1

• Excess Air Process (Metal Oxide Catalyst) • Excess Methanol Process (Silver Catalyst)

EXCESS AIR PROCESS

PLANT

EXCESS METHANOL PROCESS

PLANT However currently the modern excess air process of Formaldehyde manufacture commonly known as the metal oxide process is in vogue owing to multiple operational advantage afforded by the same. EXCESS AIR (METAL OXIDE CATALYST) FORMALDEHYDE TECH NOLOGY Formaldehyde Technology for simultaneous / individual production of AF – 37 / AF – 55 and / or UFC - 85 is based on the modern “Excess Air Process of Formaldehyde manufacture” commonly known as the Metal Oxide Process.

� FORMALDEHYDE PRODUCTS

AQUEOUS FORMALDEHYDE (AF – 37 / 55) AND UREA FORMAL DEHYDE CONCENTRATE (UFC – 85) Since its discovery in the later half of the nineteenth century, Formaldehyde has become an industrial chemical of outstanding importance. Formaldehyde Chemistry is slightly complicated by the fact that although Formaldehyde is well known in the form of its aqueous solutions and solid polymers, it is seldom encountered in pure monomeric form. Commercially, Formaldehyde is marketed chiefly in the form of aqueous solutions containing about 36 to 50 percent by weight dissolved Formaldehyde (HCHO) – the most common form being Aq. Formaldehyde (AF 37). The other most popular forms are Urea Formaldehyde concentrates (UF 80/85) and Paraformaldehyde. Among the other derivatives are amino resins, polyhydric alcohols, polycetals etc. Formaldehyde results from the exothermic oxidation and endothermic dehydrogenation of methanol: CH3OH + ½ O2 ���� HCHO + H2O ∆H = - 156 kJ CH3OH ���� HCHO + H2 ∆H = + 85 KJ These two reactions occur simultaneously in commercial units in a balanced reaction, called auto thermal because the oxidative reaction furnishes the heat to cause the dehydrogenation to take place. About 50 to 60 percent of the Formaldehyde is formed by the exothermic reaction. The oxidation requires 1.6 m3 of air per kilogram of methanol reacted, a ratio that is maintained when passing separate streams of these two materials forward.

2

Process Description The process comprises the following steps: • Evaporation of methanol. • Mixing of gaseous methanol with air and recycle gas.

• Oxidation of Methanol to Formaldehyde in an oil cooled tubular catalytic reactor. • Absorption of Formaldehyde in De-mineralized Water or Urea Solution depending on the

desired Product (AF37 / AF 55 or UF - 85).

• Catalytic incineration of tail gas.

Formation of Formaldehyde takes place in a Reactor containing tubes filled with an Iron/Molybdenum Oxide Catalyst. As mentioned the main reaction is the oxidation of Methanol to Formaldehyde, according to the equation: CH3OH + ½ O2-HCHO + H2O This reaction is strongly exothermic. In this process a metal oxide (e.g. iron, molybdenum or vanadium oxide) is used as a catalyst for the conversion of methanol to Formaldehyde. Usually, the oxide mixture has a Mo: Fe atomic ratio of 1.5-2.0, small amounts of V2O5, CuO, Cr2O3, CoO, and P2O5 are also present. Special conditions are prescribed for both the process and the activation of the catalyst. The process has been described as a two-step oxidation reaction in the gaseous state which involves an oxidized (Kox) and a reduced (Kred) catalyst.

CH3OH(g) + Kox →→→→ CH2O(g) + H2O(g) + Kred K red + ½ O2(g) →→→→ Kox ∆H = -159 kJ/mol In the temperature range 270-400°C, conversion at atmospheric pressure is virtually complete. However, conversion is temperature-dependent because at > 470°C the following side reaction increases considerably:

CH2O + ½ O2 →→→→ CO + H2O ∆H = 215 kJ/mol The heat of reaction is removed by circulating heat transfer oil on shell side of tubular reactor. The heat transfer oil partially vaporizes. The vapors are separated from the liquid and used for preheating of the reaction mixture and tail gas. Excess oil vapors can be condensed in an air cooled condenser or used for simultaneous generation of medium pressure steam, upto 25 kg/cm2g (350ps), as shown in the Schematic Flow Diagram of the process in Figure 1 below:

3

FIG 1: Schematic Flow diagram of “Excess Air Formaldehyde Process”.

The Catalyst loading scheme is designed to flatten the temperature profile, thus minimizing the rate of pressure drop increase. In order to maintain optimum temperature control and to reduce by –product formation, the Catalyst in the upper part of the tubes is diluted with inert material. This reduces hot spot temperatures and flattens the temperature profile resulting in minimized pressure drop increase. The Formaldehyde-rich gas from the Reactor is rapidly cooled in a Steam Boiler, ensuring the lowest possible formation of Formic Acid. The theoretical consumption of Methanol per metric ton of 37 wt% Formaldehyde solution is 395kg. The actual consumption will increase both with the amount of by-products formed and with the amount of unconverted Methanol. A low Methanol consumption. i.e. a high yield, can only be obtained if both the overall conversion and the selectivity are high. The overall conversion is the fraction of the feed Methanol which is converted. The selectivity is the fraction of the converted Methanol which is transformed into Formaldehyde. By varying the temperature of the thermal oil – the most important process parameter- the two figures will vary in opposite directions as shown below. The yield, which is the product of the overall conversion and the selectivity, will therefore, all other parameters equal, be maximum at a certain temperature, as shown in Figure 2 below:

FIG.2

The temperature giving the maximum yield will often be chosen as the operating temperature. But if it is important for the end user to get a product with very low Methanol content, this can be obtained by raising the operating temperature of the cooling bath. If a high conversion is not essential (e.g. if unconverted Methanol can be recycled) a relatively low operating temperature may be preferred to obtain the highest possible selectivity.

4

The Formaldehyde-rich gas from the Reactor passing via the Steam Boiler is fed to an Absorber where the Formaldehyde is absorbed in D.M. Water or Urea Solution as the case may be. The tail gas from the Absorber contains little residual Methanol and Formaldehyde, but appreciable amount of CO and Dimethyl Ether.(D.M.E.) By varying the amount of Process Water /Urea Solution fed to the Absorber, the strength of the Product can be varied. By including a catalytic tail gas Incineration Unit, the Formaldehyde plant can meet the environmental regulations of any country. The tail gas is heated to approx. 250oC and passed through a fixed bed Reactor with incineration Catalyst. The Incineration Unit operates without support fuel. As shown in the simplified Process Block Diagram at Figure 3, below ATEC’s Formaldehyde process shall afford simultaneous production of AF 37 / AF 55 and UFC – 85.

FIG. 3: Formaldehyde Process Block Diagram

Proper Reactor / Absorber designs are key success factors in the engineering of an efficient Formaldehyde Plant. Formaldehyde Reactors The Formaldehyde catalyst reactor is a multitubular heat exchanger where the heat developed inside the capacity bed, is exchanged by a cooling medium. In Industrial practice all the reactors can be classified as:

5

FIG. 3A: Mineral/Synthetic Oil Cooled Reactor

FIG. 3B: Molten Salts Cooled Reactor

FIG. 3C: DWT Cooled Reactor

FIG. 3D: Dowtherm Oil Cooled Reactor

Reactor with Tube-Boiling compound (Liquid+ vapour) heat exchange ATEC would recommend highly efficient Reactor design based on Downtherm cooling of the Reactor tubes with optimized waste heat generation, which is chosen for smooth trouble free operation. Fig. 3E shows a photograph of Downtherm cooled reactor.

6

FIG. 3E: Downtherm Cooled Formaldehyde Reactor

SERIES REACTOR SCHEME ATEC also possess the know-how for a unique Series Reactor Scheme in which the Capacity of an excess air process based Formaldehyde Plant can be virtually doubled with minimum investment. By judicious incorporation of built-in over plus capacity (at initial stage itself) in key equipment section, the plant capacity can be doubled in a very short time frame, at almost half the cost by incorporating a “Series Reactor” in the process layout, as shown in the Flow Diagram below:

FIG 4. FLOW DIAGRAM OF UNIQUE SERIES REACTOR SCHEME FOR AF37/UF85

For example, by adding a ‘Series Reactor Scheme’ a 200 M.T.P.D. Plant can be increased to 380 M.T.P.D. at 50% of the original investment. ABSORPTION COLUMNS

7

ATEC specifies a highly optimized Absorption Column design employing a combination of packed beds and tray sections. Special valve tray designs have been developed to ensure continuous sustained operation minimizing /eliminating cleaning cycles. Operating experience of nine Formaldehyde Plants has gone into evolving a perfect Column design tailor made for trouble free operation. Key components of the internals of typical absorption columns are cross – sectionally shown in the diagrams below. Column designs are of particular significance for production of Urea Formaldehyde concentrates (UFC – 85) wherein strict process control is required to prevent formation of undesirable side products like Methylene –Di –Urea. Figure 5 below presents a pictorial projection of a bench scale model of a twin Absorber Plant alongside the actual Plant built on a scaled up basis, which affords simultaneous production of AF 37, AF 55 and UFC 85 products in a single process unit.

8

FIG. 5: BENCH SCALE MODEL AND ACTUAL PHOTOGRAPH OF AF 37/ UFC

85 PLANTS SALIENT FEATURES AND ADVANTAGES OF THE EXCESS AIR P ROCESS. • Lower capital investment • Faster plant installation

• Low raw material and utility input consumptions • Higher conversion yield.

• Fully automatic DCS based instrumentation • No waste materials.

COMPARISION OF FORMALDEHYDE PROCESSES

PARAMETERS

EXCESS AIR PROCESS

(METAL OXIDE CATALYST)

EXCESS METHANOL

PROCESS (SILVER CATALYST)

Yield 91 ~ 93 % 80 ~ 83 % HCHO 45 ~ 55 % 37 ~ 45 wt%

CH3OH 0.5 ~ 1.5 wt% 3 ~ 7 wt% Product Quality

HCOOH Low Lower CH3OH 429 kg/T 435 kg/T Steam Exported 400 kg/T Consumed 270 kg/T

Consumption Figure (as 37 wt% HCHO) Electric power 100 kWH/T 20 kWH/T Catalyst Li fe 1 ~ 2 Year 0.3 ~ 0.5 Year

To catalyst posit ion

Tough Weak

Inf luence by emergency shut-down

No trouble Case crack

Start-up procedure Easy Not so easy HCHO concentration in

formalin at start-up Lower than normal

for 8 hours Lower than normal

for 24 hours Methanol concentration in formaldehyde at start-up

Same as normal Higher than normal

for 2 ~ 3 days

9

EXCESS AIR (METAL OXIDE CATALYST) AF 37 / AF 55 / U FC 85 PLANT

• PRODUCT SPECIFICATIONS

���� AQUEOUS FORMALDEHYDE SOLUTIONS (AF 37 / AF 55)

Composition, wt% Formaldehyde (HCHO) 37.00 – 55.00 Methanol (CH3OH) <1.0 Formic Acid (HCOOH) <0.05 Water (H2O) Balance

Various stabilized grades of Aq. Formaldehyde (i.e. 37% concentration Formaldehyde with varying stabilizing Methanol content of 0.40 % to 12 % and 55% concentration Formaldehyde) can be produced in the PLANT.

� UREA FORMALDEHYDE CONCENTRATE (UFC 85)

Typical Product Composition:

Constituent Formula Composition by wt.% Formaldehyde HCHO 60.0 Urea NH2CONH2 25.0 Methanol CH3OH 0.21 (max.) Formic acid HCOOH 0.01 (max.) Water H2O by balance Chlorides 0.001 (max.) Iron 0.0001 (max.) Heavy metals N.T.

•••• SPECIFICATIONS OF RAW MATERIALS

10

� COMMERCIAL GRADE ‘AA’ METHANOL Parameters Specification Methanol content >99.85 wt% Relative density 0.7928 g/cm3 Maximum boiling point range 1°C Acetone and acetaldehyde content <0.003 wt% Ethanol content <0.001 wt% Volatile iron content <2 mg / litre Sulfur content <0.001 wt% Chlorine content <0.001 wt% Water content <0.015 wt%

� UREA (Granular or Prilled) % w/w Nitrogen (Dry basis) : 46.3 Biuret (Max.) : 0.8 Delta Iron (Max) : 1 ppm Moisture (Max) : 0.3% � CAUSTIC SODA SOLUTION

Sodium Hydroxide (NaOH), wt% 49.0 min - 51.5 max. Sodium Oxide (Na2O), wt% 38.0 min – 39.9 max. Sodium Carbonate (Na2CO3), wt% 0.05 max. Sodium Chlorate (NaClO3), ppm 1 max. Sodium chloride (NaCl), ppm 50 max. Sodium Sulphate (Na2SO4), ppm 10 max. Iron as Fe, ppm 3 max.

•••• SPECIFIC CONSUMPTION OF RAW MATERIALS AND UTILITIES ON PRODUCT -WISE BASIS

���� AQUEOUS FORMALDEHYDE (AF 37) As is known AF 37 needs to be stabilized with varying proportions of Methanol depending on storage considerations and customer requirements, specific consumption for the unstabilised grade (basic AF 37) on ISBL Plant basis are: Methanol : 0.425 MT / MT AF 37 Potable Water : 2.000 MT / MT AF 37 Electricity : 105 KWH / MT AF 37 Diphenyl Heating Oil : 0.075 kg / MT AF 37

The above specific consumption figures are for Formaldehyde production by the “Excess Air (Metal Oxide Catalyst) Process”.

11

� UREA FORMALDEHYDE CONCENTRATE (UF – 85) PER M.T. UF - 85

� Methanol M.T. 0.70 � Potable water M.T. 1.90 � Electricity KWH 169 KWH � Urea M.T. 0.255 � 49% Caustic soda Kg 2.30

TWIN AF – 37 / UF 85 PLANTS

END USE APPLICATIONS OF UF – 85

Major application areas of UF concentrates are conditioning / anticaking agent for Urea Fertiliser, Spray Coating Agent for Urea Fertiliser, Slow Release Fertiliser, Urea Formaldehyde liquid resins, UF powdered resins, UF moulding compounds, UF glues & Adhesives .

SPECIFIC ADVANTAGES OF USING UREA FORMALDEHYDE CONC ENTRATE (UF-85) AS UREA CONDITIONING CUM ANTICAKING AGENT

Specific advantages to be derived from the use of UF-85 in a Urea plant instead of AF-37/H.M.T./Paraformaldehyde and other agents are as follows: (1) Use of Urea Formaldehyde as an anticaking agent serves the dual purpose of conditioning

AND coating urea prills. It imparts improved mechanical strength, moisture resistance and free flow ability characteristics to Urea merely by a single point injection. Therefore, no surface coating by surfactants or inert powders is necessary even if urea is to be exported long distances to overseas clients.

(2) The conditioned/treated Urea product is completely soluble, unlike Urea treated with

surfactants/inert materials.

12

(3) Unlike the case when H.M.T./Paraformaldehyde are used as anticaking agents, there is no

requirement for demineralized water for solution preparation in the case of UF-85. (4) As UF-85 is injected in the Urea melt itself, there is no contamination of process

condensates and purer water streams are obtained from the evaporation/ concentration sections. The entire quantity of process condensate can be recycled to the D.M. water unit for demineralized water production. Purer process condensate also eliminates the possibility of contamination of cation/anion resins in the D.M. water unit. These are considerable economic advantages.

(5) Injection of UF-85 in Urea melt reduces the load on the evaporation sections in terms of the

total throughput. (6) Adding UF-85 to the urea melt reduces total residence time. Moreover, Urea Formaldehyde

is a complex which does not convert to free Formaldehyde. Therefore, no intramolecular ring closure products of Methylene-di-Urea can be formed. The problem of precipitation of ring compounds in the first/second stage evaporators and resultant choking of prilling buckets can be completely eliminated, a notable operational advantage.

(7) In the case of some prilled Urea plant, it is possible to curb Urea carry-over losses into the waste water system, leading to a decrease in the load on the hydrolyzer.

(8) By using UF-85, heating the solution in the H.M.T. dissolution tank can be eliminated,

resulting in steam saving. (9) For every single mole of H.M.T., four moles of Ammonia are produced upon dissolution in

water. With the use of UF-85, there is no associated Ammonia release and thus the problem of Ammonia disposal is eliminated.

(10) With the dosing of UF-85 in the Urea melt itself, the problem of local crystallization due to

cold spots in the system is avoided. (11) Formation of undesirable products due to local concentration of AF-

37/H.M.T./Paraformaldehyde in Urea solutions can be avoided y using UF-85. (12) Substantial warehouse space, required for storing solid H.M.T./Paraformaldehyde, is not

needed in the case of UF-85. (13) No solid handling and solution preparation equipment is required if UF-85 is used. (14) Lesser solution volumes are required with UF-85 as compared to 40% H.M.T. or

Paraformaldehyde or 37% AF-37 solutions. Consequently, lower storage tank volume is needed. Also, lower evaporation costs are achieved due to lower water content.

(15) UF-85 products contain a very low Methanol percentage and no stabilization is required.

13

(16) UF-85 can be stored in epoxy painted carbon steel tanks whereas AISI 316 stainless steel tanks are required for storing H.M.T./Paraformaldehyde solutions.

(17) Urea Formaldehyde is a crystal retardant and therefore its use as an

anticaking/conditioning agent prevents linear crystal formation by crystal modification action, in the case of granulated Urea. It helps product bonding for granulated material; UF-85 is the only suitable anticaking/conditioning agent for granular Urea by virtue of this property.

(18) Evolution of Ammonia in the case of H.M.T. dosing adversely influences the appearance of

the product. With Urea Formaldehyde concentrate, a product of more lustrous texture is obtained.

(19) Ammonia evolution in the case of H.M.T. addition causes avoidable environmental

pollution in the product conveyor and warehouse area. This can be eliminated by using Urea Formaldehyde concentrate.

(20) The reaction of the Urea surface with Formaldehyde to form Urea Formaldehyde resin and

subsequent condensation to cross linked thermoset state improving mechanical strength, free flow ability and non adhesion/agglomeration characteristics is far more affective in the case of UF-85 than AF-37/H.M.T/Paraformaldehydes, with UF-85, no evaporative losses of free formalin occur.