Neutralisation loop

For the manufacturer of 70% AD SLES and 70-75% AD coco-PAS, rheological changes that take place during the neutralisation stage start-up can result in very high apparent viscosities (K is about 100 Ns/m or 100 000 cP) and thus hi pressure drops in the neutralisation loop reactor. This has implications for the mechanical design of pumps, mixers, pipe sizing and equipment lay-out. 

The specified circulation pump operating pressure can be as high as 10 bar with a suction pressure of 2 bar and a maximum design pressure on the loop of 30 bar. Ballestra, for example, recommend a two-speed mixer and recycle pump to run at reduced capacity and circulation rate during the neutralisation loop start-up phase (when viscosities are at their highest value) to avoid excessive pressure in the loop. 

Sodium hydroxide or other neutralising agents, water and other solvents if required are normally added to the neutralisation loop using metering pumps. Variable-speed gear pumps controlled by mass-flow meter-based systems can be used. 

The operating pressure of the neutralisation loop is normally not controlled. However, a high pressure switch must be incorporated to stop the paste recirculation pump in the event of overpressure. 

From heat balance calculations it is possible to determine the heat load (i.e. heat transferred in the heat exchangers of the sulphonation, dilution and neutralisation loops) at each stage of the total process, and hence the amount of cooling water needed. The results of these calculations are summarised in table 42. The recirculation ratio (volume of recirculating material divided by the volume of throughput) is 15 1 to give small temperature differences in the sulphonation, dilution and neutralisation loop process-side streams. 

E., Mateu, M. G., Stuart, D., and Hewat, E. A. (1999). Flexibility of the major antigenic loop of foot-and-mouth disease virus bound to a Fab fragment of a neutralising antibody Structure and neutralisation. Virology 255, 260-268. 

Figure 5.54 Inferior infarction associated with an SAH (A) When the necrosis is rather large and comprises the area where ventricular depolarisation is initiated in case of SAH (point A + C), the first vector of ventricular depolarisation (1), is neutralised by the infarction vector (Inf. V.) and the loop first goes directly upwards and then, due to the SAH (see lower FP image) instead of rotating in the clockwise direction downward, it rotates in the counter-clockwise direction upward (2). Consequently, a QS morphology...

Various loop-type reactors, consisting of a circulation pump, homogeniser (where the acid is introduced in Ae circulating alkaline paste) and heat exchanger, are used for the complex neutralisation step. 

Much of the colour produced during sulphonation is contained in the spent acid. The upper layer in the separator, which contains around 90% alkylbenzene sulphonic acid (the remainder being primarily dissolved sulphuric acid) is also removed from the separator and neutralised with sodium hydroxide solution or with sodium carbonate solution to yield the active paste. When sodium hydroxide is used a considerable amount of heat must be removed. This is done in the third loop reactor of this process, the neutralisation heat exchanger (also known as the neutraliser). If sodium carbonate solution is used, the neutralisation is much less exothermic and no heat exchanger is needed at this stage. 

The loop circulating reactor outlined above expresses in chemical engineering terms, the characteristics of a perfect mixer. This type of reactor presents the following characteristics required for the neutralisation step ... 

For Ballestra plants running a wider range of products like alkylbenzenes, alcohols and ethoxylated alcohols, the double-step neutralisation system is recommended. This system allows neutralisation to occur in two steps 95% of the neutralisation occurs in the first loop reactor, always working under strong caustic conditions and neutralisation is cpmpleted in the compact intense mixer second step, in series with the first. This procedure may be followed for LAB-SA neutralisation. 

For alcohols and alcohol ether feedstocks, complete neutralisation takes place in the first loop and buffering agents/preservative can be added in the compact intense mixer second step unit. 

The paste pH is measured by an in-line pH meter in the loop just after the homogeniser (MM and Mazzoni). Chemithon t es a small paste side-stream from the loop, diluted with water via a static in-line mixer, and after pH measurement in-line, the diluted stream is re-introduced into the loop. This pH meter controls the flow of the neutralising agent and consequently the pH of the paste in the loop. 

On the cooling water side, a loop system is normally used. Fresh cold cooling water (10-20 C) is supplied to a recirculating stream of cooling water (about 30 °C) in which the amount supplied is regulated by a temperature indicator/ controller in the cooling water loop. To avoid skin formation of paste on the inside tube surfaces, which would seriously hamper heat transfer, the differential between the cooling water temperature and the neutralisation temperature is kept close to 20 0. 

Standard loop neutralisers use caustic soda solution as neutralising agent. Other agents such as aqueous or s ydrous ammonia, caustic potash, or ethanolamine can also be used. In addition liquid additives such as ethyl alcohol and urea solutions will blend with the paste in the loop reactors. 

A sample of paste is automatically taken, diluted with water by a factor of ten and the pH continuously measured. The measured pH value influences the setting of the pH control valve, which is connected in parallel to the main flow control valve for sodium hydroxide. The control loop for the main flow control valve has to be set to the amount of NaOH necessary for neutralisation, and fine dosing takes place via the pH control valve in the pH control loop. 

Chemithon are known to have "tandem" sulphonated mixtures of alkylbenzene/primary alcohols. The process is similar to the normal operation. In the first loop 20% oleum and alkylbenzene are dosed, in the second loop (the diluter) the alcohol with extra oleum is introduced, followed by immediate neutralisation (see figure 54). A product mix of ABS/alcohol sulphate/sodium sulphate is finally obtained. 

Now a few words about pH. C02 from the kiln smoke dissolves in the prirrrary circuit water and can bring its pH down to 3.5. Usual stainless steel cannot stand such a low pH we have to neutralise the circulating water. We installed therefore a caustic soda dosing pump with a regulation loop. After a few accidents we had to an place electrical relay shutting down the installation for a pH below 5. Average NaOH usage is 80 mg pure NaOH per standard cubic meter of smoke. 

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