When the same reaction was carried out in a CSTR mode, the only products detected initially are the 1,4-butanediol and n-butanol. The first by-product detected immediately after the end of the first stage is the linear hemiacetal between the 4-hydroxybutanal with 1,4-butanediol. This species has been used as convenient tracer for determining the length of the selective region of the catalyst performance.     

Hydrogenation of 2-Butyn-1,4-diol in the Presence of Functional Crosslinked Resin Supported Pd Catalyst. The Role of Polymer Properties in Activity/Selectivity Pattern

Functional gel type resins of various crosslinking degrees (3–20%) with C=O and carboxylic groups were used as the supports for Pd catalysts (0.5–2 wt% Pd). The role of polymer properties was studied in the hydrogenation of 2-Butyne-1,4-diol (B3-D) to alkene (B2-D) and alkane (B1-D). Hydrogenation was studied at atmospheric pressure of hydrogen using THF, H₂O and THF + H₂O mixtures as the solvents. Systematic studies were carried out to determine the role of the type of solvent, crosslinking degree of polymer, the content of Pd in catalysts, initial B3-D concentration and the procedure of catalyst reduction in activity/selectivity behaviour of catalysts. Swelling degree of polymer matrix under the catalytic run exhibits crucial role in the activity and selectivity to alkene, B2-D. In the presence of highly expanded catalyst (THF solvent, 3% crosslinking degree, 1 wt% Pd) the alkyne, B3-D, is hydrogenated to alkene, B2-D, with selectivity ca. 85% up to high B3-D conversion (90%). The suppression of alkene to alkane hydrogenation in the stage of B3-D is ascribed to high ability of Pd centres in the Pd/OFP catalysts to strong adsorption of alkyne substrate. It may also be related to steric hindrances of polymer in the vicinity of active Pd centres. At small content of added water (5% by vol.) to THF the catalysts offer very attractive performance in terms of activity and 98% selectivity to alkene. Water facilitates interactions of B3-D with functional groups of polymer that leads to better expansion of polymer matrix and more effective suppression of alkene hydrogenation in the alkyne stage.     

Periodic mesoporous hybrid monolith with hierarchical macro–mesopores

We describe the synthesis of hybrid monolith with hierarchically macro–mesoporous structure by a sol–gel process from the mixture of 1,4-bis(triethoxysilyl)benzene (BTEB) and tetraethoxysilane (TEOS) using poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (P123) as structure directing agent under acid medium. The ordered mesoporous structure is embedded in the skeleton of the well-defined co-continuous macropore of the hybrid monolith. The influence of aging condition, acidic concentration, P123/Si ratio and TMB/P123 ratio on the macro- and meso-structure of the resultant monolith was investigated in details. The three-successive aging processes are necessary for the mesostructural order of the monolith to survive the surfactant removing process. The well-defined co-continuous macropore could be formed with the aid of TMB, which probably delays the phase separation rate during the sol–gel process through enhancing the interaction between the hydrophobic BTEB with P123 surfactant micelles. The macro–mesoporous hybrid monolith with phenylene bridged in the mesoporous framework may have potential application as a novel kind of stationary phase for high performance liquid chromatography (HPLC).     

酸性树脂催化1,4-丁烯二醇制备2,5-二氢呋喃

提出1,4-丁烯二醇在酸性条件下脱水关环制备2,5-二氢呋喃的反应机理。实验对照了磺酸基树脂D61、D72以及膦酸基树脂LSC-500的催化性能,在5小时的反应过程中,它们的催化活性均逐渐下降,其中D61活性最强,平均每克催化剂1小时转化2.96克1,4-丁烯二醇,D61和D72的收率逐渐下降,LSC-500的收率最高而且比较稳定,保持在80%以上。     

Hydrogenation activity and selectivity behavior of supported palladium nanoparticles

Enhancement in activity and selectivity of catalytic hydrogenation using supported nanosize palladium catalyst has been investigated. Pd/C catalyst prepared in the presence of polyvinyl pyrrolidone (PVP) as a stabilizer gave Pd particle size in a narrow range of 3–5 nm. While, evaluating for hydrogenation of 2-butyne-1,4-diol, the rate enhancement was found to be 10 times higher as compared to the conventional (bulk) Pd catalysts. A proper choice of stabilizer (PVP) giving small particle size as well as highly dispersed nature of nano particles were the major factors for such a dramatic enhancement of activity.     

Structured reactors for kinetic measurements under severe conditions in catalytic combustion over palladium supported systems

The collection of chemical kinetics data in catalytic combustion over very active palladium catalysts under conditions relevant to practical applications (e.g. gas turbine combustors) is extremely difficult, mainly due to strong exothermicity and very fast rate of combustion reactions. Within this purpose in this paper two types of laboratory structured reactors, which closely resemble industrial monolith catalysts, are investigated: (a) the annular reactor, consisting of a catalyst coated ceramic tube, co-axially placed in a quartz tube; (b) the metallic plate-type reactor, consisting of an assembled packet of metallic slabs coated with a ceramic catalytic layer.

The design of the annular reactor configurations for kinetic investigations is first addressed by mathematical modeling. The resulting advantages, including: (i) negligible pressure drops; (ii) minimal impact of diffusional limitations in high temperature–high GHSV experiments; (iii) effective dissipation of reaction heat are then experimentally demonstrated for the case of CH₄ combustion over a PdO/γ-Al₂O₃ catalyst with high noble metal loading (10% (w/w) of Pd).

The feasibility of a near-isothermal operation with the metallic plate-type reactor by an extremely effective dissipation of reaction heat through proper selection of highly conductive support material and of the geometry of the metallic slabs is finally discussed and experimentally demonstrated for the case of combustion of CO at high concentrations over a PdO/γ-Al₂O₃ (3% (w/w) of Pd) catalyst.     

NOx storage and reduction characteristics of Pd/MnOx–CeO2 at low temperature

The reaction between hydrogen and NO was studied over 1 wt.% Pd supported on NO_x-sorbing material, MnO_x–CeO₂, at low temperatures. The result of pulse mode reactions suggest that NO_x adsorbed as nitrate and/or nitrite on MnO_x–CeO₂ was reduced by hydrogen, which was spilt-over from Pd catalyst. The NO_x storage and reduction (NSR) cycles were carried out over Pd/MnO_x–CeO₂ in a conventional flow reactor at 150 °C. In a storage step, NO was removed by the oxidative adsorption from a stream of 0.04–0.08% NO, 5–10% O₂, and He balance. This was followed by a reducing step, where a stream of 1% H₂/He was supplied to ensure the conversion of nitrate/nitrite to N₂ and thus restore the adsorbability. It was revealed that the NSR cycle is much more suitable for the H₂–deNO_x process in excess O₂, compared to a conventional steady state reaction mode.     

活性炭固载磷钨酸催化合成异丁醛缩顺—2—丁烯—1，4—二醇

研究了用活性炭固载磷钨酸催化合成异丁醛缩顺 -2 -丁烯 -1,4-二醇。考察了催化剂固载量、醇醛物质的量比、带水剂用量等因素对缩合反应的影响。其优化条件为 :顺 -2 -丁烯 -1,4-二醇、异丁醛、催化剂、带水剂的量分别为 1mol、1.0 5mol、7.0 g、10 0mL ,反应在回流温度下进行 ,时间约 3h ,收率达 86.4%。催化剂可重复使用     

High performance Pd/beta catalyst for the production of gasoline-range iso-paraffins via a modified Fischer–Tropsch reaction

The direct synthesis of gasoline-range iso-paraffins from synthesis gas (CO + H₂, syngas) via a modified Fischer–Tropsch (FT) reaction was intensively studied under a wide range of reaction conditions by the combination of Co/SiO₂ and Pd/beta in a consecutive dual reactor system. Results indicate that high selectivity of gasoline-range iso-paraffins (iso-paraffins relative to C₄+ hydrocarbons was about 80%) could be achieved with the presence of Pd/beta catalyst in the lower reactor. Moreover, the performance of the Pd/beta catalyst for the titled reaction and the product composition can be significantly regulated by independently changing the reaction conditions such as catalyst amount, reaction temperature, and hydrogen partial pressure in the lower reactor. It was found that the Pd/beta catalyst used in this work was very active and stable even at a reaction temperature as low as 503 K. With the increase of hydrogen partial pressure in the lower reactor, the long-term stability of the Pd/beta catalyst was significantly enhanced.     

Pd/Fe双金属对1,2,4-三氯苯的催化脱氯

采用Pd/Fe双金属体系对1,2,4-三氯苯（1,2,4-TCB）进行了快速催化还原脱氯的研究.结果表明,在钯的催化作用下,零价铁对1,2,4-TCB有较好的还原脱氯效率.当Pd/Fe双金属的钯化氯为0.06%时,催化剂用量为1g/40mL,反应1h后TCB的脱氯率可达99%.反应速率随钯化氯的提高而增加.反应在Pd/Fe表面进行,符合准一级反应,反应速率常数为0.0837min-1.TCB在催化脱氯的过程中先脱氯成为DCB,再依次脱氯为氯苯和苯.     

Influence of alkali metal doping on selectivity behaviour of platinum catalysts for hydrogenation of 2-butyne-1,4-diol

Hydrogenation of 2-butyne-1,4-diol to 2-butene-1,4-diol (B₂D) and butane-1,4-diol (B₁D) using Pt catalysts doped with alkali metals was studied. These catalysts showed higher selectivity to the olefinic diol (B₂D) compared to that with monometallic platinum catalyst. Among various alkali metals, Cs-doped catalyst showed highest selectivity (>99%) to B₂D. The selectivity to B₂D increased (up to 99.9%) with increase in the concentration of Cs from 0.25% to 1%. The increase in the basic strength of alkali doped catalysts measured by CO₂-TPD, would be responsible for the increase in electron density of Pt hence, faster desorption and higher selectivity to the intermediate olefinic diol (B₂D). The reaction parameters, such as temperature, H₂ pressure and substrate concentration have strong influence on the catalyst activity but almost no effect on the selectivity to B₂D.     

Role of lanthanide elements on the catalytic behavior of supported Pd catalysts in the reduction of NO with methane

In this study, the role of lanthanide elements (Ce, Gd, La, and Yb) on Pd/TiO₂ catalysts in the catalytic reduction of NO with methane was investigated. Steady-state reaction experiments in the presence of oxygen showed that the addition of lanthanide elements increases the oxygen resistance of the catalyst. The post-reaction XPS characterization results revealed that majority of the Pd sites remained in the zero oxidation state in the presence of Ce or Gd. The effect of SO₂ (145 ppm) and H₂O (0–6.6%) in NO–CH₄–O₂ reaction over supported Pd and Gd–Pd catalysts was also investigated. Over the Gd–Pd catalyst with the presence of SO₂, more than 70% NO conversion was obtained for over 6 h while the Pd only catalyst showed a sharper drop in NO conversion. Over the Gd–Pd catalyst, the presence of H₂O showed no effect on NO conversion activity (>99% conversion) during the 18 h the catalyst was kept on stream. Among the lanthanide elements tested, Gd is the most effective, allowing the use of above stoichiometric oxygen concentration.