Sulphonation plants

Adami, I. New Exhaust Gas Treatment System for Sulphonation Plants. 7th International Conference on Surfactants and Detergents (paper), Shensen, 2002. 

Sulphonation plants are scattered around the globe in units with production capacities varying between 3,000 and 50,000 tons anionic surfactants annually. Assuming an average production capacity of, say, 5,000 tons per year, there are at least 800 operational sulphonation plants around the world. 

Therefore moisture in the process air entering the sulphonation plant must be kept low with an upper limit of 0.01 g/m This corresponds approximately with a dewpoint of the dried air of the dewpoint being the temperature at which moisture will condense out of the air. 

The air drawn in from the atmosphere is filtered and compressed through the compressor which produces the required pressure to overcome the resistance of the total plant, including the exhaust gas cleaning system. The pressure at the compressor exit varies with the type of sulphonation plant but is in the range 0.5 - 1 bar gauge. 

Correct operation of the burner is essential for successful functioning of the total sulphonation plant. Unbumt sulphur may evaporate and will pass upstream with the process gas causing sulphur sublimation deposits in filters and catalyst tower ("yellow fever"). Subsequent local burning of sulphur can cause severe damage to equipment such as the SO2 cooler, the SO3 filter. 

The commoner and preferred alternative is to use air coolers of simple design. The heated ambient air up to temperatures of 250-400 C is mixed with the quench air of the NSD spray tower furnace. This direct application of heat is simple and cheap provided that the distance between the sulphonation operation and the NSD spray tower is no more than 1(X) m. A lagged pipeline connects the sulphonation plant and the spray tower furnace. 

This system is preferably used with alkylate feedstocks because sulphonic acid is a stable product. For those sulphonation plants that produce exclusively alcohol sulphates, alcohol ethoxy sulphates etc. an H2SO4 absorber is recommended. 

In conclusion, the following conditions are of vital importance for successful operation of ESPs in sulphonation plants ... 

In general a very light plume or no plume at all is observed from the stack of an S03/air sulphonation plant. 

Even though the above values represent the guaranteed concentration of dioxane contamination in ether sulphates from the suppliers, in practice the formation of dioxane is extremely dependent upon the overall quality of operation of the sulphonation plant. Under ideal conditions the performance of the Ballestra, Chemithon, MM and Mazzoni plants is unlikely to be significandy different. 

Control of the level of 1,4-dioxane in the ethoxylated alcohol sulphates is often seen as a good measure of the overall performance of the sulphonation plant. All equipment suppliers have examined the effects of various operating and design parameters on the formation of 1,4-dioxane. 

The need to meet local and national demands to restrict effluent levels from sulphonation plants makes it increasingly important that installed treatment systems are effective. The existing regulations around the world for both gaseous and liquid effluents vary from the non-existent to the stringent. Effluent carried by the exhaust gas leaving the sulphonation system consists of ... 

Chemical analysis of exhaust gas leaving the sulphonation plant stack (see fig. 48)... 

The amount of sulphuric acid (oleum 20%) collected in the bottoms of the SOs/air cooler system and in the SO3 mist eliminator, is directly related to the dewpoint of the dried process air (see 5.2.2.). With an air dewpoint of -60 C, only 2 kg oleum per 24 hours will be formed for a 1 ton AD/h sulphonation plant. With increasing dewpoint the amount of oleum collected will rise sharply. For sulphonation plants working with an SO3 absorber (see section 5.2.6) it is recommended that the collected amounts of sulphuric acid/oleum be discharged into the vessel at the SO3 absorbing system. The acid coming from the various parts of the gas raising plant should be collected via gravity flow in an intermediate tank with level control from where the acid is pumped off with a membrane pump to the SO3 absorber. The use of compressed air is not recommended for safety reasons. 

For sulphonation plants without an SO3 absorber the following system is recommended via gravity flow, sulphuric acid/oleum from the various parts of the gas raising plant is collected in an intermediate tank with level control. The intermediate tank should be sufficiently large to contain about one week s production of acid. The collected acid is discharged intermittently (say once a week) with a membrane pump and is sent to a PTFE lined mixer, which is filled with glass balls. Here acid dilution with water takes place using an acid to water ratio of 1 10, so as to maintain the resultant sulphuric acid temperature below 50°C. 

The liquid effluent leaving the SO2 scrubber consists of a solution of caustic soda, sodium sulphite, sodium sulphate and traces of active matter. At 98% SO2 SO3 conversion (steady-state running conditions) about 80 kg/h of a 10% sodium sulphite solution will leave the scrubber system, based on a 10(X) kg/hr sulphonation plant (see table 19). The alkaline solution is collected in an acid/caustic-resistant pit. It is common practice to dilute this liquid stream with other effluent streams (ex slurry-making and powder manufacture) and to re-use it in the detergent powder manufacturing plant as dilution water. 

Based on a sulphonation plant producing 1000 kg AM linear alkylbenzene sulphonate or 100 kg sulphur/hour (7% SO3 in air). 

Herman de Groot W. (1989). "Liquid effluents and exhaust gas emissions from sulphur based S03/air sulphonation plants". Paper presented at Practical Sulphonation Seminar, 18-20 April 1989, The Hague, The Netherlands. Center for Professional Advancement, P.O. Box H, East Brunswick, New Jersey 08816, USA. 

The basic requirement of the sulphonation plant control system is to allow production of the desired quality acids and pastes in a safe manner within the design capacity limitations of the plant. 

The level and sophistication of instruments and process control systems is largely determined by local preference although in order to satisfy the basic requirement, as stated above, there is a minimum requirement for instrumentation, control and safety interlocks which are common to all sulphonation plants. 

A dewpoint meter for process air, with a recorded signal, should always be fitted as standard in sulphonation plants. Regular manual checks are essential (see 5.2.2.). 

At present, Ballestra has installed automatic control of the SOj/organic mole ratio in at least six new sulphonation plants. The principles of the mole ratio control are indicated in P I diagram 8. This new development is feasible because accurate and technical reliable massflow meters are available now. 

Control of the level in the acid/gas separator ensures an effective seal between the liquid handling parts of the sulphonation plant and the exhaust gas treatment section. Several methods can be used, but the one which minimizes the hold-up and residence time distribution of acids, and consequently dioxane formation during ether sulphate manufacture is based on control of a variable speed gear pump. 

Manual control of the operation of a sulphonation plant can be supplemented by computer-based data logging. Such systems are non-interactive in that analogue and digital signals from the plant are fed to the computer/data logging system, but information is not fed back. Consequently, the status of pumps etc. and other data can be displayed on the screen-based mimics, reports can be printed and the data obtained can be manipulated to show trends or used in other off-line computer programs. 

Owing to the hazardous nature of the materials handled in a sulphonation plant it should be accommodated in its own building at least 20m from other buildings. It should not be in the centre of the factory but on the periphery, remote from residential and other areas where gas emissions could be considered unsafe or a nuisance. The site should have easy access by road for the receipt of raw materials and should be near the powders/liquids processing plants so that long transfer lines for sulph(on)ated products (acids or pastes) can be avoided. 

Fig. 50. TYPICAL SULPHONATION PLANT LAYOUT MECCANICHE MODERNE 3000 kg/h...

Table 41 Typical 20% oleum sulphonation plant. Mass balance based on the assumptions listed in section 11.1. All units in kg.

Figure 54 Chemithon 20% oleum tandem sulphonation plant (LAB and PA)...

After neutralisation, the 55% AM paste is stored in a finishing tank where final quality checks are carried out before pumping the paste to the tank farm (100 m paste tanks). The distance between the sulphonation plant and the tank farm is 120 m. Further data 55% paste rheology data at 60°C (see table 16) K = 50 Ns/m n = 0.2, paste density about 1000 kg/m ... 

Imagine that your company has decided to install a sulphur-based SOa/air sulphonation plant on the household detergent factory site where you work. It is your task to introduce this new technology to the following personnel ... 

Mass balance exercise for 20% oleum sulphonation plant... 

Sulphonation Plant Troubleshooting (source Chemithon) Symptom Causes ... 

This book is about Sulph(on)ation Technology in its technical entirety, aiming at superiority in final product quality, raw material utilisation, sustained plant reliability and safety, minimisation of liquid effluent and gaseous emissions it is about the total quality of the operation. It will be of value to engineers and chemists who are, or will be, involved in the practical daily operation of sulphonation plants or R D activities. The book can also be used as a tool for the teacher in preparing final year projects in a chemical engineering curriculum. 

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