I have Instagram on my Samsung Ace 2. Would like to have my Instragram photos on Facebook, too.
It's possible just go to http://www.facebook.com/appcenter/instapp instagram facebook application and authorise app
Then go to your fb profile and click on + button near your timeline (almost right end of your monitor) and add instagram.... hence you can see all your old as well as new instagram photos
You cannot share pictures on instagram that you have already posted :( But, you can have pictures you upload on instagram also upload to facebook at the same time. all you have to do start uploading a picture like you normally would on instagram. so get your pic, crop it, edit it, and press next. okay so when you get to the part where you can write a caption for your picture there will be a section of things you can share the picture to (Facebook, twitter, email, flickr, tumblr) underneath the word "share" just click the facebook button and your pic will be uploaded to instagram and facebook! hope this helped :)
Read this: http://blog.instagram.com/post/15374104807/share-bigger-photos-to-your-facebook-album
How to post Instagram photos to a Facebook Page