Carbon dioxide removal from loop

Step 7. Ethane is an inert component that enters with the ethylene feed. It can be removed from the process only via the gas purge stream, so purge flow is used to control ethane composition. Carbon dioxide is an unwanted by-product that leaves in the C02 removal system. As long as the amount of carbon dioxide removed is proportional in some way to the C02 removal system feed, we can use this valve to control carbon dioxide composition. Oxygen inventory is accounted for via composition control with fresh oxygen feed. Inventory of ethylene can be controlled to maintain gas loop pressure, since ethylene composes the bulk of the gas recycle. 

The gas from a methanation unit will contain water, possibly from the carbon dioxide removal section and at least as formed by reaction (6) and (7). This water must be removed before the gas reaches the ammonia synthesis catalyst. The dehydration can be done either by adsorption on molecular sieves [365], whereafter the gas can be added to the synthesis loop just upstream of the synthesis converter, or by co-condensation and washing with ammonia. This last method is used in many ammonia plants, where the synthesis gas is added to the synthesis loop before the product ammonia is separated, see Sect 6.4.1. 

Material removed from the water by stripping in this manner can also be concentrated by trapping in a loop immersed in a cooling bath. The usual cooling baths are liquid nitrogen or solid carbon dioxide with or without an... 

Step 1. For this process we must be able to set the production rate of vinyl acetate while minimizing yield losses to carbon dioxide. During the lifetime of the catalyst charge, catalyst activity decreases and the control system must operate under these different conditions. To maintain safe operating conditions, the oxygen concentration in the gas loop must remain outside the explosivity region for ethylene. The azeotropic distillation column must produce an overhead product with essentially no acetic acid and a bottoms product with no vinyl acetate. The absorber must recover essentially all of the vinyl acetate, water, and acetic acid from the gas recycle loop to prevent yield losses in the CCf removal system and purge,... 

It is energetically advantageous to add the purified synthesis gas at a point in the synthesis loop where it can flow directly to the synthesis converter (see Section 4.5.1). For this reason water and traces of carbon dioxide must be removed from the makeup gas downstream of methanation. This is accomplished by passing the makeup gas through molecular sieve adsorbers, which can be positioned on the suction side or in an intermediate-pressure stage of the synthesis gas compressor. 

The chromatograms in Fig. 8.4 show the effect of enhancement columns. Each enhancement column increases the carbonic acid peak height, but the baseline conductance is also increased somewhat. A pre-column packed with anion-exchange resin in the OH" form was then placed between the pump and loop injector to remove completely and continuously the carbon dioxide in the eluent. This arrangement resulted in a significant decrease in eluent background conductance, as shown in Fig. 8.4D. An almost linear calibration plot was obtained from 0.05 to 5.0 mM bicarbonate. The detection limit was estimated to be 1.45 pM. 

In the gas-flow experiments, carbon dioxide from the purification line was allowed to flow through the irradiation cell and condensed in a large cold trap cooled in liquid nitrogen the noncondensible gases (oxygen and carbon monoxide) were removed continuously by a Toepler pump and transferred to the sample loop of a gas chromatograph, where... 

To determine the volume of the calibration loop, the following procedure is used. A gas ampoule of known volume is filled with carbon dioxide to a known pressure. The gas from the ampoule is distilled into the loop which is cooled to -196 C with liquid nitrogen. The loop is then rotated into the helium gas stream and the cooling bath removed. The carbon dioxide is passed through the gas chromatograph and the output of the recorder is integrated with... 

Fresh synthesis gas produced by the steam-reforming route is compressed to synthesis pressure in a two-stage centrifugal compressor. The compressor is usually driven by a steam turbine. The compressed make-up gas is chilled and added to the loop before the final loop chiller. After the chiller, the ammonia product is removed in the ammonia separator which operates at a typical temperature of -5 °C. Traces of carbon dioxide and water in the incoming gas are removed with the product ammonia. Topsoe have calculated that with their synthesis conditions, the saving in energy obtained by the alternative system of molecular sieves for carbon dioxide and water removal is small and does not justify either the extra investment or the risk of dust carryover from the molecular sieves. 

The product gas from steam reforming, catalytic partial oxidation, partial oxidation, or gasification processes contains in all cases significant amounts of carbon monoxide and carbon dioxide. Since the feed gas for the ammonia synthesis loop must be completely free of these compounds, they must be removed in the gas preparation part of the plant. Carbon monoxide is removed in a conversion step by the so-called water-gas shift reaction or just the shift reaction, in some cases followed by further conversion by selective oxidation. 

Nickel sulfate also is made by the reaction of black nickel oxide and hot dilute sulfuric acid, or of dilute sulfuric acid and nickel carbonate. The reaction of nickel oxide and sulfuric acid has been studied and a reaction induction temperature of 49°C deterrnined (39). High purity nickel sulfate is made from the reaction of nickel carbonyl, sulfur dioxide, and oxygen in the gas phase at 100°C (40). Another method for the continuous manufacture of nickel sulfate is the gas-phase reaction of nickel carbonyl and nitric acid, recovering the soHd product in sulfuric acid, and continuously removing the soHd nickel sulfate from the acid mixture (41). In this last method, nickel carbonyl and sulfuric acid are fed into a closed-loop reactor. Nickel sulfate and carbon monoxide are produced the CO is thus recycled to form nickel carbonyl. 

---