VULCAN VGP CRT Chloride Guard Technology
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The document discusses various technologies and materials for removing chloride ions from gas streams, focusing on activated aluminas and the newly developed Vulcan series chloride guards. It highlights the challenges of using traditional methods, such as catalyst poisoning and downstream corrosion, caused by unwanted side reactions and chemical transformations. The Vulcan series products offer a more effective solution by chemically binding HCl and minimizing adverse reactions, leading to improved performance and reduced maintenance costs.
VULCAN VGP CRT Chloride Guard Technology
- 1. GBH ENTERPRISES, LTD C2PT Catalyst Process Technology By Gerard B Hawkins Managing Director VULCAN Chloride Guard Technology
- 2. Chloride removal A number of fixed-bed adsorbents / absorbents have been proposed by various suppliers: • Activated Aluminas • Promoted Activated Aluminas • Calcium Oxide, SodaLime, Molecular sieves • PURASPECTM • VULCAN Series Chloride Guards
- 4. Activated Aluminas These are formed initially from aluminium tri-hydrate and are heated to about 500oC in a flash calciner to form an amorphous type alumina. The temperature activating step is used to form the special high surface area necessary for chemisorption reactions to occur. The surface area of the ‘gamma type’ phase is about 300-350 m2/g . This very high surface area makes it an ideal surface to promote adsorption reactions. Unfortunately, these high surface area aluminas are acidic in nature ( Lewis acid sites) and although the relative acidity of the sites are considered to be of medium strength, the high surface area ensures that the number and density of Lewis acid sites on the surface is very high. It is the presence of the large number of Lewis Acid sites that promote the unwanted side-reactions to occur.
- 5. Al Al Al Al Al Al O O O O OH O O O + + -- e - Can accept an electron Can donate an electron Lewis Acid Lewis Basic site H+ Cl- is a polar molecule and the chloride ion reacts with the Lewis acid surface sites and liberates H2
- 6. ◦ Incomplete removal of HCl leads to corrosion & ammonium chloride fouling ◦ Formation of organo-chloride gives fouling/corrosion/poisoning in downstream units. ◦ Green oil formation creates problems with pipes, valves and flanges. ◦ Short lives lead to frequent change-outs
- 7. Catalyst Poisoning Downstream Corrosion Ammonium Chloride Fouling ◦ recycle compressors/export gas compressor ◦ stabiliser column ◦ heat exchangers Product Specifications
- 8. Increased Maintenance Costs ◦ washing stabilizer column ◦ compressor maintenance ◦ replacing corroded pipes & equipment Loss of Hydrogen Source ◦ Severe problems could take unit off line ◦ Loss of production in downstream units Poisoning of Downstream Catalysts ◦ eg. Ni catalysts, Cu/Zn catalysts
- 9. 1. Activated aluminas remove HCl by adsorption. The HCl has a high dipole moment and is attracted to the polar sites on the alumina surface where it is chemisorbed ( partially dissociated).There is some evidence to suggest that some stronger bonds are actually formed. 2. Promoted activated aluminas contain a small quantity of basic metal oxide. The promoter will chemically react with the HCl. This reaction is faster than adsorption and is the dominant reaction until the promoter is exhausted. Once this stage is reached, additional chloride removal is by chemisorption but this increases the acidity of the alumina surface. 3. HCl Transformation occurs when the inlet HCl is transformed into organic chloride species that are not retained by the bed and exit the reactor with the carrier stream. This occurs over acidic aluminas and is accelerated in the presence of adsorbed HCl, adsorbed H2O and unsaturated hydrocarbons. Evidence suggests that organo-chloride formation occurs in the top layers.
- 10. (I) Al2O3 + 6HCl 2AlCl3 + 3H2O (ii) 2NaAlO4 + 2HCl Al2O3 + 2NaCl + H20 Reactions (I) and (ii) are the principal mechanisms by which chloride is adsorbed from the stream. It has been demonstrated that the presence of moisture increases the chloride capacity although whether due to a capacity or merely a rate effect is not clear. For traditional aluminas the rate limiting step is likely to be some form of solid state diffusion into the structure.
- 11. Unwanted Side Reactions Occurring Across Alumina a) Organic Chlorides R = + HCI RCI b) Green Oils R1 = + R2 = H+ R1R2
- 12. Green Oil is formed by the reaction of organic chlorides with aromatic compounds such as benzene and other unsaturated hydrocarbons – this reaction is well known in organic chemistry (Freidel Crafts) and is catalysed by highly acidic surface sites on alumina. C6H6 + RCl C6H5R + HCl C6H5R + RCl C6H5R-R + HCl Hence long chain polymeric compounds are produced of such high molecular weight that the precipitate out causing fouling and blockage.
- 13. In the case of alumina adsorbents, various condensation and polymerisation reactions are catalysed by anhydrous AlCl3.The high molecular weight polymers block pores and deposit ‘gums’ or ‘green oil’. The gums act to form lumps of agglomerated adsorbent which reduce capacity due to channelling of gas flow. The formation of complex organic chlorides , some of which are volatile, is also promoted byAlCl3, resulting in chloride loss from the adsorber and corrosion or poisoning problems. Aromatics + Anhydrous AlCl3 dark red / orange complexes polymeric tars Naphthenes + Anhydrous AlCl3 orange complexes and tar Example: A sample of liquid drained from a vessel was tested and found to be: 87% hydrocarbon boiling below 200 C and 13% polymeric naphthenes and aromatics unable to be distilled as the material is “pitch” like, setting solid on cooling.
- 14. Addition of halogens to alkenes involves attack by positive halogen to form an intermediate carbonium ion. The loosely held pi electrons of an alkene make it more reactive. The less reactive benzene molecule needs the assistance of a Lewis acid . More reactive aromatic molecules ( those whose pi electrons are more available, phenols, furans etc..) can react with halogens in the absence of a Lewis acid. Naphthenes are very prone to di & polyalkylation reactions leading to polymeric long chain structures.
- 15. R-Cl + AlCl3 AlCl4- + R + H R+ + C6H6 C6H5 + R H C6H5 + + AlCl4 - C6H5R + HCl + AlCl3 R Friedel-Crafts reaction is an electrophilic substitution with AlCl3 acting as a Lewis acid. Slow Fast C6H5R-R
- 16. Other chemical reactions may occur in the presence of AlCl3.The coupling of two aromatic molecules by treatment with a Lewis Acid and a proton acid is called the Scholl reaction. CH H+ AlCl3 This type of intramolecular reaction can also occur with activated aluminas
- 17. In normal operation there will be trace amounts of unsaturated hydrocarbons in reformer reactor product that will go into both the offgas and reformate streams. For example, in hydrogen gas ex- catalytic reformers the concentration of ‘unsaturates’ varies from 400 ppmv to 1000 ppmv. These unsaturated hydrocarbons will react with HCl when promoted by an acid catalyst . These organo-chlorides can therefore be formed across activated aluminas. These organo-chloride species are not removed by the alumina and exit the bed in the product stream. If the off-gas stream supplies H2 to hydrotreating or hydrocracking units, these organo-chlorides will be hydrogenated to HCl and initiate corrosion problems and catalyst deactivation.
- 18. • unsaturated hydrocarbon reacts with surface hydroxyl ( acid) site • reactive carbonioum ion formed • Cl chemisorbed to alumina surface • carbonioum ion reacts instantly with Cl • R-Cl formed Al Al Al O O Cl O - H O - H O - H Cl RCH2=CH RCH2CH2 + Alumina surface RCH2CH2Cl
- 19. Make gas and stabilizer feed from catalytic reformers contains a mixture of olefins which should theoretically be present from equilibrium calculations: Gas C2= to C4= Liquid C4= to C8= For typical reformate, C4= and above, the tertiary olefin is the major component, broadly inline with equilibrium calculations. The level of ethylene and propylene should only be about 15% of the total olefins. The reaction to produce organic chlorides is most easily performed with tertiary olefins due to the reactivity of the tertiary carbonium ion. Therefore, for a mixture containing equal parts of primary, secondary and tertiary butylene reacting with HCl, the major product is tertiary butyl chloride.
- 20. CH3CH2CH=CH2 + HCl CH3CH3CHClCH3 1-Butene Sec-butyl chloride CHC=CH-CH3 + HCl CH3-C-CH2-CH3 2-Methyl-2-Butene tert-pentyl chloride CH3-C=CH2 + HCl CH3-C-CH3 CH3 Cl CH3 CH3 Cl Isobutylene Tert-butyl chloride
- 21. Reactivity of alkenes with HCl C=CH2 > CH3CH=CHCH3, CH3CH2CH=CH2, CH3CH=CH2 >CH2=CH2 CH3 CH3 Stability of carbonium ions: 3 > 2 > 1 > CH3+ o o o
- 22. Leaching of components from the adsorbents can be a potential problem, leading to both loss of chloride and contributing to fouling of the adsorbent mass. Evidence for the mechanisms leading to leaching point to some form of dissolution via: AlCl3 Soluble in liquid water and organic solvent AlCl3 + 3H2O Al(OH)3 + 3HCl NaCl Soluble in liquid water only Analysis of agglomerated lumps from one refinery application of their spent activated aluminas has shown NaCl in the binding phase and unexpectedly high LOI on the samples. This suggested that water must have been present.
- 23. - Enhanced chloride protection - Proven track record in gaseous and liquid duties - Reliable and safe operation - Low capital cost - Cost-effective operation - Environmentally friendly - No process losses - Guaranteed solution to a problem
- 24. High Temperature ◦ VGP CRT-3000 Low Temperature Gases ◦ VGP CRT-2000
- 25. VULCAN Series Chloride Guards Bi-metallic promoted Low acidity / medium surface area Low ‘side-reaction’ inducing characteristics A.B.D. 0.60-0.80 kg/l Theoretical capacity 32% w/w
- 26. VULCAN Series Chloride Guards • New products are absorbents – HCl removed by chemical reaction – They have been manufactured with a reduced surface area to minimise aromatic and hydrocarbon adsorption and its constituent components-( bi-metallic promotion and highly porous support - do not have adsorption properties for HCl. • HCl does not exist freely or in an adsorbed or in a partially dissociated state within the particle or on its surface. • The HCl is irreversibly chemically bound within the matrix. • VULCAN Series products are not acidic and minimises / retards organic chloride synthesis or condensation and polymerisation reactions. • Chloride pick-up in excess of 30 % w/w in gas phase tests • HCl removal to < 0.1 ppmv
- 27. Chemisorption: Alumina MO- H+ ……... CI- H+ - Reversible - Equilibrium loading function of T, pHCI, pH2O Chemical Reaction: VGP CRT 3000 Na2O + 2HCI => 2NaCI + H2O 2NaAIO4 + 2HCI => 2NaCI + H2O + AI2O3 - Irreversible - Chloride loading constant
- 28. Chloride Guards - History & Development Activated Alumina ( unpromoted) 3-5% Activated Alumina ) (5% calcium -promoted) 5-8% Activated Alumina ( 10% sodium promoted) 10-12 % VGP CRT-3000 ( BIMETALLIC) 25-32% Saturated Chloride capacity
- 29. Pick-up depends on temperature, pressure, flowrate, feed composition, inlet chloride level Different locations in a flow scheme will give different expected lives Lead-lag gives better absorbent usage and continuous protection Must change bed when chloride first breaks through