Rhodia process

An elegant example is the Rhodia process for the manufacture of the flavor ingredient, vanillin [30]. The process involves four steps, all performed with a heterogeneous catalyst, starting from phenol (Fig. 1.48). Overall, one equivalent of phenol, H202, CH3OH, H2CO and 02 are converted to one equivalent of vanillin and three equivalents of water. 

Alternatively, caprolactam can be produced from butadiene, via homogeneous nickel-catalysed addition of HCN (DuPont process) followed by selective catalytic hydrogenation of the adiponitrile product to the amino nitrile and vapor phase hydration over an alumina catalyst (Rhodia process) as shown in Fig. 1.49 [137]. 

Comparison of the block diagrams of the Rhodia process and the previous classical process in figures 14.1 and 14.2, respectively, reveals the simplifications resulting from the zeolite process. 

NB The Rhodia process is referred to as Macromolecular Design via the Interchange of Xanthates (MADIX), yet... 

The Rhodia process for the production of p-hydroxyacetophe-none from methoxybenzene using clay as the catalyst eliminates the use of toxic chemicals such as AICI3 and BF3 and also eliminates toxic waste (see Fig. 3.14). 

FIGURE 9.29. Catalytic vanillin synthesis Rhodia process. 

A.sahi Chemical EHD Processes. In the late 1960s, Asahi Chemical Industries in Japan developed an alternative electrolyte system for the electroreductive coupling of acrylonitrile. The catholyte in the Asahi divided cell process consisted of an emulsion of acrylonitrile and electrolysis products in a 10% aqueous solution of tetraethyl ammonium sulfate. The concentration of acrylonitrile in the aqueous phase for the original Monsanto process was 15—20 wt %, but the Asahi process uses only about 2 wt %. Asahi claims simpler separation and purification of the adiponitrile from the catholyte. A cation-exchange membrane is employed with dilute sulfuric acid in the anode compartment. The cathode is lead containing 6% antimony, and the anode is the same alloy but also contains 0.7% silver (45). The current efficiency is of 88—89%, with an adiponitrile selectivity of 91%. This process, started by Asahi in 1971, at Nobeoka City, Japan, is also operated by the RhcJ)ne Poulenc subsidiary, Rhodia, in Bra2il under Hcense from Asahi. 

In recent months, three nylon producers (DMS, DuPont, and Honeywell) have developed closed-loop recycling processes for nylon carpet,15 thereby joining companies like BASF, Allied, and Rhodia, which have been recycling nylon on a modest level for years. DuPont is building a demonstration plant in Maitland, Ontario, which will be dedicated to the chemical recycling of nylon-6,6 and nylon-6. The newly developed ammonolysis process invented by DuPont can be used to depolymerize both nylon-6 and nylon-6,6. However, the cost of recycled nylon is estimated to exceed that of virgin nylon by ca. 25%. 

Rhodaks A process for removing hydrogen cyanide from coke-oven gas, developed by Rhodia. See also Fumaks-Rhodaks. 

Several syntheses exist for vanillin. A process recently developed by Rhodia seems to be superior [11]. The process (Scheme 5.2) involves four catalytic steps starting from phenol aromatic ring hydroxylation, O-methylation, hydroxymethyl-ation, and oxidation. The process combines elegance and precision in organic synthesis. 

Several producers such as Bayer, Dow (LFT-PP concept) and Rhodia (PMA - Plastics Metals Assembly, and MOM - Metal Overmoulding - processes) have developed their own hybrid technologies. 

The ultimate greening of fine chemical synthesis is the replacement of multistep syntheses by the integration of several atom-efficient catalytic steps. For example. Figure 9.9 shows the new Rhodia, salt-free caprolactam process involving three catalytic steps. The last step involves cyclization in the vapor phase over an alumina catalyst in more than 99% conversion and more than 99.5% selectivity. 

Another example of the substitution of classic routes for chemical synthesis by multistep catalytic processes is the Rhodia vanillin process (Figure 9.10), which involves four steps, all employing a heterogeneous catalyst. 

In 2000, Rhodia began the production of triflic acid by a new process, which includes sulfination of potassium trifluoroacetate, oxidation of the resulting potassium triflinate, followed by acidification and purification23 [Eq. (2.11)]. 

With Rhodia s high activity catalyst in the DCN process, efficient catalytic reduction ofNOx to nitrogen and water is possible at temperatures as low as 180°C without measurable ammonia in the tail gas. This catalyst has operated for over 10 years in some installations". 

An important intermediate for synthetic p-ionone (36) is the C8 building block methyl heptenone (37). In addition to the synthesis shown above, two further processes are known for its industrial production. In the process of Rhodia INC 36), the starting material is isoprene, and methyl heptenone (37) is obtained via prenyl chloride. At BASF, methyl heptenone (37) is produced, for economic reasons, in the form of its double bond isomer (37 a) by thermal condensation of isobutylene, formaldehyde and acetone 37) (see page 13). By suitable choice of the reaction conditions, various side-reactions, such as the Cannizzarro reaction of formaldehyde, the oligomerization of isobutene and aldol condensation between formaldehyde and acetone, can largely be suppressed. 

Monsanto Enviro-Chem offers NOx abatement technology that is licensed from Rhodia of France. It includes a high efficiency absorption (HEA) section for extended absorption and a catalytic reduction section (SCR) for catalytic destruction of NOx (i.e., the DCN technology).99 Additional process details are given in Reference 99. The operating conditions for the steps in the Monsanto technology are compared in Table 22.19. 

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