1、PDF外文：http:/ 3452 字 出处： Catalysis today, 1999, 53(1): 3-9 Catalytic strategies for industrial water re-use F.E. Hancock Synetix, Billingham, Cleveland, TS23 1LB, UK Abstract The use of catalytic processes in pollution abatement and resource recovery is wides
2、pread and of significant economic importance R.J. Farrauto, C.H. Bartholomew, Fundamentals of Industrial Catalytic Processes, Blackie Academic and Professional,1997. For water recovery and re-use chemo-catalysis is only just starting to make an impact although bio-catalysis is well established J.N.
3、Horan, BiologicalWastewater Treatment Systems； Theory and Operation, Chichester, Wiley, 1990. This paper will discuss some of the principles behind developing chemo-catalytic processes for water re-use. Within this context oxidative catalytic chemistry has many opportunities to underpin the developm
4、ent of successful processes and many emerging technologies based on this chemistry can be considered . Keywords: COD removal； Catalytic oxidation； Industrial water treatment 1.Introduction Industrial water re-use in Europe has not yet started on the large scale. However, with potential
5、 long term changes in European weather and the need for more water abstraction from boreholes and rivers, the availability of water at low prices will become increasingly rare. As water prices rise there will come a point when technologies that exist now (or are being developed) will make water recy
6、cle and re-use a viable commercial operation. As that future approaches, it is worth stating the most important fact about wastewater improvement avoid it completely if at all possible! It is best to consider water not as a naturally available cheap solvent but rather, difficult to purify, easily co
7、ntaminated material that if allowed into the environment will permeate all parts of the biosphere. A pollutant is just a material in the wrong place and therefore design your process to keep the material where it should be contained and safe. Avoidance and then minimisation are the two first steps i
8、n looking at any pollutant removal problem. Of course avoidance may not be an option on an existing plant where any changes may have large consequences for plant items if major flowsheet revision were required. Also avoidance may mean simply transferring the issue from the aqueous phase to the gas p
9、hase. There are advantages and disadvantages to both water and gas pollutant abatement. However, it must be remembered that gas phase organic pollutant removal (VOC combustion etc.,) is much more advanced than the equivalent water COD removal and therefore worth consideration 1. Because these aspect
10、s cannot be over-emphasised， a third step would be to visit the first two steps again. Clean-up is expensive, recycle and re-use even if you have a cost effective process is still more capital equipment that will lower your return on assets and make the process less financially attractive. At presen
11、t the best technology for water recycle is membrane based. This is the only technology that will produce a sufficiently clean permeate for chemical process use. However, the technology cannot be used in isolation and in many (all) cases will require filtration upstream and a technique for handling t
12、he downstream retentate containing the pollutants. Thus, hybrid technologies are required that together can handle the all aspects of the water improvement process6,7,8. Hence the general rules for wastewater improvement are: 1. Avoid if possible, consider all possible ways to minimise.
13、2. Keep contaminated streams separate. 3. Treat each stream at source for maximum concentration and minimum flow. 4. Measure and identify contaminants over complete process cycle. Look for peaks, which will prove costly to manage and attempt to run the process as close to typical values
14、as possible. This paper will consider the industries that are affected by wastewater issues and the technologies that are available to dispose of the retentate which will contain the pollutants from the wastewater effluent. The paper will describe some of the problems to be overcome and how the tech
15、nologies solve these problems to varying degrees. It will also discuss how the cost driver should influence developers of future technologies. 2. The industries The process industries that have a significant wastewater effluent are shown in Fig. 1. These process industries
16、can be involved in wastewater treatment in many areas and some illustrations of this are outlined below. Fig. 1. Process industries with wastewater issues. 2.1. Refineries The process of bringing oil to the refinery will often produce contaminated water. Oil pipelines
17、 from offshore rigs are cleaned with water； oil ships ballast with water and the result can be significant water improvement issues. 2.2. Chemicals The synthesis of intermediate and speciality chemicals often involve the use of a water wash step to remove impurities or wash
18、 out residual flammable solvents before drying. 2.3. Petrochemicals Ethylene plants need to remove acid gases (CO2, H2S) formed in the manufacture process. This situation can be exacerbated by the need to add sulphur compounds before the pyrolysis stage to improve the proce
19、ss selectivity. Caustic scrubbing is the usual method and this produces a significant water effluent disposal problem. 2.4. Pharmaceuticals and agrochemicals These industries can have water wash steps in synthesis but in addition they are often formulated with water-based s
20、urfactants or wetting agents. 2.5. Foods and beverages Clearly use water in processing and COD and BOD issues will be the end result. 2.6. Pulp and paper This industry uses very large quantities of water for processing aqueous peroxide and enzymes
21、for bleaching in addition to the standard Kraft type processing of the pulp. It is important to realise how much human society contributes to contaminated water and an investigation of the flow rates through municipal treatment plants soon shows the significance of non-process industry derived waste
22、water. 3. The technologies The technologies for recalcitrant COD and toxic pollutants in aqueous effluent are shown in Fig. 2. These examples of technologies 2,6,8 available or in development can be categorised according to the general principle underlying the mechanism of
23、action. If in addition the adsorption (absorption) processes are ignored for this catalysis discussion then the categories are: 1. Biocatalysis 2. Air/oxygen based catalytic (or non-catalytic). 3. Chemical oxidation 1. Without catalysis using chemical oxidants 2. With c
24、atalysis using either the generation of _OH or active oxygen transfer. Biocatalysis is an excellent technology for Municipal wastewater treatment providing a very cost-effective route for the removal of organics from water. It is capable of much development via the use of different types of bacteria
25、 to increase the overall flexibility of the technology. One issue remains what to do with all the activated sludge even after mass reduction by de-watering. The quantities involved mean that this is not an easy problem to solve and re-use as a fertilizer can only use so much. The sludge can be toxic
26、 via absorption of heavy metals, recalcitrant toxic COD. In this case incineration and safe disposal of the ash to acceptable landfill may be required. Air based oxidation 6,7 is very attractive because providing purer grades of oxygen are not required if the oxidant is free. Unfortunately, it is only slightly soluble in water, rather unreactive at low temperatures and, therefore, needs heat and pressure to deliver reasonable rates of reaction. These plants become capital intensive as pressures (from _10 to 100 bar) are used. Therefore, although the running costs
