Synthesis of polyether polyols based low dosage gas hydrate inhibitors using double metal cyanide catalyst

Abstract

A series of different metals (Zn / Fe / Co / Sn / Mg / La / Al / Cr) based double metal cyanide (DMC) catalyst is disclosed herein. Benzene-1,3,5-tricarboxylic acid (BTC) is incorporated as an organic complexing agent (CA) in the DMC catalyst. The DMC catalysts prepared with BTC and its derivatives as CAs are highly active towards ring opening polymerization (ROP) of propylene oxide (PO) and imparts heterogeneity as compared to the DMC prepared without any CA. The polyether polyols (PEPOs) with controlled molecular weight (Mw), polydispersity index (PDI), hydroxyl value (OH), and iodine value (I2) are produced using a DMC catalyst. PEPOs of the present invention relate to low-dosage gas hydrate inhibitors (LDHIs) utilized to mitigate / manage the formation, growth, and deposition / agglomeration of gas hydrate crystals in oil and gas production pipelines (especially applicable to deep and ultra-deep developments), and drilling or fracturing operations during natural gas hydrate exploration.

Description

[0001] SYNTHESIS OF POLYETHER POLYOLS BASED LOW DOSAGE GAS HYDRATE INHIBITORS USING DOUBLE METAL CYANIDE CATALYST

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to benzene- 1, 3, 5 -tricarboxylic acid (BTC) incorporated double metal cyanide (DMC) catalyst. More particularly, the present invention relates to the synthesis of DMC catalysts using BTC and its derivatives as novel organic complexing agents (CAs). The synthesized DMC catalyst was highly active toward the ring-opening polymerization (ROP) of propylene oxide (PO), ethylene oxide (EO), styrene oxide (SO), cyclohexene oxide (CHO), 1 -epoxy hexane (1-EH), and their mixture to prepare a series of polyether polyols (PEPO). Furthermore, PEPO series paved the way for their use as low-dosage hydrate inhibitors (LDHIs). The prepared series of PEPO inhibits the formation, growth, and deposition / agglomeration of gas hydrate crystals in oil and gas production pipelines and drilling or fracturing operations during natural gas hydrate exploration.

[0004] BACKGROUND OF THE INVENTION

[0005] Polyether polyols are mainly prepared by ring-opening polymerization (ROP) of heterocyclic monomers such as propylene oxide (PO), ethylene oxide (EO), styrene oxide (SO), etc., using single metal-based or double metal cyanide (DMC) catalyst. Polyether polyols have their applications as a precursor for various applications, including polyurethane foams, adhesives, coatings, elastomers, sealants, etc. The single metal-based catalyst includes the use of KOH for the ROP. Another is the DMC catalyst, which has been employed for the production of PEPO using PO or a combination EO / PO as monomers. The conventional process for the synthesis of DMC catalyst for the ROP of epoxides is disclosed in EP0932445. The use of DMC catalysts in the ROP buttresses the physicochemical properties of PEPO, including controlled molecular weight (Mw), polydispersity index (PDI), and unsaturation as compared to the KOH-based catalysts. The DMC catalyst is prepared by homogenizing the metal halide and metal cyanide salt. The CA is incorporated into the catalytic framework to enhance the efficacy of the DMC catalyst. Even the DMC catalysts recognized as the most superior in this field still have room for enhancement and refinement. For example, with respect to the unsaturation content in the final PEPO, US 4,985,491 was able to achieve the PEPO with unsaturation number upto 0.04 meq. g1. Furthermore, the majority of catalysts used in the field are composed of fine particles, which tend to cause filter clogging and necessitate centrifugation for catalyst isolation (US 5,470,813). Ideally, it would be preferable to have a catalyst that can be easily washed and isolated through simple filtration. Moreover, most DMC catalysts are subjected to a drying process to form a solid cake prior to usage, and this cake must be vigorously crushed to obtain a free-flowing powder (JPH 03245848 A). The requirement to pulverize DMC catalysts results in significant time and effort expenditure.

[0006] DMC catalysts pose more challenges in terms of removal from polyols, and numerous methods involving chemical treatments have been devised to address this issue (US 4,355,188). Any catalyst removal process incurs expenses and involves time-consuming, labor-intensive steps, along with the use of treatment materials. Ideally, a preferred DMC catalyst would be effortlessly separated from polyol products through ordinary filtration, obviating the need for chemical treatment, which reduces the cost of the catalyst and ROP process. Furthermore, the polyol treatment generates waste products, including wastewater from water washing, filter cakes from adsorbents, and spent ion-exchange resins. Moreover, an ideal catalyst would yield PEPO with minimal unsaturation and exhibit sufficient activity to enable usage at very low concentrations, ideally negating the necessity of catalyst removal from the PEPO. The DMC catalyst that eliminates the requirement for catalyst removal in numerous end-use applications would undoubtedly hold significant value for PEPO manufacturers. To summarize, there is a demand for novel DMC catalysts which should possess a predominantly non-crystalline nature and impart heterogeneous character with minimum unsaturation in the final PEPO. Also, it would be advantageous if these catalysts could be easily separated during the preparation process through simple filtration and yield a cake that can be easily crushed upon drying. Generally, the DMC catalysts are prepared by homogenizing an aqueous solution of metal halide and metal cyanide salt in the presence of an organic CA, followed by the subsequent filtration / centrifugation and drying under vacuum at a moderate temperature. The most common metal halide includes zinc(II)chloride, zinc(II)bromide, zinc(II)acetate, zinc acetylacetonate, zinc(II)benzoate, zinc(II)nitrate, iron(II)sulfate, iron(II)bromide, cobalt(II)chloride, cobalt(II)thiocyanate, nickel(II)formate, nickel(II)nitrate, and metal cyanide salts include potassium hexacyanocobaltate (III), potassium hexacyanoferrate (II), potassium hexacyanoferrate (III), calcium hexacyanocobaltate (III), and lithium hexacyanocobaltate (III). The synthesis of DMC includes the homogenization of zinc chloride and potassium hexacyanoferrate or potassium hexacyanocobaltate in the presence of alcohol or ethers as CAs. The various ligands based on alcohols, esters, ketones, amides, urea, and similar (US 3,427,256) have also been explored as CAs for the synthesis of DMC catalysts. The co-CAs are also incorporated to further enhance the activity of the DMC catalyst along with CAs by increasing the amorphous character of the catalyst (US 5,482,908). The PEPOs have been considered as the most reliable co-CA to enhance the catalytic activity towards ROP of epoxides (EP 09,32,445). Most preferably, the PEPOs with a molecular weight of more than 500 g mol1are used as a co-CA with improved catalytic activity.

[0007] Previously, we have also used EDTA as a CA to make the catalyst heterogeneous in nature (US20220259374A1). In another work, different Schiff bases including 2-(((3- hydroxypropyl)imino)methyl)phenol, 2,2'-((ethane- 1 ,2-diylbis(azanylylidene))bis

[0008] (methanylylidene)) diphenol, 2-(((2-hydroxyethyl)imino)methyl)phenol, 3- (benzylideneamino)propan- 1 -ol, 2-(benzylideneamino)ethanol, N1,N2-dibenzyl ideneethane- 1,2-diamine, 3-((2-methoxybenzylidene)amino)propan-l-ol, 2-((2-methoxybenzylidene) amino)ethanol, N1,N2-bis(2-methoxybenzylidene)ethane-l,2-diamine) were incorporated as CAs to prepare a series of DMC catalysts. These Schiff base ligands were bidentate in nature and did not allow metals to leach out from the PEPOs and assisted in producing the colorless PEPOs (US 18 / 305,077). The prepared DMC catalysts were used for the synthesis of PEPO with high yield (>90%). The minimum catalyst amount used for PEPO synthesis was 200 ppm. The catalyst prepared in US 20220259374A1 was active using low molecular weight initiators such as EG, DPG and able to produce >95% yield of PEPO. On contrary, the catalyst in US 18 / 305,077 was active with high molecular weight initiators such as PEG-600 and PEG-2000. The PEG-600 initiator was found most active for the synthesis of PEPO with controlled molecular weight and hydroxyl functionality.

[0009] In US 20220259374A1, colorful products were obtained, however, in US 18 / 305,077, colorless PEPOs were obtained because of the bidentate nature of the CAs of the DMC catalyst due to which metals did not leach out during ROP process. Furthermore, the in-detail comparison of the prior arts with the present work is shown in Table 8.

[0010] Gas hydrates, also known as clathrate hydrates, are crystalline compounds, morphologically similar to ice. These hydrates are formed when low molecular weight gases are entrapped in the hydrogen-bonded cages of the water molecules at suitable temperature and pressure conditions only (low temperature and high pressure). In common practice, the gas hydrates growth increases continuously as the gases start encapsulating more into the water cages, which results in the formation of the crystalline mass. After this, the crystalline mass agglomerates to form the gas hydrates in bulk in order to clog the oil and gas pipelines. The low molecular weight gases most commonly used in the formation of gas hydrates include methane, ethane, propane, n-butane, iso butane, n-pentane, iso-pentane, and combinations of these gases. For example, typical natural gas of composition CH493%, C2H62%, C3H8o 5 % CO2 2.5 %, N2 1.5%, and balanced other components like n"C4H10, I-C5H12 E^C,CANform hydrate crystals at 600 psi pressure below 10 °C. Thesehydrates exist in solid form, which are generally not soluble in the fluid present in pipelines. Hence, these solids, like hydrates, become inconvenient when used for special industrial processes such as production, handling, and transport. Commonly, the major troublesome faced by the formation of gas hydrates in oil and gas pipelines includes plugging and / or blockage of pipelines or transfer lines or other conduits, valves, and / or safety devices and / or other equipment, resulting in shutdown, loss of production and risk of explosion or unintended release of hydrocarbons into the environment either on - land or off shore. Two major techniques have been explored to mitigate the hydrate formation in the oil and pipelines industries for decades. The first technique is thermodynamic hydrate inhibitors (THIs), and the other is low-dosage hydrate inhibitors (LDHIs) (WO2016109388A1). The LDHIs are named because less volume is required for the inhibition process as compared to the thermodynamic inhibitors. For the thermodynamic inhibition process, various physical methods like water removal, increasing temperature, decreasing pressure, the addition of antifreeze or a combination of all are performed.

[0011] A complete hydrate avoidance is the most conventional approach in oil and gas industries, which requires a considerable quantity of THIs (e.g., antifreezes like methanol and ethylene glycols in the pipeline (e.g., up to 40 wt% ethylene glycol with respect to the aqueous phase, which shift the hydrate forming conditions toward lower temperature or high pressure. However, due to high dosages of THIs, gas fields in deep water and / or with large water fractions are often economically unviable. Therefore, it is vital to develop effective dosage chemistries that will reduce MEG usage and formulate a more economically feasible process.

[0012] On the other hand, the LDHI approach is further divided into two separate chemistries i.e., anti-agglomerants (AAs) and kinetic inhibitors (KHIs). AAs allow hydrates to form, but they prevent them from accumulating into large masses. AAs enable the hydrate to form as a transportable non-sticky slurry of hydrate particles dispersed in the liquid hydrocarbon phase (US20140106991A1). In general, AAs perform well below the water cut of 50%. On the other hand, KHIs prevent / delay the hydrate nucleation / formation and also reduce the growth of hydrate crystals. Most of the KHIs are water-soluble polymers, for example: of commercially used KHIs may include poly(N-vinyl pyrolidone) (PVP), poly(N-vinyl caprolactam) (PV- Cap), hyperbranched polyester amides (WO2010114761 Al). However, non-polymeric chemistries have also been used along with KHIs as synergists, for e.g., tetra pentyl ammonium bromide, butoxy ethanol, certain ether amines (US7452848B2, EP1196497A1). Major limitations of KHIs are their i) high cost, ii) reduced performance at high sub-cooling (above 10 K), iii) polymer deposition problems near the injection point. In spite of the many commercially available CAs for the synthesis of DMC catalysts, the use of benzene- 1,3, 5 -tricarboxylic acid (BTC) and its derivatives including BTC / triethyl ester, BTC / trimethyl ester, BTC / sodium salt hydrate remains underexplored for their use as a CA in order to impart the heterogeneous character to the catalyst. The prepared series of PEPOs have never been used as LDHIs. Thus, keeping in view the drawbacks of the hitherto reported prior arts, there was a need to solve the problem, the present invention is aimed to develop novel chemistries (LDHIs) which may have dual characteristics, KHI as well as AA or effective KHIs alone and / or AAs.

[0013] OBJECTIVES OF THE INVENTION

[0014] Accordingly, the main objective of the present invention is to synthesize BTC-incorporated double metal cyanide (DMC) catalyst to prepare PEPOs-based LDHIs.

[0015] Another objective of the present invention is to synthesize a series of Zn, Cr, Mg, La, Sn, Al, Ee, and Co-based DMC catalyst using BTC and its derivatives including BTC / triethyl ester, BTC / trimethyl ester, BTC / sodium salt hydrate as organic complexing agents (CAs).

[0016] Yet another objective of the present invention is to provide an appropriate method for the synthesis of DMC catalysts to enhance its catalytic activity towards ring opening polymerization (ROP) of propylene oxide (PO), SO, CHO, 1-EH, and combination of EO-PO. Still another objective of the present invention is to use the synthesized DMC catalysts for preparing polyether polyols (PEPO) with controlled molecular weight and PDI.

[0017] Yet another objective of the present invention is to use different molecular weight-based initiators with a focus on controlling the molecular weight of PEPO.

[0018] Still, another objective of the present invention is to optimize reaction conditions such as catalyst amount, and monomer to the initiator (M / I) ratio to attain a high (>90%) PEPO yield. Yet another objective of the present invention is to scrutinize the effect of the synthesized PEPOs for their use as LDHIs to suppress the formation, growth, and deposition / agglomeration of formed gas hydrates in gas pipelines.

[0019] Yet another objective of the present invention is to use LDHIs with effective dosages ranging from 0.01 to 5 wt%. Yet another objective of the present invention is to significantly reduce the gas hydrate formation kinetics.

[0020] Yet another objective of the present invention is to prevent the upward growth of hydrate crystals and hydrate slurry formation (anti-agglomerating effect) with PEPO.

[0021] SUMMARY OF THE INVENTION

[0022] Additional features and embodiments of the present disclosure will better be understood through the techniques and other aspects of the disclosure. Other embodiments of the invention are described in detail herein and are considered a part of the claimed disclosure. Accordingly, to accomplish the objectives, the present invention provides the synthesis of DMC catalyst and its use for PEPO synthesis and the application of prepared PEPO as LDHI.

[0023] In an aspect, the present invention provides a synthesis of double metal cyanide (DMC) catalyst comprising;

[0024] (a) 35 to 90 wt% double metal cyanide (DMC) complex;

[0025] (b) 10 to 65 wt% an organic CA.

[0026] In an embodiment of the present invention, the DMC complex is selected from the groups consisting of zinc(II) hexacyanoferrate(III), zinc(II) hexacyanocobaltate(III), tin(II) hexacyanocobaltate(III), magnesium(II) hexacyanocobaltate(III), lanthanum(III) hexacyanocobaltate(III), cobalt(II) hexacyanocobaltate(III), aluminum(III) hexacyanocobaltate(III), and chromium (II) hexacyanocobaltate(III).

[0027] In yet another embodiment of the present invention, BTC and its derivatives including BTC triethyl ester, BTC trimethyl ester, BTC sodium salt hydrate are used as complexing agent (CAs).

[0028] In yet another embodiment of the present invention, the said DMC is selected from a group consisting of (i) zinc hexacyanocobaltate / BTC

[0029] (ii) zinc hexacyanoferrate / BTC

[0030] (iii) tin hexacyanocobaltate / BTC

[0031] (iv) magnesium hexacyanocobaltate / BTC

[0032] (v) lanthanum hexacyanocobaltate / BTC

[0033] (vi) cobalt hexacyanocobaltate / BTC

[0034] (vii) aluminum hexacyanocobaltate / BTC

[0035] (viii) chromium hexacyanocobaltate / BTC

[0036] (ix) zinc hexacyanoferrate / BTC triethyl ester

[0037] (x) zinc hexacyanoferrate / BTC sodium salt hydrate

[0038] (xi) zinc hexacyanoferrate / BTC trimethyl ester

[0039] (xii) In yet another embodiment, the present invention details the process for the preparation of the DMC catalyst comprising of;

[0040] (i) mixing the BTC or BTC derivatives in an ethanol / water solution and stirring the same at 500 rpm for 5 min;

[0041] (ii) mixing M(A)nin water solution and stirring it at 500 rpm for 5 min;

[0042] (iii) adding the solution obtained in step (i) to the solution obtained in step (ii) for 5 to 30 min at a temperature range of 60 to 70 °C to prepare M-BTC / BTC derivatives solution;

[0043] (iv) preparing another metal cyanide salt (A*)xM*(CN)ysolution by homogenizing it for a period in the range of 30 to 40 minutes at room temperature in the range of 20-30 °C; wherein A* is selected from an alkali metal ion or alkaline earth metal ion;

[0044] M* is selected from the group consisting of Fe(III) and Co(III);

[0045] M is selected from the group consisting of Zn, Sn, Mg, La, Co, Al, and Cr.

[0046] (v) adding the solution obtained in step (iv) to the solution obtained in step (iii) (M- BTC / BTC derivatives) at a temperature range of 60-70 °C followed by homogenizing it for 24 h;

[0047] (vi) centrifuging the solution at 6000 rpm obtained in step (v) thrice with distilled water and twice with ethanol to obtain a solid cake;

[0048] (vii) drying the solid cake in a vacuum oven overnight at a temperature range of 50 to 70 °C to obtain the DMC catalyst.

[0049] In yet another embodiment, the present invention provides a process for the ring-opening polymerization (ROP) of PO, EO, SO, CHO,1-EH, and their mixture in a single step to prepare polyether polyols (PEPO) using DMC catalyst

[0050] In yet another embodiment of the present invention, the process for the ROP of PO comprises of;

[0051] (i) mixing the initiator, epoxides (PO / EO / SO / CHO / l-EH / their mixture), and DMC catalyst in a Teflon lined reactor and keeping the reaction at a temperature ranging from 10 °C to 150 °C, pressure from 1 to 25 bar, for a time period ranging from 1 to 24 h;

[0052] (ii) cooling down the Teflon reactor to room temperature ranging from 10 to 42 °C, followed by collecting and washing the obtained product in a solvent;

[0053] (iii) centrifuging the product obtained in step (ii) twice to settle down the DMC catalyst in order to check the recyclability; (iv) drying the above product by using a rota evaporator at a temperature ranging from 40 to 70 °C for a time ranging between 15 to 30 min;

[0054] (v) vacuum drying the product at a temperature ranging from 40 to 70 °C in order to remove a trace amount of solvent from the final product;

[0055] In yet another embodiment of the present invention, the solvent used in step (ii) is chloroform (CHC13).

[0056] In still another embodiment of the present invention, the DMC catalysts were scrutinized for the ROP of PO.

[0057] In another embodiment of the present invention, initiators including dipropylene glycol [DPG], neopentyl glycol [NPG], PEG (Mw= 200 to 2000), and 1,3 -butanediol [1,3-BD], 1,4- butanediol [1,4-BD] were to control molecular weights of the PEPO.

[0058] In yet another embodiment of the present invention, the molecular weight of the PEPO is in the range of 200 to 6000 g mol1and PDI in range of 1.01 to 2.21.

[0059] In still another embodiment of the present invention, the OH value of the PEPO is in range of 10.8 to 124.9 mg KOH g1, and I2 value in range of 0.0005 to 0.0184 meq. g1.

[0060] In yet another embodiment of the present invention, prepared PEPOs were used as KHIs with a concentration ranging from 0.01 to 5 wt%.

[0061] In yet another embodiment of the present invention, a high-pressure visual reactor apparatus is employed to examine the kinetic and thermodynamic performance along with the morphological observation through a visual window of the reactor.

[0062] In yet another embodiment, ~65±2% reduction in the hydrate formation kinetics compared to the baseline is reported using PEPO as KHIs.

[0063] In still another embodiment, the kinetic reduction is ~40±2% in comparison to the commercially available KHI (e.g., PVP). In yet another embodiment, a substantial reduction in the hydrate formation temperature (nucleation temperature) is reported with our LDHIs as compared to the commercial additive (PVP).

[0064] In yet another embodiment of the present invention, our PEPO reduces the hydrate formation temperature from 12±0.2 °C (baseline) to 5.0±0.5°C while in the presence of commercial additive (PVP) onset temperature was 8±0.4°C.

[0065] In yet another embodiment of the present invention, a high-pressure visual reactor coupled with a torque sensor is employed to examine hydrate anti-agglomerating characteristics of our LDHIs.

[0066] In yet another embodiment of the present invention, torque signals were comparatively lower than the baseline data, which suggests the non-stickiness of hydrate particles in the presence of our LDHIs.

[0067] In still another embodiment of the present invention, our LDHIs showed potent ability in upstream oil and gas production lines (especially deep and ultra-deep developments) and / or drilling or fracturing operations during natural gas hydrate exploration.

[0068] BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Fig. 1 represents the PXRD spectra of the synthesized DMC catalysts (DMC-1 to DMC-8).

[0070] Fig. 2 represent the comparison of hydrate nucleation temperature with 0.1 wt% LDHIs.

[0071] Fig. 3 represents the comparison of gas hydrate formation kinetics with 0.1 wt% LDHIs along with the repeated trials of PEPO-24 in DIW water.

[0072] Fig. 4 represents the comparison of gas hydrate formation kinetics measured for 0.1 wt% of our LDHIs and commercially available KHIs.

[0073] Fig. 5 represents the effect of LDHIs concentration gas hydrate formation kinetics. Fig. 6 represents the gas hydrate formation kinetics measured for 1 wt% of PEPO-24 in saline water (3 repeated trials).

[0074] Fig. 7 represents the visual observations captured during hydrate formation in the presence of our LDHIs.

[0075] Fig. 8 represents the comparison of the fractional torque signals measured for (a) 80, (b) 60, and (c) 40 watercut with respect to paraffin oil in the presence / absence of PEPO-24 EDHI.

[0076] DETAILED DESCRIPTION OF THE INVENTION

[0077] The foregoing detailed description of the disclosure is elaborated to provide a clear understanding to the person who is skilled in the art. Additional features, embodiments and advantages of the invention will be described hereinafter which form the subject of the claims of the disclosure, However, the set forth disclosure provide in the specification will best be understood in conjunction with the appended claims and figures as provide heretofore. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that such equivalent processes do not depart from the spirit and scope of the disclosure as set forth in the appended claims. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure.

[0078] While the invention has been disclosed with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made, and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material to the teachings of the invention without departing from its scope. Throughout the specification and claims, the following terms take the meanings explicitly associated herein unless the context clearly dictates otherwise. The meaning of "a", "an", and "the" include plural references. The meaning of "in" includes "in" and "on." Referring to the drawings, like numbers indicate like parts throughout the views. Additionally, a reference to the singular includes a reference to the plural unless otherwise stated or inconsistent with the disclosure herein.

[0079] In line with the above objectives, the present invention provides BTC-incorporated double metal cyanide catalysts for the synthesis of a series of polyether polyols. The method for the synthesis of the DMC catalyst comprises;

[0080] (a) homogenizing the metal halides and BTC, or its derivatives at an elevated temperature.

[0081] (b)mixing the metal cyanide salt in the step mentioned in step (a) at an elevated temperature.

[0082] (c) centrifuging the mixture obtained in step (b) with water or water / ethanol mixture twice to obtain a solid cake.

[0083] (d)vacuum drying the product obtained in step (c) for 24 h in temperatures ranging from 50 to 70 °C.

[0084] A combination of zinc / iron, zinc / cobalt, tin / cobalt, magnesium / cobalt, lanthanum / cobalt, cobalt / cobalt, aluminum / cobalt, and chromium / cobalt was chosen as metals for the synthesis of DMC catalysts.

[0085] The DMC catalyst has gained significant prominence over single metal-based catalysts, such as KOH, in the production of PEPO, polyester polyols, and polycarbonate polyols. This heightened preference arises from its remarkable activity when compared to its single metalbased counterparts. The DMC catalyst is typically prepared through a reaction involving aqueous solutions of metal salt and metal cyanide salts in the presence of an organic complexing agent. The water-soluble metal salts employed in this process adhere to the general formula M(A)n, wherein M represents a metal chosen from the group comprising Zn(II), Fe(II), Pb(II), Mo(IV), Al(III), W(IV), W(VI), Co(II), Sn(II), Cu(II), Cr(III), Mn(II), V(IV), V(V), and Ni(II). Notably, the preferred metals within this group include Zn(II), Co(II), Fe(II), Fe(III), Cr(III), and Ni(II). A, on the other hand, denotes an anion that is typically selected from the following set including halides, sulfates, hydroxides, cyanides, oxalates, isocyanates, thiocyanates, isothiocyanates, carboxylates, and nitrates. The variable "n" can range from 1 to 3 to satisfy the valency of M. The metal salts utilized encompass various examples, such as zinc(II) chloride, zinc(II) bromide, zinc(II) acetate, zinc acetylacetonate, zinc(II) benzoate, zinc(II) nitrate, iron(II) sulfate, iron(II) bromide, cobalt(II) chloride, cobalt(II) thiocyanate, nickel(II) formate, nickel(II) nitrate, and other similar compounds, either in isolation or in combination. The metal cyanide salts employed in creating DMC complexes conform to the general formula (A*)xM*(CN)y, where A* represents an alkali metal ion or alkaline earth metal ion, and M* represents a metal chosen from the group comprising Fe(II), Fe(III), Co(II), Ir(III), Ni(II), Rh(III), Ru(II), Co(III), Cr(II), Cr(III), Mn(II), Mn(III), V(IV), and V(V). Notably, the preferred metals within this group include Co(II), Co(III), Fe(II), Fe(III), Cr(III), Ir(III), and Ni(II). In this formula, A represents an anion chosen from the following set including halides, hydroxides, sulfates, carbonates, cyanides, oxalates, thiocyanates, isocyanates, isothiocyanates, carboxylates, and nitrates. It is important to note that the variables x and y are integers greater than or equal to 1 , and the combined charges of x and y maintain a balanced charge with M*.

[0086] Examples of suitable water-soluble metal cyanide salts are potassium hexacyanocobaltate (III), potassium hexacyanoferrate (II), potassium hexacyanoferrate (III), calcium hexacyanocobaltate (III), and lithium hexacyanocobaltate (III). Potassium (K) is selected as an alkali metal in metal cyanide salt, and considered as the most effective and preferred alkali metal for the synthesis of highly active DMC catalysts. Fe(II) and Co(II) was chosen as a metal centre to synthesize DMC catalysts. Also, metals including Zn(II), Co(II), Sn(II), Mg(II), La(II), Al(III), and Cr(II) were explored as metal halide composition. In this invention, the developed DMC catalysts are based on Zn3[Fe(CN)6]2 / Zn3[Co(CN)e]2, Sn3[Co(CN)e]2, Mg3[Co(CN)6]2, La2Co(CN)6]2, Co3[Co(CN)6]2, Al2[Co(CN)6]2 and Cr3[Co(CN)6]2 complexes.

[0087] The chain-transfer reaction, also known as abstraction reaction due to the abstraction of methyl proton, can hardly be avoided during the base-catalyzed (single metal-based catalyst) polymerization of PO, which not only enhances the unsaturation of the PEPO product but also limits the degree of polymerization. During the ROP of epoxides, a side reaction of the base in polymerization is the isomerization reaction such as PO isomerizes to allyl alcohol, and as a result, vinyl-terminated monofunctional polyols are formed, also known as monols. The final products obtained from monols have a detrimental effect on the mechanical properties of the PU properties. The monol formation in the polyols can be suppressed by using a DMC catalyst, e.g., zinc (II) hexacyanocobaltate (III), zinc hexacyanoferrate (II), and zinc hexacyanoferrate (III), nickel (II) hexacyanoferrate (II). This type of catalyst is known as the DMC catalyst, which is the focus of our present work, justifying the reason to produce PEPO using DMC catalysts.

[0088] In the present invention, the key organic linker of the present invention is BTC or its derivative, which have been used as an organic CAs. The Zn / Fe, Zn / Co, Sn / Co, Mg / Co, Cr / Co, Al / Co, La / Co, and Co / Co-based DMC catalysts using BTC and its derivatives as an organic complexing agent were prepared at an elevated temperature. The DMC catalyst prepared in the presence of BTC and its derivatives showed enhanced activity than the DMC prepared without BTC. The DMC catalyst of the present invention is heterogeneous in nature and recyclable for up to seven cycles. A series of PEPO with yields ranging from 8 to 99% having different molecular weights ranging from 200 to 6000 g mol1was prepared using synthesized DMC catalysts. The produced PEPOs have PDI in the range of 1.02 to 2.21, OH value in the range of 10.8 to 124.9 mg KOH g1, and E value in the range of 0.0005 to 0.0184 meq. g1. Different initiators, including dipropylene glycol [DPG], neopentyl glycol [NPG], PEG (Mw= 200 to 2000), 1,3 -butanediol [1,3-BD], and 1 ,4-butanediol [1,4-BD] have been employed to control the molecular weight, PDI, OH value, I2 value.

[0089] EXAMPLES

[0090] The following examples, which include preferred embodiments, will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purpose of illustrative discussion of preferred embodiments of the invention. This invention involves the synthesis of DMC catalysts for the production of PEPO. The prepared PEPO was further utilized for the low doses gas hydrate inhibitors (LDHI). The present invention is further explained with reference to Example 1-43.

[0091] Example 1: Preparation of DMC catalyst (DMC-1)

[0092] This example illustrates the preparation of a DMC catalyst (DMC-1) using BTC as an organic complexing agent. In the preparation of the DMC-1 catalyst, a solution of 6.01 g of BTC in 50 mL water / ethanol (1:1 v / v) mixture is prepared and labeled as solution 1. In addition, solution 2 was prepared by dissolving 12 g of ZnCh in 50 mL water. Solution 1 was added to solution 2 slowly and homogenized for 2 h at an elevated temperature. Solution 3 was prepared by adding 9.06 g potassium hexacyanoferrate [K3Fe(CN)e] in 50 mL water and added to the solution obtained. This solution was centrifuged with water twice and a water-ethanol mixture twice. The obtained solid cake was dried under vacuum at 70 °C for 24 h. The catalyst was designated as DMC- 1.

[0093] Powder X-Ray Diffraction (PXRD) of the solid DMC-1 catalyst showed broad signals of 2 theta value at 17.4°, 18.4°, 23.5°, 24.8°, and 27.6°.

[0094] Example 2

[0095] This example illustrates the preparation of DMC catalyst (DMC-2) using potassium hexacyanocobaltate [K3Co(CN)e] instead of [K3Fe(CN)e], and the procedure of example 1 is followed. The final solid cake was isolated and dried as described in example 1 , and this DMC catalyst was designated as DMC-2.

[0096] PXRD of this solid DMC-2 catalyst showed broad signals of 2 theta value at 16.3°, 19.8°, 21.7°, 24.8°, and 27.8°.

[0097] Example 3

[0098] This example illustrates the preparation of DMC catalyst (DMC-3) using potassium hexacyanocobaltate [K3Co(CN)e] as metal cyanide salt and tin chloride (SnCh) as metal halide salt, and the procedure of example 1 is followed. The final solid cake was isolated and dried as described in example 1, and this DMC catalyst was designated as DMC-3.

[0099] PXRD of this solid DMC-3 catalyst showed broad signals of 2 theta value at 26.6° and 51.5°.

[0100] Example 4

[0101] This example illustrates the preparation of DMC catalyst (DMC-4) using potassium hexacyanocobaltate [K3Co(CN)e] as metal cyanide salt and magnesium chloride (MgCh) as metal halide salt, and the procedure of example 1 is followed. The final solid cake was isolated and dried as described in example 1 , and this DMC catalyst was designated as DMC-4.

[0102] PXRD of this solid DMC-4 catalyst showed broad signals of 2 theta value at 16.1°, 17.6°, 24.3°, 26.6°, and 27.8°.

[0103] Example 5

[0104] This example illustrates the preparation of DMC catalyst (DMC-5) using potassium hexacyanocobaltate [K3Co(CN)e] as metal cyanide salt and lanthanum chloride (LaCh) as metal halide salt, and the procedure of example 1 is followed. The final solid cake was isolated and dried as described in example 1, and this DMC catalyst was designated as DMC-5.

[0105] PXRD of this solid DMC-5 catalyst showed broad signals of 2 theta value at 15.0°, 18.5°, 24.1°, 33.5°, and 34.8°.

[0106] Example 6

[0107] This example illustrates the preparation of DMC catalyst (DMC-6) using potassium hexacyanocobaltate [K3Co(CN)e] as metal cyanide salt and cobalt nitrate hexahydrate [CO(NO3)2- 6H2O] as metal halide salt, and the procedure of example 1 is followed. The final solid cake was isolated and dried as described in example 1, and this DMC catalyst was designated as DMC-6. PXRD of this solid DMC-6 catalyst showed broad signals of 2 theta value at 17.3°, 24.4°, 35.1°, and 39.4°.

[0108] Example 7

[0109] This example illustrates the preparation of DMC catalyst (DMC-7) using potassium hexacyanocobaltate [K3Co(CN)e] as metal cyanide salt and aluminium nitrate [ AlfNO^)^] as metal halide salt, and the procedure of example 1 is followed. The final solid cake was isolated and dried as described in example 1, and this DMC catalyst was designated as DMC-7.

[0110] Example 8

[0111] This example illustrates the preparation of DMC catalyst (DMC-8) using potassium hexacyanocobaltate [K3Co(CN)e] as metal cyanide salt and chromium chloride (CrCk) as metal halide salt, and the procedure of example 1 is followed. The final solid cake was isolated and dried as described in example 1, and this DMC catalyst was designated as DMC-8.

[0112] PXRD of this solid DMC-8 catalyst showed broad signals of 2 theta value at 17.8° and 36.2°.

[0113] The accumulative PXRD details of the DMC-1 to DMC-8 catalysts are shown in Table 1.

[0114] Example 9

[0115] This example illustrates the preparation of DMC catalyst (DMC-9) using BTC triethyl ester instead of BTC and the procedure of example 1 is followed. The final solid cake was isolated and dried as described in example 1, and this DMC catalyst was designated as DMC-9.

[0116] Example 10

[0117] This example illustrates the preparation of DMC catalyst (DMC- 10) using BTC sodium salt hydrate instead of BTC and the procedure of example 1 is followed. The final solid cake was isolated and dried as described in example 1 , and this DMC catalyst was designated as DMC- 10. Example 11

[0118] This example illustrates the preparation of DMC catalyst (DMC-11) using BTC trimethyl ester instead of BTC and the procedure of example 1 is followed. The final solid cake was isolated and dried as described in example 1 , and this DMC catalyst was designated as DMC- 11. Table 1: PXRD of DMC catalysts:

[0119] Example 12: Synthesis of Polyether polyols (PEPO)

[0120] This example illustrates the synthesis of PEPO, wherein ethylene glycol (EG) (Mw= 62.07 g mol1) was used as an initiator using zinc hexacyanocobaltate / BTC (DMC-1) as a catalyst [PO : PEG-300 = 30 : 1]. In the synthesis of PEPO, the Teflon-lined reactor was charged with 5.32 g of PEG-300, 33.0 g of PO, and 0.03 g of zinc hexacyanocobaltate / BTC (DMC-1) catalyst.

[0121] In this reaction, PEG-300 was used as an initiator. The autoclave was purged with nitrogen (N2) at 50 mL / min for 5 - 10 min to remove dissolved gases and to create an inert atmosphere. The mixture was then heated and stirred until the reactor temperature reached 105 °C and pressurized with N2 to 5 bar to carry forward the polymerization reaction. Then reaction temperature was maintained at 105 °C for 24 h with continuous stirring. The reactor pressure reached 11 - 12 bar after a few hours of the reaction, then gradually decreased with the reaction progress (time), showing the conversion of PO to PEPO. The reactor was cooled down to room temperature. A viscous liquid was obtained as a product after the reaction. The PEPO was then filtered at room temperature and dried under vacuum at 70 °C. This polyol is designated as PEPO-1. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI, are compiled in Table 2.

[0122] Table 2: Effect of various PMC catalysts, initiators, epoxides on the production of PEPO (Catalysts = DMC-1, DMC-2, DMC-3, DMC-4, DMC-5, DMC-6, DMC-7, and DMC-8 catalysts. Initiators = PPG, NPG, EG, PEG-200, PEG-300, PEG-400, PEG-600, PEG- 2000, 1,3-BD, 1,4-BD, Epoxides = PO, EQ, SO, CHO, 1-EH) Reaction Conditions: Epoxide : Initiator = 30 : 1, Temperature = 105 °C, Time = 24 h, Pressure = 5 bar, Catalyst amount = 2500 ppm.

[0123] Example 13

[0124] This example illustrates the synthesis of PEPO, wherein zinc hexacyanocobaltate / BTC (DMC-

[0125] 2) as a catalyst [PO : PEG-300 = 30 : 1] using PEG-300 as an initiator. The procedure of example 12 was used, except DMC-2 was used as a catalyst. The product was a poly(oxypropylene)diol and was designated as PEPO-2. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI of the PEPO-2 obtained, are compiled in Table 2.

[0126] Example 14

[0127] This example illustrates the synthesis of PEPO, wherein tin hexacyanocobaltate / BTC (DMC-

[0128] 3) as a catalyst [PO : PEG-300 = 30 : 1] using PEG-300 as an initiator. The procedure of example 12 was used, except DMC-2 was used as a catalyst. The product was a poly(oxypropylene)diol and was designated as PEPO-3. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI of the PEPO-3 obtained, are compiled in Table 2.

[0129] Example 15

[0130] This example illustrates the synthesis of PEPO, wherein magnesium hexacyanocobaltate / BTC (DMC-4) as a catalyst [PO : PEG-300 = 30 : 1 ] using PEG-300 as an initiator. The procedure of example 12 was used, except DMC-4 was used as a catalyst. The product was a poly(oxypropylene)diol and was designated as PEPO-4. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI of the PEPO-4 obtained, are compiled in Table 2.

[0131] Example 16 This example illustrates the synthesis of PEPO, wherein lanthanum hexacyanocobaltate / BTC (DMC-5) as a catalyst [PO : PEG-300 = 30 : 1] using PEG-300 as an initiator. The procedure of example 12 was used, except DMC-5 was used as a catalyst. The product was a poly(oxypropylene)diol and was designated as PEPO-5. The yield and key characteristics of PEPO, such as hydroxyl number, Mw, and PDI of the PEPO-5 obtained, are compiled in Table 2.

[0132] Example 17

[0133] This example illustrates the synthesis of PEPO, wherein cobalt hexacyanocobaltate / BTC (DMC-6) as a catalyst [PO : PEG-300 = 30 : 1 ] using PEG-300 as an initiator. The procedure of example 12 was used, except DMC-6 was used as a catalyst. The product was a poly(oxypropylene)diol and was designated as PEPO-6. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI of the PEPO-6 obtained, are compiled in Table 2.

[0134] Example 18

[0135] This example illustrates the synthesis of PEPO, wherein aluminium hexacyanocobaltate / BTC (DMC-7) as a catalyst [PO : PEG-300 = 30 : 1 ] using PEG-300 as an initiator. The procedure of example 12 was used, except DMC-7 was used as a catalyst. The product was a poly(oxypropylene)diol and was designated as PEPO-7. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI of the PEPO-7 obtained, are compiled in Table 2.

[0136] Example 19

[0137] This example illustrates the synthesis of PEPO, wherein chromium hexacyanocobaltate / BTC (DMC-8) as a catalyst [PO : PEG-300 = 30 : 1] using PEG-300 as an initiator. The procedure of example 12 was used, except DMC-8 was used as a catalyst. The product was a poly(oxypropylene)diol and was designated as PEPO-8. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI of the PEPO-8 obtained, are compiled in Table 2.

[0138] Example 20

[0139] This example illustrates the synthesis of PEPO, wherein DPG (Mw= 134.17 g mol1) was used as an initiator instead of PEG-300 and zinc hexacyanocobaltate / BTC (DMC-2) as a catalyst [PO : DPG = 30 : 1]. The procedure of example 12 was used, except DPG was used as an initiator. The product was a poly(oxypropylene)diol and was designated as PEPO-9. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI of the PEPO-9 obtained, are compiled in Table 2.

[0140] Example 21

[0141] This example illustrates the synthesis of PEPO, wherein NPG (Mw= 104.14 g mol1) was used as an initiator instead of PEG-300 and zinc hexacyanocobaltate / BTC (DMC-2) as a catalyst [PO : NPG = 30 : 1]. The procedure of example 12 was used, except NPG was used as an initiator. The product was a poly(oxypropylene)diol and was designated as PEPO- 10. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI of the PEPO-10 obtained, are compiled in Table 2.

[0142] Example 22

[0143] This example illustrates the synthesis of PEPO, wherein PEG-200 (Mw= 200 g mol1) was used as an initiator instead of PEG-300 and zinc hexacyanocobaltate / BTC (DMC-2) as a catalyst [PO : PEG-200 = 30 : 1]. The procedure of example 12 was used, except PEG-200 was used as an initiator. The product was a poly(oxypropylene)diol and was designated as PEPO-11. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI of the PEPO- 11 obtained, are compiled in Table 2.

[0144] Example 23 This example illustrates the synthesis of PEPO, wherein PEG-300 (Mw= 300 g mol1) was used as an initiator instead of EG and zinc hexacyanocobaltate / BTC (DMC-2) as a catalyst [PO : PEG-300 = 30 : 1]. The procedure of example 12 was used, except PEG-200 was used as an initiator. The product was a poly(oxypropylene)diol and was designated as PEPO- 12. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI of the PEPO- 12 obtained, are compiled in Table 2.

[0145] Example 24

[0146] This example illustrates the synthesis of PEPO, wherein PEG-400 (Mw= 400 g mol1) was used as an initiator instead of PEG-300 and zinc hexacyanocobaltate / BTC (DMC-2) as a catalyst [PO : PEG-400 = 30 : 1]. The procedure of example 12 was used, except PEG-400 was used as an initiator. The product was a poly(oxypropylene)diol and was designated as PEPO-13. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI of the PEPO- 13 obtained, are compiled in Table 2.

[0147] Example 25

[0148] This example illustrates the synthesis of PEPO, wherein PEG-600 (Mw= 600 g mol1) was used as an initiator instead of PEG-300 and zinc hexacyanocobaltate / BTC (DMC-2) as a catalyst [PO : PEG-600 = 30 : 1]. The procedure of example 12 was used, except PEG-600 was used as an initiator. The product was a poly(oxypropylene)diol and was designated as PEPO- 14. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI of the PEPO- 14 obtained, are compiled in Table 2.

[0149] Example 26

[0150] This example illustrates the synthesis of PEPO, wherein PEG-2000 (Mw= 2000 g mol1) was used as an initiator instead of PEG-300 and zinc hexacyanocobaltate / BTC (DMC-2) as a catalyst [PO : PEG-2000 = 30 : 1]. The procedure of example 12 was used, except PEG-2000 was used as an initiator. The product was a poly(oxypropylene)diol and was designated as PEPO-15. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI of the PEPO- 15 obtained, are compiled in Table 2.

[0151] Example 27

[0152] This example illustrates the synthesis of PEPO, wherein 1,3-BD, (Mw= 90.1 g mol1) was used as an initiator instead of PEG-300 and zinc hexacyanocobaltate / BTC (DMC-2) as a catalyst [PO : 1,3-BD = 30 : 1]. The procedure of example 12 was used, except 1,3-BD was used as an initiator. The product was a poly(oxypropylene)diol and was designated as PEPO- 16. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI of the PEPO- 16 obtained, are compiled in Table 2.

[0153] Example 28

[0154] This example illustrates the synthesis of PEPO, wherein 1,4-BD, (Mw= 90.1 g mol1) was used as an initiator instead of PEG-300 and zinc hexacyanocobaltate / BTC (DMC-2) as a catalyst [PO : 1,4-BD = 30 : 1]. The procedure of example 12 was used, except 1,4-BD was used as an initiator. The product was a poly(oxypropylene)diol and was designated as PEPO- 17. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI of the PEPO-17 obtained, are compiled in Table 2.

[0155] Example 29

[0156] This example illustrates the synthesis of PEPO, wherein EO was used as an epoxide instead of PO and zinc hexacyanocobaltate / BTC (DMC-2) as a catalyst [EO : PEG-300 = 30 : 1]. The procedure of example 12 was used, except EO was used as an epoxide. The product was a poly(oxypropylene)diol and was designated as PEPO- 18. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI of the PEPO- 18 obtained, are compiled in Table 2.

[0157] Example 30 This example illustrates the synthesis of PEPO, wherein SO was used as an epoxide instead of PO and zinc hexacyanocobaltate / BTC (DMC-2) as a catalyst [SO : PEG-300 = 30 : 1]. The procedure of example 12 was used, except SO was used as an epoxide. The product was a poly(oxypropylene)diol and was designated as PEPO- 19. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI of the PEPO- 19 obtained, are compiled in Table 2.

[0158] Example 31

[0159] This example illustrates the synthesis of PEPO, wherein CHO was used as an epoxide instead of PO and zinc hexacyanocobaltate / BTC (DMC-2) as a catalyst [CHO : PEG-300 = 30 : 1]. The procedure of example 12 was used, except CHO was used as an epoxide. The product was a poly(oxypropylene)diol and was designated as PEPO-20. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI of the PEPO-20 obtained, are compiled in Table 2.

[0160] Example 32

[0161] This example illustrates the synthesis of PEPO, wherein 1-EH was used as an epoxide instead of PO and zinc hexacyanocobaltate / BTC (DMC-2) as a catalyst [1-EH : PEG-300 = 30 : 1]. The procedure of example 12 was used, except 1-EH was used as an epoxide. The product was a poly(oxypropylene)diol and was designated as PEPO-21. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI of the PEPO-21 obtained, are compiled in Table 2.

[0162] Furthermore, the reaction parameters, such as, catalyst amount (500 - 2500 ppm, and monomer-to-initiator ratio (30 - 70) are compiled in Table 3.

[0163] Table 3: Effect of monomer to initiator ratio, catalyst amount (Monomer = PO, Initiator = PEG-300) and other DMC-BTC derivatives on PEPO properties

[0164] Reaction Conditions: Temperature = 105 °C, Time = 24 h, Pressure = 5 bar

[0165] Example 33

[0166] This example illustrates the synthesis of PEPO, wherein zinc hexacyanocobaltate / BTC triethyl ester (DMC-9) as a catalyst [PO : PEG-300 = 30 : 1] using PEG-300 as an initiator. The procedure of example 12 was used, except DMC-9 was used as a catalyst. The product was a poly(oxypropylene)diol and was designated as PEPO-33. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI of the PEPO-33 obtained, are compiled in Table 3.

[0167] Example 34

[0168] This example illustrates the synthesis of PEPO, wherein zinc hexacyanocobaltate / BTC sodium salt hydrate (DMC-10) as a catalyst [PO : PEG-300 = 30 : 1] using PEG-300 as an initiator. The procedure of example 12 was used, except DMC-10 was used as a catalyst. The product was a poly(oxypropylene)diol and was designated as PEPO-34. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI of the PEPO-33 obtained, are compiled in Table 3.

[0169] Example 35

[0170] This example illustrates the synthesis of PEPO, wherein zinc hexacyanocobaltate / BTC trimethyl ester (DMC-11) as a catalyst [PO : PEG-300 = 30 : 1] using PEG-300 as an initiator. The procedure of example 12 was used, except DMC-11 was used as a catalyst. The product was a poly(oxypropylene)diol and was designated as PEPO-35. The yield and key characteristics of PEPO, such as hydroxyl number, unsaturation number, Mw, and PDI of the PEPO-35 obtained, are compiled in Table 3.

[0171] Example 36 Synthetic natural gas mixture used for hydrate formation and assess the performance of LDHIs had the composition as shown in Table 4.

[0172] Table 4: Synthetic natural gas mixture used for hydrate formation

[0173] Hydrate inhibition test of the synthesized LDHIs: (a): Cooling-Heating method (Hydrate formation-dissociation cycle)

[0174] • A high-pressure visual reactor setup that can be operated under subsea pipeline conditions and deliver the evidence for hydrate formation kinetics, thermodynamics and slurry formation, wall deposition, or plugging with hydrate crystals through visual observations.

[0175] • While utilizing this setup, we evaluated the hydrate inhibition performance of the various commercial and CSIR-IIP synthesized LDHIs.

[0176] • A pre-determined amount of water (37.1 mL), liquid hydrate former cyclopentane (2.9 mL or 1.5 mol% to dissolve hydrophobic LDHIs), and LDHIs (0.1 -1.0 wt%) was loaded inside the reactor which corresponds to a total liquid volume of 40 mL.

[0177] • The reactor was pressurized with synthetic natural gas at 45±1.0 bar and 25 °C, and liquid was stirred at 400 rpm. The corresponding gas (110 cm3) to liquid ratio was 2.75.

[0178] • In step-1, the reactor content was cooled to 1.0 ±0.5°C while using the recirculation chiller. This step corresponds to the hydrate formation step wherein hydrate formation / onset temperature (nucleation temperature) was confirmed through pressure and temperature profile as well as visual observations.

[0179] • After completion of step-1, the reactor temperature was increased again to 25±0.5°C temperature which corresponds to hydrate dissociation (step-2), (cooling-heating method of hydrate formation and dissociation)

[0180] • The real-time data for pressure, temperature, and visuals were recorded throughout the experiments.

[0181] The results obtained from the cooling-heating method for hydrate nucleation temperature and the amount of hydrate formed (gas uptake data) are shown in Table 5. Table 5: Summary of the tests conducted using the cooling-heating method, test conditions, and test results

[0182] Tn: Nucleation Temperature

[0183] Pn: Nucleation pressure

[0184] Pexp: Experimental Pressure

[0185] B-l: Additive from batch- 1 B-2: Additive from batch-2 *Gas uptake date for hydrate growth phase at the end of experiment (-100-200 min data)

[0186] (b): Isothermal method:

[0187] • To understand the performance of our LDHIs at constant temperature / sub-cooling, experiments were also performed using the isothermal method. • A predetermined amount of water (37.1 mL), 1.5 mol% cyclopentane (2.9 mL), and our LDHIs (1 wt%) were filled in high-pressure visual reactor with a total volume of ~40mL.

[0188] • In step 1, the isothermal conditions were maintained by cooling of the reactor at 1.0 ±0.5 °C by using a recirculating chiller. • When the reactor temperature is achieved, the reactor is pressurized to 45±1.0 bar, and the liquid was stirred at 400rpm.

[0189] • The pressure and temperature profile obtained during hydrate formation by the addition of 1 wt% of our LDHIs along with morphological observation was recorded.

[0190] After step 1, the reactor was set to 25±0.5°C to dissociate the formed hydrate (hydrate dissociation step)

[0191] The results obtained from the isothermal method for the amount of hydrate formed (gas uptake data) at different sub-coolings are shown in Table 6.

[0192] Table 6: Summary of tests conducted using isothermal method, test conditions, and test results

[0193] *Gas uptake date for hydrate growth phase (-60-100 min data)

[0194] DIW : Deionised water

[0195] SW: Saline water

[0196] Pexp: Experimental Pressure B - 1 : Additive from batch- 1 B-2: Additive from batch-2

[0197] #Subcooling Temperature = Equilibrium temperature-experimental temperature

[0198] (c): Resistance-to-Flow Measurements:

[0199] • To probe the anti-agglomerating characteristics of the synthesized LDHIs, we measured the resistance-to-flow build due to the formation of hydrate-in-oil slurry. The resistance-to-flow was correlated with the motor torque data which further can be correlated with the pipeline differential pressure generated due to hydrate deposition / blockage.

[0200] • Depending on the watercut, a predetermined amount of water (112-56 mL) and paraffin oil (28-84 mL), was used which corresponds to a total volume of -140 mL.

[0201] • Synthetic natural gas mixture presented in Table 4 was used for hydrate formation at 60 and 40 bar pressure.

[0202] Table 7 corresponds to the torque data obtained to hydrate formation at different watercut.

[0203] Table 7: Summary of the experiments performed to assess the anti-agglomerating characteristics of our LDHIs along with test conditions and test results

[0204] Tn= Nucleation Temperature

[0205] Pn= Nucleation pressure

[0206] Equilibrium Temperature: 15.85 °C at 60 bar and 13.30 °C at 40 bar Example 37

[0207] This example illustrates the comparison of hydrate nucleation temperature (also presented in table 5) evaluated in the presence of our LDHIs, no additive, and commercially available LDHIs (PVP). The graph reveals the hydrate inhibition performance of our LDHIs while shifting the nucleation temperature towards a lower temperature (refer to Figure 2). PEPO-24 was found to be the best LDHI. Example 38

[0208] This example illustrates the comparison of gas hydrate formation kinetics evaluated in the presence of our LDHIs along with the repeated trials of one of the LDHI (PEPO-24) [Refer to Figures 3(a) and 3(b)]. More precisely, Figure 3 (a) reveals that the amount / rate of hydrate formation has been significantly reduced in the presence of our EDHIs. Further, Figure 3 (b) illustrates the deviation in the hydrate formation kinetics in the presence of PEPO-24 (three independent repeated trials). Further, Figure 4 compares the performance of our EDHIs with the commercially available EDHIs (PVPs) and reveals the excellent hydrate inhibition performance of PEPO-24.

[0209] Example 39

[0210] This example illustrates the effect of EDHIs concentration gas hydrate formation kinetics. The moles of gas consumed / mol of water presented in Figure 5 corresponds to the amount of hydrate. The graph reveals that hydrate inhibition performance increases with the dosage of EDHIs.

[0211] Example 40

[0212] This example illustrates the comparison of gas hydrate formation kinetics evaluated in the presence of our EDHI in the saline environment at isothermal conditions. The moles of gas consumed presented in Figure 6 correspond to the amount of hydrate. The graph reveals the hydrate inhibition performance of PEPO-24 in all the repeated trials.

[0213] Example 41

[0214] This example illustrates the visual observations of the aforementioned tests illustrating the substantial reduction in the hydrate crystal growth. No upward growth was observed in the presence of our EDHIs. Hydrate slurry formation (no hard plug) was observed visually (refer to Figure 7).

[0215] Example 42 This example illustrates resistance-to-flow build due to the formation of hydrate-in-oil slurry which represents the anti-agglomerating characteristics of our LDHIs. In Figure 8, we measured the motor torque data and correlated these torque signals to the resistance-to-flow mimicking oil and gas pipelines. More precisely, Figure 8 (a-c) compares the fractional torque signals measured for 80, 60, and 40 watercut with respect to model paraffin oil in the presence / absence of PEPO-24, respectively. As evident from Figure 8, PEPO-24 reduced the hydrate agglomeration significantly for the fluid having watercut below 60% and flowable hydrate slurry formed.

[0216] Example 43

[0217] This example illustrates resistance-to-flow build due to the formation of hydrate-in-oil slurry which represents the anti-agglomerating characteristics of new batch of LDHIs and their derivatives. In Figure 9, we measured the motor torque data and correlated these torque signals to the resistance-to-flow mimicking oil and gas pipelines. More precisely, Figure 9 compares the fractional torque signals measured for 40 watercut with respect to model paraffin oil in the presence / absence of newly synthesized batch of PEPO-24 and its derivatives respectively at 40 bar pressure. As evident from Figure 9, PEPO-24 (new batch) also reduced the hydrate agglomeration 60-65% compare to the baseline and flowable hydrate slurry formed.

[0218] ADVANTAGES OF THE INVENTION

[0219] 1. Synthesis of zinc, iron, tin, magnesium, lanthanum, aluminum, chromium, and cobaltbased DMC catalyst Zn3[Fe(CN)6]2 / Zn3[Co(CN)6]2 / Sn3[Co(CN)6]2 / Mg3[Co(CN)6]2 / La2Co(CN)6]2 / CO3[CO(CN)6]2 / A12[CO(CN)6]2 / Cr3[Co(CN)6]2at an elevated temperature.

[0220] 2. Use of benzene- 1, 3, 5 -tricarboxylic acid (BTC) and its derivatives as organic complexing agents for the synthesis of DMC catalyst.

[0221] 3. Attaining high activity towards ROP of PO using DMC catalyst prepared with BTC and its derivatives as CA in comparison to the DMC prepared without any CA. 4. Synthesis of PEPO with controlled molecular weight ranging from 200 to 6000 g mol"

[0222] PDI 1.01 to 2.21, 10.8 to 124.9 mg KOH g'1, and b value in range of 0.0005 to 0.0184 meq. g'1.

[0223] 5. Synthesized DMC catalyst is heterogeneous in nature and recyclable up to seven cycles. 6. Synthesized Polyether polyols (PEPO) reduces the hydrate growth at 0.1 wt% more than commercial additives used in the oil and gas industries.

[0224] 7. Polyether polyols (PEPO) delays the hydrate crystal nucleation and disrupted crystal growth up to a considerable extent.

[0225] 8. The inhibition was tested at a lower concentration (0.01 to 5 wt%) for better performance of the Polyether polyols (PEPO).

[0226] 9. PEPO having a molecular weight of 1000 g mol1(PEPO-24) worked best among other PEPO while reducing the hydrate formation kinetics by 65±2% compared to the baseline or no additive system.

[0227] 10. Gas hydrate inhibitors [LDHIs] have shown hydrate anti-agglomerating characteristics and formed a flowable hydrate slurry below 60% watercut.

Claims

We claim1. A double metal cyanide (DMC) catalyst comprising(a) 35 to 90 wt% a double metal cyanide [DMC] complex;(b) 10 to 65 wt% an organic complexing agent.

2. The catalyst as claimed in claim 1, wherein the DMC complex is selected from the group consisting of zinc(II) hexacyanoferrate(III), zinc(II) hexacyanocobaltate(III), tin(II) hexacyanocobaltate(III), magnesium(II) hexacyanocobaltate(III), lanthanum(III) hexacyanocobaltate(III), cobalt(II) hexacyanocobaltate(III), aluminum(III) hexacyanocobaltate(III), and chromium(II) hexacyanocobaltate(III).

3. The catalyst as claimed in claim 1 , wherein the organic complexing agent is selected from the group consisting of benzene- 1,3, 5 -tricarboxylic acid (BTC), and its derivatives including BTC triethyl ester, BTC trimethyl ester, BTC sodium salt hydrate and mixture thereof.

4. The catalyst as claimed in claim 1, wherein the DMC catalyst is selected from the group consisting of: i. zinc hexacyanoferrate / BTC; ii. zinc hexacyanocobaltate / BTC; iii. tin hexacyanocobaltate / BTC; iv. magnesium hexacyanocobaltate / BTC; v. lanthanum hexacyanocobaltate / BTC; vi. cobalt hexacyanocobaltate / BTC; vii. aluminum hexacyanocobaltate / BTC; viii. chromium hexacyanocobaltate / BTC; ix. zinc hexacyanoferrate / BTC trimethyl ester; x. zinc hexacyanoferrate / BTC triethyl ester; xi. zinc hexacyanoferrate / BTC sodium salt hydrate.

5. A process for the preparation of DMC catalyst as claimed in claim 1, comprising the steps of: (a) mixing 10 to 65 wt% benzene- 1,3, 5 -tricarboxylic acid (BTC) or BTC derivative in an ethanol / water solution to obtain a solution;(b) preparing another solution by mixing a M(A)nin an aqueous solution at a temperature ranging from 10 to 40 °C; wherein M is a metal ion selected from a group consisting of Zn(II), Fe(II), Pb(II), Mo(IV), Al(III), Mn(II), V(IV), V(V), W(IV), W(VI), Co(II), Sn(II), Cu(II), Cr(III), Ni(II); wherein A is an anion selected from a group consisting of halides, sulfates, hydroxides, cyanides, oxalates, isocyanates, thiocyanates, isothiocyanates, carboxylates, and nitrates; and n is an integer having value from 1 to 3 to balance the charge of M;(c) adding the solution obtained in step (a) to the solution obtained in step (b) and homogenizing it for 10 to 24 h at a temperature ranging from 60 to 70 °C to obtain a M- BTC solution;(d) preparing another aqueous solution of metal cyanide salt of formula (A*)xM*(CN)ymixing it for a period in the range of 30 to 40 minutes at a temperature in the range of 20-30 °C, wherein A* is selected from an alkali metal ion or alkaline earth metal ion; M* is selected from the group consisting of Fe(III) and Co(III); andBoth x and y are integers greater than or equal to 1 , and the sum of the charges of x and y balances the charge of M* ;(e) homogenizing the solution obtained in step (d) in the M-BTC solution obtained in step (c) at a temperature in the range of 60 to 70 °C followed by homogenizing it for 24 h, followed by washing and centrifuging the solution at 6000 rpm thrice with distilled water and twice with ethanol to obtain a solid cake;(f) drying the solid cake in a vacuum oven overnight at a temperature in the range of 50 to 70 °C to obtain the DMC catalyst.

6. A process for the ring-opening polymerization (ROP) of propylene oxide (PO) to produce polyether polyols (PEPO) as low-dosage gas hydrate inhibitors (LDHIs)in presence of double metal cyanide (DMC) catalyst as claimed in claim 1, the process comprising the steps of:(a) homogenizing an initiator, propylene oxide (PO), and a DMC catalyst in a Teflon lined reactor and performing the reaction at a temperature ranging from 10 °C to 150 °C, pressure from 1 to 25 bar, for a time period ranging from 1 to 24 h;(b) cooling down the Teflon reactor of step (a) to a temperature ranging from 10 to 42 °C, followed by collecting and washing the obtained product in a solvent;(c) centrifuging the product obtained in step (b) twice to settle down the DMC catalyst in order to check the recyclability;(d) drying the product of step (c) by using a rota evaporator at a temperature ranging from 40 to 70 °C for a time period ranging from 15 to 30 min;(e) vacuum drying the product of step (e) at a temperature ranging from 40 to 70 °C to remove a trace amount of solvent from the final product; wherein the polyether polyols (PEPO comprise molecular weight ranging from 200 to 5000 g mol1, PDI ranging from 1.1 to 2.21, OH value in range of 10.8 to 124.9 mg KOH g1and b value in range of 0.0005 to 0.0184 meq. g1.

7. The process as claimed in claim 6, wherein Gas hydrate inhibitors [LDHIs) PEPO having hydroxyl and ether groups show 65±2% reduction in the hydrate formation kinetics compared to a baseline.

8. The process as claimed in claim 6, wherein the PEPO reduces a hydrate nucleation temperature from 12±0.2 °C (baseline) to 5.0±0.5°C.

9. The process as claimed in claim 6, wherein the PEPO reduces the hydrate agglomeration below 60% watercut and flowable hydrate slurry formed.

10. The process as claimed in claim 6, wherein the PEPO is added in a concentration ranging from 0.1 to 5 wt% with respect to watercut of a fluid (gas -water-oil systems).

11. The process as claimed in claim 6, wherein the initiator is selected from ethylene glycol, dipropylene glycol (DPG), neopentyl glycol (NPG), poly ethylene glycol (PEG)-200, PEG- 300, PEG-400, PEG-600, PEG-2000, 1,3 -butanediol (1,3-BD), 1 ,4-butanediol (1,4-BD).

12. The process as claimed in claim 6, wherein the solvent used in step (ii) is chloroform.

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