新大化工院研究生专业英语

Membrane reactors for hydrogenation and dehydrogenation processes based on supported palladium

基于支撑的加氢\脱氢钯膜反应器

Abstract摘要

Membrane reactors applied to catalytic reactions are currently being studied in many places world-wide.

目前，应用于各类催化反应的膜反应器正受到世界范围内的广泛研究。

Significant developments in membrane science and the vision of process intensification by multifunctional reactors have stimulated a lot of academic and industrial research, which is impressively demonstrated by more than 100 scientific papers on catalytic membrane reactors being published per year.

膜科学的显著发展成果和通过多功能反应器强化过程工艺的前景激励了学术和应用领域的诸多研究。每年公开发表的关于催化膜反应器的科学论文超过100篇就强烈的证实了这一点。

Palladium as a noble metal with exceptional hydrogen permeation properties and, at the same time, broad applicability as a catalyst, first of all for hydrogenation is part of many of these developments. This paper discusses two different membrane reactor concepts which both rely on supported palladium, on the one hand as a permselective membrane material, and on the other hand as base component of a membrane-type hydrogenation catalyst .

作为一种贵金属，钯具有只允许氢渗透通过的性质，同时，又是广泛使用的催化剂。钯首先被应用于加氢过程是这一领域诸多研究成果的一部分。这篇论文讨论了两类不同的支撑型钯膜反应器。在此，金属钯一方面作为选择渗透性的膜材料，另一方面又是膜型加氢催化剂的主要成分。

Dense palladium composite membranes can be used for hydrogen separation from packed-bed catalysts in gas-phase hydrocarbon dehydrogenation reactions. Mesoporous membranes containing dispersed bimetallic Pd/X-clusters can be employed as so-called catalytic diffusers for liquid-phase hydrogenation, e.g. of nitrate and nitrite in water.

致密型复合钯膜能够用于从填料床气固相烃类脱氢反应中分离氢。含

有分散双金属串（Pd/X-clusters)的中空型钯膜，即所谓的催化扩散器，可用于液固相加氢反应。例如，硝酸盐与亚硝酸盐在水中的加氢反应。The principles of both concepts are introduced, recently obtained experimental data are evaluated in connection with literature results, and the perspectives for further development are highlighted.

本文介绍了这两类钯膜反应器的基本原理，结合文献结果结果评价了最新获得的实验数据，展望了钯膜反应器未来的发展前景. Keywords

Membrane reactor; 膜反应器

Composite palladium membrane; 复合钯膜

Catalytic membrane; 催化膜

Palladium catalyst; 钯催化剂

Liquid-phase hydrogenation; 液相加氢反应

Gas-phase hydrocarbon dehydrogenation；气相烃类脱氢反应Abbreviations

CMR: catalytic membrane reactor; 催化膜反应器

CNMR: catalytic non-permselective membrane reactor; 非选择性催化膜反应器

CSTR: continuous stirred tank reactor ; 连续搅拌槽反应器

CVD: chemical vapour deposition;化学汽相沉淀法

FBCMR: fluidised-bed catalytic membrane reactor; 流化床催化膜反应器

FBMR: fluidised-bed membrane reactor;流化床膜反应器

GHSV: gas hourly space velocity (m3 feed/m3 catalyst·h); 气体小时空速

HVOF: high-velocity oxy-fuel flame spraying; 高速氧燃料火焰喷射IMCR: inert membrane catalytic reactor;惰性膜催化反应器

IMR: inert membrane reactor;惰性膜反应器

LHSV: liquid hourly space velocity (m3 feed/m3 catalyst h); 液体小时空速

MOCVD: metal organic chemical vapor deposition; 金属有机化学汽相沉淀法

PBCMR: packed-bed catalytic membrane reactor; 填料床催化膜反应器PBMR: packed-bed membrane reactor; 填料床膜反应器

PEM：proton exchange membrane；质子交换膜

PV AL: polyvinyl alcohol; 聚乙烯醇

PVD: physical vapor deposition; 物理汽相沉淀法

S/O: steam to oil ratio (kg/kg or mol/mol); 汽/油比

SS, stainless steel，weighted sum of squares defined by Eq. (12); 由方程12定义的总面积的不锈钢重量和

WHSV: weight hourly space velocity (kgfeed/kg catalyst· h) 重量小时空速

1.Membrane reactor concepts膜反应器概念

According to the IUPAC definition a membrane reactor is a device that combines a membrane-based separation process with a chemical reaction step in one unit. Various possibilities exist for such a combination.

根据国际理论与应用化学联合会的定义，膜反应器是一个把膜分离过程与化学反应组合于一个单元的设备。基于这样一个结合，就存在多种结构的膜反应器

The most widely used concept is the selective removal of products from the reaction zone (cf. Fig. 1a), which is applied first of all to equilibrium limited reactions to increase the yield beyond the corresponding equilibrium value, or, generally speaking, to repress undesired secondary reactions of the products.

应用最为广泛的一类膜反应器是从反应区选择性移走反应产物，如图1a所示。这类膜反应器首先被应用于受平衡限制的反应，目的是提高低于相应平衡转化率的产率，或者，一般来说，抑制不期望产生的副反应产物。

In a different approach only particular reactants are supplied selectively via a membrane to the reaction zone (cf. Fig. 1b), e.g. to establish an optimum concentration profile along the reactor.

另一类膜反应器是通过膜把部分反应物选择性地送入反应区。如图1b所示。例如沿着反应器形成适宜的浓度分布。

A third concept refers to a membrane that creates a well-defined reaction interface (or region) between two reactant streams (cf. Fig. 1c).

第三类膜反应器指的是能够在两种反应物流之间提供确切的反应界

面或者反应区的膜，如图1c所示。The mass transport across a membrane can be permselective if only some components of a mixed stream permeate through the membrane (cf. Fig. 1a and b) or non-permselective if all species permeate at comparable rates (cf. Fig. 1c).

若混合物流中的某些组分渗透通过膜，该质量传递便为选择性渗透，如图1a和b ；若所有组分以相当的速率通过膜，则为非选择性渗透，如图1c.

Permselective transport is found first of all in dense membranes.It is governed by a solution-diffusion mechanism. Non-permselective transport normally occurs in macro- and mesoporous membranes. In the latter Knudsen diffusion is often the dominating transport mechanism.

选择性传递首先是在致密性膜中发现的，此过程受溶解-扩散机理控制。非选择性传递一般发生在大孔和中空膜内，受努森扩散机理控制。Microporous membranes represent a bit of both: permselective and non-permselective transport is possible depending on the size of the permeating molecules in view of the pore size of the membrane (bottlenecks) as well as on the chemical nature of the permeating molecules and the membrane material.

微孔膜介于上述两者之间。究竟是选择性渗透还是非选择性渗透取决于膜孔径与渗透分子的相对大小以及渗透分子的化学性质与膜材料。

When the membrane reactor is used for carrying out a catalysed reaction the questions arises whether the membrane itself has a catalytic function or not. If the membrane acts as a catalyst we refer to this as a catalytic membrane reactor (CMR, cf. Fig. 1e and f), if not we have an inert membrane catalytic reactor (IMCR, cf. Fig. 1d).

当将膜反应器用于催化反应时，所提出的问题是膜自身是否具有催化功能。若该膜具有催化功能，则称为催化膜反应器，如图1e和f所示；若无催化功能，则称为惰性膜催化反应器，如图1d所示。

The CMR-case may be further subdivided into two categories, i.e. when the membrane acts as the sole catalyst (cf. Fig. 1e), and when a conventional catalyst is present in addition to the membrane (cf. Fig. 1f). 催化膜反应器又分为两种。一种是膜作为唯一的催化剂，如图1e；另一种是将催化剂担载于膜上，如图1f 。

other authors have introduced similar acronyms for an easy reference to the different membrane reactor types. Tsotsis et al. [1] refer to a catalytic non-permselective membrane reactor (CNMR) as to a reactor with a catalytic membrane which is not permselective but provides for a well-defined interface for two (or more) reactants flowing on opposite sides of the membrane (cf. Fig. 1c).

为了便于指代不同类型的膜反应器，其他作者还给出了类似的首字母缩略词。文献[1]用CNMR代表非选择性催化膜反应器，即其膜具有催化功能，而无选择性，但能够为流过膜两侧的两种或多种反应物提供确切的反应界面，如图1c 。

In contrast their definition of a catalytic membrane reactor (CMR) requires a permselective membrane (cf. Fig. 1e). In both cases the membrane acts as the sole catalyst.

相对而言，用CMR代表选择渗透膜反应器。这类反应器需要一种选择渗透性膜，如图1e。对于这两种反应器，膜是唯一的催化剂。The same authors assigned the acronyms PBMR and FBMR to the packed-bed and fluidised-bed membrane reactor where the membrane is permselective but not catalytic (cf. Fig. 1d). The opposite cases, i.e. with catalytic and permselective membrane, are referred to as PBCMR and FBCMR, respectively (cf. Fig. 1f).

文献[1]分别用PBMR 和FBMR代表填料床和流化床膜反应器。在这两种反应器内，膜只具备选择渗透性，而无催化性，如图1d；若同时具有催化性和选择渗透性，则分别用PBCMR 和FBCMR来表示，如图1f 。

Coronas and Santamaria [2] used the notations CMR and IMR to distinguish between the catalytic and the inert membrane reactor. According to their definition the CMR has no other type of catalyst except the membrane. Consequently a third category ―combined‖ is introduced to refer to membrane reactor configurations where the catalyst is placed both inside and outside the membrane.

文献[2]用CMR 和IMR来区分催化膜反应器和惰性膜反应器。根据其定义，ＣＭＲ除膜外，无另外的催化剂。由此出现了第三种结构的膜反应器，即催化剂填装于膜的两侧。

No further distinction is made in view of the permselectivity, i.e. whether

the membrane performs a separation task, whether it provides a reaction interface for different reactant streams, or whether it acts only as a special type of catalyst support, e.g. to minimise the mass transport resistance when the whole feed stream is passed through it in cross-flow.

就选择性渗透而言，未进一步区别膜究竟是起分离作用，还是为不同反应物流提供反应界面，或只是充当一种特殊的催化剂载体，例如，全部进料以错流方式通过膜时，将传质阻力减到最小。

In the past 15 years many valuable reviews on membrane reactors have been published. It is not the intention of this paper to add one more to the list but rather to emphasise the use of palladium in this field.

在过去的15年里，已发表了许多关于膜反应器的有价值的文献。本文的目的不是在这众多文献中再增加一篇，而是为了进一步强调钯在这个领域里的用途。

2. Membrane reactors based on palladium allo membranes基于钯合金膜上的膜反应器

It is well established that dense palladium and palladium alloy membranes are permeable for hydrogen only. Two main possibilities arise from this feature to employ these in membrane reactors, namely

已完全证实只有H2能够渗透通过致密型的钯膜和钯合金膜。当把这两种膜应用于膜反应器时，就出现了两种主要的可能性，即，1. to promote a dehydrogenation reaction by removal of the produced hydrogen from a dehydrogenation catalyst through the membrane, i.e. preventing the establishment of the chemical equilibrium, or

1.通过钯膜从脱氢催化剂中除去生成的H2，促进脱氢反应，即阻止其化学平衡的建立；

2. to carry out a hydrogenation reaction on the palladium surface with supply of hydrogen through the membrane.

2.或者，通过钯膜提供氢气，在膜表面完成加氢反应。

The purpose of the use of the palladium membrane as well as its function differs considerable in both types of applications.

在这两类应用中，使用钯膜及其功能的目的是不径相同的。

In case(1) the aim is to increase the conversion of an equilibrium limited reaction by removal of one of the products.

1.在第一类应用中，目的是通过除去一种生成物提高被化学平衡所限制的反应转化率。

The dehydrogenation occurs in the gas phase over a conventional catalyst (e.g. a packed-bed) which is surrounded by the palladium membrane .

装有普通催化剂的气固相脱氢反应就是一例。例如填料床反应器，钯膜包裹着催化剂。

In principle the palladium surface could act as a dehydrogenation catalyst too, but then the reaction rate would be too small due to the low surface area. Hence, the membrane has no primary catalytic function.

从原理上说，金属钯的表面也能够充当脱氢催化剂。然而，因其表面积小，脱氢反应速率太低，故认为它基本无催化功能。

In case (2) the purpose can be two-fold; to promote a selective hydrogenation by deliberately dosing hydrogen through the membrane, or to utilize an existing diluted hydrogen gas to perform the hydrogenation. In both situations the palladium membrane has a catalytic function.

在第2类应用中，其目的又分为2种。其一，通过膜准确计量氢气流量，提高加氢反应的选择性。其二，利用已有的稀浓度氢气发生加氢反应。在这两种情况下，钯膜都具有催化作用。

From an engineering point of view case (2) has a limited potential, at least for gas-phase hydrogenations.

就工程角度而言，情况(2)的应用潜力受到限制，至少对于气相加氢反应的应用。

It is true that palladium is a versatile hydrogenation catalyst, but the reaction rate normally is proportional to the surface area of the catalyst, provided no diffusion limitation occurs and the active sites are uniformly distributed over the surface.

事实上，钯是一种多功能加氢催化剂，倘若不是扩散控制，反应活性点在钯膜的整个表面上均匀分布，则其加氢反应速率恰好与催化剂的表面积成正比。

Conventional hydrogenation catalysts have the palladium in highly dispersed form, e.g. as nanoscale metal clusters inside a porous pellet, and hence do offer a large palladium surface area. Compared to this the accessible surface area of a dense palladium membrane is small.

普通加氢催化剂含有高分散形状的金属钯，例如，在一个多孔的催化

剂圆柱内，含有多个纳米级的钯金属串，由此，确实提供了大的钯表面积。相对于这种钯催化剂，致密型钯膜的可用面积是小的。

If the hydrogenation is to be performed in the liquid phase the situation may be different because then the reaction rate is often controlled by the kinetics of hydrogen mass transfer, and the available active surface inside the porous catalyst is utilized anyway only in part.

如果加氢反应是在液相中进行，因为液相加氢反应速率往往受到氢的传质动力学控制，多孔催化剂内部的有效活性表面无论如何只能被利用一部分，情况有可能是不同。

Liquid-phase hydrogenations are carried out at high pressure due to the poor solubility of hydrogen in most organic liquids. Palladium membranes would allow for a simplification of the process design ,as they could take over both the catalytic function and the task of dosing hydrogen. High pressure operation could then be avoided.

由于氢在大多数有机液体中的溶解度都很小，故液相加氢反应都是在高压下完成的。假如这两种钯膜能够兼顾催化作用和准确计量氢气流量的话，或许可简化这一工艺过程，还可以避免高压操作。Combined with a clear benefit in selectivity there might be interesting applications of this concept in the fine chemicals area.

结合钯膜在选择性方面的明显好处，简化后的工艺可能在精细化学品生产领域中具有许多令人感兴趣的应用.

However, most of the recent studies using palladium-based membranes in literature are aimed at hydrogen removal from packed-bed catalysts either to boost the yield of industrially important dehydrogenation reaction ( propane , iso-butane/n-butane , ethyl-benzene , etc . )

然而,目前对于钯类膜的应用研究，大多数旨在从填料床催化剂中除去氢，或者提高具有工业重要性的脱氢反应的产率，例如：丙烷脱氢，异丁烷/丁烷脱氢,乙苯脱氢，等等。

or to provide pure hydrogen ( steam reformring of methane or methanol, water-gas-shift reaction),e.g. for use in low-temperature ( PEM ) fuel cell stack.Hence ,the discussion here is restricted to this type of application only.

或者是为低温燃料电池提供纯氢。例如，甲烷或甲醇的水蒸汽重整反

应，水煤气变换反应。因此,本文仅限于讨论膜反应器的这类应用。

2.1Working principle of an inert membrane catalytic reactor with removal of hydrogen

2.1一种能够移去氢的惰性膜催化反应器工作原理

The principle of a hydrogen permselective membrane reactor equipped with a packed-bed of catalyst and a surrounding palladium-based membrane has been described many times in literature. Fig. 2 illustrates the situation.

如图2所示，文献中已多次介绍过一种催化剂用钯类膜包裹着填料床式氢选择性渗透膜反应器的工作原理。

The dehydrogenation occurs on the packed-bed catalyst, and the produced hydrogen is withdrawn through the membrane. The transport through the membrane is driven by the hydrogen partial pressure difference between the packed-bed (i.e. retentate) side and the permeate side. Three different possibilities exist to create the driving force:

脱氢反应在固定床催化剂上发生,生成的氢通过膜取出。通过膜的传质推动力是反应区和渗透区间的氢气分压差。产生这一推动力的方式有三种:

1. Use of an inert sweep gas in the permeate compartment (e.g. nitrogen, helium, etc.).

2. Application of a pressure difference between retentate and permeate compartment (if necessary by evacuation of the permeate).

https://www.360docs.net/doc/f21194728.html,e of a reactive sweep gas to consume the permeated hydrogen (e.g. oxygen, air, carbon monoxide, unsaturated hydrocarbons, etc.).

1.在渗透区使用一种惰性吹扫气。例如N2, He, 等等。

2.利用反应区和渗透区的压差（必要时渗透区抽真空）。

3.使用一种活性吹扫气消耗透过的H2。如可使用O2，空气，CO或不饱和烃，等等。

Which of these possibilities is the best depends on the particular situation. In general, the worst case is the inert sweep gas because this has to be provided and compressed, and a diluted hydrogen gas is produced which can be used only as a fuel gas with low calorific value .

这3种措施究竟哪一个最好呢？这需要依据具体情况而定。一般来说，最糟糕的情况是使用惰性吹扫气。因为，这样做必须提供和压缩

所用的气体，且获得是低浓度氢气。这种氢气只能作为低热值燃料气使用。

If the kinetics of the hydrogen producing reaction do allow an operation at elevated pressure, for instance in the range of 1–3MPa, this becomes an attractive option because then the pressure difference is sufficiently large to flush out the permeated hydrogen.

若生成氢反应的动力学确实允许在提高压力条件下操作，例如反应压力在1-3MPa，则第二种情况就是一个具有吸引力的选择。因为，此时可提供足够大的压差，将所渗透的氢气全部排出。

The advantages are that no sweep gas is required and that pure hydrogen is obtained as a marketable product. On the other hand, the feed gas has to be compressed but the produced hydrogen is obtained at low pressure, which limits its usability and could make a recompression necessary.

第二个措施的优点是不需要吹扫气，可获得达到商品浓度氢。但缺点是必须压缩原料气，而且获得的是低压氢气。这就限制了氢气的用途，必要时还需对其进行二次压缩。

If pure hydrogen, e.g. for a fuel cell, is the target product of the membrane reactor, then an operation at elevated retentate pressure is the only viable option.

如果纯氢气，如用于燃料电池，是膜反应器的目标产品，那么提高反应物压力是唯一可行的选择。

The third option, i.e. reacting the permeated hydrogen with the sweep gas, is promising because it avoids the disadvantages of the other two.

第三种方式，即透过的氢气与吹扫气发生反应，是大有可为的。因为它避免了前两2者的缺点。

Moreover, since hydrogen producing reactions are endothermic in most cases (hydrocarbon dehydrogenation and hydrocarbon steam reforming) it is favourable to generate the required heat right in the permeate compartment.

而且，因为在大多数情况下生成氢的反应都是吸热反应，如烃类的脱氢反应和烃类湿法重整反应，渗透区恰好可产生反应所需的热量。这显然是有利的。

An exothermic hydrogen-consuming reaction can be carried out for this purpose, if possible employing the palladium membrane surface as a

catalyst.

为此，如果钯膜表面可作为催化剂使用，耗氢的放热反应便能够完成。Hydrogen oxidation with air or hydrogenation of an organic compound are candidates if they fit with the required reactor temperature. The disadvantage of hydrogen oxidation is that a high-valued product is used to heat the dehydrogenation.

只要能够适应这种反应器所需的温度，氢与空气的氧化反应或与某一有机物的加氢反应都是可考虑的对象。氢气氧化反应的缺点是用高附加值的氢提供脱氢反应所需要的热量。

The other case, coupling of the dehydrogenation process to a second synthesis, is difficult to run at optimized conditions in a commercial-scale reactor because of the reduced degree of freedom.

另一种情况，即把脱氢反应与二次合成组合起来，因这样做使过程的自由度减少，达到生产规模的膜反应装置难以在优化条件下运行。2.2 Development of palladium-based membranes 2.2 钯类膜的进展

First investigations of the hydrogen absorption and diffusion through palladium were reported by Graham in 1866. Today it is well known that hydrogen permeates with an infinite selectivity via a solution-diffusion mechanism through palladium and its alloys. The permeation is based on a multi-step process.

最早关于氢吸收扩散透过钯的研究是Graham于1866年公开发表的。如今，氢以溶解-扩散原理无限制性选择通过钯及其合金，已是众所周知。这种渗透基于多步过程。

First molecular hydrogen is adsorbed on the palladium surface, where the dissociation into atomic hydrogen takes place. Then the hydrogen atoms enter the palladium lattice and diffuse through the lattice, while the electrons interact with the metal lattice. On the adjacent side the hydrogen atoms leave the lattice and recombine on the surface, before they are finally desorbed as hydrogen molecules [23]。

第一步，分子氢吸附于钯的表面，解离为原子氢。然后, 原子氢进入钯的晶格。当氢电子与钯的晶格发生作用时，原子氢扩散穿过晶格，在另一侧与晶格脱离，在钯表面重新结合，最终，以氢分子的形式脱附。

It is also well known that the use of pure palladium membranes is hindered by the fact that palladium shows a transition from the α-phase (hydrogen-poor) to the β_-phase (hydrogen-rich) at temperatures below 300 ℃and pressures below 2MPa, which depends on the hydrogen concentration in the metal.

纯钯膜的使用受到如下原因的影响，即当温度＜300 ℃和压力＜2MPa时，钯表现出由α相（贫氢相）向β相（富氢相）的转变，且这一转变过程与氢在钯里的浓度有关。这也已是众所周知的。Since the lattice constant of the β-phase is 3% larger than that of the α-phase this transition leads to lattice strain and, consequently, after a few cycles to a distortion of the metal lattice .

因β相的晶格常数比α相的晶格常数大3％，这一转变过程会引起晶格应变，故此，当经过几次循环之后，钯的晶格就产生形变。Alloying the palladium, especially with silver, reduces the critical temperature for this embrittlement and leads to an increase of the hydrogen permeability.

对钯进行合金，特别是钯与银合金，可降低发生这种氢脆现象的临界温度，并且可提高氢的渗透能力。A maximum value of the hydrogen flow is reached for an alloy with approximately 23 wt.% silver [25,26]. Similar to Pd/Ag, other alloys, e.g. Pd/Y or Pd/Ce show high hydrogen permeability and good mechanical stability[27].

当钯银合金中银的质量分率约为23%时，氢的流量达到最大值。类似于钯银合金，其它合金，例如钯铱合金或钯鈰合金均表现出良好的氢渗透性和优异的机械稳定性。

Palladium-based membranes have been used for decades to provide ultra-pure hydrogen, e.g. in the semiconductors industry and for the operation of fuel cells [28,29] .

用钯类膜生产超纯度的氢气，例如半导体行业和燃料电池，已经几十年了。

They were exploited to extract tritium from liquid-metal tritium breeders. In recent years there has been a growing interest in the industrial application of palladium-based membranes for hydrogen producing reactions.

这两种用途都是利用钯类膜从液态金属氚的原子滋生反应器中萃取

氚。近年来，用于制氢反应钯类膜的工业应用受到日益关注。Extensive investigations were conducted for the employment of palladium-based membranes for hydrogen removal to shift thermodynamic (equilibrium) limitations towards higher conversions, e.g. during dehydrogenation of hydrocarbons，steam reforming of methane and the water-gas-shift reaction .

广泛探索了采用钯类膜移去氢气以改变热力学（平衡）限制，进一步提高转化率。例如，烃类的脱氢反应，甲烷水蒸汽重整反应和水煤气转换反应。

And it was shown that hydrogen feeding through palladium membranes can improve the selectivity of hydrogenation reactions .

还有，研究表明通过钯类膜供氢能够改善加氢反应的选择性。

Key requirements for the successful development of palladium-based membranes are low costs as well as high hydrogen permeability and permselectivity combined with good mechanical /thermal and long-term stability.

成功研发钯类膜的关键要求是在膜具有优异且长期稳定的机械/热力学性能前提下，成本要低，氢的渗透性能和选择渗透性能要好。

2.2.1 Dense palladium-based Membranes致密型钯膜

Early work focused on the application of relatively thick unsupported dense metal membranes prepared by conventional metallurgical processes.

早期的研究工作是针对采用传统冶金工艺制备的致密型金属膜的应用。这类膜相对较厚，无需支撑。In 1964 Johnson Matthey developed a hydrogen purification equipment which employed a Pd/Ag tube [39]. However, the use of these membrane reactors is limited by the low hydrogen flow which is inversely proportional to the thickness of the membrane.

1964年，由Johnson Matthey 研发了一套装有一根钯银合金管的氢气纯化装置[39]。然而，这类膜反应器的使用因氢流率小而受到限制。原因是氢流率与膜的厚度成反比。

Self supporting dense palladium-based membranes possess wall thicknesses greater than 50～100μm to keep a sufficient mechanical strength。

自撑式致密型钯膜的厚度超过50～100微米，才能保持足够的机械强度。

These membranes are too thick to obtain a satisfactory hydrogen flux. Besides the low permeance, thick palladium membranes are too expensive for an economic use, in particular since the price of palladium has tremendously increased over the last few years.

这类膜太厚了，以至于不能获得令人满意的氢气通量。除此之外，就经济性而言，各种厚型钯膜的价格太贵了，尤其是近年来钯价格猛涨。For practical use it is necessary to reduce the thickness of the palladium layer. Composite metal membranes and composite porous membranes seem to be an advisable choice to overcome these disadvantages.

要想实际使用钯膜，必须降低钯层的厚度。为了克服上述缺点，复合金属型钯膜和复合多孔钯膜似乎是一个明智的选择。

2.2.2 Palladium-based composite metal membranes 复合金属型的钯类膜

Palladium-based composite metal membrane consist of a thin layer of palladium or a palladium alloy coated on one or both sides of a hydrogen permeable base refractory metal such as niobium, vanadium or tantalum. These metals possess a high mechanical strength and are less expensive than palladium . Furthermore ,the hydrogen flow through these body-centred cubic metals is higher than through the face-centred cubic palladium.

复合金属钯类膜是将一薄层钯或钯合金单面或双面涂镀于氢可透过的耐熔金属，诸如铌、钒或钽，载体表面构成。铌、钒或钽这类金属机械强度高，比钯便宜。而且,这些金属是体心立方结构，钯是面心立方结构。故氢通过它们的流速比通过钯的大。

Unfortunately the direct replacement of palladium for these metals is not possible due to the formation of oxide layers and to surface reactions which reduce the hydrogen flow through the membrane [42].

可惜的是,不可能用这些金属直接替代钯。原因是会形成多个氧化层以及发生表面反应。由此，降低了氢通过膜的流率。

In 1967 Makrides et al. [43] filed a patent for plating foils of Group VB metals with thin layers of palladium using sputter deposition. However, it

has been reported that the hydrogen flux through palladium-based composite metal membranes decreases with time at high temperatures. 1967年，Makrides et al. [43] 申请了一项制备复合金属钯膜的专利。该专利是采用喷溅法在第五类副族元素的镀箔上沉积多层钯。然而,据报道这种复合金属膜的氢气流率高温下随时间而降低。Intermetallic between the metal layer and the base metal is the most likely reason for this notice [44]. To overcome this problem it was suggested to use a diffusion barrier between the base and the coating metal, e.g. thermal stable oxide layers such as alumina[44,45].

钯层与载体层间金属的相互作用是发生这一现象最有可能的原因。为了克服这个问题,曾建议在载体和钯膜之间增加扩散障碍物。例如，增加几层诸如氧化铝类的热稳定性能优异的氧化物。

2.2.3 Palladium-based composite porous membranes 钯类复合多孔膜Palladium-based composite porous membranes consist of a thin dense layer of palladium or a palladium alloy on a porous support. Tubes or discs of porous glass, porous ceramics or porous stainless steel can all be employed as supports.

复合钯类多孔膜就是将一层致密的钯或钯合金膜置于多孔载体上。多孔的玻璃管或盘、多孔陶瓷管或盘、多孔不锈钢管或盘都能作为载体使用。

Different techniques such as chemical vapor deposition [46,47], magnetron sputtering [46,48], electrodeposition [49] and spray pyrolysis [50] have demonstrated the ability to coat palladium-based films on porous substrates [51].

由文献[51]可知，把钯类膜涂敷在多孔载体上的方法有多种。例如，文献[46,47]提到的化学汽相沉积法，文献[46,48]提到的磁电管喷溅法，文献[49]所提到的电沉积法，文献[50]所提到的喷雾热解法。Each method has its advantages. However, due to its simplicity, relatively low costs and uniformity of the deposition, electroless plating is the most popular and most successful procedure so far [52–55].

每种方法各具优点。但由于无电电镀法操作简单、造价相对低廉、沉积均匀，故迄今为止，它是使用最为广泛、最为成功的方法。

It is based on the autocatalytic reduction of a metastable metallic salt complex on an activated substrate surface. New preparation methods

combine the electroless plating with reverse osmosis to obtain composite membranes with better thermal stability and higher permeance.

这种方法的基本原理是一种介稳态钯盐络合物在经过活化的载体表面上发生自催化还原反应。目前，新的制备方法是把无电电镀与反渗透相结合，将可获得具有更好热稳定性和更高渗透率的复合钯膜。Excellent results have been reported recently for ultrathin composite membranes prepared by a modified electroless plating method, where the classical substrate surface activation has been replaced by a new photocatalytic deposition method .

据最新的报道，用改进的无电电镀法可制备出超薄型的复合膜。在这种方法中，传统载体表面活性被一种新的光催化沉积物所取代。

2.3 Experimental

2.3.1 Preparation of palladium-based composite membranes钯类复合膜的制备

Many academic and industrial groups have developed palladium-based composite membranes in researach projects 。but so far no such products are available on a normal commercial basis .

许多学术的、企业的研究小组在其研究项目中开发了多种钯类复合膜。但迄今为止这类产品还未应用于实际生产。

For our studies on the dehydrogenation of hydrocarbons in palladium membrane reactors we too have looked at different techniques for the manufacture of hydrogen permselective palladium and palladium-silver composite membranes . Details are reported in [60,61] .

对于用钯膜反应器进行烃类脱氢反应的研究，我们已经考虑到有多种制备氢选择性渗透钯膜和钯银复合膜方法。详细内容可见参考文献[60] 和[61] 。

For the results presented in this paper mainly electroless plating was use. Asymmetric sintered porous stainless steel tubes supplied by GKN Sinter Metals Krebsoge Filters GmbH, Radevormwald (Germany), and asymmetric porous α—alumina tubes purchased from Inocermic GmbH, Hermsdorf (Germany), were employed as supports for the palladium plating.

本文所得结果主要采用无电电镀法。所用的镀钯载体非对称烧结多孔不锈钢管和非对称多孔α铝矾土管分别由德国GKN 和IGH公司提

供。

Both types have the same outer diameter of 10 mm and a comparable inner diameter of 6.5mm for the sinetered metal tubes and 7 mm for the ceramic tubes.

这两种载体管外径相同，均为10 mm，当量内径分别是烧结管 6.5 mm ，陶瓷管7mm。

The sintered metal tubes consist of two layers with different pore size. The nominal pore diameter of the fine layer, located on the shell side, is around 500 nm. The ceramic tubes have four layers with graded pore size. The finest layer has a mean pore diameter of 100 nm. The palladium was deposited always onto the layer with the finest pores.

金属烧结管由孔径不同的两层组成。小孔径层的公称孔径大约500纳米，且位于管外侧。铝陶瓷管由不同孔径尺度的4层组成。孔径最小层的平均孔径是100纳米。这样，钯总是可以沉积到这一层的最小孔上。

The porous substrates were first cut to 11 cm length and cleaned with ammoniac solution, isopropyl alcohol and de-ionised water. Following the cleaning the substrate surface was seeded with Pd nuclei, which initiates the auto-catalytic reduction of the palladium complex in the subsequent plating step.

首先，将多孔载体切割为11厘米长，用氨水、异丙醇和去离子水依次清洗。然后，在载体表面植入钯核。这样做是为了引发下一步电镀过程中钯络合物的自催化还原反应。

For this purpose the tubes were successively immersed at ambient temperature in a tin chloride solution followed by an acidic palladium chloride bath. This sequence was repeated 10 times.

为了植入钯核，在室温条件下，用氯化锡、酸性氯化钯溶液依次浸泡这些金属管。这一过程重复10次。Afterwards the palladium deposition was carried out at 60℃in a plating bath containing a palladium–amine complex as palladium source, hydrazine reducer and EDTA as stabilising agent (cf. Table 1).

接着，在温度为60 ℃的电镀槽内完成钯的沉积过程。如表1所示，钯胺络合物为钯源，联氨作还原剂，EDTA作稳定剂。

The plating solution was changed every hour to keep the plating rate

constant. Palladium deposition occurred according to Eq. (1).

2Pd 2+ + N2H4 + 4OH－→2Pd + N2 + 4H2O (1) After the plating the membranes were rinsed with de-ionised water and dried overnight at 120℃ in a drying oven.

每小时更换一次镀液，以保证钯的沉积速率不变。钯沉积反应按方程(1)进行。镀后，用去离子水冲洗，再置于120℃干燥箱内一个通宵。Palladium–silver composite membranes were prepared by successive deposition of palladium and silver on the porous supports followed by a heat treatment [53]. The first step was the preparation of a palladium layer as described above.

制备钯银复合膜是先将钯和银依次沉积在载体上，再热处理。第一步先镀钯层。方法同上，

Afterwards silver was deposited on the palladium film also by the electroless plating technique, which leads to the formation of a thin double layer of palladium and silver on the porous tube.

然后，也用无电电镀法，把银沉积在钯膜上，在载体表面形成一张薄的钯银双金属膜。

The silver plating solution consisted mainly of an EDTA stabilised silver–amine complex with hydrazine as reducing agent (cf. Table 1).

如表1所示，银镀液主要由EDTA 、银铵络合物和联氨组成。EDTA 作稳定剂，联氨作还原剂。

Silver deposition occurred according to Eq. (2).After the plating the membranes were heated up to 700℃for 12 h under an atmosphere of argon. These high temperatures lead to the formation of a homogeneous palladium–silver film by thermal diffusion [53].

4Ag+ + N2H4 + 4OH－→ 4Ag + N2 + 4H2O（2)

银沉积反应按方程式(2)进行。镀后，在氩气环境下，将制备的膜加热到700℃，保持12 h。这样的高温，在热扩散作用，形成的钯－银膜均匀一致。

The thickness of the palladium and palladium–silver layers was determined from SEM micrographs and from the weight difference before and after the plating combined with the densities of the metals and under the assumption of uniform coverage.

用电子扫描显微镜和镀膜前后质量差除以金属的密度与面积两种方

法，确定所制两种膜的厚度。在此，假定膜表面均匀。

2.3.2 Permeation measurements渗透测定值

The separation behaviour of the palladium composite membranes was investigated in the permeation apparatus shown schematically in Fig. 3.

钯复合膜分离特性的考察是在如图3所示的渗透装置中完成的。Details of the permeation unit are given in Fig. 4. The experiments were conducted with pure hydrogen and pure nitrogen as well as with a binary gas mixture of hydrogen with nitrogen.

图4给出了渗透器的详细信息。实验中使用了纯氢、纯氮以及氢氮二元混合气体。

The temperature was varied between350 and 650℃, and the pressure difference reached up to 400 kPa. Measurements were carried out with no sweep gas at atmospheric or low pressure on the permeate side and with nitrogen as sweep gas at atmospheric pressure. The heating rate was 1 K/min and below 300℃both sides of the membrane were kept under nitrogen to void hydrogen embrittlement.

测定条件:温度在350和650℃间变化，压差增加到400 kPa，渗透区常压或低压，无吹扫气；常压，有氮气作吹扫气；加热速率为1K/分钟。氮气环境下，保持膜两侧的温度低于300 ℃，避免发生氢脆现象。The desired feed gases were introduced with the aid of thermal mass flow controllers. The pressures on the retentate and permeate sides of the membrane were adjusted with back pressure controllers. The axial temperature profile of the reactor was monitored with thermocouples. The temperature variation over the whole length of the membrane did not exceed ±4℃.

所要求的原料气通过热式质量流量控制器输入。膜两侧的压力用反馈式压力控制阀调节。膜反应器的轴向温度分布用热电偶监测。沿膜长的温度变化不超过±4℃。

The gas flows leaving the reactor were measured by a thermal mass flow meter or a digital soap bubble flow meter. A gas chromatograph was used to analyse the composition of the permeate and the retentate. The membrane was installed in the reactor by sealing both ends of the tube with graphite rings.

从反应器两侧离开的气体流量用热式质量流量计或数字皂泡流量计

计量，其组成用气相色谱分析。安装在反应器里。膜反应管两端用石墨环密封。

2.4 Results and discussion结果与讨论

2.4.1 Characterisation of the composite membranes by SEM用扫描电镜表征所制备的复合膜

The surface morphology of an electroless deposited palladium film is shown in Fig.5.

图5给出了无电沉积法制备的钯膜表面形态。

It can be seen that the palladium film is composed of fine palladium grains. These grains are grown well together and form a dense palladium layer on the support. The minimum thickness of the palladium layer must be about 3μm or greater with the above technique to get layers without pinholes.

由图5可见，该膜由细小的钯粒组成。这些钯粒完全生长在一起，在载体上形成了一层致密的钯膜。用无电沉积法制备钯膜，最小厚度必须超过3微米或更大，才能获得无气孔膜。

Fig. 6 shows a SEM micrograph of a palladium–silver surface after the final heat treatment.

图6给出了热处理后的钯银膜SEM图像。

X-ray diffraction patterns of the surface of this membrane before (a) and after (b) the heat treatment are given in Fig. 7.

图7分别给出了热处理前（a）和后（b）这个膜的X射线衍射图。After the plating the reflection peaks of pure silver and pure palladium can be seen among the peaks of the alumina support. After the heat treatment the peaks of the pure metals have disappeared and peaks of the palladium–silver alloy can be observed.

镀后，在载体Al2O3的群峰之间，可见到银和钯的衍射峰。热处理后，钯、银的衍射峰都消失了，只能见到钯银合金的衍射峰。These peaks lie between those for silver and palladium and shift with higher palladium contents to higher diffraction angles.

这些峰都位于银和钯的衍射峰之间，且钯的含量越高，转换的衍射角越大。

2.4.2 Permeation behaviour of the composite membranes 复合钯膜的渗透性质