Hydrogen Exchange Processes

The deuterium exchange reaction between liquid methylamine and gaseous hydrogen, 

17 and 13.18). For this reason, Atomic Energy of Canada, limited (AECL), has undertaken a development program for a dual-temperature process using methylamine and hydrogen from a synthetic ammonia plant with a flow sheet similar to Fig. 13.37. 

Enriched steam for the synthesis-gas generator (A) is produced in the series of sieve-plate contactors (E), (F), and (G). In (E) deuterium is transferred from methylamine liquid to methylamine vapor, reducing the deuterium content of the liquid from 10.916A to 1.06A while increasing that of the vapor from 1.02N to lOA. In (F) deuterium is transferred from methylamine vapor to water, increasing the deuterium content of the latter from N to 8A. This two-step transfer of deuterium from liquid methylamine leaving (C) to water leaving (F) is necessary to prevent chemical reaction between water and the catalyst dissolved in liquid methylamine. 

Because of the reduced rate of the deuterium exchange reaction at —50°C, the stages of the cold tower (D) are to be of the type developed by Sulzer [LI ] for the ammonia-hydrogen exchange process and used in the Maangarbe plant. Sec. 9.1. For the methylamine-hydrogen system at —50°C, a stage efficiency of 70 percent has been obtained [W6]. 

At the temperature of the hot tower, 40°C, potassium methylamide slowly decomposes into potassium dimethyl formamidide  

---

The reduction in the selectivity of forming C2HgN+ as the alkyl chain length is increased reflects the enhanced rate of hydrogen exchange processes which allow a deuterium atom to be transferred to a position in which it is incorporated in the immonium ion. 

The effect of fluorination on the reactivity of carbanions has been reviewed.65 66 Fluorination has the same influences on carbanion stability as does the effect of fluorination on acidity (see Section 1.2.). A lot of information has been derived from the effect of fluorination on CH acidity.43 The effect of fluorination on deuterium-hydrogen exchange processes in the case of highly fluorinated substances has been examined with estimates of pKa for highly fluorinaled substrates.67... 

The monothermal ammonia-hydrogen exchange process was developed in France. The first plant was built at Mazingarbe and five plants have been built in India. 

Similar bridging hydrogen exchange processes have been observed for neutral and cationic (zj -allyL/i-IIjMD, complexes 25 (Scheme 3)23.58,63 j ny of these complexes are prepared by the protonation of the corresponding anionic or neutral (/j4-dicnc)MLn complexes 26 (see Section V.C.l). Migration of the metal about a cyclic ) -allyl ligand (i.e. 25a to 25b) is proposed to involve an (/j" -diene)MLn hydride intermediate/transition state 27. 

The application of proton resonance techniques to deuterated derivatives enables qualitative and quantitative observations of the hydrogen exchange process. With tritium-labeled bases the gain in radioactivity of the protic solvent provides a convenient means of monitoring the reaction course. The comparative ease with which either deuterium or tritium can be inserted at the 8-position, compared with corresponding replacements at the 2- and... 

Figure 13.23 Monothermal ammonia-hydrogen exchange process. Flow quantities, kg-mol/h.

DUAL-TEMPERATURE AMMONU-HYDROGEN EXCHANGE PROCESS... 

Table 13.26 Comparison of hydrogen exchange processes monothermal and dual-temperature ammonia-...

DUAL-TEMPERATURE WATER-HYDROGEN EXCHANGE PROCESSES... 

Availability of this catalyst has led to interest in its possible use in dual-temperature water-hydrogen exchange processes. With liquid-water feed and recirculated hydrogen gas, this catalyst could be used in a dual-temperature process similar in principal to the GS process, with a schematic flow sheet like Fig. 1325. With ammonia synthesis-gas feed and recirculated water, this catalyst could be used in a dual-temperature process similar to the ammonia-hydrogen process flow scheme of Fig. 13.37, provided that impurities in synthesis-gas feed that would poison the catalyst can be recovered sufficiently completely. 

The dual-temperature, methylamine-hydrogen exchange process described in Sec. 13 could also be used to concentrate deuterium from ammonia synthesis gas produced from natural gas and steam containing the normal abundance of deuterium instead of the enriched steam used in the Sulzer flow sheet. Fig. 13.40. Figure 13.42 is a flow sheet for such a process giving the deuterium content of each stream in the first stage of the plant. 

Figure 13.42 Primary concentration step in dual-temperature methylamine-hydrogen exchange process fed with synthesis gas made from normal water. Flow rates G and L in kg-mol/h. [ DY) = 135 parts deuterium per million parts deuterium -h hydrogen.

---