Construction Of Rapid Formation System Of Methane Hydrate Based On Hydrogel

Natural gas has widely applications in daily life due to its advantages of green,clean and efficient.natural gas hydrates(NGH)are compound formed by natural gas and water molecules under high pressure and low temperature.It has the advantages of high gas storage density,mild conditions of storage and transportation,good safety and so on,and has broad application prospects in natural gas storage and transportation.However,the randomness of induction time and low growth rate seriously restricted the industrial application of NGH.Adding sodium dodecyl sulfate(SDS)was one of the efficient methods to promote the formation of natural gas hydrates at present.However,SDS also faced some problems:SDS usually led to loose structure and low density of methane hydrates,which was not conducive to large-scale transportation and preservation.SDS significantly promoted the formation of methane hydrate mainly due to its rich-SO₃^-groups.As a porous medium,hydrogel had a large specific surface area,and the interaction between three-dimensional network and water molecules endowed hydrogel with excellent water absorption and retention ability.In this paper,superabsorbent sulfonic hydrogels were prepared by adding-SO₃^-groups to the three-dimensional network of hydrogels based on the significant promoting effect of SDS and excellent properties of hydrogels,and studied the effects of preparation dosage on water absorption capacity of hydrogel;Sulfonate hydrogels were used as promoters to generate methane hydrate,and the advantages of sulfonate hydrogels were highlighted by comparing the promoting effects of sulfonate hydrogels and SDS.By changing the swelling ratio,the promotion effect of sulfonic hydrogel on methane hydrate formation under different water content conditions was studied.The mechanical properties of sulfonic hydrogels were improved and the recyclability of hydrogels as promoters was optimized.The research contents and results were followed:(1)Preparation and characterization of sulfonic hydrogel promoter.On the basis of the successful preparation of sulfonic hydrogels,the monomer ratio,polymerization temperature,the dosage of crosslinker and initiator in the free radical polymerization were adjusted to optimize the water absorption capacity,and the hydrogels were characterized by SEM and FTIR.The results showed that when the dosage of sodium p-styrene sulfonate,acrylamide,N,N'-dimethyldiacrylamide and ammonium persulfate were 13.38 g,16.62 g,0.1 g and0.7 g,respectively,and the polymerization temperature was 90?,the sulfonate hydrogel had the best water absorption performance,which was 184.18±3.45 g g^-1.At the same time,SEM and FTIR were used to characterize the successful introduction of rich-SO₃^-group into the sulfonic hydrogel three-dimensional network chain.(2)Study on construction and efficiency of sulfonic hydrogel promotion system.Superabsorbent sulfonic hydrogel was applied to promote the formation of methane hydrate,and the influence on the formation kinetics of methane hydrate was studied.Compared with pure water,SDS,Polyacrylic(PAA)hydrogels and PAA-SDS,the advantages of sulfonic hydrogels were highlighted.The results showed that compared with PAA hydrogel,the growth rate of sulfonic hydrogel increased from 0.0012±0.0003 mmol ml^-1min^-1to 0.1773±0.0152 mmol ml^-1min^-1.The gas storage capacity increased from 4.58±3.26 v/v to 110.84±1.01 v/v.It could significantly promote the formation of methane hydrate and improve the kinetics of formation of methane hydrate.At the same time,compared with SDS system and PAA-SDS system,the foam height of hydrate generated by sulfonic hydrogel was also reduced from 232mm to 59.0±1.7mm in the decomposition process,which solved the serious problem of hydrate foam generated by SDS system.(3)Study on the efficiency of sulfonic hydrogel promoter at different swelling ratios.Combined with DSC to characterize the contents of freezable and non-freezable water in sulfonic hydrogels under different swelling ratios,the influence of sulfonic hydrogels on methane hydrate promotion efficiency under different swelling ratios was studied.The results showed that increasing the swelling ratio could significantly improve the promotion efficiency of sulfonic hydrogel on methane hydrate:the induction time of methane hydrate formation was shortened from 459.7±391.2 min to 136.3±155.1 min.The formation rate increased from 0.0788±0.0053 mmol ml^-1min^-1to 0.1773±0.0152 mmol ml^-1min^-1,and the gas storage capacity increased from 93.82±1.79 v/v to 115.65±4.39 v/v.With the increase of swelling ratio,the proportion of freezable water increased,and the promotion efficiency of sulfonic hydrogel on methane hydrate increased.The optimal swelling ratio range was 60-120g g^-1.(4)Study on enhancing performance of sulfonic hydrogel recyclability.The modified carbon nanotubes(PSCS@CNTs)were introduced into the hydrogel system to prepare nano-particles composited hydrogels,in order to improve the mechanical properties of hydrogels and optimize the ability of hydrogels cycling to promote the formation of methane hydrate.The results showed that the recyclability of sulfonate hydrogel to promote the formation of methane hydrate increased from four times to eight times after the introduction of carbon nanotubes modified by poly(styrene-sodium p-styrene sulfonate)macromolecular chain,and the recyclability was greatly improved.Sulfonic hydrogels were introduced into carbon nanotubes with high mechanical strength and mechanical properties were improved.