One-Reactor Process

Figure 5.29 Potential environmental impact of the one-reactor process.

In the one-stage process (Fig. 2), ethylene, oxygen, and recycle gas are directed to a vertical reactor for contact with the catalyst solution under slight pressure. The water evaporated during the reaction absorbs the heat evolved, and make-up water is fed as necessary to maintain the desired catalyst concentration. The gases are water-scmbbed and the resulting acetaldehyde solution is fed to a distUlation column. The tad-gas from the scmbber is recycled to the reactor. Inert materials are eliminated from the recycle gas in a bleed-stream which flows to an auxdiary reactor for additional ethylene conversion. 

The emulsion process can be modified for the continuous production of latex. One such process (68) uses two stirred-tank reactors in series, followed by insulated hold-tanks. During continuous operation, 60% of the monomers are continuously charged to the first reactor with the remainder going into the second reactor. Surfactant is added only to the first reactor. The residence time is 2.5 h for the first reactor where the temperature is maintained at 65°C for 92% conversion. The second reactor is held at 68°C for a residence time of 2 h and conversion of 95%. 

Some processes use only one reactor (57) or a combination of liquid- and vapor-phase reactors (58). The goal of these schemes is to reduce energy consumption and capital cost. Hydrogenation normally is carried out at 2—3 MPa (20—30 atm). Temperature is maintained at 300—350°C to meet a typical specification of less than 500 ppm benzene in the product at higher temperatures, thermodynamic equiUbrium shifts to favor benzene and the benzene specification is impossible to attain. Also, at higher temperatures, isomerization of cyclohexane to methylcyclopentane occurs typically there is a 200 ppm specification limit on methylcyclopentane content. 

Polypropylene polymers are typically modified with ethylene to obtain desirable properties for specific applications. Specifically, ethylene—propylene mbbers are introduced as a discrete phase in heterophasic copolymers to improve toughness and low temperature impact resistance (see Elastomers, ETHYLENE-PROPYLENE rubber). This is done by sequential polymerisation of homopolymer polypropylene and ethylene—propylene mbber in a multistage reactor process or by the extmsion compounding of ethylene—propylene mbber with a homopolymer. Addition of high density polyethylene, by polymerisation or compounding, is sometimes used to reduce stress whitening. In all cases, a superior balance of properties is obtained when the sise of the discrete mbber phase is approximately one micrometer. Examples of these polymers and their properties are shown in Table 2. Mineral fillers, such as talc or calcium carbonate, can be added to polypropylene to increase stiffness and high temperature properties, as shown in Table 3. 

Electrochemical Process. Applying an electrical current to a brine solution containing propylene results in oxidation of propylene to propylene oxide. The chemistry is essentially the same as for the halohydrin process. AH of the chemistry takes place in one reactor. Most of the reported work uses sodium or potassium bromide as the electrolyte. Bromine, generated from bromide ions at the anode, reacts with propylene and water to form propylene bromohydrin. Hydroxide generated at the cathode then reacts with the bromohydrin to yield propylene oxide (217—219). The net reaction involves transfer of two electrons ... 

Because PEA is such an important fragrance material this simple, essentially one-step process has been exhaustively studied to optimize reaction conditions and purification procedures. Because of the high reactivity of the iatermediates and the tendency toward polymer formation, critical factors such as throughput, temperature, molar ratios of reactants, addition rates, reactor materials and design, and agitation rate must be carefully balanced to provide an economical product with acceptable odor properties. 

Space time, ST, is defined as the time required to process one reactor volume of feed measure at specified conditions. The relationship between space velocity SV and ST is as follows ... 

There are many processes used in tail-gas treating. The Sulfreen and the Cold Bed Absorption (CBA) processes use two psirallel reactors in a cycle, where one reactor operates below the sulfur dew point to absorb the sulfur while the second is regenerated with heat to recover molten sulfur, tiven though sulfur recoveries with the additional reactors are normally 99-99.5% of the inlet stream to the Claus unit, incineration of the outlet gas may still be required. 

In the second section, unconverted hydrogen sulfide reacts with the produced sulfur dioxide over a bauxite catalyst in the Claus reactor. Normally more than one reactor is available. In the Super-Claus process (Figure 4-3), three reactors are used. The last reactor contains a selective oxidation catalyst of high efficiency. The reaction is slightly exothermic ... 

D. Blum Just going a bit further, the liquid-phase methanation process now uses one reactor. You can or you cannot use a polishing reactor as the economics dictate. You can actually go right to pipeline quality gas in one reactor, which is equivalent to about 99.8% conversion of a 20% CO feed gas. We envision at this moment that combined shift-methanation could be done in the same single reactor. It would obviously require lower feed gas rates so you may need two of these reactors. We don t exactly have the numbers yet. I think that s one of the areas that deserves future work. 

Ammoxidation illustrates several principles. First, it shows the benefit of telescoping two successive processes into one reactor. The Sohio inventor, James D. Idol, Jr., observed that catalysts for two successive stages in an earlier ammoxidation procedure were very similar. He then found that the same catalyst could be used for both, thus eliminating a complete plant stage, at great saving of capital and operating cost ... 

The above-mentioned targets refer to general advantages of micro reactors [42, 80, 100, 114, 119]. Enhanced transfer and better controlled residence time improve conversion and selectivity. The tools have small internal volumes, allowing one to generate flexibly a multitude of samples in serial or parallel fashion. Synthesis can be combined with a multi-step procedure. The economy of micro-reactor processes has not really been analyzed so far however, it is clear that as laboratory tools they allow in a number of cases technical expenditure, personnel and costs to be reduced. 

Later developments which have had more impact on copper smelting relate to an approach which combines roasting, smelting and converting steps in one reactor, thereby making the copper production process continuous. The three unique continuous processes tried in operation are (i) the Worcra process, (ii) the Noranda process and (iii) the Mitsubishi process. The principles of the processes are respectively shown in Figures 4.5 to 4.7. 

Time required to process one reactor volume of feed]... 

Table 1 illustrates the effect of hydrogen pressure on the selectivity to MIBK based on the initial rate of MIBK production and the rate of IPA production. Palladium gives very high selectivity to MIBK, typically in excess of 93% with the selectivity improving significantly with decreasing pressure. This result is of particular importance since the CD process for MIBK production is carried out at relatively low pressure (< IMPa). In contrast, alternative one-step processes for MIBK production are carried out in the liquid phase in trickle-bed reactors at pressures as high as 10 MPa. 

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